GLAST Large Area Telescope: Mechanical Systems Peer Review 27 March 2003 Section 4.4

1. Gamma-ray Large Area Space Telescope GLAST Large Area Telescope: Mechanical Systems Peer Review 27 March 2003 Section 4.4 Heat Pipe Thermal Design Aaron Avallon Heat Pipe Product Center Design Engineer aaron.r.avallon@lmco.com

2. Heat Pipe Performance Requirements Based on: Results of Overall LAT Thermal Math Model Verification Methods A: Analysis T: Test Margin is determined by: EP/Req Must be > 1.3

3. Heat Pipe Sizing (1 of 2) • All worst case pipe requirements derived from detailed thermal model hot case with the following assumptions and results • Top Flange • 1 of 5 pipes failed • Cumulative heat load and transport requirement calculated directly from Heat Flux (W/m) vs Length Along Pipe (mm) graph • Results in a 9.2 W-m requirement for each pipe • Downspout • 1 of 6 pipes failed • Maximum environmental load on one radiator panel • Maximum dissipation from the grid of 252 W • All grid heat load must be transported to one radiator • Resulting power requirement for each pipe is 40 W

4. Heat Pipe Sizing (2 of 2) • X-LAT • 1 of 6 pipes failed • Cumulative heat load and transport requirement calculated directly from Heat Flux (W/m) vs Length Along Pipe (mm) graph • Results in a 59.5 W-m requirement for each pipe • VCHP • 1 of 6 pipes failed • Maximum environmental load on one radiator panel Maximum dissipation from the LAT of 612 W to be dissipated into one radiator panel • Resulting power requirement for each pipe is 94 W

5. Heat Pipe Qual/Acceptance Tests (1 of 2) • Qualification Tests • Extrusion charge optimization (VCHP only, new extrusion) • Burst: 4 * MEOP (Maximum Expected Operating Pressure) • Constant Conductance Heat Pipe Acceptance Tests • Leak: Ammonia leak < 1x10-7 scc/sec • Proof Pressure: Greater of 1.1 * MPP (Maximum Processing Pressure) or 1.5 * MEOP • Non-Condensable Gas: Verify acceptable level • Transport: Capability > 1.3 times requirement • Ammonia Charge: Mass recorded before and after charging

6. Heat Pipe Qual/Acceptance Tests (2 of 2) • Variable Conductance Heat Pipe Acceptance Tests • Leak: Ammonia leak < 1x10-7 scc/sec • Proof Pressure: Greater of 1.1 * MPP (Maximum Processing Pressure) or 1.5 * MEOP • Transport: Capability > 1.3 times requirement • Control Gas (He/Ne) Charge Quantity: Verify correct quantity • Ammonia Charge: Mass recorded before and after charging • Wicking: Tested to insure sufficient wicking (In process test) • Control Performance: Deferred to radiator assy level

7. Heat Pipe Structural Analysis (1 of 2) • Top Flange and Downspout Heat Pipes external loads insignificant relative to internal loads due to mounting configuration • Structural integrity demonstrated by heat pipe Qual./Acceptance tests • X-LAT Heat Pipe covered in X-LAT Plate structural analysis presentation • VC Heat Pipe covered in Radiator Assembly structural analysis presentation, preliminary analysis covering reservoir and transition complete with the following assumptions and results: • MEOP of 377 PSI (140ºF)**(requirements changed to 490 PSI) • MPP of 882 PSI (210 ºF) • Acceleration loads of 35 G’s replace external flight loads

8. Heat Pipe Structural Analysis (2 of 2) MEOP: Maximum Expected Operating Pressure MPP: Maximum Processing Pressure

9. VCHP Reservoir & Radiator Sizing • Reservoir Sizing: • Hot case effective sink temperature = 233 K • Cold case effective sink temperature = 193 K • Computed storage volume ratio = 1.1 (-10ºC to +15ºC) • Required reservoir volume = 75 cc

10. Document Status