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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 Facts
Outgassing test accord­ing to ECSS-Q-ST-70-02

Sample dimen­sions
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

Vacuum
p < 10-5 mbar

Temperatures
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