Instrument Requirements
Parameter Requirement FeaturesWaveband 95μm Matches Available
SIRTF FPA’sDetector AngularSubtense
48 seconds Oversamplingdiffraction blur
Field of View ~26 minutes Matches 32x32 currentdetectors
S/N Req: 150 Goal: 600Cooling Detectors<2K;
Optics<6KLight shade limitingcryo load on lastproposal
Instrumentpolarization
<1% Analysis meets
Calibration <1% source Use standard source
Ball Heritage• Currently building SIRTF CTA and instrument which
uses Ge:Ga FPA’s– Past CDR in subassembly test
– No major technical showstoppers
• IRAS flying successfully– very similar from a cryo design - only smaller
• Conceptually simple design– simple electronics, tested FPA’s, small/few element optics,
but….
– Cryo design never simple
Spacecraft Requirements
• Low Cost - less than $15M?
• Accept >125 kg instrument
• Provide > 30 Watts of power to payload
• Pointing Stability < 24 seconds per data acquistion
• Fit into selected Launch Vehicle
• Data Storage: 200 Mbytes
Spacecraft Key Performance Requirements
Description X-12M SMEX LITE SA-200SMiniStar
Spacecraft Bus Mass 65.6 kg 75kg 98kgPayload Mass Capability 200 kg 91kg 200kg
180kgAvailable Payload Power > 100 W 150W 60W 17.5WACS Configuration 3-axis stabilized 3 axis zero momentum
Gravity GradientAttitude Knowledge 28 μrad 5μrad
.5 degreesAttitude Control 32 μrad 96μrad 10 degreesPayload Data Storage 256 Mbytes 130 Mbytes 8Gbyte
3MbytesCommunications S-Band S-Band S-band S-bandTelemetry Rate 4Mbps 2.25Mbps 10Mbps 1 Mbps
Equipment Shelf Provides Ample Area For Subsystem Units
TRANSPONDER
TORQUE ROD
(3 PL)
INERTIAL
REFERENCE
UNIT
BATTERY
STAR TRACKER
REACTION WHEEL
(3 PL)
FLIGHT COMPUTER
RELAY BOX
S/C Selection• Meets minimum requirements
• Lowest total cost– nearly all COTS buses will need changes
– integration issues
– heritage of performance: technical, cost, schedule
• Willing to work with team
• Selection not mandatory for 1st round - a solution, not the solution needed
Issues/risks/options• Need good story for aperture cover - esp. after
WIRE
• Light shade a key driver in itself and for cryo design
• Star tracker vs. gyro
• battery size vs. eclipse
• CPU capabilities/memory - on orbit computation vs. downlink
• configuration drivers: LV, COTS, star tracker location, timeline, launch date
Launch Options
Option Pros ConsDedicated Launch We have more timing
control, fewer constraintson design, right orbit
$$$$$$$$$
Share with equal Workable timing, co-manifest layout, right orbit
How to find the partner,stay coordinated throughoutprogram
Rent a ride Save $$$$$ - maybe$15M, huge mass margin
No launch timing control,not many LEOopportunities, feweropportunities that wouldaccept cryo, orbit may beproblematic
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