Tuesday, September 12, 2017

Example of a Large Vacuum Chamber Used at NASA

Facility 238 is a large, vertical, cylindrical thermal vacuum chamber which is used for thermal vacuum and thermal balance testing, and baking out spacecraft hardware. Test articles are normally loaded through the top of the chamber using the building crane; however, small payloads can be transported through the personnel entrance. Ports for electrical feedthroughs, liquid/gas feedthroughs, and viewing are located around the perimeter of the chamber. A clean tent at the chamber entrance provides class 10,000 cleanliness conditions.

Mode of Operation


With the chamber dome rolled back, the overhead crane is used to lower the payload onto the support fixture. In most cases, special fixturing must be designed due to the uniqueness of the test article support system. Once installed, the payload is instrumented and connected to the ground support equipment via feedthroughs. Access to the chamber is throught a clean tent. The use of cleanroom procedures and the wearing of clean garments are required when working in the chamber.

Initial chamber evacuation is provided by two rotary piston mechanical pumps, with four closed cycle cryopumps for high vacuum pumping. Each cryopump is isolated from the chamber by a sliding gate main valve to allow off-line cool down and regeneration.

Parameters

  • Test Pressure: 5 x 10-7 mmHg
  • Shroud Temperature: GN2 mode -90°C to +90°C , LN2 mode -190°C
  • Chamber Pump: 4 cryopumps
Physical Characteristics
  • Test Volume: 12' x 15'
  • Payload Support: Floor level - 4' square platform
  • Side Wall: Hardpoints at 6' and 12' levels
  • Crane Capacity: 5 tons Viewports: 9" diameter
  • Standard Electrical Feedthroughs: 36 - 37 pin connectors (RF feedthroughs available on request)
Integral Instrumentation
  • Pressure: Capacitance manometer - Atm to 10-3 mmHg
  • Ion Gauge: 10-3 mmHg to ultimate
  • Payload Temperature: 324 channels of thermocouple or thermistor channels
  • Contamination Monitor: TQCM, coldfinger, residual gas analyzer