ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design T....

ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design

T. Nakagawa (ISAS/JAXA)S. Sakai (ISAS/JAXA)

26th ISTS @Hamamatsu [2008-f-17]

S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design 2

ISAS/JAXA small scientific satellite series

• The Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency (ISAS/JAXA) has recently started to develop a series of small scientific satellites, and has a plan to launch three to five minisats (300-400 kg) per five years.

• The series aims at ‘cheaper and faster realization of unique space experiments’ as a complementary program of mainstream medium-class scientific satellites.

• In order to shorten the period of satellite development with low cost, it is considered to be reasonable to employ standard bus architecture, where the bus and payloads are clearly separated in a modular manner.- The modular configuration is

attained in exchange of resources like mass.

Mission payload

Standard bus

The mission payloads are on the roof of the bus system.


Working Groups for small scientific satellites

Scientific missions:

TOPS Tele-observation of planetary plasma

FFAST X-ray observation w/ formation flight

PPM-Sat Precise positioning w/ GPS occultation

CAST Gamma-ray burst observation

DPF Gravity wave observation

DIOS X-ray observation (dark baryons)

ELMOS Seismic Electromagnetism

ERG Plasma observation in Geospace

POLARIS X-ray polarization observation

Engineering missions:

Tether Tether technology demonstration

SPS Solar power generation

SLIM Lunar lander

Venus balloon Venus balloon

MAGSAIL Pure magneto-sail

EGG Gas-balloon re-entry

First flight (2012)


This presentation

• The missions for small scientific satellites have various kinds of requirements:- three-axis/spin-stabilized attitude control, - a wide range of power (50 to 300 W), - a variety of orbit (LEO, SSO, HEO, etc), ...

-> A traditional rigid standard bus will be unable to satisfy the diversity of mission requirements.

• In this presentation, several concepts to enhance flexibility of the standard bus are introduced:- Layers of standardization- Semi-custom-made bus system - Tradeoff between integration and modularization


Layers of standardization

• Specifications of most conventional standard buses are strictly regulated for a particular mission in the whole system/subsystem of satellites. (e.g., communication satellites on GEO)- Effectiveness of the rigid standardization depends on the number of satellites

with the particular mission.

• Traditionally, medium-class scientific satellites in ISAS/JAXA were dedicatedly developed in order to satisfy various requirements and pursue resource-optimal design, so that fruitful achievements would be brought.- Optimization of satellite-by-satellite consumes relatively large cost and long

development time.

-> ‘layers of standardization’ concept

scientific satellites with a wide variety of requirements

S.Sakai: ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design

SpaceWire as standard data network•Promising technology because of high speed, simplicity, and testability•RMAP (Remote Memory Access Protocol) over SpaceWire is a powerful method, which enables one component to read and write directly from memory and registers of another component over the network.

6

Layers of standardization [Cont’d]

The Layer (IV): Configuration- Similar to the conventional rigid standard buses

- Possible to omit mechanical/thermal model tests

- Applicable to most scientific observation missions by adding selectable or alternative options

The Layer (III): Instruments- Advantageous for engineering missions where

the satellite configuration itself is hard to be standardized (e.g., the small lunar lander with a large-scale propulsion system)

- Valuable concerning economics of bundling order

The Layer (II): Interfaces- Essential for higher levels of standardization

The Layer (I): Design Methods- Standard method of modeling satellites

-> reuse of GSE software, etc


Semi-custom-made bus system

• Consideration of the bus specifications using a requirement matrix- Three categories:

Core, alternative option, and selectable option

• The alternative and selectable options are crucial for the flexible standard bus to realize diverse missions with time- and cost-saving strategies.Semi-custom-made bus system

For small scientific satellitesReady-made standard bus

full-custom-made medium-class scientific satellites

• The idea is similar to Product Line or Product Platform engineering in development of commercial products.- The capability of adding or replacing options is based on recent progress in

technology of modular design and Plug and Play.- A tradeoff between the number of options and effectiveness of the

standardization should be carefully investigated.


Semi-custom-made bus system[Cont’d]

Selectable options•solar array drive assembly (SADA)•GPS receiver•X-band transmitter•monopropellant propulsion system•design for EMC (Electro-Magnetic Compatibility) Alternative options

•number of solar panels (one, two, or three panels

per wing)•capacity of Li-ion batteries (35Ah/50Ah)•accuracy of attitude sensors such as a star tracker and an inertial reference unit (corresponding to requirements)•size of reaction wheels (corresponding to requirements of perturbation immunity)

Note: Nominal specifications are underlined.


Tradeoff between integration and modularization

Conventional Integration Modularization

Cost analysis says that present satellite cost has strong correlation with the number of onboard components. -> Common functions which belong to different components have to be integrated into a single component.The integrated architecture is intrinsically appropriate for small satellites because it will consume less resources such as mass, size, and electric power.

The integrated architecture, however, has latent difficulties in testability and reusability. -> Modularization is attempted in the next step.The modular architecture seems preferable in many cases, if a resource budget including cost allows it.

What is important is to standardize interfaces between modules. -> The standard interfaces will facilitate change of architecture from integration to modularization, and vice versa.


Tradeoff between integration and modularization [Cont’d]

WDE4WDE3WDE2

IRU

SMU (Satellite Management Unit)

APR

SAP1

Mission Payload64bit CPU (MIPS) +

PROM/ EEPROM/ RAM

DHFS

DC/ DC converter

MTQ-Z

MTQ-XMTQ-Y

SAP1

SADA1

DreamCubeSAt

各Heater(24ch max)

Data Handling Network(DH-N/ W) 100Mbps×n max

DR(2Gbytes)

RCS

3N thruster

S-H

YB

S-RTM(S-band Routing module)

S-ANT1

50V Primary Power from PCU

TCIM(ON/ OF

)

NIC (Network Interface Circuit)

SAP2

SAP2

SADA2

64bit CPU (MIPS) + PROM/ EEPROM/ RAM

ACFS TCFS

ADC/ MUX

(Temp)

DRUS-TRP1、S-TRP2

WDE1～WDE4STT-E, IRU

unregulated 50 voltage

ACIM(MW)

ADC/ MUX

Avionics Control Network (AC-N/W)

S-ANT2 S-ANT3

Space Packet only on NW

TCIM(TLM/ C

MD)

S-ＴRP1

S-ＴRP2

To WDE1～WDE4、STT-E、IRU Power ON/ OFF

PCUMission × 2ch

NEA

NEA× 4ch

× 4ch

STT-E

STT-S

SPS

STT

CSAS1

CSAS2

SPS

from Temp. Sensors (64ch max)

GFD

PFD FLT

TNK

LV

RCSHeater

ODC

Li- ion BAT35AH

ACIM(Sensor)

SpWRouter(12port)

Analog TLM(32ch max)

ACIM(STT)

SpWRouter(12port)

SADA Driver

Heater Driver × 3ch

Thruster Driver

MTQ Driver

DRU(Drive Unit)

ACIM(STT)

PRE

1 2 3 4

Valve Module 2

Valve Module 1

S-DIP2

S-DIP1

S-SW

AC-NW

DH-NW

WDE1

ＲＷ1～RW4

Valve Driver

SMOS(RealTimeOS)

RD TLMSA SEP

System block diagram of the standard bus for small scientific satellites

(baseline)

The functional integration is considerably pursued.


Tradeoff between integration and modularization [Cont’d]

System block diagram of the standard bus

for small scientific satellites (modification)

Now studying to modify the architecture to more modular one so as to enhance testability and reusability

WDE4WDE3WDE2

SMU (Satellite Management Unit)

APR

SAP1

Mission Payload


DHFS

MTQ-Z

MTQ-XMTQ-Y

SAP1

SADA1

DreamCubeSAt

Data Handling Network(DH-N/ W) 100Mbps× n max

RCS

3N thruster

50V Primary Power from PCU

NIC (Network Interface Circuit)

SAP2

SAP2

SADA2


ACFS TCFS

DRUS-TRP1、S-TRP2

WDE1～WDE4STT-E, IRU

unregulated 50 voltage

Avionics Control Network (AC-N/W)

Space Packet only on NW

PCUMission × 2ch

NEA

NEA× 4ch

× 4ch

STT-E

STT-S

SPS

GFD

PFD FLT

TNK

LV

ODC

Li- ion BAT35AH

ACIM(STT)

PRE

1 2 3 4

Valve Module 2

Valve Module 1

AC-NW

DH-NW

WDE1

ＲＷ1～RW4

SMOS(RealTimeOS)

DR(2Gbytes)

S-H

YB

S-RTM(S-band Routing module)

S-ANT1 S-ANT2 S-ANT3

TCIM(TLM

/ CMD)

S-ＴRP1

S-ＴRP2S-

DIP2

S-DIP1

S-SW

RD TLMSA SEP

TCIM(ON

/ OFF)

DC/ DC converter

SpWRouter(14port)

STT

CSAS1

CSAS2SPSIRU

ACIM (Avionics Control Interface Module)

μ HCE

μ HCE

μ HCE

SpW Router (14port)


“Semi-order-made” approach[e.g. AOCS]

So, now “semi-order-made” approach is considered. Example: what is the appropriate attitude &

orbit control system (AOCS) configuration to implement this concept. IRU

Type-A (Fine, larger, expensive) Type-B (Coarse, small, cheaper)

Reaction Wheel ….Um… IRU should be Type-B for

my mission…

Example of “semi-order-made” approach

To achieve this concept, one important thing is to distinguish and separate the AOCS into two categories: one which is independent of the AOCS components selection, and ones dependent on components.


New Architecture for AOCS Data Interface

For slightly difference component configuration…

Conventional ISAS approach

• Monolithic AOCS computer unit.+ Effective to minimize weight, size, number of parts, …– Component change affect wide area in the unit.


New Architecture for AOCS Data Interface [Cont’d]

New approach

• Distributed AOCS computer unit.+ Minimize the are influenced by the component change.– Weight etc. are not minimum.


New Architecture for AOCS Data Interface [Cont’d]

• In this novel approach, function to interface each component is distributed in the individual ACIM (attitude control interface module), not implemented in the computer unit.

• Thus the connection between ACIMs and the computer unit should behaves just like local bus.

• Then, what is the appropriate data interface for this purpose?

• “SpaceWire” is assumed to be a solution, because of- Speed,- Simplicity,- Open standard, - …


Architecture for ground test equipments

For software development & test, flight operation simulation, etc.

For static closed loop test, etc.


Conclusion

• A standard bus system for the ISAS/JAXA’s new series of small scientific satellites has been presented. Some ideas and concepts to enhance flexibility of the bus system have been shown.

• The TOPS project which is the first satellite of the series will proceed to the Phase B soon.

• On and after the second flight, the development time will be no more than two years from determination of mission interfaces to the launch including integration tests.

• As the estimated cost is worldwide competitive, the standard bus has potential to be applied to earth observation or disaster monitoring missions in the future.

Thank you very much for your attention.

ISAS/JAXA Small Scientific Satellite Series Program with Flexible and Reusable Bus Design T....

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