The Balloon Launch “Spacecraft” and Environment ACES Presentation T. Gregory Guzik February 20, 2003

Conditions During Flight Flight lasts 2 to 3 hours Max altitude 80 kft to 110 kft Max range (20 miles to infinity) – Try to keep within ~40 miles range Gets cold at the tropopause (~ -60 o C) Any water vapor will condense out and cause frost Good vacuum ( < 0.02 atmosphere) Landing can be rough (shock, trees, rocks, dragging) High velocity during initial descent (~500 mph)

Cartoon of BalloonSat Train

Typical Flight Profile

Views of Balloon Launch Ground PerspectiveBalloon Perspective

Balloon Burst at ~100,000 ft

Payload is Returned Safely to the Ground by Parachute

Temperatures During Flight External temperature Minimum of –60 o C Internal temperature Minimum of –25 o C

Preliminary Balloon Layout FAA rules – Low density – Single box < 2.7 kg – Total payload < 5.4 kg Weight estimate – Parachute 300 g – Primary beacon 734 g – Backup beacon 515 g – Cabling 122 g – Contingency 250 g – Payloads 3520 g

Weight Trade Offs Note that 3520 g / 5 = 704 g Could support up to three payloads of 1 kg each per flight Last two payloads require second flight – Require recovery of first flight – Require two consecutive launch days Trade “weight coupons” between payloads – i.e. Limit all 5 payloads to 3500 g Limit each payload to 700 g

Option A: Central Telemetry Spacecraft controls telemetry by signaling each payload in turn when it is time to transmit Payload would return a predefined format packet to the primary beacon over RS232 bus – T#ddd,ddd,ddd,ddd,ddd,ddd,bbbbbbbb,string

Option A: Trade Offs Extra weight in spacecraft systems – Reduced weight limit on all payloads Extra cost to develop this spacecraft service – Allocate $75 of payload budget to pay for this service Slightly increased software complexity Significantly increased interface complexity No need to store everything on-board or do own telemetry system

Option B: Store Onboard No cost hit, minimize weight constraint, no interface issues Store in EERAM – No addition components needed – Lifetime of EERAM limited – Major problems if the code is wrong Store in auxiliary memory chip – Avoid EERAM problems – Significantly increased storage – Increased software complexity Payload recovery required

Option C: Payload Telemetry Would need to use 5 W HAM radio – 0.5 W FRS radio insufficient for balloons – Would need two radios at $300 each Increased payload weight – ~170 g for radio, 150 – 200 g for extra battery Would need ground station – Spacecraft ground station channels are used by beacons

Charge to IWG Meet now in room 331 for 30 to 45 minutes and bring back decisions on the following issues. How to handle the payload weight issue. How to handle to data storage / telemetry issue.