Effects of Atomic Oxygen and Grease on Outgassing and Adhesion of Silicone Elastomers for Space Applications

Groh, H. C. De; Puleo, Bernadette J.; Steinetz, Bruce M.

doi:10.1007/978-3-642-30229-9_19

Cited by 7 publications

(5 citation statements)

References 3 publications

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“…Typically, small O-rings have been used for material screening tests to help select the final seal material for an application. 4,5 However, larger O-rings have also been tested as potential seal designs for various applications.…”

Section: O-ringsmentioning

confidence: 99%

An Overview of Advanced Elastomeric Seal Development and Testing Capabilities at NASA Glenn Research Center

Dunlap¹

2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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NASA is developing advanced space-rated elastomeric seals to support future space exploration missions to low Earth orbit, the Moon, near Earth asteroids, and other destinations. This includes seals for a new docking system and vehicle hatches. These seals must exhibit extremely low leak rates to ensure that astronauts have sufficient breathable air for extended missions. Seal compression loads must be below prescribed limits so as not to overload the mechanisms that compress them, and seal adhesion forces must be low to allow the sealed interface to be separated when required (e.g., during undocking or hatch opening). NASA Glenn Research Center has developed a number of unique test fixtures to measure the leak rates and compression and adhesion loads of candidate seal designs under simulated thermal, vacuum, and engagement conditions. Tests can be performed on fullscale seals with diameters on the order of 50 in., subscale seals that are about 12 in. in diameter, and smaller specimens such as O-rings. Test conditions include temperatures ranging from -238 to 662°F (-150 to 350°C), operational pressure gradients, and seal-on-seal or seal-on-flange mating configurations. Nominal and off-nominal conditions (e.g., incomplete seal compression) can also be simulated. This paper describes the main design features and capabilities of each type of test apparatus and provides an overview of advanced seal development activities at NASA Glenn. Nomenclature CBM= Common Berthing Mechanism GRC = Glenn Research Center ISS = International Space Station LVDT = linear variable displacement transformer RTD = resistance temperature detector RTV = room temperature vulcanizing

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Section: O-ringsmentioning

confidence: 99%

An Overview of Advanced Elastomeric Seal Development and Testing Capabilities at NASA Glenn Research Center

Dunlap¹

2014

50th AIAA/ASME/SAE/ASEE Joint Propulsion Conference

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“…This stickiness helps to make a good seal; however, can cause problems when spacecraft undock . There are several options to mitigate this unwanted adhesion such as targeted use of AO, radiation in the vacuum‐UV range <200 nm, and application of a suitable grease . The grease‐based sunscreens developed to block UV were also designed to control adhesion; thus another objective of the research presented here was to sufficiently lower seal adhesive forces with the application of a UV blocking sunscreen.…”

Section: Introductionmentioning

confidence: 99%

Antiadhesion elastomer seal coatings for UV and atomic oxygen protection

Groh

Puleo

Waters

et al. 2014

J of Applied Polymer Sci

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Radiation blocking sunscreen coatings have been developed for the protection of elastomer seals used in low-Earth-orbit (LEO). The coatings protect the seals from ultraviolet (UV) radiation and atomic oxygen (AO) damage. The coatings were developed for use on NASA docking seals. Docking seal damage from the UV and AO present in LEO can constrain mission time-line, flight mode options, and increases risk. A low level of adhesion is also required for docking seals so undocking push-off forces can be low. The coatings presented also mitigate this unwanted adhesion. Greases with low collected volatile condensable materials (CVCM) and low total mass loss (TML) were mixed with slippery and/or UV blocking powders to create the protective coatings. Coatings were applied at rates up to 2 mg/cm 2 . Coated seals were exposed to AO and UV in the NUV (near-UV) and UV-C wavelength ranges (300 to 400 nm and 254 nm, respectively). Ground based ashers were used to simulate the AO of space. The Sun's UV energy was mimicked assuming a nose forward flight mode, resulting in an exposure rate of 2.

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“…[7] While a concrete conclusion cannot be drawn from such a result, it is worth discussing as an observed trend.…”

Section: Control Tml% Ao Tml%mentioning

confidence: 93%

“…One study did show a relationship between AO and outgassing, as AO exposure was shown to slightly reduce outgassing of an O-ring. [7] It is possible to visualize all three mechanisms of outgassing being affected by AO. The breaking of bonds and oxidation that occurs on material surfaces due to AO could change the amount of material desorbed from the surface.…”

Section: Combined Atomic Oxygen and Outgas Testingmentioning

confidence: 99%

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The Effects of Atomic Oxygen on the Outgassing Properties of Spacecraft Materials

Gurnee¹

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The space environment contains many harsh characteristics that are harmful to spacecraft and threaten the success of space missions. Atomic oxygen (AO) and outgassing are among the chief concerns that spacecraft engineers must design for in order to ensure the safety of a spacecraft. AO is monatomic oxygen (O1) that is created when Ultraviolet (UV) radiation photochemically disassociates diatomic oxygen (O2) in space. AO is the dominant atmospheric constituent between 175 and 600 km, and is a great concern in low earth orbits. Orbital AO has an average impact energy of 4.5 ± 1 eV with orbiting spacecraft and is also very reactive; this makes AO very corrosive to spacecraft materials. Outgassing is the process by which trapped and adsorbed gases are expelled from materials. The high temperatures and low pressure of the spacecraft environment exacerbate the process of outgassing. Outgassing is problematic for spacecraft because outgassed material can condense on sensitive surfaces such as optical and thermal surfaces, or the material can create clouds that impede sensors ability to observe their target. While it has been shown that many aspects of the spacecraft environment act synergistically together to further degrade spacecraft performance, there is very little information and data available on the interactions between AO and outgassing. Cal Poly's Space Environments Lab is equipped with an AO simulation vacuum chamber (MAX) and an outgas testing chamber (Micro-VCM) which is capable of testing materials for total mass loss (TML) and collected volatile condensable mass (CVCM) outgassing values. MAX and Micro-VCM were used in tandem to test different spacecraft materials in order to determine if AO exposure had any effect on the respective materials TML and CVCM values. Prior to conducting testing, Micro-VCM was refurbished and validated since it was recently donated to Cal Poly and was not in working order upon arrival. Three Sheldahl materials were tested: aluminum coated 1.0 mil Kapton tape, 2.0 mil Kapton film coated with ITO on one side and aluminum on the other, and 2.0 Kapton film coated with aluminum. The materials were exposed to an average AO fluence of 1.33 ± 0.130 × 10 21 atoms/cm 2 for AO testing. The TML and CVCM results from four of the six tests did not show any significant changes between AO samples and control samples, partially due to large error bars that stem from using a semi-microbalance instead of a full microbalance. However, the AO exposed ITO-Kapton-Al did show an increase in TML from -0.03 ± 0.09% to 0.19 ± 0.08% for one procedure, while the aluminum Kapton tape CVCM decreased from 0.81 ± 0.12% to 0.63 ± 0.12% for another procedure. These results show that two materials exhibited a change in their outgassing properties after AO exposure. More testing on the subject is warranted and should be conducted in order to collect more data points and begin defining trend lines that can further describe the effects of AO on outgassing.iv ACKNOWLEDGMENTS

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Effects of Atomic Oxygen and Grease on Outgassing and Adhesion of Silicone Elastomers for Space Applications

Cited by 7 publications

References 3 publications

An Overview of Advanced Elastomeric Seal Development and Testing Capabilities at NASA Glenn Research Center

An Overview of Advanced Elastomeric Seal Development and Testing Capabilities at NASA Glenn Research Center

Antiadhesion elastomer seal coatings for UV and atomic oxygen protection

The Effects of Atomic Oxygen on the Outgassing Properties of Spacecraft Materials

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