# Presentation: 033963

## SuperNova/ Acceleration Probe (SNAP)

**June 28, 2001**

**SuperNova/ Acceleration Probe (SNAP)**

**Thermal**

## 
Overview
Mission Requirements 
Selected Configuration and Rationale
Mass, Power, and Cost Summary
Risk Assessment
Issues and Concerns

**Overview**
**Mission Requirements **
**Selected Configuration and Rationale**
**Mass, Power, and Cost Summary**
**Risk Assessment**
**Issues and Concerns**

**Thermal****Topics**

## 
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 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**

## 
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 

**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**

## 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**

## Bus Layout

**Propulsion Tanks**

- 5# thrusters
- (4 sets of 2)

- Sub-system electronics

- Sub-system electronics

**Anti-sun radiator**

## 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%**

## Telescope Configuration

**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

## 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**

## 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**

## Thermal Risk Assessment

**Thermal design is low risk. **
**Off-the-shelf hardware; custom designed heat pipe panels.**

## 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**