Wes Ousley June 28, 2001

1. SuperNova/ Acceleration Probe (SNAP) Thermal Wes Ousley June 28, 2001

2. ThermalTopics • Overview • Mission Requirements • Selected Configuration and Rationale • Mass, Power, and Cost Summary • Risk Assessment • Issues and Concerns SNAP, June 25-28, 2001Goddard Space Flight Center

3. ThermalOverview SNAP spacecraft thermal requirements can be accommodated with standard thermal control techniques (blankets, heaters, heat pipes) • Spacecraft bus is thermally coupled to reduce eclipse cooldown • Instrument CCD radiator should be moved to accommodate spacecraft radiator SNAP, June 25-28, 2001Goddard Space Flight Center

4. Thermal SystemMission Requirements • High Earth orbit • No significant albedo or earth IR • Eclipse time (max 6 hours) drives bus thermal design • CCD camera operates at 150K • Passive radiator dissipates camera power and parasitic loads SNAP, June 25-28, 2001Goddard Space Flight Center

5. Spacecraft Thermal Configuration • Bus thermal design radiates heat from anti-sun side • Much smaller radiators than sun-side for same heat transfer • Reduces eclipse heater power requirement • Most internal bus components mounted to bottom deck • Deck is honeycomb panel with imbedded heat pipes • Thermal masses coupled to reduce eclipse cooldown • Heat pipes transfer heat from deck to anti-sun radiator • Prop system thermally isolated from deck • Current configuration shows no anti-sun radiator margin! • Restricting roll angle allows up to 200% size margin • Moving CCD radiator permits 100% margin with +/-45O roll SNAP, June 25-28, 2001Goddard Space Flight Center

6. Bus Layout Sub-system electronics Sub-system electronics 5# thrusters (4 sets of 2) Propulsion Tanks Anti-sun radiator SNAP, June 25-28, 2001Goddard Space Flight Center

7. Solar Array Thermal Configuration • Solar array thermally isolated from telescope • Telescope thermal stability is essential to mission success • Array temperatures change significantly with pitch and roll angle • Low-conductivity mounting and MLI behind array provide isolation • Pitch of 30O away from normal sun cools entire array by 10OC • With isolation, this lowers thermal environment inside baffle by less than 1% • Roll angle of 45O heats up sun-normal area by 30C, and cools opposite area by 100C • Alters entire temperature field on secondary mirror structure • Change in local environment input inside baffle up to 5% SNAP, June 25-28, 2001Goddard Space Flight Center

8. Telescope Configuration Solar Array Wrap around, body mounted 50% OSR & 50% Cells Secondary Mirror and Mount Primary Mirror Optical Bench Thermal Radiator Sub-system electronics Propulsion Tanks SNAP, June 25-28, 2001Goddard Space Flight Center

9. Telescope Thermal Configuration • Baffle has MLI blankets on outside to reduce thermal swings • MLI blankets between spacecraft and telescope optics volume • Radiator of 2m2 can remove 36W from 150K camera • CCD radiator should be moved toward aperture to allow anti-sun area for spacecraft radiator SNAP, June 25-28, 2001Goddard Space Flight Center

10. Thermal Mass, Power, and Cost Summary • Thermal system mass 67kg • Heat pipes for deck and radiator 37kg • MLI blankets on spacecraft total 28kg • Heater power of 38W for prop thermal control • Eclipse average heater power 40W • Hardware cost is $910K • Heat pipe panel cost $700K SNAP, June 25-28, 2001Goddard Space Flight Center

11. Thermal Risk Assessment • Thermal design is low risk. • Off-the-shelf hardware; custom designed heat pipe panels. SNAP, June 25-28, 2001Goddard Space Flight Center

12. Thermal Issues and Concerns 1. Allowed roll angle of 45O causes substantial changes in secondary structure thermal environment 2. Relocation of CCD radiator is required to allow spacecraft radiator area if 45O roll angle is baselined SNAP, June 25-28, 2001Goddard Space Flight Center