Promoting Science and Education through High Altitude Balloons and Amateur Radio

www.eoss.org Low-cost Payload Design ConsiderationsLow-cost Payload Design Considerations

Low-Cost Access to Near Space WorkshopSouthwest Research Institute, Boulder CO,

26 April 2007

Mike Manes, President EOSSw5vsi@eoss.org

What Is EOSS?

Founded January 1991 as a Colorado scientific & educational non-profit corporation 501(c)(3)

Funded by donations and 60+ volunteer members 117 flights to date with 100% payload recovery record Charter:

– Promoting Science and Education Through Amateur Radio and High Altitude Balloons

“The Poor Man’s Space Program”– Payloads to Near Space for $200 to $500

– Provide students hands-on experience with science and technology to the edge of of space

– Provide near space transport and recovery for scientific experiments

Key economies of high-altitude balloon flight

Lowest cost access to Near Space Feasible for vertical integration by small organizations

– Operational simplicity

– Commercial availability of balloons, fill gas and payload materials

– Free / low cost forecasting, tracking utilities

– Support by peer non-profits

– Local launch site and scheduling mitigates travel costs

» Launch with short notice of suitable trajectory & weather

» Launch site should be selected to avoid risks to the public, but can be little more than a wide spot in the road.

» Coordination and cooperation with FAA is important when operating in civil airspace (CFR 14 Part 101)

Most important economic factor: Payload Recovery

Top-level design considerations

“Things should be made as light as possible, …

Launch costs vary directly with payload weight “Payload weight” excludes 2 – 4 kg flight system

components necessary for recovery:– 0.7 – 2.0 kg parachute

– 0.8 – 1.7 kg GPS telemetry beacon

– 0.5 kg DF beacon / cutdown command receiver

Payload weight drives balloon selection

Expendables costs: Plastic vs. Latex

Balloon expendibles cost vs. Payload weight1000 fpm to 100,000 ft MSL apogee

$0

$500

$1,000

$1,500

$2,000

$2,500

$3,000

0.0 50.0 100.0 150.0 200.0

Payload wt, lb(assumes 4.3 lb beacons & parachute)

Co

st,

US

$

Latex

Plastic

Balloon type selection

Latex balloon pros:– Lowest cost

– Lightest weight

– Simple prep and fill process

– Multiple commercial sources

– Self destructs & biodegrades

Latex balloon cons:– Limited to 12 kg max payload

– +/- 10% apogee uncertainty

– Loiter valving still developmental

– Flight duration limited by UV degradation

Plastic balloon pros:– Required for > 12 kg

– Required for loiter missions

– Long duration flights feasible

» ballast dumps on ZP

» super-pressure envelope

Plastic balloon cons:– Costly (base price > US$400)

– Envelope film is heavy and fragile

– Complex prep and fill process

– Single domestic source (Raven)

– Redundant destruct devices required

– Used envelope is livestock hazard

Plastic balloon fill

54,000 cu ft Raven top fill burster

Latex balloon fill

3000 gm Totex with 10 kt surface wind

Latex balloon expendables

Latex balloon expendibles vs. Payload weight1000 fpm to 100,000 ft MSL apogee

$0

$50

$100

$150

$200

$250

$300

$350

$400

$450

$500

0.0 5.0 10.0 15.0 20.0 25.0 30.0

Payload wt, lb(assumes 4.3 lb beacons & parachute)

Co

st,

US

$

Flight environment considerations

“… but not more so.” (Apologies to A. Einstein)

Payload structures and flight string must survive environmental rigors:– Launch jerk: 0 to 5 m/sec in 0.1 sec.

– Air temperatures down to -80ºC at tropopause

– Barometric pressure < 10 mbar (poor thermal convection)

– Strong solar flux, especially UV (IR help thermals)

– High initial descent rates > 100 m/sec

– Parachute instability (Post-burst chaos)

– Parachute drag upon windy landing

Some flight environments …

… can’t be designed for.

Payload line design methodologies

Consider string of small payloads vice single integrated package– GPS telemetry beacons can upset analog, fast digital electronics

– Multiple experiments can share a flight w/o integration headaches

– Use wireless LAN to link separate payloads in lieu of cable

Use low modulus payload cordage to absorb shock– MIL-C-7515E woven nylon is preferred (50% stretch to yield)

» 250# tensile minimum, 500# for > 6 kg strings

– Dacron core, Kevlar may transmit shock > tensile strength

– Allow plenty of slack on parallel electrical conductors, antennas

Use low-stress “marlinspike seamanship”– Double bowline is strong & unties easily

– Figure 8 knot is lower stress than half hitch

Multiple payload launch

Payload package materials & methods

Foamcore board structures with thru-tube support– Low-cost “honeycomb” available from art, big box stores

– Easily formed to < 0.5mm tolerances using hand tools, hot-melt glue

– 8mm foamcore provides adequate thermal insulation for most payloads

– With thin coat of acrylic spray paint, resists UV. moisture & shock

– Thru-tube isolates support line tension from enclosure structure

– With sound design, expect over 20 flights

Building sheet insulation and closed-cell HDPE– Superior thermal insulation and shock resistance

– Low precision dimensions

– 3D cavities difficult to form

Off-the-shelf (or dumpster)– Workable, but sizing is inflexible.

Some EOSS payloads

Design for Recovery

A significant operational economy– Payload reuse, refurb, modification– On-board data storage eliminates telemetry cost, weight, EMC

On-board data storage – Onset Computing “Hobo” loggers are lightweight, easy to use– Flash memory up to 2 Gbytes is suitable for bulk data, imaging– Sample species in situ & store on board for later analysis

» NOAA “Aircore” profiler» CU bacteria sampler

Supply at least 24 hr battery power to beacons– LiSO2 primary cells have excellent energy density, low temp operation– Available at low cost on surplus market

Recovery requires GPS telemetry, RDF, mobile skills– Amateur radio is a useful tool

Command & Telemetry radios

Amateur radio VHF & UHF bands for CMD/TLM and GPS tracking– Only option if gov’t frequencies not provided; Part 15 range is too

short

– Also useful for coordination amongst launch, recovery teams

– Ham license required, but exam by volunteers and no Morse required

– FCC Part 97 prohibits commercial use, but support of science, education is OK.

– Internet gating to findu.com deemed essential by some FAA offices

GMRS & FRS– Limited frequency selection and range

– Possible alternative to ham radio, but not compatible with findu.com

Launch site communications

Tracking Operations

– Trajectory forecasting and launch site selection

– Track and recovery team deployment around

forecast landing site before launch

– Tracking team coordination via radio net on UHF

repeaters

Skilled trackers beat payload to landing site

Prime directive:No Trespassing!

Locate land owners, obtain permission to enter property

Most owners are happy to join in

Another successful recovery

…And the students arrive!

Plastic envelope recovery

Separate tracking and recovery from main payload string

Separate GPS & DF beacons required, along with termination devices

Recent & emerging technical developments

Payload electronics– Low power, inexpensive microprocessors– High capacity non-volatile memories– Low cost digital cameras & DVRs– Part 15 wireless LAN amongst payloads, flight system– Lithium battery advances

Tracking technologies– VHF RDF triangulation made way for Loran-C and now GPS– Automated relay of APRS downlink to internet & to FAA controllers

Recovery techniques– Ground & air search for DF beacon replaced by real-time GPS tracking

displayed on ground mobile laptops– Computerized trajectory forecasting using sophisticated NOAA

models yields visual observation of landing– Steerable / homing descent emerging to replace common parachutes

Any questions?