Exploring the Design Space of the Dry Configuration of the

Nanoparticle Field Extraction Thruster in Microgravity

Team ZESTT Reflight (Zero-g ElectroStatic Thruster Testbed Reflight)

Test Equipment Data Package

Institution:

University of Michigan

Student Space Systems Fabrication Laboratory

Space Research Building

2455 Hayward St.

Ann Arbor, MI 48109

University of Michigan Faculty Advisor: Professor Brian Gilchrist

Electrical Engineering and Space Systems

gilchrst@umich.edu

(734) 763-6230

University of Michigan Principal Investigator:

Thomas Liu

Aerospace Engineering

liutm@umich.edu

(720) 984-4481

Team Contact: Mike Huang

Junior, Electrical Engineering

huxuli@umich.edu

(248) 974-0597

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Change Page

Version Date Authority signature Description

First Submission May 5, 2010 Brian Gilchrist

Thomas Liu

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Quick Reference Sheet

Principal Investigator: Thomas Liu, Brian Gilchrist

Contact Information:

Thomas Liu

1320 Beal Ave., 1052 FXB

Ann Arbor, MI 48109

liutm@umich.edu

(720) 984-4481

Mike Huang

45499 Irvine Dr

Novi, MI 48104

huxuli@umich.edu

(248) 974-0597

Experiment Title: Exploring the Design Space of the Dry Configuration of the Nanoparticle Field

Extraction Thruster in Microgravity

Work Breakdown Structure (WBS): Integrated Systems Tests – Present – June 3th

; Flight Readiness

Review – June 4th

; Packing Completion/Travel to Ellington Field – June 15th

Flight Date(s): June 17th

-26th

Overall Assembly Weight (lbs): 366.4lbs

Assembly Dimensions (L x W x H): 59” x 24” x 28”

Equipment Orientation Requests: Long axis aligned with plane’s axis

Proposed Floor Mounting Strategy (Bolts/Studs or Straps): Bolts/Studs for chassis frame, straps for

individual component mounting to chassis frame

Gas Cylinder Requests (Type and Quantity): 1 Nitrogen K-Bottle (for ground testing)

Overboard Vent Requests (Yes or No): No

Power Requirement (Voltage and Current Required): 115V 60Hz, 20A

Free Float Experiment (Yes or No): No

Flyer Names for each Proposed Flight Day: Flight Day One: Vritika Singh, Dave Chen, John

Orlowski; Flight Day Two: Mike Huang, Duncan Miller, Nathan Van Nortwick

Camera Pole and/or Video Support: One camera pole requested for overall flight experiment

observation

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Table of Contents

1 Flight Manifest .................................................................................................................................. 9

2 Experiment Background ................................................................................................................... 9

3 Experiment Description .................................................................................................................. 10

3.1 M-2 Thruster Prototype ............................................................................................................. 11

3.2 Induction Charge Detector ........................................................................................................ 11

3.3 Faraday Probe ........................................................................................................................... 13

3.4 Experiment Operation .............................................................................................................. 14

4 Equipment Description ................................................................................................................... 14

4.1 Vacuum System ........................................................................................................................ 14

4.1.1 Vacuum Chamber .............................................................................................................. 15

4.1.2 Viewports .......................................................................................................................... 16

4.1.3 High Voltage Feedthroughs ............................................................................................... 16

4.1.4 Instrumentation Feedthroughs........................................................................................... 17

4.1.5 Gate Valve ......................................................................................................................... 18

4.1.6 Leak Valve ......................................................................................................................... 19

4.1.7 Exhaust Filtration .............................................................................................................. 20

4.1.8 Thruster Prototype and Probe Mount ................................................................................ 20

4.1.9 Mounting Vacuum Chamber to Chassis ............................................................................ 21

4.1.10 Vacuum Chamber Certification ......................................................................................... 22

4.2 Pumping System ....................................................................................................................... 22

4.2.1 Piston Roughing Pump (Ground use only) ....................................................................... 23

4.2.2 Turbo Pump and Controller (Turned off in flight) ............................................................ 24

4.2.3 Pressure Gauge and Controller ......................................................................................... 24

4.3 Humidity Mitigation ................................................................................................................. 25

4.3.1 Heat (Ground use only) ..................................................................................................... 25

4.3.2 Nitrogen Purging (Ground use only)................................................................................. 27

4.4 Electrical Equipment ................................................................................................................ 28

4.4.1 Master Kill Switch ............................................................................................................ 28

4.4.2 DC Power Supply.............................................................................................................. 29

4.4.3 High Voltage System ......................................................................................................... 29

4.4.4 Piezo System ..................................................................................................................... 31

4.5 Data Acquisition System .......................................................................................................... 33

4.6 Extra Ground Equipment.......................................................................................................... 34

4.7 Chassis Layout and Flyer Positioning ...................................................................................... 35

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4.8 Special Handling Requirements ............................................................................................... 35

4.9 Free Float Experiment .............................................................................................................. 36

5 Structural Verification ..................................................................................................................... 36

5.1 Analysis Method....................................................................................................................... 36

5.1.1 Free Body Diagrams ......................................................................................................... 36

5.1.2 Component Specifics ........................................................................................................ 36

5.1.3 Minimum Margin of Safety Table ..................................................................................... 41

6 Electrical Analysis........................................................................................................................... 41

6.1 Schematic ................................................................................................................................. 41

6.2 Outside Chamber Wiring .......................................................................................................... 41

6.2.1 High Voltage Wiring ......................................................................................................... 42

6.2.2 Piezo Drive Line Wiring ................................................................................................... 43

6.3 Vacuum Side Wiring ................................................................................................................. 43

6.4 Electrical Load Analysis ........................................................................................................... 43

6.5 High Voltage Discharging ........................................................................................................ 44

6.6 Electrical Kill Switch ............................................................................................................... 45

6.7 Loss of Electrical Power........................................................................................................... 45

6.8 MATLAB Automation Scheme ................................................................................................ 45

7 K-Bottle ........................................................................................................................................... 47

8 Laser Certification........................................................................................................................... 48

9 Parabola Details and Crew Assistance ............................................................................................ 48

10 Institutional Review Board (IRB) ................................................................................................... 49

11 Hazard Analysis .............................................................................................................................. 49

11.1 Integrated Hazard Analysis ...................................................................................................... 49

12 Tool Requirements .......................................................................................................................... 58

13 Photo Requirements ........................................................................................................................ 58

13.1 Photographers ....................................................................................................................... 58

13.2 S-Band Downlink ................................................................................................................. 58

13.3 Fixed Camera Poles .............................................................................................................. 58

13.4 Product Format and Quantities of Imagery .......................................................................... 58

14 Aircraft Loading .............................................................................................................................. 59

14.1 Ground Equipment ................................................................................................................ 59

14.2 Hardware Manipulation Strategy .......................................................................................... 59

14.3 Weights and Loading ............................................................................................................ 59

15 Ground Support Requirements........................................................................................................ 59

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15.1 Power .................................................................................................................................... 59

15.2 K-bottles ............................................................................................................................... 59

15.3 Chemicals ............................................................................................................................. 59

15.4 Building Access .................................................................................................................... 59

15.5 Tool Requirements ................................................................................................................ 60

16 Hazardous Materials ....................................................................................................................... 60

17 Material Safety Data Sheets ............................................................................................................ 60

18 Experiment Procedures Documentation.......................................................................................... 60

18.1 Equipment Shipment to Ellington Field ............................................................................... 60

18.2 Ground Operations ................................................................................................................ 60

18.3 Loading/Stowing ................................................................................................................... 60

18.4 Pre-Flight .............................................................................................................................. 60

18.5 Take-off/Landing .................................................................................................................. 61

18.6 In Flight ................................................................................................................................ 61

18.7 Prior to First Parabola ........................................................................................................... 61

18.8 2-G Period ............................................................................................................................. 61

18.9 Reduced Gravity Period ........................................................................................................ 61

18.10 Turnarounds .......................................................................................................................... 62

18.11 Emergency Procedures, Precautions, and Contingencies ..................................................... 62

18.12 Post Flight ............................................................................................................................. 62

18.13 Off-Loading .......................................................................................................................... 62

18.14 Emergency/Contingencies .................................................................................................... 63

References ............................................................................................................................................... 64

Appendix A: Exceptions/Deviations/Waivers ......................................................................................... 65

Appendix B: Isopropyl Alcohol MSDS .................................................................................................. 67

Appendix C: Acetone MSDS ................................................................... Error! Bookmark not defined.

Appendix D: Compressed Nitrogen Gas MSDS ...................................... Error! Bookmark not defined.

Appendix E: 5 Micron Silver Coated Particles MSDS ........................................................................... 78

Appendix F: RTV Silicone MSDS .......................................................................................................... 81

Appendix G: Conductive Epoxy (Part A) MSDS ................................................................................... 89

Appendix H: Conductive Epoxy (Part B) MSDS ................................................................................... 93

Appendix I: Vacuum Chamber Leak Check Certification ...................................................................... 97

Appendix J: Welding Certification .......................................................................................................... 98

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Table of Figures

Figure 1: M-2 Prototype .......................................................................................................................... 11 Figure 2: ICD prototype cross section view

4 ......................................................................................... 12

Figure 3: ICD differential signal amplification circuitry ....................................................................... 13

Figure 4: ICD with Faraday Probe ......................................................................................................... 13 Figure 5: Faraday Probe amplification circuitry .................................................................................... 14 Figure 6: A CAD model of 12" spherical chamber with attached flanges/feedthroughs ....................... 15 Figure 7: Kodial glass viewport from Kurt J. Lesker Company ............................................................ 16 Figure 8: Single pin HV feedthrough from Kurt J. Lesker Company .................................................... 17

Figure 9: Barrel connectors used to make wire connections on the vacuum side of electrical

feedthroughs ............................................................................................................................................ 17 Figure 10: A BNC feedthrough will be used for piezo lines going in and out of the vacuum chamber 18

Figure 11: 50 pin, D-Sub connector used for instrumentation connections to and from vacuum chamber

................................................................................................................................................................. 18 Figure 12: Aluminum gate valve from Pascal Technologies .................................................................. 19

Figure 13: Leak valve used to vent and nitrogen purge the vacuum chamber ....................................... 19 Figure 14: A picture of the Ahlstrom Grade 142 glass microfiber filter with 3um pore size taken under

an optical microscope.............................................................................................................................. 20

Figure 15: Left: thruster and probe mount rod welded to 8" flange Right: thruster prototype and probe

assembled on the mount rod .................................................................................................................... 21

Figure 16: The chamber mounted to the 6061 Al plate .......................................................................... 22 Figure 17: The pumping system consists of the turbo pump and piston pump mounted to a 4.5” CF

after the gate valve .................................................................................................................................. 23

Figure 18: The XtraDry 150-20 roughing pump will be used to pump dowm from atmosphere to 0.2

Torr .......................................................................................................................................................... 23 Figure 19: Varian Turbo-V 70 LP pump and controller ......................................................................... 24 Figure 20: PKR 251 Compact FullRange Gauge and Controller........................................................... 25

Figure 21: A bake-out heater tape will allow the vacuum chamber to be baked-out at a set temperature

to speed up the pump down process ........................................................................................................ 26

Figure 22: Variable AC power supply to power the bake-out heater strip ............................................. 26 Figure 23: Pump down curves for normal air, humid air, and humid air with heat ............................... 27 Figure 24: Over pressure burst valve from Accu-Glass Products, Inc. on a 1.33”CF that will be

attached to a 6” CF using a reducer flange ............................................................................................. 28 Figure 25: AC power strip and Master Kill Switch ............................................................................... 29 Figure 26: Keithley 2400 Sourcemeter .................................................................................................. 29 Figure 27: HVRack front panel .............................................................................................................. 29

Figure 28: HVRack D-Sub control interface ......................................................................................... 30 Figure 29: PD-1301 Piezo driver front panel ......................................................................................... 31 Figure 30: Piezo switch box with Pearson coil ...................................................................................... 32 Figure 31: Piezo control feedback scheme ............................................................................................ 32

Figure 32: Top: 2.5X preamp for piezo driver Bottom: 10Hz low pass filter ........................................ 33 Figure 33: Left: NI USB 6218 Right: NI USB 6259 DAQs .................................................................. 33 Figure 34: Panasonic Tough-book ......................................................................................................... 34 Figure 35: Chassis layout and flyer positioning .................................................................................... 35 Figure 36: 80/20 beam cross section ...................................................................................................... 37 Figure 37: Beam distribution: 1515 beams shown in blue. 1530 beams shown in green. 1010 beams

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shown in red ............................................................................................................................................ 37 Figure 38: Aircraft mounting brackts span the width of the chassis ...................................................... 38

Figure 39: Electrical schematic .............................................................................................................. 41 Figure 40: HV Cap on 2.75" flange ....................................................................................................... 42 Figure 41: In-vacuum D-Sub cable with PEEK connector and Kapton wire, the non-terminated side

will have quick disconnects to connect to the ICD and Faraday Probe8 ................................................. 43

Figure 42: High voltage discharging time constant ............................................................................... 45 Figure 43: MATLAB automation scheme .............................................................................................. 46 Figure 44: Schematic of nitrogen purging pressure system ................................................................... 47

List of Tables

Table 1: Flange Usage ............................................................................................................................ 15

Table 2: Extra Ground Equipment ......................................................................................................... 34 Table 3: Component Mounting .............................................................................................................. 38

Table 4: Mass Budget ............................................................................................................................. 39 Table 5: Current Load Chart ................................................................................................................... 44 Table 6: NI USB 6218 ............................................................................................................................ 45

Table 7: NI USB 6259 ............................................................................................................................ 46 Table 8: Nitrogen purging pressure vessel design specifications ........................................................... 48

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1 Flight Manifest

Each flight day will require three flyers: one to run the MATLAB automation of the experiment and

two to monitor the equipment.

Flight crew: Mike Huang (huxuli@umich.edu)

Junior Electrical Engineering

Vritika Singh (singhv@umich.edu)

Sophomore Aerospace Engineering

David Chen (drchen@umich.edu)

Senior Electrical Engineering

Duncan Miller (duncanlm@umich.edu)

Freshman Aerospace Engineering

John Orlowski (jorlo@umich.edu)

Junior Atmospheric Oceanic and Space Sciences

Nathan Van Nortwick (nvannort@umich.edu)

Freshman Aerospace Engineering

Ground crew: David Liaw (liawd@umich.edu)

Graduate student Electrical Engineering

David Yu (yudavid@umich.edu)

Graduate student Aerospace Engineering

2 Experiment Background

The Nano-particle Field Extraction Thruster (NanoFET) is currently under development at the

University of Michigan in collaboration with ElectroDynamic Applications (EDA). Development

started in 2005 as a projected funded by the NASA Institute for Advanced Concepts (NIAC). NanoFET

electrostatically charges micro/nano-particle propellant utilizing an electric field to accelerate them

through a series of gate electrodes at varying electric potentials. As a result, NanoFET has a variable

specific impulse, a measure of propellant usage efficiency, which can be adjusted by changing the

magnitude of the applied electric field. Particles are pushed against a charging sieve in the form of a

constant force spring. A piezoelectric ceramic (piezo) mounted against the charging sieve provides the

energy necessary to overcome cohesion forces between particles and adhesion forces between the

particles and sieve. Due to the particle’s size, particle-particle cohesive forces cause the particles to

clump together, inhibiting their ability to pass through the sieve. Particles also tend to adhere to the

sieve and reservoir walls. The piezo provides an inertial kickoff to overcome these forces, thus

allowing the particles to be subjected to the applied electric field and accelerated to create thrust1. By

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varying the piezoelectric actuation frequency and thus changing the rate at which layers of particles are

kicked off the sieve, one can control the overall thrust generated.

As shown in Equation 1, NanoFET’s specific impulse (Isp) is proportional to the charge to mass ratio of

each particle. The particle charge (q) is controlled by the applied charging electric field2.

(1)

Variable specific impulse and variable thrust provides NanoFET with a large range of operating

capabilities, thus allowing the optimal configuration to be selected for specific maneuvering tasks3.

NanoFET also has several proposed terrestrial uses beyond space propulsion, including sub-dermal

injection and dry printing applications.

The 2008-2009 ZESTT group designed and tested the first generation NanoFET macro-scale prototype

(M-1). This year, the ZESTT Reflight team has shifted focus to developing the diagnostic tools

necessary to measure the current generation and future generation NanoFET performance

characteristics. Traditionally, NanoFET testing has relied on Particle Tracking Velocimitry (PTV) data

using a laser and fastcam to measure particle velocity. However the particle exhaust plume becomes

increasingly difficult to image as the particles continue to scale smaller in size and speed up due to

larger accelerating electric fields. To measure particle velocity, particle charge, and exhaust plume

current density, the ZESTT Reflight team is designing and building an Induction Charge Detector

(ICD) and Faraday Probe. NanoFET’s thrust and specific impulse can then be estimated from these

measured values. By flying the NanoFET thruster along with these diagnostic tools in microgravity, the

ZESTT Reflight team will be validating NanoFET’s feasibility in a vacuum and microgravity

environment, thereby increasing the NanoFET’s Technology Readiness Level and proving diagnostic

capabilities.

The goal of the ZESTT Reflight team is to implement a vacuum testbed for current and future

NanoFET ground and microgravity related experiments. The following are the technical objectives for

the ZESTT Reflight program.

1. Implement a vacuum testbed for characterizing NanoFET prototypes’ performance in laboratory

and microgravity test conditions.

a. Upgrade pumping capability relative to ZESTT (i.e., faster pumpdown times).

b. Maintain low pressure (10-5

Torr) for extended periods in absence of pumping.

c. Prepare and accommodate for humid test conditions

2. Measure emission current and throughput with a Faraday probe.

3. Measure particle charge and time-of-flight with an Induction Charge Detector.

4. Demonstrate piezoelectric feedback control on NanoFET prototypes.

5. Conduct an automated experiment that that is triggered into operation only in microgravity

while collecting data describing emission characteristics.

3 Experiment Description

The microgravity experiment is comprised of a particle emission source, the NanoFET Prototype, and

sensors, ICD and Faraday Probe to be housed in a vacuum chamber. The equipment drives for this

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experiment are described in detail in Section 4.

3.1 NanoFET Thruster Prototype

One NanoFET thruster prototypes will be flown in flight shown in Figure 1. The polycarbonate spring

block houses the particle reservoir in the form of a syringe and plunger. The particles that are being

loaded into the syringe are 38-45um silver coated glass particles from MO-SCI Specialty Products, see

Appendix E for MSDS. A constant force spring applies backpressure to the plunger, pushing the

particles into the charging sieve.

Figure 1: M-2 Prototype

Beneath the spring block is the sieve block. The sieve is a 60um weaved mesh conductive epoxied to a

washer and clamped between a ceramic spacer and the polycarbonate spacer below it. The sieve will be

charged to 15kV for testing. A grounded acceleration gate is placed 1cm away from the sieve followed

by another grounded gate 1cm below the first gate. Between the two grounded gates is piezoelectric

ceramic, CMAR04, from Noliac. The outer diameter of the ring piezo is 15mm with an inner diameter

of 9mm. The maximum operating voltage is 200V and maximum operating temperature is 200oC with a

Curie temperature of 350oC. In flight, the thruster prototype will be tested with a piezo operated with

various input waveforms ranging between 10 and 12kHz 150V sinusoids. Emission from the thruster

then either strikes the surface of a Faraday Probe, or enters the 300um orifice of the ICD.

3.2 Induction Charge Detector

An Induction Charge Detector prototype is currently on loan from NASA Jet Propulsion Laboratory

(JPL) for characterizing NanoFET’s performance. The ICD prototype consists of two sensor tubes each

connected to electrical ground through a 2GΩ resistor. As a charged particle passes through the 2.5mm

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diameter sensor tube, a reflective charge is induced on the sensor. The current that passes over the 2GΩ

resistor is measured through an amplifier circuit. After the particle passes through both sensor tubes, it

strikes a collection anode through which the particle discharges over a resistor. The sensors and anode

are supported by an insulating skeleton inside a conductively grounded tube casing that shields the

sensors from electro-magnetic noise. The particle emission plume is spatially filtered by a 300um hole

at the face of the casing aligned axially with the thruster to increase the likelihood of particles entering

the sensor.

Figure 2: ICD prototype cross section view4

The sensor tube voltages are measured differentially, V1-V2, corresponding to the current pulled to the

first sensor as particle passes through and current pulled to the second sensor. The output waveform is

expected to look like a series of three voltage spikes.: the first down, then an up spike approximately

twice the magnitude of the first, then a second down spike. A second output measures the anode

voltage (V3) minus V1. When the particle strikes the anode, the V3-V1 signal will spike and RC decay.

An estimate of particle velocity can be made by dividing the 1.8cm length of each sensor tube by the

time between down to up spikes of the V1-V2 signal. The AD549 amplifiers in the ICD circuitry are low

noise buffers that drive the downstream differential instrumentation amplifiers, IN126s. The INA126s

amplify the differential signals V1-V2 and V3-V1.

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Figure 3: ICD differential signal amplification circuitry

3.3 Faraday Probe

The Faraday Probe is the collection plate for the particle emission plume. The probe is placed on the

top face of the ICD with a 300um hole in the center to allow for particles to enter the ICD. The plate is

attached to and surrounded by a grounded tube, see Figure 4, such that the unit fits over the ICD and is

screwed into the ICD cap. The grounded tube also serves as additional shielding of the probe from

electro-magnetic noise.

Figure 4: ICD with Faraday Probe

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As the particle plume strikes the Faraday Probe, particle charge is flows over a 1MΩ resistor, over

which the voltage is measured. This voltage is then passed through three gain stages totaling 1000X

amplification. The net effect of a large number of particle strikes results in a DC shift in the noise floor

through which the total emission current can be measured.

Figure 5: Faraday Probe amplification circuitry

3.4 Experiment Operation

The vacuum chamber will be pumped down to the target level of 10-7

Torr throughout the week leading

up to flight. Pressure is to be held during flight by closing the gate valve between the vacuum chamber

and turbo pump. The pumps are then turned off. In flight, the experiment is automated by a MATLAB

program. At the beginning of flight, high voltage is turned on to supply the charging and accelerating

field to the particles. Upon the entrance of microgravity, the piezo is turned on; the piezo is turned off

after a second of operation. The data from the ICD and Faraday probe are measured by a data

acquisition device and stored to the flight laptop. See Section 6.8 for a detailed explanation of the

MATLAB automation scheme.

4 Equipment Description

The following sections describe the flight and ground equipment to be used at Ellington Field. The

experiment equipment can be divided into four main subsystems: vacuum system, pumping system,

humidity mitigation system, electrical system, and data acquisition system.

4.1 Vacuum System

A vacuum system will aid in producing space-like conditions to test the thruster prototypes. Air drag

greatly reduces particle velocity by an order magnitude (from m/s to cm/s), thus the vacuum system is

an important component of ZESTT Reflight’s experiment in order to gain the most representative data.

The vacuum system consists of the vacuum chamber with flanges/feedthroughs, pumping system, gate

valve, and pressure measurement device. The aimed ultimate pressure for the vacuum chamber is 10-7

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Torr, but the chamber will be pumped down to at least 10-5

Torr during all testing. All parts installed

into the vacuum chamber will also be allowed to outgas the week prior to flight.

4.1.1 Vacuum Chamber

The vacuum chamber to be used with this experiment is a 12” spherical vacuum chamber from Kurt J.

Lesker Company, shown in Figure 6 below.

Figure 6: A CAD model of 12" spherical chamber with attached flanges/feedthroughs

This spherical chamber is constructed of 3/16” thick, 304 stainless steel, has a volume of about 905 in3

and weight of approximately 52 lbs without flanges, is rated to 10-10

Torr, and is equipped with 11

Conflat Flanges (CF) to accommodate the feedthroughs and vacuum equipment necessary for the

experiment. Of the 11 flanges, four flanges are 2.75” CF, one is 4.5” CF, two are 6” CF, and the final

four flanges are 8” CF. The overall flange usage is shown in the table below.

Table 1: Flange Usage

Flange Usage on 12” Spherical Vacuum Chamber

2.75” Pressure Gauge

2.75” Leak Valve

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2.75” 4 pin

BNC Feedthrough

2.75” 1 pin High Voltage Feedthrough

4.5” Gate Valve and Pump System

6” Viewport

6” Over pressure burst valve with reducer flange

8” Custom Thruster Mount

8” D-Sub Instrumentation Feedthrough

8” Front Viewport

8” Bottom Viewport

4.1.2 Viewports

Two viewports are mounted on two of the 8” flanges of the vacuum chamber and another to a 6”

flange. These viewports are used instead of blank flanges to reduce mass and provide viewing angles

into the chamber. This viewing capability will aid in monitoring the prototypes during testing and in

watching for high voltage arcing within the chamber. The viewports are made from Kodial glass,

shown below, which has maximum transmission in the visible wavelengths, ensuring visibility of

internal components as well as ultra high vacuum (UHV) compatibility.

Figure 7: Kodial glass viewport from Kurt J. Lesker Company

4.1.3 High Voltage Feedthroughs

One of the available four 2.75” flanges are occupied by a single pin, high voltage (HV) feedthrough.

Each HV feedthrough, shown in Figure 8 below, is rated to 25kV and UHV.

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Figure 8: Single pin HV feedthrough from Kurt J. Lesker Company

The HV feedthrough will be supplied with 15kV. The feedthrough will be connected to of the sieve

ofthe thruster. On the vacuum side of the HV feedthrough are single stainless steel pins, and barrel

connectors, shown in Figure 9, that will be used to connect wires to this pin.

Figure 9: Barrel connectors used to make wire connections on the vacuum side of electrical

feedthroughs

On the air side of these feedthroughs, ring terminals will be used to secure leads to the HV pin. An ultra

high molecular weight polyethylene (UHMWPE) protective cap will cover the air side of the HV

feedthrough. This is to prevent flyers from coming into contact with HV. See Section 6.2.1 for more

information on the HV cap.

4.1.4 Instrumentation Feedthroughs

Two types of instrumentation feedthroughs are used on the vacuum chamber to make all the

instrumentation connections required inside the chamber. This includes a BNC feedthrough and a D-

Sub feedthrough.

The BNC feedthrough, shown below, will be used for all the piezoelectric signal and ground lines. The

BNC connection was chosen for the piezoelectric lines due to their inherent electrical shielding

properties.

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Figure 10: A BNC feedthrough will be used for piezo lines going in and out of the vacuum chamber

In addition to shielding, the BNC connectors provide quick, easy, and secure connections for the piezo

leads. The BNC feedthrough is a 2.75” flange with four separate BNC connections. Two of the

available four BNC connections will be used for piezo control lines, and fourth third BNC connection

will be used for all piezo ground/common lines. On the vacuum side, the BNC feedthrough has pins to

which wires will be connected using barrel connectors, shown in the figure above. Each BNC

connection is rated to 500V, 3A, and UHV.

For the ICD, Faraday Probe, and thermocouple lines, a D-Sub connector on an 8” flange, shown below,

will be used.

Figure 11: 50 pin, D-Sub connector used for instrumentation connections to and from vacuum chamber

The D-Sub connector has 50 pins and is double sided. On the vacuum side, wires will be connected to

the D-Sub connector using a vacuum compatible D-Sub cable assembly. See Section 6.3 for more on

the vacuum side D-Sub cable assembly and wiring scheme.

4.1.5 Gate Valve

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An aluminum gate valve will be attached to the 4.5” CF before the pumping system interface. This gate

valve, shown in the figure below, is manually operated, rated to 10-10

Torr, and has a leak rate of 10-8

std cc/sec.

Figure 12: Aluminum gate valve from Pascal Technologies

The purpose of the gate valve is to seal the vacuum chamber after it has been pumped down to the

desired pressure. This will allow the vacuum chamber to retain the pressure even without continuous

pumping, thus the pumping system will not be required on-board the flight. The goal is to keep enough

pressure overnight that the chamber can easily be pumped back down to the desired pressure right

before flight. Please see Section 18.4 for more details on the use of the gate valve with the pumping

system.

4.1.6 Leak Valve

In order to return the vacuum chamber to atmospheric pressure, a leak valve is installed onto one of the

bottom 2.75” flanges. This is the Nupro SS-4H bellows leak valve pictured below.

Figure 13: Leak valve used to vent and nitrogen purge the vacuum chamber

Not only does this leak valve allow the chamber to vent to atmospheric pressure, but it also allows for

nitrogen purging of the chamber as part of the humidity mitigation plan. Please See Section 4.3 for

more on nitrogen purging and humidity mitigation.

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4.1.7 Exhaust Filtration

Microparticles are not anticipated to escape into the atmosphere through leaks in the chamber or

through the pumps. This is because only a small amount of particles are used with the prototypes.

Additionally, the microparticles used with these prototypes are not harmful to humans (MSDS

Appendix C).

On the other hand, precautions in the form of filters will be attached to the chamber at several

interfaces, and these filters will also protect equipment from possible contamination by microparticles.

The filters to be used are made of 30um weaved mesh.

Figure 14: A picture of the Ahlstrom Grade 142 glass microfiber filter with 3um pore size taken under

an optical microscope

A filter will be attached to the 2.75” flange between the chamber and pressure gauge, 4.5” flange

between the chamber and the gate valve to protect the pumps, the 2.75” flange between the chamber

and the leak valve, and the reduced 6” flange in front of the over pressure burst valve. Ahlstrom Grade

142 filters were chosen allow maximum air flow rate while still capturing wayward particles.

4.1.8 Thruster Prototype and Probe Mount

One thruster and a ICD/Faraday probe are vertically suspended in the middle of the vacuum chamber.

They attach to a stainless steel hexagonal rod. The rod is welded to the center of a blank 8” flange.

The rod is 7/8” thick with side lengths of ½”. A series of holes is drilled into rod enabling the

attachment of the thruster and ICD/Faraday probe. The thruster and ICD/Faraday probe are attached

to the rod via ¼-20 screws and are easily accessible for ease of attachment. Two handles are welded to

the outside of the 8” inch flange. These allow for the thruster and probe mount to be lifted and held up

for in chamber wiring. This assembly is then inserted into the vacuum chamber through the top 8”

flange. A photograph of the mounting scheme is shown below in Figure 15. See the Structural Analysis

Report for the load analysis conducted on the mount rod.

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Figure 15: Left: thruster and probe mount rod welded to 8" flange Right: thruster prototype and probe

assembled on the mount rod

The thruster and probes can be seen through the view port flange located near the front of the chassis.

The thruster and probe assembly can be seen in Figure 15.

4.1.9 Mounting Vacuum Chamber to Chassis

The vacuum chamber is mounted to the chassis on a 6061 Aluminum alloy base plate. The plate has a

thickness of 3/8” and dimensions of 14”x16”. The steel bolts will extend through the bottom 8” flange

and plate to keep all components rigidly connected. The plate will be screwed down to the 1530 Lite

and 1515 Lite beams in the center of the chassis bottom.

22

Figure 16: The chamber mounted to the 6061 Al plate

4.1.10 Vacuum Chamber Certification

The 12” spherical vacuum chamber utilized in this experiment is considered a Category D system

according to NASA’s AOD 33897 document, Section 2.3. The flanges on the chamber are the weakest

points on the vacuum chamber. In case of a rupture, the worst case scenario, the vacuum chamber

would simply return to atmospheric pressure, thus does not pose a significant danger to personnel. See

Appendix D for vacuum chamber certification documentation.

4.2 Pumping System

A two stage pumping system will be utilized to pump the vacuum chamber to the desired pressure. The

first stage consists of a piston roughing pump, and the second stage is a turbo pump. A pressure gauge

will be used to measure the pressure inside the chamber and initiate the second stage of pumping at the

right pressure. Shown below is a schematic of the pumping system.

23

Figure 17: The pumping system consists of the turbo pump and piston pump mounted to a 4.5” CF

after the gate valve

The turbo pump will be attached to the gate valve, which is attached to the 4.5” flange on the vacuum

chamber. The piston pump will be attached to the turbo pump using a 0.5” diameter metal tube and

clamps with O-Rings.

4.2.1 Piston Roughing Pump (Ground use only)

The first stage of the pumping system consists of the XtraDry 150-2 piston roughing pump, pictured

below, from Pfeiffer Vacuum with a nominal pumping speed of 7.5 m3/h.

Figure 18: The XtraDry 150-20 roughing pump will be used to pump dowm from atmosphere to 0.2

Torr

This 403 mm by 344 mm by 308 mm pump is completely dry (no oil). The piston pump will be used

until the vacuum chamber achieves a pressure of approximately 0.2 Torr, which takes around 25

minutes to accomplish, at which point the second pumping stage will be initiated. The XtraDry 150-2

24

pump will only be used on the ground. See Section 18 for details on pump and vacuum chamber

operation/procedure.

4.2.2 Turbo Pump and Controller (Turned off in flight)

The second stage of the pumping system consists of the Turbo-V 70 LP, which has a pumping speed of

68 L/sec.

Figure 19: Varian Turbo-V 70 LP pump and controller

The controller associated with the turbo pump starts and stops the pump when appropriate. The

controller initiates operation by ramping up the pump to full speed in 60 seconds or less. The pump is

6.6” in height and 4.5” in diameter. The turbo pump will be started when the vacuum chamber reaches

0.2 Torr, and the roughing pump will remain on while the turbo pump is activated. This pump will only

be used on the ground, however, it will be fly with the vacuum chamber. The controller will not be

flown.

4.2.3 Pressure Gauge and Controller

A micropirani/cold cathode pressure gauge will be used to monitor the pressure within the vacuum

chamber. The micropirani sensor measures from atmosphere to 10-4

Torr. After 10-4

Torr, the cold

cathode sensor takes over measurement and is able to measure to 10-9

Torr. These sensors have been

confirmed to be the most rugged combination of pressure sensors available, thus they are expected to

survive flight. The associated controller displays the pressure reading in real time in Torr

25

Figure 20: PKR 251 Compact FullRange Gauge and Controller

The role of the pressure gauge/controller, as part of the pumping system, is to provide the pressure

reading to signal when the second pumping stage needs to be initiated. The pressure gauge’s

information is also important to notice the ultimate pressure achieved for each test and relating that

pressure to test results, as the pressure impacts the performance of the thrusters.

4.3 Humidity Mitigation

Humidity is a big concern for this experiment as it poses a challenge to pumping down to the desired

pressure of 10-7

Torr. The accumulation of water on the inner surfaces of the vacuum chamber causes

outgassing during pump down. It may take days to fully dissipate accumulated moisture in the vacuum

chamber to get down to a low enough ultimate pressure, thus mitigation methods were investigated and

are detailed below.

4.3.1 Heat (Ground use only)

One of the simplest ways to dissipate moisture is to energize water molecules by adding heat, causing

the water to vaporize more quickly. Once the water has vaporized, the pumping system can draw out

the water vapor from the chamber. A bake-out heater tape will be wound around the vacuum chamber,

as shown below, to heat the entire chamber during the pump down process.

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Figure 21: A bake-out heater tape will allow the vacuum chamber to be baked-out at a set temperature

to speed up the pump down process

The heater tape will be supplied voltage using a variable AC power supply, pictured below. This power

supply and heater strip will only be used on the ground as the chamber is pumped down.

Figure 22: Variable AC power supply to power the bake-out heater strip

The bake-out heater strip will be used at around 43o C, to be monitored by a thermocouple and

multimeter, to avoid overheating the pressure gauge which has a maximum operating temperature of

55o C. The pump down curves below show that while exposing the vacuum chamber to one hour of

humid air increases pump down time by about 20 minutes, using the bake-out strips during the pump-

down decreases that time by about 10 minutes.

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Figure 23: Pump down curves for normal air, humid air, and humid air with heat

While the time to pump down with heat on humid air is still more than time to pump down with non-

humid air (normal air), this time is still less than pumping down with purely humid air, and it is

expected that with nitrogen purging, the pump down time will challenge even the normal air pump

down time.

4.3.2 Nitrogen Purging (Ground use only)

An additional method to lessen the affect of humidity is to purge the vacuum chamber with pure

nitrogen gas. By purging the system with nitrogen, that is bringing the system back to atmosphere from

vacuum by leaking in nitrogen gas instead of regular air, less water molecules are anticipated to enter

and settle on the inner surfaces of the vacuum chamber. This will cause less outgassing during pump

downs, thus reducing the time needed to get down to the desired ultimate pressure.

The equipment needed for this includes a nitrogen K-bottle, regulator, over pressure burst valve, and

hose. The nitrogen K-bottle will have a regulator set at 15 psi (760 Torr) to ensure that the vacuum

chamber is never pressurized. The over pressure burst valve will act as the final check to keep the

vacuum chamber from becoming pressurized, as it will burst between 15-25 psi. This over pressure

burst valve, seen in the figure below, will be mounted on the back 6” flange using a 6” to 1.33” CF

reducer flange.

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Figure 24: Over pressure burst valve from Accu-Glass Products, Inc. on a 1.33”CF that will be

attached to a 6” CF using a reducer flange

A schematic, table of specifications, and some additional details on the K-bottle and associated parts

are included in Section 7. None of the nitrogen purging equipment will be flown except the leak and

over pressure valve which is already mounted onto the vacuum chamber.

To purge the vacuum system with nitrogen gas, a chamber that has been pumped down to at least 10-7

Torr will be allowed to take in nitrogen instead of air as it climbs back to atmosphere. First the turbo

pump will be turned off while the leak valve is gradually opened to allow nitrogen to leak into the

chamber. While the nitrogen leaks in, the roughing pump will continue to run. During this time period,

air may also leak in, therefore the piston pump and nitrogen will be allowed to run together until the

chamber is full of only nitrogen. After this, the gate valve will be lowered and sealed, and the leak

valve will be closed to maintain the nitrogen inside the chamber. This procedure will occur every time

the vacuum chamber needs to be brought back up to atmospheric pressure after it has been pump down.

4.4 Electrical Equipment

The following sections describe the equipment used in the high voltage system, piezo system, and data

acquisition system.

4.4.1 Master Kill Switch

The master kill switch is the power switch on a Belkin Surge Suppressor AC power strip connected to

aircraft 115V 60Hz power. In flight, this strip will directly power the DC power supplies, high voltage

power supply, piezo amplifier, NI-DAQ 6259, and flight laptop. It is easily accessible to the flyers

since it is placed in front of the vacuum chamber as shown in Figure 25. The DC power source, high

voltage power source, piezo amplifier, and NI-DAQ 6259 will all turn off immediately once the switch

is hit.

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Figure 25: AC power strip and Master Kill Switch

4.4.2 DC Power Supply

A BK Precision 1761 DC power supply will be used to supply +/-18V power to the ICD/Faraday probe

circuitry. The circuits regulate the +/-18V supply down to +/-15V to provide the nominal voltage level

the circuitry.

Figure 26: BK Precision 1761

4.4.3 High Voltage System

The high voltage power supply that will be used is an UltraVolt HVRack supply and was successfully

flown in the 2008-2009 ZESTT campaign. The UltraVolt HVRack and has four individually

configurable 40kV channels. The front panel, as seen in Figure 27, contains the manual controls for the

HVRack. This includes dials to set the voltage level for each channel as well as dials for DC current

compliance. Additionally, LED displays on the front panel show the voltage and current levels for each

channel. To keep flyers safe during the experiment and away from high voltage while in microgravity,

the high voltage system will be automated by a MATLAB program described in Section 6.8.

Figure 27: HVRack front panel

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4.4.3.1 High Voltage Flow

The HVRack will be controlled by the flight laptop and DAQ through a 37 pin D-Sub control interface

on the back panel of the HVRack, see Figure 28. Channel A will feed into one of the single pin, high

voltage feedthroughs on the vacuum chamber. Once inside the chamber, the high voltage line will feed

in parallel to the charging sieves of both thrusters. Similarly, channel B will feed through the other

single pin, high voltage feedthrough and to the acceleration gates.

4.4.3.2 High Voltage Control

The HVRack can be controlled via a 37 pin D-Sub connector shown in Figure 28.Pin control and signal

recording are handled by a data acquisition system as described in Section 6.8. Pins 1, 8, 15, and 22

toggle the output on and off of channels A, B, C, and D respectively. A logic 5V signal enables

respective channels and 0V disables the channels. Pins 2, 9, 16, and 23 control the voltages of channels

A, B, C, and D. A 0-5V signal corresponds to 0-43.2kV output. Pins 3, 10, 17, and 24 return the voltage

levels of the channels with a 0-5V signal that corresponds to 0-43.2kV on the channel output. Pins 3,

11, 18, and 24 control the current compliance of each channel with a 0-5V signal corresponding to 0-

108% of the maximum current allowance. Pins 4, 12, 19, and 25 returns the current being sourced out

of each channel with a 0-5V signal corresponding to 0-108% of the maximum current allowance.

Figure 28: HVRack D-Sub control interface

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4.4.3.3 High Voltage Safety

See Section 6.2.1 for flyer protection scheme from high voltage. This scheme implements an insulating

high voltage cap and RTV Silicone at the high voltage feedthrough interface to insulate the otherwise

exposed high voltage pin. See Section 6.5 for analysis of high voltage discharging.

4.4.4 Piezo System

A PD-1301 piezo amplifier from Nihon Ceratec Co. is a 20X amplifier that will be used to drive the

thruster piezos. The piezo amplifier can provide operational ranges of -10 – 150V output and 2 Arms.

Figure 29: PD-1301 Piezo driver front panel

4.4.4.1 Piezo Switch Box and Pearson Coil

A Pearson coil will be used to measure the current sourced by the piezo amplifier. A Model 110 Pearson

coil from Pearson Electronics Inc. measures current linearly with 0.1Vout/1Ain. By wrapping the

piezoelectric drive line around the Pearson coil ten times, 1Vout/1Ain is achieved. A 1/50X voltage

divider is also built into the piezo switch box that will provide the signal for a piezo feedback control

scheme.

The Pearson coil will be housed in an electrically grounded box to protect other signal lines from the

non-shielded lines inside the box. This box will also contain switches to select which of the two

thruster piezos will be driven.

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Figure 30: Piezo switch box with Pearson coil

4.4.4.2 Feedback control

A closed loop feedback control scheme as shown in Figure 31 will be used to actuate the piezos. A

microcontroller measures the piezo voltage and current to provide feedback control.

Figure 31: Piezo control feedback scheme

Control of the piezoelectric system will be done with a TI Piccolo microcontroller. The Piccolo has

thirteen, 12bit analog to digital inputs as well as eight pulse-width-modulated (PWM) outputs that,

once filtered, will simulate a function generator. The piezoelectric system calls for four ADC inputs,

one from each of the thruster’s thermocouple sensor outputs, one for piezo voltage, and one for piezo

current. The system will also use one of the PWM outputs that will provide the compensated signal to

the feedback loop of the thruster selected in the piezo switch box. Because the piezo draws a large

amount of power, a thermocouple is used to monitor piezo temperature. This thermocouple is a Fluke

type K thermocouple. The thermocouple measurement will be used to first ensure that the piezo does

not reach a temperature above its maximum operating (200oC) temperature or Curie temperature

(350oC). A temperature to piezoelectric constant mapping will also be used to modify the control signal

to compensate for a varying piezoelectric constant as temperature increases.

A pre-amplification stage is implemented to filter and amplify the thermocouple output. The cutoff

frequency of the filter is 10Hz to ensure that electromagnetic noise from the piezo does not contaminate

33

the temperature reading. This amplification circuit is placed directly on the M-2 spring block inside the

vacuum chamber. A second preamp circuit will be placed between the microcontroller PWM output

and the piezo driver to map the 3V max output of the microcontroller to the 7.5V max input to the

piezo driver.

Figure 32: Top: 2.5X preamp for piezo driver Bottom: 10Hz low pass filter

4.5 Data Acquisition System

The data during flight will be managed using two data acquisition devices provided by National

Instruments. The NI-USB-6259 has a maximum sampling rate of 1.25 MS/s, with 16 analog inputs and

16bit conversion. The NI-USB-6218 has a maximum sampling rate of 250 KS/s, with 32 analog inputs

and 16bit conversion. Both devices accept input signals of -10 to + 10 V.

Figure 33: Left: NI USB 6218 Right: NI USB 6259 DAQs

34

The laptop used in flight is a Panasonic Tough-book 52 Semi-Rugged laptop. This particular model is

designed to withstand shock, dust intrusion and water damage. With regards to flight, the laptop serves

as an information relay between the two DAQ modules and necessary controls via MATLAB, see

Section 6.8. The laptop has 1.8Ghz processing speed, 2Gb SDRAM, 80Gv hard drive, and weighs

7.4lbs.

Figure 34: Panasonic Tough-book

4.6 Extra Ground Equipment

In addition to the equipment listed above, several items will be brought to Ellington Field to serve as

only ground equipment.

Table 2: Extra Ground Equipment

Ground Equipment Quantity Purpose

Contained 5um Particles 2 Vials Back-Up

Contained 53um Particles 2 Vials Back-Up

Extra Vacuum Chamber Bolts 20 Back-Up

Extra Chassis Bolts 10 Back-Up

Extra Shrink Wrap 1 Roll Back-Up

Extension Cord 4 Power Components

Extra Wire 1 Roll Back-Up

Kapton Tape 2 Rolls Back-Up/Assembly

Blow Dryer 1 Assembly

Exacto-Knife Set 1 Assembly

Extra Copper Gaskets 20 Chamber Assembly

Dremmell Kit 1 Assembly

First Aid Kit 1 Safety

Box Nitrile Gloves 1 Safety/Assembly

Box Masks 1 Safety/Assembly

Box Kimwipes 2 Clean-up

Isopropanol 1 Liter Clean-up

Acetone 1 Liter Clean-up

Copper Barrel Connectors 10 Chamber Assembly

35

Vented Screws 10 Assembly

Extra High Voltage Wire 10ft. Back-Up

USB O-Scope 1 Ground Electrical Diagnostics

Digital Multimeter 2 Ground Electrical Diagnostics

Extra Banana Cable 5 Ground Electrical Diagnostics

Extra BNC Wire 5 Ground Electrical Diagnostics

Extra BNC and Banana Connectors 10 Ground Electrical Diagnostics

Solder 1Roll Back-Up/Assembly

Soldering Iron 1 Back-Up/Assembly

RTV Silicone 1 Tube Back-Up/Insulation

Silver Conductive Epoxy 1 Tube Back-Up/Assembly

4.7 Chassis Layout and Flyer Positioning

Figure 35: Chassis layout and flyer positioning

As indicated in Figure 35, two fliers will be located at the front of the chassis and a third will be

positioned to the left of the chassis. Flier 1 will monitor the pressure gauge controller (shown in

brown). Flier 1 will also periodically check the piezo amplifier (shown in grey). Flier 2’s primary

responsibility is initializing the automation code from the laptop (shown in blue) and switching the

piezo switch box every parabola. Flier 3 will view the thruster firing through the front 8” vacuum

chamber viewport and monitor the HV power supply during flight.

In the off-nominal case that Flier 1 gets ill, Flier 2 will manage the pressure gauge controller, piezo

driver and automation while the piezo switching will fall to Flyer 3. Should Flyer 2 get ill, Flyer 1 will

take over automation and again, Flier 3 will take piezo switching. If Flyer 3 falls ill, Flyer 2 will also

monitor thruster firing.

4.8 Special Handling Requirements

Nitrile gloves and masks should be worn at all time when working with particles. This includes loading

and cleaning of thrusters. When dealing with particles, use slow, steady motion to decrease likelihood

of particles becoming airborne. When not in use, the particles shall be tightly sealed in their vials.

36

During all testing all high voltage lines used must be HV rated wire: XLPE 40kV wire outside of the

chamber and 30kV silicone insulated wire inside the chamber. The high voltage power supply, when

not needed shall be turned off and unplugged.

4.9 Free Float Experiment

This experiment is not a free float experiment.

5 Structural Verification Structural analysis was performed on the chassis beam structure, vacuum base plate, aircraft mounting

brackets, and thruster mounting rod. A combination of finite element analysis (FEA) and hand

calculations using simplified and linearized equations of elastic mechanics of materials was used to

determine the maximum stresses, deformations, and worst-case factors of safety. The full entirety of

this analysis can be found in the Stress Analysis Report submitted accompanying the TEDP. All

structural configurations comply with NASA-specified worst case loading scenarios and have a

minimum factor of safety above 2.

All stress analysis was performed using the setup shown in Figure 35.

5.1 Analysis Method

ANSYS Workbench was chosen to create the mesh and perform analysis on the structure because of its

relatively simple mesh generation setup, and its unique global acceleration loading field. Refer to

section 7.2 of the Stress Analysis Report, for a comprehensive FEA analysis of the chassis beams and

vacuum chamber mounting plate.

5.1.1 Free Body Diagrams

Free Body Diagrams can be found in Section 6.0 of the Stress Analysis Report.

5.1.2 Component Specifics

The chassis is built from three types of 6105-T5 beams differentiated by their cross-sections: 1.5” by

1.5” 1515-Lite beams serve as the four vertical and bottom perimeter beams; the thicker 1.5” by 3”

1530 beams support the vacuum chamber with their increased girth; and the slender 1” by 1” beams

provide further support to the chassis on the middle perimeter and lower interior sections.

37

Figure 36: 80/20 beam cross section

Figure 37: Beam distribution: 1515 beams shown in blue. 1530 beams shown in green. 1010 beams

shown in red

The chassis is 59” in length, 24” wide and 28” tall. All beams are bolted together using 6105-T5

aluminum L-brackets and a combination of 5/16”-18 and 1/4"-20 steel bolts. The only two welds in our

setup are the handles on the top 8” blank vacuum flange, and the thruster mount rod within the

chamber. However, the handles are non-load bearing during flight, and the thrusters are fully enclosed

within the vacuum chamber and thus pose safety hazard to flyers. Welding certification documentation

is also included in the Appendix J.

The chassis will be secured to the aircraft hull at four mounting points via two angled aluminum

brackets that span the width of the chassis as seen in Figure 38. Each bracket interfaces with the aircraft

at two corners and connects with the chassis using five steel bolts. Sections 7.1.2 and Appendix of the

38

Stress Analysis Report details the methods used to obtain a minimum factor of safety of 3.8.

Figure 38: Aircraft mounting brackts span the width of the chassis

All sides of the chassis excluding the front are enclosed with heavy duty plastic insulation sheeting.

This shields from the “kick loads” of 125 lbf over a 2” radius and prevents accidental contact to

components during flight. All components except for the vacuum chamber and dry scroll pump, which

are bolted to the chassis directly, will be fastened in the chassis via Velcro, zip ties, and straps in two

directions to ensure all degrees of freedom are fully restricted. Table 3 outlines component securement.

A random vibration test will be used to verify proper attachment.

Table 3: Component Mounting

Component Mounting Method Mounting Surface

Chamber Mounting Plate 5/16” Steel Bolts 1530 Beams

DC Power Supply Straps Piezo Amplifier

Fan Velcro HV Power Supply

HV Power Supply Straps 1010/1515 Beams

DAQs Velcro 1515 Beams

Laptop Velcro/Zip-ties 1010 Beams

Piezo Amplifier Straps 1010/1515 Beams

Piezo Switch Box Velcro/Straps 1515 Beams

Power strip Zip-ties 1010 Beams

Vacuum Chamber 5/16” Steel Bolts Mounting Plate

Vacuum System-Dry Scroll

Pump

¼” Steel Bolts Mounting Plate

Vacuum System-Pressure Gauge

Controller

Straps, Velcro 1010 Beams

Vacuum System-Pump Controller Straps, Velcro 1010 Beams

The total system mass will not exceed 390.4 lbs with contingency, though we have obtained a mass

waiver of 100 lbs giving us a mass constraint of 400 lbs. However, we have weighed our complete

assembly and we do not expect it to exceed 366.4 lbs.

39

The entire experiment will not exceed 400 lbs of weight. The supporting area footprint of our

experiment is 9.83 square feet; thus, the aircraft floor will not exceed 40.6 pounds per square foot.

Table 4: Mass Budget

Item Quantity

Unit Weight

(lbs) Contingency

Mass with

Contingency

Chassis - 80/20 + Bolts + Hardware 1 73.5 5% 77.18

Chassis - Chamber Mounting Plate 1 5.4 5% 5.67

Probe Setup 1 10 20% 12.00

Shielding Mesh 1 2 20% 2.40

Mounting Rod 1 10 20% 12.00

Thruster 2 2 20% 4.80

Vacuum System - BNC Feedthrough 1 0.6 5% 0.63

Vacuum System - BNC Feedthrough 1 0.6 5% 0.63

Vacuum System - 8" Viewport 2 5.3 5% 11.13

Vacuum System - Chamber 1 51.5 5% 54.08

Vacuum System - Chamber Bolts 1 11.1 5% 11.66

Vacuum System - Converter Flange 1 5.3 5% 5.57

Vacuum System - Copper Gaskets 1 1.3 5% 1.37

Vacuum System - Hose 1 0.6 5% 0.63

Vacuum System - 6" D-Sub 1 6.4 10% 7.04

Vacuum System - Leak Valve 1 2.6 5% 2.73

Vacuum System - 8”Blank Flange 2 11.6 5% 24.36

Vacuum System - Pressure Gauge 1 1.6 20% 1.92

Vacuum System - Gate Valve 1 12 5% 12.60

Vacuum System - HV Feedthrough 2 1.4 5% 2.94

Piezo Switch Box 1 2.2 10% 2.42

DC Power Supply 1 6.9 5% 7.25

Vacuum System - Dry Scroll Pump 1 21.6 5% 22.68 Vacuum Sysem - Pressure gauge Controller 1 2.5 20% 3.00

Master Kill switch 1 2 50% 3.00

Grounding Rod 1 1.5 5% 1.58

HV Power Supply 1 21.6 5% 22.68

NI USB-6255 DAQ 1 2.7 10% 2.97

Piezoelectric Amplifier 1 25.6 5% 26.88

function generator 1 7 10% 7.70

Panasonic Toughbook 1 9 5% 9.45

Chassis - Plastic Wrap 1 0.6 5% 0.63

Wiring 1 10 15% 11.50

Systems Margin 1 10 10% 11.00

Expected Weight w/Contingency

40

Total(lbs.) 323.8 369.135

41

5.1.3 Minimum Margin of Safety Table

Refer to section 2.0 of the included Stress Analysis Report for a comprehensive margin of safety table

for all load bearing components. No factor of safety falls below the 2.0 dictated by NASA

requirements.

6 Electrical Analysis

The follow sections show the schematic and load analysis of the electrical system.

6.1 Schematic

Figure 39 shows a schematic of the electrical layout. The high voltage power supply, piezoelectric

amplifier, DC power supply, laptop, and NI-DAQ 6259 are powered by the aircraft 115V 60Hz power

through a Belkin surge suppressor. The high voltage power supply is used to charge up the accelerating

gates of the thruster. The piezoelectric amplifier drives the thruster piezos while piezo line voltage and

current measurements are made an intermediate piezo switch box. Piezo voltage and current, Faraday

Probe data, ICD data and HV voltage and current data is taken by the DAQs. The entire scheme is

automated by a MATLAB program except switching of the piezos between thrusters which is done

through the piezo switch box.

Figure 39: Electrical schematic

6.2 Outside Chamber Wiring

All wiring besides high voltage and piezo drive lines are both low current and low voltage lines and are

42

carried over either 22 gauge wire or 26 gauge BNC wire.

6.2.1 High Voltage Wiring

The high voltage output of the HVRack will be connected directly to a high voltage feedthrough. The

wire that will be used is 40kV rated XLPE wire. A B110YX10 connecter that is rated for 40kV will be

used to interface the HVRack with the XLPE wire. The XLPE wire is 12 gauge wire. The maximum

current flowing through these wires is on the order of microAmps via a settable current compliance on

the high voltage power supply. A ring terminal will be used to attach the XLPE wire to the high voltage

feedthrough pin. Room Temperature Vulcanizing (RTV) silicone will be used to enclose the exposed

feedthrough pin/ring terminal interface. RTV silicone has a high dielectric constant that will act to

protect the flyers from high voltage during flight.

A high voltage cap will also be used to enclose each of the high voltage feedthroughs from the flyers.

These caps are made of ultra high molecular weight polyethylene (UHMWPE). The maximum voltage

that the high voltage power supply can supply is 40kV. As shown in Figure 40, the high voltage cap has

a 3.5in diameter and 0.25in side wall and top thickness. The caps also have grooves that fit over the

2.75in high voltage flange to ensure that they do not come off during flight. The two halves of the high

voltage cap are screwed together and further held together by Kapton tape. The side wall thickness of

the high voltage caps provides a factor of safety of 14.3 given that the dielectric constant of UHMWPE

is 900kV/cm and the wall thickness is 0.25in. This high voltage cap has flown successfully in the 2008-

2009 ZESTT campaign. The RTV silicone layer provides an additional layer for high voltage protection

with a dielectric strength of 19.7kV/mm. Potential areas subject to a high probability of high voltage

arcing mainly within the M-2 thruster wiring interfaces and in chamber high voltage feedthrough

connector interface will be identified throughout integrated systems tests prior to travel to Ellington

Field and will be coved in 2.7mil thick Kapton tape. Each layer of Kapton tape applied provides an

additional 8,000V dielectric standoff.

Figure 40: HV Cap on 2.75" flange

43

6.2.2 Piezo Drive Line Wiring

The highest gauge BNC wiring that is used with the piezo drive lines are 26 gauge. The wiring gauge in

the piezo switch box carrying piezo drive currents is 22 gauge. The maximum current limitation of the

piezo amplifier is 2rms before overdrive protection is activated and output drops to zero.

6.3 Vacuum Side Wiring

Inside the vacuum chamber, special attention must be taken with selection of wires to ensure both

vacuum compatibility and electrical compliance.

For the piezo lines entering and exiting the vacuum chamber through the BNC feedthrough, a 24AWG,

Kapton insulted, silver plated copper wire was chosen. This wire is able to take up to 4A and 600V, and

is rated to 10-10

Torr. This wire will also be twisted paired for added electromagnetic shielding for the

piezo lines. Please see Section 4.1.1 for more on the BNC feedthrough.

The other instrumentation lines, the signal and ground lines for the ICD and Faraday Probe, will be fed

through the D-Sub feedthrough. This D-Sub feedthrough has a male D-Sub connector on both vacuum

and air sides, thus both sides will make use of a D-Sub cable with a female connector to connect to the

feedthrough. On the vacuum side, a cable assembly with a polyetheretherketone (PEEK) female D-Sub

connector attached to a Kapton insulated ribbon cable with 28AWG wire will connect the diagnostic

instruments to the D-Sub feedthrough. This cable is rated to 600V, 2A, and 10-10

Torr.

Figure 41: In-vacuum D-Sub cable with PEEK connector and Kapton wire, the non-terminated side

will have quick disconnects to connect to the ICD and Faraday Probe8

The high voltage (HV) coming into the vacuum chamber through the high voltage feedthroughs will

flow through a silicone insulated, 12AWG, stranded core, silver plated copper wire once inside the

chamber. This wire is rated to 30KV, 20A, and 10-8

Torr, and will be connected to the pins on the

vacuum side of the HV feedthrough using barrel pins, pictured in Figure 9.

6.4 Electrical Load Analysis

All loads that will be powered by aircraft 115V 60Hz power are shown in Table _. Under maximum

current draw conditions, the total current drawn from the aircraft will be 12.92A which is less than 16A

44

or 80% of the 20A circuit breaker limitation on aircraft power. The total +/- 15V DC power coming

from the DC power supply that will be used to power the instrumentation amplifiers associated with the

ICD, Faraday Probe, and microcontroller/piezo feedback scheme is less than 400mA which is less than

the maximum 1.05A current limitation of the DC power supply.

Table 5: Current Load Chart

Part Max Instantaneous Current

Draw

Supply Voltage

Laptop 0.75 A 115 V 60Hz

DC PS 1.6A 115 V 60Hz

HV PS 0.47 A 115 V 60Hz

Pressure Gauge 0.1 A 115V 60Hz

Piezo

Amplifier

10 A 115V 60Hz

TOTAL 12.92A

20A max outlet current

6.5 High Voltage Discharging

The high voltage system will be discharged directly back to the HVRack. As shown in Figure 42, the

high voltage supply takes 1.29 seconds to discharge 67% of its initial voltage when connected to two

plates similar in capacitance to NanoFET. This configuration was flown successfully during the 2009

ZESTT campaign. As such, no additional discharging mechanisms will be needed. A grounding rod

will be kept on the chassis as a precaution to actively discharge conductive surfaces that may be

suspected to still be charged after high voltage has been turned off.

45

Figure 42: High voltage discharging time constant

6.6 Electrical Kill Switch

In an emergency, only the master kill switch located on the Belkin power strip and located in the front

of the chassis needs to be switched. All component power is routed from this line and all electrical

drivers will discharge back to ground. High voltage will discharge as shown in Figure 42.

6.7 Loss of Electrical Power

In the event of a loss in electrical power, all components are turned off to a safe state. As a precaution a

grounding rod will be kept with the chassis to manually discharge conductive surfaces if needed. A loss

in electrical power to the vacuum pumps will only cause air to slowly leak back into the vacuum

chamber and will not damage any equipment.

6.8 MATLAB Automation Scheme

During flight, all experiment processes will be managed by a MATLAB program providing efficient

experiment operation and data collection, as well as flier safety. MATLAB determines which control

signals are to be sent from the flight computer, while all data collection will be managed by the DAQ

modules and then sent to the computer to be saved. The following tables show the number of samples

collected per signal line.

Table 6: NI USB 6218

Devices Number Sampling (Samples/s)

HV Power Supply Voltage 2 100

HV Supply Currents 2 100

46

Thermocouples 2 100

Accelerometer 1 100

Total Devices 7 700

Table 7: NI USB 6259

Devices Number Sampling (Samples/s)

Piezo Voltage 1 200,000

Piezo Current 1 200,000

ICD 1 200,000

Faraday Probe 1 200,000

Microcontroller Output 1 200,000

Total Devices 7 1.00E+06

To ensure the safety of the flyers as well as the experiment, safety precautions have been implemented

into the MATLAB code. The “Run/Stop” toggle button allows users to easily decide if there is a need

for sampling or if automation needs to be terminated because of danger. The initial button state is

“Run” upon the first click, and automation continues at that point. Another click of the same button will

terminate everything; including the HVPS, piezo system as well as all other controls.

The MATLAB program relies on coercion of three components; those being hardware, data and

programmable operations. The figure below demonstrates the logic behind the automation scheme.

Figure 43: MATLAB automation scheme

47

The automation scheme begins with user input. The only button that the users will have to press in

flight is the Run/Stop button. This will tell the HV power supply, via DAQ analog output signal, what

high voltage levels the M-2 charging and accelerating gates must hold. Once in microgravity, triggered

by the aircraft acceleration signal, the DAQ will tell the microcontroller via digital I/O, what waveform

to generate. Data is then taken on the ICD, Faraday probe signal, piezo current and voltage, and

microcontroller output during the duration of microgravity. Once out of microgravity, the piezo will

turn off due to a zero command from the microcontroller and the saved files will close. At this point the

fliers will have to manually switch on the piezo of the other thruster using the piezo switch box.

Meanwhile the MATLAB program waits for the next microgravity period. This process continues until

the flier presses the Stop button at the end of flight.

7 K-Bottle Team ZESTT Reflight will be bringing a nitrogen K-bottle to Ellington Field. This compressed

nitrogen gas will be used in purging the vacuum chamber as it is brought up to atmosphere from

vacuum to aid in humidity mitigation. The vacuum chamber will never be pressurized above

atmosphere, and an over pressure burst disk installed on the vacuum chamber will work to prevent the

chamber from ever going above 25 psi, although it is expected to burst closer to 15 psi than 25 psi.

Please see Section 4.3.2 for more details on this nitrogen K-bottle. A schematic of this pressure system

and a corresponding design specifications table is shown below.

Figure 44: Schematic of nitrogen purging pressure system

48

Table 8: Nitrogen purging pressure vessel design specifications

Schematic

Reference

Number

Component

Description

MAWP

(psi)

Relief Valve

Setting (psi)

Regulator

Setting

(psi)

Built By Cert.

Test/Calib.

Date

Proof Test-

Certified By

1 Nitrogen K

bottle 2400 N/A N/A Airgas, Inc. unknown On “k”

bottle DOT

sticker

2 Regulator 3000 N/A 15 Victor

Equipment

Co.

unknown unknown

3 Hose 40 N/A N/A Airgas, Inc. unknown unknown

4 Leak Valve N/A N/A N/A Kurt J.

Lesker Co. N/A N/A

5 Stainless

Steel Vacuum

Chamber

15+ N/A N/A Kurt J.

Lesker Co. Jan 29,

2009

Ron Smith,

KJLC

6 Over Pressure

Burst Disk

25 15-25 N/A Accu-Glass

Products, Inc N/A N/A

See Section 4.2 and Section 4.3.2 for additional information on the vacuum system and nitrogen K-

bottle respectively.

8 Laser Certification

No lasers will be used during flight or ground testing at Ellington Field. This section does not apply to

the experiment.

9 Parabola Details and Crew Assistance

A minimum of twenty microgravity periods is required for this experiment, per flight day. These

twenty parabolas will allow each thruster to be tested at least ten times and give enough data for proper

analysis of the M-2 and diagnostic tools. In addition to the minimum twenty microgravity parabolas,

the first two parabolas will be set aside for flyers to adjust to the microgravity and 2g conditions, the

third and fourth parabolas will test MATLAB code function with the onboard accelerometer, and any

other additional parabolas will be evenly distributed among the two M-2 prototypes to gather additional

data. The last few parabolas will be used to perform the secondary outreach experiment suggested by a

pre-college student from our outreach programs.

This experiment is almost completely automated by MATLAB, thus NASA crew member assistance

should not be required. The prototypes will also not need any handling, since they will remain sealed in

the vacuum chamber at all times. The flight crew will only interface with the GUI to initiate MATLAB

49

and monitor instruments and in-chamber conditions during the parabolas. See Section 6.8 for details on

automation.

At the turnaround period, flyers will check for proper function of the background camera and replace

the camera mini disc such that video can be taken for the remainder of the flight. Additionally, another

flight crew member will ensure that data is being stored properly. Thruster prototypes will not be

running during the turnaround time, and the prototypes do not need to be tested in consecutive

microgravity periods, thus time between parabolas is acceptable.

10 Institutional Review Board (IRB)

Neither human nor animal test subjects are part of this experiment, and no biological tests will be

conducted, thus this section is not applicable to this experiment.

11 Hazard Analysis The follow Integrated Hazard analysis contain the hazard analysis involved the ZESTT Reflight

experiment. Controls are designed to mitigate these hazards. Specifically, the high voltage system

posses the largest hazard risk of the ZESTT Reflight experiment. The only high voltage exposed to the

flyers is at the high voltage feedthrough interface. The control to be used is a high voltage cap to be

used as a high voltage standoff between the feedthrough and potential flyer contact. In chamber high

voltage arcing will be controlled by applying layers of Kapton tape to identified areas of potential

arcing. See Section 6.2.1 for details on the high voltage wiring used and dielectric standoff strength of

the high voltage cap and Kapton tape.

11.1 Integrated Hazard Analysis

Date: 5 May 2010

Hazard Analysis of ZESTT Reflight System

Facility: Microgravity Aircraft and Ellington Field, Houston, Texas

Prepared by: Team ZESTT Reflight

Organization: University of Michigan Student Space Systems Fabrication Lab (S3FL)

Risk Assessment Code

RAC Description

1 Unacceptable – All operations cease until hazard is controlled 2 Undesirable 3 Somewhat acceptable with controls

4-7 Acceptable with controls

Severity Class

Class Description I Catastrophic

50

II Critical III Moderate IV Negligible

Probability Codes

Code Description A Likely to occur B Probably will occur C May occur D E

Unlikely to occur Improbable

RAC

Assignment Probability

Severity Class A B C D E

I 1 1 2 3 4

II 1 2 3 4 5 III 2 3 4 5 6

IV 3 4 5 6 7

Hazard Condition Cause Effect Disposition

Before Controls

Controls Verification Disposition

After Controls Electrostatic Discharge

(ESD)

Contact with

exposed wiring or

close conductive

component, likely

near high voltage

Injury to person(s),

damage to

equipment

I/B/1 40kV rated XLPE

wire is used outside of

chamber and 30kV

rated silicone

insulated wire is used

inside chamber. High

voltage caps made of

UHMWPE covers the

high voltage

feedthroughs which is

the most likely place

for HV interacting

with flyers. In

addition, the air side

of the flange will be

covered with RTV

silicone rated to

19.7kV/mm before

the HV caps. All

connectors on HV

lines will be covered

with silicone tape as

well, and these lines

carrying HV will be

routed behind the

equipment on the

chassis where full

panels of plastic wrap

serve as an extra

barrier for people

from HV. Grounding

rod will serve for

manual discharging

Test continuity of

chassis structure to

ground, inspect all wires

designed to carry HV

paying special attention

to the ends to make sure

insulation is intact all

over. Check for

discontinuity between

chassis and HV to

ensure no short circuits

to HV thus unobserved

exist.

I/E/4

"K" bottle explosion Improper storage,

cap loose, improper

handling and

Equipment damage,

injury to person(s)

I/C/2 Cylinder will always

be strapped to a wall

or table, and a

Ensure strap(s) holding

cylinder to the

wall/table/vehicle is/are

I/E/4

52

trasportation regulator or cap will

always be on the

cylinder. All safety

procedures regarding

compressed air tanks

will be observed.

During transportation,

the cylinder will be

secured to keep it

from rolling around.

secure and tight, ensure

compliance with

suggested safety

precautions for

compressed air tanks.

Vacuum Chamber

Explosion/Implosion

Chamber rupture or

suddenly acquires

leak, chamber

acquires pressure

differential at 8000ft

cabin pressure due to

malfunctioning

pressure gauge

Injury to person(s),

damage to

equipment, aircraft

damage. If chamber

ruptures due to

higher pressure

inside than the

ambient pressure,

particles may

escape into the

atmosphere.

Otherwise, if

chamber ruptures, it

will likely have an

air flow in and, at

worst, will implode,

thereby not causing

injury to person(s)

though it may

damage equipment

inside the chamber

I/D/3 In the case of a

pressure differential,

installed pressure

burst valve should

burst or puncture

before the chamber

has a chance to

explode. A filter

between the chamber

and burst valve should

keep particles from

escaping in case of

this situation. For

leaks, copper gaskets

are placed between

the flange and

chamber to ensure the

best seal, or o-rings

are used, and

everything is

tightened down as

well as possible.

Inspect vacuum

chamber to be sure

pressure burst valve has

been mounted, and

through viewport, make

sure each flange has a

copper gasket. While

pumping down, ensure

all flanges have been

tightened down using

wrenches, and tighten

down any leaks found.

III/D/5

Chassis comes loose

from aircraft mounting

Improper or loose

mounting to aircraft,

overloading of

mounting brackets

Injury to person(s),

equipment damage

II/D/4 There will be many

points of connection

of the chassis to the

aircraft so if one fails,

there will be others to

hold the chassis to the

Ensure tightness of

mounting bolts, inspect

condition of brackets

and bolts

II/E/5

53

aircraft. The fasteners

will be tightened, and

structural analyses

were used to ensure

the chassis can

withstand adverse

conditions of hyper-g

forces.

Vacuum Chamber mount

comes loose

Bolts not tightened,

overloading of

chamber mount plate

Injury to person(s),

equipment damage

II/D/4 There are many points

of connection on the

mount plate to ensure

chamber will remain

in place even if one

bolt fails. The bolts

will be tightened as

much as possible.

Ensure tightness of

mounting bolts, inspect

condition of brackets

and bolts

II/E/5

Sharp Edges or Pinch-

Points

Structure/equipment

has sharp edges

made from metal or

hard plastic

Increased injury to

person(s) during 2g,

lesser extent of

injury with other

conditions

(microgravity and

1g)

II/A/1 All sharp edges and

corners will be

padded with foam.

The plastic wrap

casing of the chassis

will prevent flyers'

body parts from

entering the chassis

and making contact

with sharp equipment

points and other

objects.

Inspect structure for

sharp point and cover

with foam, ensure foam

has been secured firmly

and coverage is

acceptable, ensure

plastic wrap is in place,

snug, and coverage is

acceptable

III/D/5

High Voltage Arcing Close conductive

material with high

voltage components,

inadequate

insulation, sharp

solder joints and

other sharp metal

points at high

potential

Injury to person(s),

damage to

equipment

II/B/2 Use high voltage rated

insulated wiring;

Have adequate

distance between high

voltage components

and conductive

materials, Automate

experiment to reduce

human interaction

with high voltage

Extensive testing of

high voltage system;

Inspect all circuits and

wiring prior to each

experiment; Rehearse

emergency procedures

including methods of

turning off the high

voltage power supply

and master kill switch

II/D/4

54

components, Design

for proper discharging

of the high voltage

system, Insulate

exposed high voltage

regions, Grounding

rod for manual high

voltage discharging

Heavy Item Drop Poor mounting of

equipment to

structure

Injury to person(s),

equipment damage

II/C/3 Straps will be used to

secure all equipement

to the chassis. Load

analyses of chassis

beams have shown

their ability to

withstand equipment

weight through the

cases outlined by

NASA.

Ensure tightness of

straps and equipment

inside the straps. Make

sure straps are in good

condition. Ensure

correctness of load

analyses.

II/D/4

Handle(s) break during

lift

Weight distribution

over the handles too

large during chassis

lift, improperly

placed handles,

handles not secured

down well

Damage to

personnel and

equipment

II/C/3 Handles will be

positioned after

analysis of chassis to

find best possible

locations. All screws

will be secured down

firmly. A cart will be

used to move chassis

around as much as

possible to minimize

need for lifting.

Inspect tightness of

bolts holding handles

onto the chassis, ensure

handles are in a

comfortable position for

lifters and that

positioning is optimal

for minimizing stress on

each handle

II/D/4

Overheating vacuum

chamber during baking

Heat tape and

temperature not

monitored,

prolonged use of

heat strip

Damage to

equipment, damage

to wire and HV

feedthrough

insulation, injury to

person(s)

II/D/4 A thermocouple

placed on the vacuum

chamber will be used

to monitor the

temperature at all

times. The power

supply for the heat

strip can be turned

down or turned off in

Ensure proper

placement of

thermocouple and that it

has been activated,

ensure the hard stop is

in place, ensure easy

access to off switch of

power supply

IV/D/6

55

the event that the

temperature goes over

40oC, and a hard stop

will be placed on the

power supply at 40V

to prevent going

above this voltage and

increase the

temperature at a

higher rate.

Bent chassis beam due to

lift or flyer hanging onto

it

Stress on beam

during lift or flyers

hanging on to beams

in flight

Weakened structural

support, Injury to

person(s),

equipment damage

II/D/4 Analysis has been

conducted on all

beams with NASA

specified conditions

and have been found

to be safe with 2 or

more FOS. Top and

middle beams, where

flyers are most likely

to hang on, do not

have equipment to

bear. There will also

be foam padding on

the beams so flyers

are not injured in case

of bent beam.

N/A N/A

Airborne Micro-particles Particles leak out of

thruster and out of

vacuum chamber,

mishandling of

particles during

loading into thrusters

Injury to person(s) III/C/4 Vacuum chamber will

be properly sealed at

all flanges, and a filter

will be placed at gate

valve flange and over

pressurization disk

flange. Particles will

be kept sealed in vials

and personnel will be

trained in inserting

particles into the

reservoir properly to

Examine inner vacuum

chamber surfaces

through viewport to

ensure filters are in

place and secured.

While pumping down,

ensure leaks have been

mitigated.

III/D/5

56

keep particles from

being loosed into the

air.

Foreign objects floating

from chassis

Objects lodged in

chassis or on chassis

before flight

Injury to person(s),

equipment damage

III/C/5 Plastic wrap covering

chassis should prevent

accidental placement

of items inside

chassis. Plastic wrap

will also aid in

keeping foreign

objects in chassis

from getting out in

microgravity before

object can be

contained. A thorough

check of the entire

chassis and all

equipment will occur

before flight to ensure

no loose objects.

Ensure no loose objects

on chassis and

equipment, ensure

plastic wrap is in place

and un-ruptured

III/D/5

Shatter-able Materials Object or flyer

impacting equipment

(nothing on the

structure is

particularly shatter-

able besides the

flight laptop)

Injury to person(s),

Equipment damage

III/D/5 Sides of the structure

are covered with

plastic wrap which

has been tested to

survive 125lb kick

loads over 2" radius

and 180 lbf impact at

2m/s. Flyers will be

secured with straps

provided on the

aircraft, and handles

on the structure will

allow flyers to hold on

and keep themselves

from impacting

things.

Inspect plastic wrap and

make sure it is secured

to chassis firmly in all

places before flight.

Make sure handles are

reachable and can be

used easily by flyers.

Ensure straps are

available for flyers to

use near the chassis on

the aircraft.

III/E/6

Isopropanol expelled by

pumps in liquid form

Isopropanol enters

chamber during leak

Equipment damage III/C/4 Roughing pump will

not be used during

Ensure pump is away

from equipment,

III/D/5

57

testing due to

presence of leaks

flight so no alcohol

will ever be spewed in

flight, roughing pump

will be placed as far

away from equipment

as possible during use

remove pump from

aircraft before takeoff

Piezo overheating parts

inside vacuum chamber

due to poor heat transfer

Aggressively driving

the piezo for long

duration of time

Equipment damage

to thruster and

probes, piezo draws

an increasing

amount of current as

temperature

increases

IV/A/3 Overdrive failsafe on

the piezo driver will

prevent piezo current

from exceeding

2Arms. A

thermocouple attached

to the piezo will

monitor piezo

temperature and

maintain a maximum

temperature of 60oC

(below glass transition

temperature of

particles at 68oC)

Monitor the piezo

temperature applying an

aggressive piezo

command to check if the

piezo turns off when it

reachs >60oC

IV/E/7

Electronics overheating Current draw above

expected values

Damage to probe

circuitry

IV/C/5 Extra wires used to

heat sink regulators to

the electrical casing

box and thruster/probe

mount

Check with a

thermocouple

temperature of

regulators with and

without additional heat

sinking

IV/E/7

Batteries N/A N/A N/A N/A N/A N/A

Toxic Chemicals N/A N/A N/A N/A N/A N/A

Raioactive

Substances/Materials

N/A N/A N/A N/A N/A N/A

12 Tool Requirements

Team ZESTT Reflight is planning on bringing several of the tools required for our experiment

including: wire cutters, Allen wrenches, soldering iron and solder, oscilloscope, and digital

multimeters. The team will also make use of the following RGO supplied tools before flight: flyer

straps, velcro, grey tape, scissors, screwdrivers, wrenches, diagonal pliers, and needle nose pliers.

13 Photo Requirements

ZESTT Reflight does not have any special photo requirements, as outlined in the sections below.

13.1 Photographers

No professional photographers are needed.

13.2 S-Band Downlink

The team does not require an S-band downlink.

13.3 Fixed Camera Poles

The ZESTT Reflight Team is requesting the use of one fixed camera pole on which to mount the

overview video camera. This camera will record footage of all experimental activities during the

microgravity flight. The camera pole will need to be placed at a position where the Sony DCR-HC26

mini DV Digital Handycam can oversee the entire structure, experiment, and flyers. No other cameras

will be used, and no other camera poles are needed.

13.4 Product Format and Quantities of Imagery

The Sony DCR-HC26 mini DV Digital Handycam is the only camera that will used with this

experiment during flight testing and will be mounted to the fixed camera pole requested above. This

camera will record footage on 60-minute mini discs with a frame rate of 30 frames per second and a

quality of 0.680 megapixels. The camera’s mini disc will be replaced with an unused disc during the

turnaround period on each flight day. The camera footage will not be synchronized with any other data.

59

14 Aircraft Loading

The following sections outline requirements needed in order to successfully load the test bed and

prototypes onto the aircraft.

14.1 Ground Equipment

A powered lift will be required to load the experiment onto the aircraft.

14.2 Hardware Manipulation Strategy

In accordance with NASA requirements, there will be eight handles for the 366.4lb chassis. This

ensures that no handle will exceed 50 lbs for loading. Two handles will be placed in each corner of the

chassis. The handles will be on the four horizontal middle beams of the chassis. These handles will

assist the fliers with lifting the chassis as well as providing locations for fliers to stabilize themselves

during the zero-g flight. All components will be secured within the chassis and will be entirely

enclosed within the chassis, thus no component will infringe on the chassis volume of 59”x28”x24”.

14.3 Weights and Loading The maximum weight of the entire experiment hardware will be no more than 400 lbs. A factor of

safety of two or more has been ensured for all structural parts, see Structural Report for details. The

total base area of the experiment is 9.83, thus loading onto the aircraft floor will not exceed 40.69

pounds per square feet.

15 Ground Support Requirements

15.1 Power

Ground testing will require access to 115V 60Hz power.

15.2 K-bottles

Team ZESTT Reflight will be delivering Please see Section 7 for details on this Nitrogen k-bottle.

15.3 Chemicals

No chemicals are utilized in this experiment, except for the cleaning chemicals isopropanol and

acetone.

15.4 Building Access

60

Access to the high bay area at Ellington Field is requested for this experiment. This is due to the need

to have a controlled environment with as little humidity as possible for pumping down the vacuum

chamber. Additionally, it is possible that the pumping system may need to be run overnight.

15.5 Tool Requirements

Please see Section 12.

16 Hazardous Materials No corrosive, toxic, or explosive chemicals will be used with this experiment. This experiment will

make use of isopropanol and acetone on the ground only for cleaning purposes, but these chemicals are

not hazardous under normal circumstances. MSDS are provided for these chemicals in Appendix C.

17 Material Safety Data Sheets Please see Appendix C to I for all material safety data sheets. These include MSDS for isopropanol,

acetone, 5 micron particles, compressed nitrogen gas, room temperature vulcanizing (RTV) silicone,

and silver conductive epoxy.

18 Experiment Procedures Documentation

The following sections describe the procedures associated with this experiment and each step of the

microgravity testing program.

18.1 Equipment Shipment to Ellington Field

All of the equipment needed for this equipment, including the chassis and its components, will be

brought to Ellington Field with the team. The team will travel to Houston in vans from Ann Arbor, MI

with the equipment packed and stowed in the back, thus the equipment will not require shipment.

18.2 Ground Operations

The following sections describe the procedures associated with this experiment.

18.3 Loading/Stowing

The following sections describe the procedures associated with this experiment.

18.4 Pre-Flight

During the time before flight, the vacuum chamber will always be purged with nitrogen gas to keep

61

moisture from accumulating inside, which would to additional out gassing. Two days before the first

flight day, the vacuum chamber will begin to be pumped down for the flight. The pumps will be run

overnight if access to high bay is granted, and if not, at the end of each day, the gate valve will be

lowered to seal the chamber from the vacuum pumps. The vacuum chamber will be loaded and fully

pumped down before loading onto the plane the day before flight. Once loaded onto the plane, till the

end of that day, pumping will continue onboard the airplane, but the gate valve will be initiated when

the pumps are disengaged for the night. The morning of flight, the pumps will be reactivated for as

long as possible. Right before flight, the following items will be removed from the plane: piston pump,

turbo controller, heat strip’s power supply, and pump connecting hose. The experiment will then be

ready for flight.

18.5 Take-off/Landing

All loose items will be stored in a duffle bag, which is able to fit in the supplied 1‘x2‘x2’ area or stored

in over head bins. These loose items include: secondary outreach materials, over head camera, two

mini disks for camera, and a clip board with an attached pen. All other equipment will be bolted to the

aircraft or secured to the chassis using straps.

18.6 In Flight

Each part of the microgravity flight required a different set of procedures to ensure the experiment can

be smoothly run throughout.

18.7 Prior to First Parabola

During the first level period, right before the first parabola, the following tasks will be executed:

1. Attach overview camera to the fixed pole, plug it into its power source, load with a fresh mini

disk, activate, and properly position it to view all experimental activities.

2. Perform a check to ensure all components on the chassis are plugged in and turn on the master

kill switch.

3. Turn on the HVPS, laptop, DC power supply, piezo driver, gauge controller, and DAQ.

4. Open MatLab file

5. Flyers position themselves for the start of parabolas

18.8 2-G Period

After each microgravity period:

1. Record the passing of a parabola on the clipboard

2. Flip switch on piezo box

3. Ensure correct MatLab file is still running

18.9 Reduced Gravity Period

During the microgravity period:

1. One flight crew member will monitor the inside of the vacuum chamber for arcs

62

2. One flight crew member will monitor MATLAB

3. One flight crew member will monitor the instruments to ensure proper function

4. Entering into the 2g period will cause MATLAB to stop data collection

18.10 Turnarounds

During the turnaround period:

1. Replace mini disc in overview camera

2. Ensure MATLAB is storing data properly

3. Mitigate any issues that may have arisen during the flight thus far

18.11 Emergency Procedures, Precautions, and Contingencies

The following emergencies may occur:

1. Arcing on the chassis: kill the electricity using the master kill switch immediately

2. MatLab failure: restart computer and MatLab

3. Ill flyer: only one flyer is needed to run the experiment at any time

4. Thruster prototype failure: use other prototype for remaining parabolas

5. Fire: use fire extinguishers and call for NASA crew

6. Loss of vacuum pressure: continue to test in atmosphere

18.12 Post Flight

After the first flight day:

1. Turn off components (not master kill switch)

2. Discharge high voltage

3. Bring piston pump, turbo controller, AC power supply, and pump hose back on board, plug in,

and engage pumps and heat strip to pump back down for flight day two

4. At the end of the day, stop pumps and engage gate valve

5. Retrieve mini disc from camera and other loose items taken on board

6. Insert new mini disc into camera to prepare for flight day two

7. Debrief second flight crew group on problems encountered and changes that need to be made

8. Save data from flight onto backup memory device and clear laptop’s memory

9. Review flight footage to see how testing progressed and notice any other problems that can be

solved for second flight day

10. Overview data taken thus far and see if any problems occurred

18.13 Off-Loading

To unload the chassis structure from the aircraft, a powered lift will be needed. No special

requirements are present for off-loading the experiment. Once off the plane, the chassis will be loaded

into a van to take back to the University of Michigan.

63

18.14 Emergency/Contingencies

Please see Section 18.11 for emergency procedures.

64

References

1 Liu, T., Wagner, G., Gallimore, A., Gilchrist, B., Peterson, P., “Mapping the Feasible Design

Space of the Nanoparticle Field Extration Thruster,” IEPC-2009-004, 31st International Electric

Propulsion Conference, Ann Arbor, MI, 20-24 Sept. 2009.

2 Musinski, L., Liu, T., Gilchrist, B., and Gallimore, A., “Electrostatic Charging of Micro- and

Nano-Particles for Use with Highly Energetic Applications,” Journal of Electrostatics, 4

November 20080, pp. 1-8

3 Liu, T., Musinski, L., Patel, P., Gallimore, A., Gilchrist, B., and Keidar, M., “Nanoparticle

Electric Propulsion for Space Exploration,” Space Technology and Applications International

Forum – STAIF 2007, edited by M. S. El-Genk, American Institue of Physics, Albuquerque,

NM, 2007, pp. 787-94

4 Gamero-Castano, M., “Induction charge detector with multiple sensing stages,” Review of

Scientific Instruments 78, 043301, 11 Apr. 2007.

65

Appendix A: Exceptions/Deviations/Waivers

A 100 lb mass waiver was requested and granted by the Reduced Gravity Office for this experiment.

Please see below for the email transcript granting this mass waiver.

-------- Original Message --------

Subject: RE: Requested Mass Waiver for ZESTT Reflight

Date: Thu, 15 Apr 2010 16:13:21 -0500

From: "Del Rosso, Dominic L. (JSC-CC411)" <dominic.l.delrosso@nasa.gov>

To: Duncan L Miller <duncanlm@umich.edu>, "Goforth, Douglas W. (JSC-AD421)"

<douglas.w.goforth@nasa.gov>

Duncan,

If I understand correctly you would like to have an upper limit of #400 for

your experiment, within the same volume envelope. This should not be a

problem as long as you provide lifting and handling provisions as defined

(i.e. no more than #50 per person lift etc.).

Please include this email in your TEDP when submitted.

Thanks

Dom

-----Original Message-----

From: Duncan L Miller [mailto:duncanlm@umich.edu]

Sent: Thursday, April 15, 2010 3:16 PM

To: Goforth, Douglas W. (JSC-AD421)

Cc: Aquilina, Rose M. (JSC-CC)[REDE CRITIQUE NSS JV]; Del Rosso, Dominic L.

(JSC-CC411); Lee, Terry A. (JSC-CC411); Krolczyk, Kevin D. (JSC-CC)[CSC

APPLIED TECHNOLOGIES LLC]

Subject: RE: Requested Mass Waiver for ZESTT Reflight

Douglas~

Thanks for the quick response! Of course. I understand there's a lot on

your plate. I would like to stress though that we won't be able to lay out

a final chassis model and experimental setup without confirmation of a mass

waiver.

Regards,

Duncan

On Thu, 15 Apr 2010 15:04:17 -0500, "Goforth, Douglas W. (JSC-AD421)"

<douglas.w.goforth@nasa.gov> wrote:

Duncan -

66

We are finishing up a RG flight week today and tomorrow. Would it be

okay if Dom or Terry contacted you on Tuesday or Wednesday of next week?

Douglas Goforth

________________________________________

From: Aquilina, Rose M. (JSC-CC)[REDE CRITIQUE NSS JV]

Sent: Thursday, April 15, 2010 2:49 PM

To: Del Rosso, Dominic L. (JSC-CC411); Lee, Terry A. (JSC-CC411);

Goforth, Douglas W. (JSC-AD421); Krolczyk, Kevin D. (JSC-CC)[CSC APPLIED

TECHNOLOGIES LLC]

Subject: FW: Requested Mass Waiver for ZESTT Reflight

Would someone please contact this student??!!

-----Original Message-----

From: Duncan L Miller [mailto:duncanlm@umich.edu]

Sent: Thursday, April 15, 2010 2:45 PM

To: Aquilina, Rose M. (JSC-CC)[REDE CRITIQUE NSS JV]

Subject: Requested Mass Waiver for ZESTT Reflight

To Whom It May Concern:

At this time, we formally request a 100 lb mass waiver for the Zero-g

ElectroStatic Thruster Testbed Reflight at the University of Michigan. We

have been closely tracking our expected mass and have found that it would

be very difficult to reach the 300lb limit without compromising our

experiment. Our chassis structure was safely flown in June 2009 at 340

lbs

and this year's additional component weight has amounted to a total of

390.4 lbs with contingency.

To account for the added mass, we have lengthened the aircraft mounting

brackets and analyzed the chassis structure under the appropriate

acceleration fields to verify our chassis does indeed comply with NASA

requirements. Both our FEA and hand calculations have shown factors of

safety comfortably above 2.

We have attached CAD models of our chassis design, a mass budget, FEA

solved models in ANSYS and a few sample hand calculations. A more

comprehensive structural report will be included with our TEDP in May.

Thank you,

ZESTT Structures Team