In order to design a successful space system, the unique challenges of the space environment it will operate in must be considered during the design process. Atomic oxygen (AO) is a detrimental environmental effect found in Low Earth Orbit (LEO) that affects spacecraft surfaces by oxidizing and eroding material over time, particularly polymers. Carbon fiber/epoxy composites are a commonly used spacecraft material affected by AO exposure. Carbon composites are used as a structural material, such as on solar panels; their large surface area therefore is a potential contamination source to sensitive components. The Space Environments and Testing Lab at California Polytechnic State University, San Luis Obispo (Cal Poly SLO) includes an apparatus that can simulate AO in the LEO environment. This apparatus was used to expose carbon composite samples to AO before being tested for short beam strength to measure the effect on material properties. Results showed no significant difference in short beam strength for a 24-hour AO exposure compared to unexposed samples, but a 4% decrease for samples with a 48-hour exposure. Previous work at Cal Poly SLO found that AO-exposed composite generated particulate contaminants. Tape lift tests and mass measurements of samples were conducted before and after AO exposure to characterize the particulate contamination generated and percent mass loss. It was found that AO exposure increased the percent mass loss by 1.5% for 24-hour exposure and 3% for 48-hour exposure. The tape lift percent area coverage increased by 2.5% near sample ends and 0.35% in the middle after AO exposure.

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 × 1021 atoms/cm2 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.

This thesis describes an experimental technique for measuring the atomic-oxygen concentration under simulated upper atmosphere conditions.

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Understanding the space environment and contamination concerns of a spacecraft is critical in designing a successful mission. The ability for a spacecraft to meet its science objectives relies on systems functioning as intended. A concern for maintain- ing performance while on orbit is molecular contamination. Silicones have previously been shown to form a silica layer on their surfaces when exposed to atomic oxygen. For silicone contamination, this translates to a silica film on the contaminated surface. Missions such as Long Duration Exposure Facility and Evaluation of Oxygen Interactions with Materials III have indicated that the silica film can trap deposits of carbon contamination to the surface during its formation. This phenomenon was explored in this research using RTV-S 691 silicone and Braycote 601EF for the carbon-based contaminant. The experiment involved contaminating an aluminum substrate in three different configurations; one for each contaminant individually on the substrate, and one with both contaminants. These samples were exposed to atomic oxygen for a period of 24 hours, then analyzed with Fourier transform infrared spectroscopy. The trends in infrared spectra for the different test cases were characterized for comparison. The trend for samples with a carbon-to-silicone contamination ratio of greater than ten to one showed peaks corresponding to those seen on the singularly contaminated samples. When the concentration of silicone was increased, the trend in spectral results showed peaks corresponding to Braycote before atomic oxygen exposure. At certain concentrations of RTV silicone to Braycote, the trends suggest Braycote is partially protected from atomic oxygen by a silica film. This indicates that silicone conversion to silica in atomic oxygen can trap contaminants to a surface.

An important consideration for spacecraft material selection is the space environment that the spacecraft will be operating in. Two features of the space environment that drive material selection are material outgassing and the presence of atomic oxygen in low Earth orbit (LEO). Materials that are considered for use in space are tested to be able to understand how they’ll outgas on orbit and how they’ll respond to interactions with atomic oxygen. However, testing to understand how atomic oxygen interaction with a material will affect how the material will outgas is rare and not standardized. This thesis used a vacuum chamber intended to determine the outgassing properties of materials using ASTM E595 and another vacuum chamber intended to determine how materials are affected by atomic oxygen using ASTM E2089 to determine how atomic oxygen affects outgassing of silicones, which are of interest as atomic oxygen can alter the chemical composition of the surface of silicones. CV-2500, CV2-2289- 1, and SCV2-2590, three silicone elastomers that are products of NuSil Technology LLC, were tested. Significant trends in atomic oxygen reducing the amount of matter outgassed from these three materials were observed. This can be explained by the conversion of the surface of silicone to silica, which was confirmed using Fourier Transform Infrared (FTIR) spectroscopy. Retesting of these three materials in a chamber designed for ASTM E595 with a temperature measurement system capable of adhering to ASTM E595 to confirm the results of this thesis with more confidence in uniform temperature exposure is recommended.

The Ram Energy Distribution Detector (REDD) is a new CubeSat-compatible space science instrument that measures neutral wind characteristics in the upper atmosphere. Neutral gas interactions with plasma in the ionosphere/thermosphere are responsible for spacecraft drag, radio frequency disturbances such as scintillation, and other geophysical phenomena. REDD is designed to collect in-situ measurements within this region of the atmosphere where in-flight data collection using spacecraft has proven particularly challenging due to both the atmospheric density and the dominating presence of highly reactive atomic oxygen (AO). NASA Marshall Space Flight Center has a unique AO Facility (AOF) capable of simulating the conditions the sensor will encounter on orbit by creating a supersonic neutral beam of AO. Collimating the beam requires an intense magnetic field that creates significant interference for sensitive electronic devices. REDD is undergoing the final stages of validation testing in the AOF. In this presentation, we describe the LabVIEW-automated system design, the measured geometry and magnitude of the field and the specially designed mount and passive shielding that are utilized to mitigate the effects of the magnetic interference. / Master of Science / The Ram Energy Distribution Detector (REDD) is a new CubeSat-compatible space science instrument that measures winds in near-Earth space. Gas interactions with plasma in the upper regions of the atmosphere are responsible for spacecraft drag, radio wave disturbances, and other phenomena. REDD is designed to collect direct measurements within this region of the atmosphere where in-flight data collection using conventional spacecraft has proven particularly challenging. The environmental testing needed to demonstrate the sensor requires a specialized system located at NASA Marshall Space Flight Center. To simulate the conditions the sensor will encounter on orbit within a laboratory requires exposing REDD to a supersonic beam of gas using NASA’s unique Atomic Oxygen Facility. Forming this gas into a beam requires an intense magnetic field that creates significant interference for sensors such as REDD. Testing in this facility requires a specially-designed sensor mount and magnetic shielding system. REDD is undergoing the final stages of validation testing in the Atomic Oxygen Facility. In this presentation, we describe the computer software-automated system for testing the sensor, the shape and strength of the magnetic field, the specially designed sensor mount, and magnetic shielding that are used to mitigate the effects of the interference.

The temperature-programmed desorption profiles of water from three lunar analogs were measured. These experiments showed that glassy materials were hydrophobic, that water on multiphase materials occupied a continuum of adsorption sites, and that feldspar exhibited significant chemisorption of water. The competition between photodissociation and photodesorption of amorphous solid water (ASW) was investigated on three substrates: copper with a thin oxide coating, an impact melt breccia from Apollo 16, and a mare basalt from Apollo 17. The rotational temperature of desorbing H₂O did not vary significantly with substrate, but the H₂O time-of-flight spectra were broader on the lunar slabs than on copper. Additionally, the cross sections for water removal at low coverages were higher on the lunar slabs than on copper. O(³PJ) produced by 157-nm irradiation of ASW on the same three substrates was measured as a function of spin-orbit state, H₂O exposure, and irradiation time. The same Maxwell-Boltzmann components were present in each case, with translational temperatures of 10,000 K, 1800 K, 400 K, and the surface temperature, but the relative intensities of these components differed widely between substrates. Evidence for diffusion out of pores in the ASW and in the lunar slabs was observed for H2O exposures of at least 1 Langmuir. Cross sections for H2O and O(3PJ) depletion due to 157-nm irradiation of ASW were applied to icy grains in the rings of Saturn, and corresponding cross sections on the lunar substrates were used to estimate the flux of water desorbing from the Moon and the density of oxygen atoms in the lunar atmosphere.

The space environment presents various challenges when designing systems and selecting materials for applications beyond Earth’s atmosphere. For mission success, these challenges must be considered. One of the detrimental aspects of the space en- vironment is Atomic Oxygen, AO. Only present in harmful quantities in Lower Earth Orbit, LEO, AO causes significant damage to materials by breaking molecular bonds. California Polytechnic State University’s, Cal Poly’s, space environments laboratory features an apparatus capable of simulating this environment. Very thin or short samples were tested to observe the mass loss due to erosion of the sample material. Recent modifications to the system allow it to expose surfaces of three dimensional objects to AO rather than only those two dimensional objects. Simulating this effect on taller samples makes available the opportunity to test coupons that are then used in additional testing to measure the effect of that erosion on other properties. Challenges in adapting the AO system are explored and addressed, as well as some possible use cases for future work. As a use case, bending moment specimens were exposed to AO prior to testing in four point bending. Multiple regression models were constructed to determine variables contributing to slope changes between specimen pairs’ linear-elastic regions of force-displacement graphs. Results show that AO exposed specimens had significantly gentler slopes in the linear elastic region of the force-displacement curve, meaning that AO exposure reduced structural rigidity of the coupons.

The space environment is a volatile and challenging place for satellites to survive in. For Low Earth Orbiting (LEO) satellites, atomic oxygen (AO) is a constant corrosive effect that degrades the outer surface of satellites over long durations. Atomic oxygen exists in the atmosphere between 180 and 675 km and has a relatively high energy at 4.5 eV, which allows AO to break molecular bonds in materials on the surfaces of spacecraft. As the number and complexity of CubeSat missions increase, there is an increased risk that AO degradation on commercial off the shelf parts (COTS), such as antenna, could degrade the satellite’s ability to communicate with ground systems. This thesis looks at how AO erosion affects the performance of patch antennas for CubeSat applications. Patch antennas are small, cheap, low-profile antennas that can be used on CubeSats to communicate with the ground or other satellites. Patch antennas are semi-directional, providing higher gain and higher available frequencies than omnidirectional antennas. An AO chamber in the California Polytechnic State University San Luis Obispo’s (Cal Poly) Spacecraft Environments Testing Lab was used to expose the patch antennas for 24-hour and 48-hour tests. The 24-hour exposure saw an average AO fluence of 8.757 ± 0.807•1020 atoms/cm2 which corresponds to roughly 3.5 months of on-orbit AO exposure on the Ram side when in a 28.5° inclined orbit with an altitude of 400 km. The 48-hour exposure saw an average AO fluence of 1.595 ± 0.076•1021 atoms/cm2 which corresponds to approximately 6.4 months of on-orbit AO exposure on the Ram side when in a 28.5° inclined orbit with an altitude of 400 km. To test the performance of the patch antenna before and after AO exposure, an anechoic chamber in the Microwave Lab at Cal Poly was used to measure boresight gain and radiation pattern in the E-plane and H-plane. From the testing in the anechoic chamber it was determined that there was no apparent difference in the patch antenna’s gain and radiation pattern before and after AO exposure. By using a Fourier Transform Infrared Spectrometer (FTIR) it was discovered that the outer surface of the patch antennas were forming a silicon dioxide layer, which did not affect the performance of the patch antenna. Since silicon dioxide is resistant to AO erosion, it may be beneficial for CubeSats to include silica additives to their exposed antenna surfaces to prevent erosion.