Elastomerics Blog

Spaceborne electronics use low outgassing materials for environmental sealing and thermal and electrical insulation. Silicone rubber is a good choice because it maintains its flexibility and sealing integrity across extreme temperatures without outgassing volatile contaminants that can degrade spaceborne electronics. Yet not all silicones are low outgassing.

Stockwell Elastomerics converts low outgassing silicones into enclosure gaskets and other cut or molded parts for spacecraft and space vehicles. These solid silicones are platinum-cured for low outgassing and then post-cured under heat and vacuum to meet stringent ASTM E595 testing standards used by NASA and the space industry.

Why is Silicone Outgassing a Problem in Space?

In the near-vacuum of space, silicone gaskets are subjected to a severe reduction in ambient pressure. They’re also exposed to solar radiation and elevated temperatures. Under these conditions, standard peroxide-cured silicones can release low-molecular-weight cyclic siloxanes, absorbed atmospheric gases and moisture, and plasticizers, solvents, and processing aids.

Outgassing degrades space-grade electronics through condensation, but it can also lead to corona discharge and arcing. Outgassed species that condense as thin films on surfaces increase solar absorption and the risk of overheating. In addition, gaskets made of standard peroxide-cured silicones can lose their resilience and physical sealing force.

Low Outgassing Silicones and ASTM E595 Compliance

Platinum-cured silicones exhibit significantly less outgassing than peroxide-cured silicones. Yet platinum curing alone doesn’t ensure conformance with the ASTM E595 test standard used by NASA and the aerospace industry. This test exposes material samples to a thermal vacuum environment and measures Total Mass Loss (TML) and Collected Volatile Condensable Material (CVCM).

Stockwell Elastomerics offers space grade silicones that arrive platinum-cured and are post-cured after molding to drive off unreacted volatiles and meet the ≤ 1.00% TML and ≤ CVCM thresholds required by both NASA and the European Space Agency (ESA). This post-curing also improves a material’s resistance to compression set and improves its mechanical properties.

Space Grade Silicones with Low Temperature Flexibility

Stockwell Elastomerics fabricates space grade silicone gaskets from materials with low temperature flexibility. General purpose silicone can withstand temperatures as low as -73°C (-100°F), but that’s not enough for the near Earth region of space. When cold causes an elastomer to become brittle, a gasket loses its ability to flex with changing thermal conditions.

Engineers can choose from among three space grade silicones. SSP4716 is a 65 durometer, phenyl-based silicone that remains flexible at extreme temperatures as low -116°C (-177°F). SSP4734-50LV and SSP4734-70LV are methyl-based and available in 50 and 70 durometers (Shore A), respectively. Methyl-based options offer better high temperature resistance while phenyl-based options offer a wider standard operating temperature range, but all three low outgassing silicones meet ASTM E595.

Choose Low Outgassing Silicones for Spaceborne Electronics

Stockwell Elastomerics is an experienced gasket fabricator that also supports the air and space industry by helping design engineers with material selection. From prototyping to production, we can help you achieve mission success. To talk to our Applications Engineering Team, complete our on-line form, email service@stockwell.com, or call (215) 335-3005.