Outgassing of materials under space environment
To qualify materials for their suitability for space applications, assessment of outgassing properties is required.“Outgassing” is defined as the mass loss of a sample due to vacuum conditioning at elevated temperature. The test is ESA certified and is performed in accordance to ECSS-Q-ST-70-02C: “Thermal vacuum outgassing test for the screening of space materials”. For investigation of mass loss as function of time a sublimation test may be performed
(see Advanced Outgassing).
Outgassing tests are performed in the following steps
- The samples are submitted to pre-conditioning (24 hours at 22°C and 55%rH) to allow moisture uptake.
- During the thermal test (125°C for 24 hours) the outgassing behaviour is assessed by measuring the weight of the samples before and after thermal treatment. Furthermore, the mass gain of collector plates (cooled to 20°C) due to condensed matter is measured. Thus, it is possible to evaluate the possible contamination of sensible components (such as mirrors) by outgassed material.
- As for many applications the water-loss is not relevant, samples are also weighted after a post-conditioning (24 hours at 22°C and 55%rH) allowing recovery of lost moisture.
Example for total mass loss (TML) and regained mass loss (RML) during vacuum test (125°C) and sample conditioning (22°C, 55% RH)
The following parameters are determined as result of an outgassing test:
- TML (Total Mass Loss): Total mass loss relative to the initial sample mass
- RML (Recovered Mass Loss): Mass loss after water absorption during post-conditioning (relative to initial sample mass)
- CVCM (Collected Volatile Condensable Material): mass gain of collectors relative to initial sample mass.
Outgassing test according to ECSS-Q-ST-70-02
3 samples per material required for statistical evaluation
Each sample weight 100 – 300 mg
Max. size per sample 8x8x10 mm
Materials per test run
For each test run max. 4 materials plus 1 empty sample cup (reference) are measured
p < 10-5 mbar
22°C 24 hours (pre-conditioning at 55%rH)
125°C 24 hours (thermal vacuum test) - up to 300°C on request (non-ECSS)
22°C 24 hours (post-conditioning at 55%rH)
Results & ECSS requirements
TML: mean value < 1.0% standard deviation < 0.1 * mean value
RML: mean value < 1.0% standard deviation < 0.1 * mean value
CVCM: mean value < 0.1% standard deviation < 0.2 * mean value