Promoting Science and Education through High Altitude Balloons and Amateur Radio www. eoss. org Low-cost Payload Design Considerations Low-Cost Access to Near Space Workshop Southwest Research Institute, Boulder CO, 26 April 2007 Mike Manes, President EOSS w 5 vsi@eoss. org
What Is EOSS? n n 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 n “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 highaltitude balloon flight n n Lowest cost access to Near Space Feasible for vertical integration by small organizations – – – n 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, … n n 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 n Payload weight drives balloon selection
Expendables costs: Plastic vs. Latex
Balloon type selection n Latex balloon pros: – – – n 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 Lowest cost Lightest weight Simple prep and fill process Multiple commercial sources Self destructs & biodegrades Latex balloon cons: – – n n 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 n 54, 000 cu ft Raven top fillburster
Latex balloon fill n 3000 gm Totex with 10 kt surface wind
Latex balloon expendables
Flight environment considerations “… but not more so. ” (Apologies to A. Einstein) n Payload structures and flight string must survive environmental rigors: – – – – Launch jerk: 0 to 5 m/sec in 0. 1 sec. Air temperatures down to -80 at tropopause ºC 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 n 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 n Use low modulus payload cordage to absorb shock – MIL-C-7515 E 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 n 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 n Foamcore board structures with thru-tube support – – – n Low-cost “honeycomb” available from art, big box stores Easily formed to < 0. 5 mm tolerances using hand tools, hot-melt glue 8 mm 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 – 3 D cavities difficult to form n Off-the-shelf (or dumpster) – Workable, but sizing is inflexible.
Some EOSS payloads
Design for Recovery n A significant operational economy – Payload reuse, refurb, modification – On-board data storage eliminates telemetry cost, weight, EMC n 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 n Supply at least 24 hr battery power to beacons – Li. SO 2 primary cells have excellent energy density, low temp operation – Available at low cost on surplus market n Recovery requires GPS telemetry, RDF, mobile skills – Amateur radio is a useful tool
Command & Telemetry radios n Amateur radio VHF & UHF bands for CMD/TLM and GPS tracking – – Only option ifgov’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 tofindu. com deemed essential by some FAA offices n 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! n n Locate land owners, obtain permission to enter property Most owners are happy to join in
Another successful recovery n …And the students arrive!
Plastic envelope recovery n n Separate tracking and recovery from main payload string Separate GPS & DF beacons required, along with termination devices
Recent & emerging technical developments n Payload electronics – – – n 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 n 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?
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