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

SNAP, June 25-28, 2001 Goddard Space Flight Center System Introduction Page 2  Overview  Mission Requirements  Selected Configuration and Rationale  Mass, Power, and Cost Summary  Risk Assessment  Issues and Concerns Thermal Topics

SNAP, June 25-28, 2001 Goddard Space Flight Center System Introduction Page 3 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 Thermal Overview

SNAP, June 25-28, 2001 Goddard Space Flight Center System Introduction Page 4  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 Thermal System Mission Requirements

SNAP, June 25-28, 2001 Goddard Space Flight Center System Introduction Page 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 +/-45 O roll

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

SNAP, June 25-28, 2001 Goddard Space Flight Center System Introduction Page 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 30 O away from normal sun cools entire array by 10 O C  With isolation, this lowers thermal environment inside baffle by less than 1%  Roll angle of 45 O 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, 2001 Goddard Space Flight Center System Introduction Page 8 Telescope Configuration Propulsion Tanks Sub-system electronics Secondary Mirror and Mount Optical Bench Primary Mirror Thermal Radiator Solar Array Wrap around, body mounted 50% OSR & 50% Cells

SNAP, June 25-28, 2001 Goddard Space Flight Center System Introduction Page 9 Telescope Thermal Configuration  Baffle has MLI blankets on outside to reduce thermal swings  MLI blankets between spacecraft and telescope optics volume  Radiator of 2m 2 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, 2001 Goddard Space Flight Center System Introduction Page 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, 2001 Goddard Space Flight Center System Introduction Page 11 Thermal Risk Assessment  Thermal design is low risk.  Off-the-shelf hardware; custom designed heat pipe panels.

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