What is the outgassing requirement for RF materials used in space and how is it tested?
Space Material Outgassing Control
Outgassing control is a fundamental space materials discipline that directly affects the long-term performance and reliability of RF payloads. Contamination that accumulates over a 15-year GEO mission can significantly degrade antenna performance and increase system noise temperature.
| Parameter | GEO | MEO | LEO |
|---|---|---|---|
| Altitude | 35,786 km | 2,000-35,786 km | 200-2,000 km |
| Latency (one-way) | ~270 ms | 50-150 ms | 1-20 ms |
| Coverage per Sat | Full hemisphere | Regional | Local footprint |
| Handover | None | Periodic | Frequent |
| Path Loss (Ku-band) | ~206 dB | 190-206 dB | 170-190 dB |
Frequently Asked Questions
What happens if a material fails outgassing requirements?
Options when a preferred material exceeds TML or CVCM limits: (1) Bake-out: pre-heat the assembled component or material at 100-125°C in vacuum for 24-48 hours to remove volatiles before integration with the spacecraft. Many materials pass after bake-out that fail in the as-received condition (moisture and residual solvents are removed). (2) Barrier coating: apply a low-outgassing conformal coating (Parylene C) over the high-outgassing material to slow the volatile release rate. (3) Isolation: physically separate the high-outgassing material from sensitive surfaces using baffles or thermal shields. Place venting ports so that outgassing products exit toward deep space rather than toward antennas. (4) Material substitution: find an alternative material with equivalent RF/mechanical properties that meets outgassing requirements (check the NASA outgassing database for alternatives). (5) Waiver: for some applications, a material that slightly exceeds limits may be accepted with a documented contamination analysis showing that the deposition on critical surfaces remains below performance thresholds.
Is outgassing only a concern in vacuum?
Outgassing rate depends on both temperature and pressure: in vacuum (space): outgassing rate is highest because there is no atmospheric pressure to suppress volatile release. At ground ambient pressure: outgassing still occurs but at lower rates, and volatiles disperse into the atmosphere rather than depositing on nearby surfaces. During launch: the transition from atmospheric pressure to vacuum occurs over 3-5 minutes (fairing jettison). Materials with weakly bonded volatiles may release a burst of gas during this transition. Thermal cycling in orbit: outgassing rate increases exponentially with temperature (approximately doubling for every 20°C increase). Hot surfaces (sun-facing equipment panels at +80°C) outgas faster than cold surfaces. The worst-case contamination scenario is often the first few orbits, when components experience their highest temperatures after months of ambient storage.
How do I find outgassing data for a specific material?
Three primary sources: (1) NASA Outgassing Database (https://outgassing.nasa.gov): over 10,000 materials tested per ASTM E595. Searchable by material name, manufacturer, and generic type. Includes TML, CVCM, and WVR for each entry. (2) ESA ECSS-Q-ST-70-02 database: European equivalent with similar data. (3) Manufacturer datasheets: space-qualified component and material suppliers (Rogers, Gore, Henkel/Loctite, 3M) publish outgassing data for their space-grade products. If no data exists for your specific material: submit samples for ASTM E595 testing at qualified laboratories (NASA Goddard, Jet Propulsion Laboratory, and commercial labs like NTS, EAG). Test cost: $500-1,500 per material sample, with 2-4 week turnaround.