20 Mar 2007

1. Pressure Systems 20 Mar 2007 Prepared by Chris Tutt ESCG Project Manager

2. Introduction • Pressure systems data primarily covered in three hazard reports • AMS-02-F03 covers potential rupture of the cryosystem pressure vessels. • AMS-02-F04 covers potential overpressurization of the Orbiter payload bay. • AMS-02-F05 covers potential rupture of all other pressure systems. • Pressure systems occasionally referenced in individual controls in other hazard reports.

3. Pressure Systems Overview • Certain generic statements apply to all pressure systems. • MDPs developed for all pressurized segments based on thermal analysis including two hardware faults (heater runaway, thermostat failure, etc) where appropriate. • Fill procedures have been reviewed to ensure that analysis uses worst-case liquid/gas masses. • All welded pressure vessels have been inspected and verified per AMS-02 weld control plans. • Stress analysis or test confirms burst pressure meets all factor of safety and Leak Before Burst requirements. • All these results are documented in the hazard reports and the attached pressure tables.

4. Sample Pressure Table

5. Major AMS-02 Pressure Systems • Five major pressure systems on AMS-02 • Cryomagnet • Warm Helium Gas Supply • Transition Radiation Detector • Tracker Thermal Control System • Cryocooler Loop Heat Pipes • Several smaller heat pipes and loop heat pipes exist within the TCS. • Cryocoolers also have small pressurized volume.

6. Cryomagnet • The cryomagnet pressure system includes the following individual vessels and loops: • Vacuum Case (ground only) • Main Helium Tank • Superfluid Cooling Loop • Vapor-Cooled Leads • Warm Helium Gas Supply • Pilot Valve Vacuum Vessel (ground only) • Cool-Down Circuit (not nominally pressurized)

7. Cryosystem Schematic

8. Vacuum Case • VC is the outer surface of the cryomagnet dewar. • Maximum positive pressure is 0.8 bar based on burst disks. • Maximum negative pressure is -1.0 atm based on sea level air pressure. • System will be proof tested for both pressures after final weld.

9. Vacuum Case • System has dual O-ring seals around support rings and each pass-through. • Acoustic testing done to verify seals do not leak under launch vibration environment.

10. Main Helium Tank • Main Helium Tank is the primary helium reservoir for the cryomagnet. • Contains 2500 liters of superfluid helium. • MDP of 3 bar, defined by burst disks. • Successfully survived proof pressure test to 1.1xMDP. • MMOD analysis shows PNP meets ISS requirements. • All welding done with close oversight of ES4.

11. Superfluid Cooling Loop • Superfluid Cooling Loop (SCL) is primary heat exchanger between the magnet coils and the main tank. • SCL is also filled with superfluid helium. • MDP of the SCL is 23 bar, defined by burst disks that vent back into the main helium tank.

12. Helium Venting • During nominal operations, AMS-02 will vent small amounts of helium gas (3.2 l/min) from the main tank. • Vent will be opened by baroswitch once payload bay has depressurized (approximately three minutes after liftoff). • Emergency venting could occur 23 minutes after VC sustains maximum credible breach. • Cryosystem pressures and temperatures will be monitored up to nine minutes prior to launch and nominal readings will be a Launch Commit Criterion. • Shuttle safety and PSRP have reviewed vent rates and analysis and concurs that system is non-hazardous with LCC in place.

13. Cryosystem Flight Vents • Several vents support the cryosystem. • Flight Vent will continuously emit small quantities of helium. • Emergency Helium Vent could vent large quantities if helium tank burst disks burst. • Other vents protect small contingency volumes. • First two vents are tees to prevent net thrust loads • Design shown in picture will be updated to include an actual tee section. • Neither vent impinges on EVA translation paths or worksites. • Neither vent directly impinges on Orbiter hardware.

14. Burst Disks • Burst disks used in cryosystem are built by Fike. • Design is reverse-acting, circumferentially-scored, with cutting teeth. • Multiple disks from same lot burst to establish performance, including bursts at cryogenic temperatures (2 bursts for each flight disk). • Design and qualification plan have been reviewed by PSRP and meets TA-88-074 requirements for one-fault-tolerance.

15. Vapor-Cooled Leads • Electrical leads used to charge magnet require dedicated cooling loop. • When in use, leads filled with superfluid helium from main tank via thermo-mechanical pump. • After charging operations, helium in leads is vented to space. • MDP of system is 10 bar based on burst disks.

16. Warm Helium Gas Supply Schematic

17. Warm Helium Gas Supply • Warm Helium Gas Supply provides gas to actuate cryogenic valves inside main helium tank. • Warm Helium Tank serves as primary gas reservoir. • Provides gas to pilot valves which operate the warm and cold cryosystem valves and current lead disconnects. • Once helium in main tank is expended, remaining helium in warm tank can be slowly vented to release pressure. • Failure of either warm or cold helium valves has no safety impacts, only mission success impacts.

18. Warm Helium Tank • Main tank is an Arde-designed COPV mounted on lower support ring of vacuum case. • MDP of tank is 273 bar based on thermal analysis.

19. Warm Helium Valves • Warm helium valves are pressure-actuated through a spring-loaded bellows. • Bellows only pressurized during actuation, then vented. • MDP of warm helium valves, pilot valves, and associated tubing is 8 bar, based on relief valves. • Proof tested to 1.1xMDP to avoid damage to bellows – test plan coordinated with PSRP.

20. Cold Helium Valves • Cold helium valves function identically to warm helium valves. • Valves previously used on CRISTA-SPAS. • All valves have undergone functional and pressure testing at cryogenic temperatures. • Bellows pressurized for actuation, then vented through pilot valves. • Valves completely contained within Vacuum Case.

21. Pilot Valve Vacuum Vessel • PVVV is vacuum vessel surrounding the pilot valves for the cold valves, mounted on the upper support ring of the VC. • Like VC, only required for ground and launch operations. • MDP is 10 bar, based on burst disks. • Pilot valves could see negative pressure of 2 bar.

22. End-of-Life Procedures • Superfluid helium in main tank will be slowly expended during life of mission. • Once superfluid helium is expended, there is no need to operate current leads or valves inside the magnet. • Remaining gas in warm helium tank will be slowly released to space to reduce risk.

23. Transition Radiation Detector • TRD uses xenon and carbon dioxide gas to detect incoming particles. • Pressure systems divided into four parts • Gas Supply Tanks • Gas Supply Box (Box “S”) • Gas Circulation Box (Box “C”) • Straw Tubes and Manifolds

24. TRD Gas Supply Tanks • Primary Xenon and CO2 tanks built by Arde based on previously NASA-certified designs. • Xe tank used on PCU • CO2 tank used on X-33 • Tank manufacturing and testing matches most recent COPV standard. • When one tank runs out of gas, other tank will be slowly emptied to reduce risk.

25. TRD Gas Tank Heaters • Gas tanks include several heaters to prevent liquid formation, which prevents mass measurement. • Two separate strings of heaters per tank, each with three thermostatic controls. • Heater installation processes reviewed with ES4 and with tank manufacturer.

26. TRD Box S • From the main tanks, gas flows through a series of filters, orifices, and valves to the mixing vessel. • Mixing vessel is Arde-designed cylindrical pressure vessel. • Preheaters directly outside of supply tanks prevent introduction of liquid into tubing of Box S.

27. TRD Box S Schematic

28. Box S Maximum Design Pressures • Box S has two separate pressure environments. • MDP of gas tanks and nearby lines is 206.8 bar based on thermal analysis and valve failure allowing gases to mix. • Mixing vessel and related lines has maximum MDP of 20.7 bar, based on relief valves. • High-pressure lines have 100 psi check valves back to gas tanks to relieve pressure in case of liquid release into first metering volume.

29. TRD Box C • Gas released from Box S into detector circulation in Box C as needed. • Monitor tubes contain small quantities of Fe55 to measure gas mixture. • Amount has been approved by Radiation Constraint Panel. • MDP of Box C is 2 bar based on relief valves.

30. TRD Straws and Manifolds • After Box C, gas mixture flows through one of the 41 manifolds into one of 5248 straw tubes. • Small amounts of gas will diffuse through straw composite wall. • Each manifold can be individually isolated in case of more signficant leak. • MDP of manifolds, modules, and straws is 2 bar based on relief valves in Box C.

31. Tracker Thermal Control System • Tracker thermal control system is a two-phase CO2 system designed to keep the tracker as isothermal as possible. • Liquid is heated to saturation temperature before entering evaporator. • Gas flows up to condensers and transfers heat to heat pipes in tracker radiator panels. • Liquid pumped back down to pre-heater, where excess liquid flows into accumulator. • Two separate loops – primary and secondary – on port and starboard side of payload. • System has nominal MDP of 160 bar based on thermal analysis including failed-on heaters. • Condenser tubing also susceptible to freezing.

32. TTCS Schematic

33. Accumulator • Accumulator is a cylindrical reservoir used to control temperature within TTCS main loop and store excess liquid. • MDP of 160 bar determined by thermal analysis. • Failed-on heaters not included, because all accumulator heaters have three thermostatic controls.

34. Accumulator Heat Pipe • Accumulator Heat Pipe (AHP) is independent ammonia heat pipe extending outside of accumulator. • AHP uses an inserted artery wick design. • Thermostats on external portion of heat pipe allow monitoring of internal temperature. • Heaters on external portion allow accumulator contents to be heated when necessary.

35. Freeze/Thaw Cycles • CO2 inside the condenser capillary tubes can freeze. Thawing the plug could lead to high pressures. • Test showed maximum pressure seen during thaw cycle was 3009 bar. • Analysis shows Inconel 718 can survive this pressure with factor of safety of 4.6. • Will be confirmed by burst testing of flight-like tube sample.

36. Cryocooler Loop Heat Pipes • Temperature of each cryocooler maintained by two independent loop heat pipes connected to Zenith Radiator panel. • Loop heat pipes similar to those on COM2PLEX, which flew on STS-107, but use propylene to avoid freezing concerns. • Most of system consists of 3mm steel tubing, which transitions to 4mm aluminum tubing at bimetallic joint near radiator panel. • MDP of loop determined to be 18 bar by thermal analysis.

37. Bypass Valve • System includes bypass valve to prevent system from falling below minimum storage temperature. • Control valve is bellows operated by sealed reservoir of argon. • Operating pressure of bypass valve is 6 bar – MDP by default as system is not pressurized at higher temperatures.

38. Cryocoolers • Cryocoolers themselves include a small pressurized volume. • System was identified as “pressurized device” by JSC Fracture Control Board. • MDP of 20.3 bar based on thermal analysis, including failed-on heaters. • Burst factor of safety of 6.1.