Vacuum Technology for Space Simulation Chambers
March 6, 2020
For this test, the pressure has to be in the high-vacuum range: 10-07 to 10-06 mbar. The test is done mostly in combination with the temperature cycle test. This is because satellites experience the heat and cold in space depending on whether they are in the earth’s shadow.
For the temperature cycle test, we use a thermal vacuum chamber test; some test chambers even simulate the solar wind! These chambers have volumes of up to 10,000 m³
Evacuating thermal vacuum chambers means pumping out the air and then pumping the gases released from the walls and the test objects. Here water vapor normally contributes to more than 80% of the residual gas composition. Evacuation time can be a day or more as satellites are not mass products and the tests need long preparation anyway.
The required pumping speed for different chamber volumes can be taken as a rule of thumb.
In thermal vacuum chambers, an internal shroud is capable of supplying variable temperatures. The temperature ranges from 77 K (if liquid nitrogen is used) up to 450 K. This shroud is reflective on the outside (polished steel or nickel plated) to reduce heat radiation and painted black inside. For the vacuum layout, this means that the vacuum surface is almost tripled, resulting in a high degassing load.
Figure 2 shows a typical simplified vacuum scheme; a 60 m³ chamber with a 30.000 l/s cryopump and a single large screw pump for roughing. Not shown are the gate valve of the cryopump, the regeneration line for the cryo and the vacuum gauges.
(1) DRYVAC DV 650 S
(1) ⌀ 0,16 x 5 m
(1) Angle Valve DN 160
Chamber 3 x 9 m
(1) ⌀ 0,8 x 0,3 m
(1) COOLVAC 30.000
Figure 4 shows the result with thermal shroud. Evacuation time is much longer due to the larger surface and the degassing especially from the black paint. In this case an additional roots blower in the dry roughing system or a large turbomolecular pumps would reduce the roughing time below the crossover pressure of the cryopump.
Without simulation of space conditions prior to launch, space flights would be not possible. Space simulation is, therefore, an important and attractive application of vacuum technology. Tests under vacuum (in space simulation chambers) are mandatory for all equipment to be used in space. The recent developments for electrical propulsion are a driver for the development of vacuum technology for effective pumping of Xenon.