Effect of Atomic Oxygen Exposure on Surface Resistivity Change of Spacecraft Insulator Material

Abstract

Spacecraft surface charging can lead to arcing and a loss of electricity generation capability in solar panels or even loss of a satellite. The charging problem may be further aggravated by atomic oxygen (AO) exposure in Low Earth orbits, which modifies the surface of materials like polyimide, Teflon, anti-reflective coatings, cover glass etc, used on satellite surfaces, affecting materials properties, such as resistivity, secondary electron emissivity and photo emission, which govern the charging behavior. These properties are crucial input parameters for spacecraft charging analysis. To study the AO exposure effect on charging governing properties, an atomic oxygen exposure facility based on laser detonation of oxygen was built. The facility produces AO with a peak velocity value around 10-12km/s and a higher flux than that existing in orbit. After exposing the polyimide test material to the equivalent of 10years of AO fluence at an altitude of 700-800km, surface charging properties like surface resistivity and volume resistivity were measured. The measurement was performed in a vacuum using the charge storage decay method at room temperature, which is considered the most appropriate for measuring resistivity for space applications. The results show that the surface resistivity increases and the volume resistivity remains almost the same for the AO exposure fluence of 5.4 x 10 18 atoms cm-2 .

Atomic Oxygen in Low Earth Orbits, a Retrospective Review Study

“…Solar UV radiation (<< 190 nm) has enough energy to photodissociate O 2 forming free and hyperenergized AO, as shown in Fig. 5 [3].…”

“…It was stated by [3] that the formation of AO i n LEOs occurs by the photodissociation of O 2 molecules. These molecules absorb the near solar UV radiation and then dissociate into free oxygen atoms O in the outer ionosphere (at altitudes higher than 80 km), as shown in Fig.…”

“…Exposure to AO leads to a high erosion rate of materials such as organic films, composites and many polymers, as well as extreme mass loss and changes in the physical and chemical properties of the surface. These changes, directly and indirectly, affect the functionality of the spacecrafts and, thus, its lifetime [3].…”

“…AO exists, with different densities, in LEOs and HEOs (Highly Elliptical Orbits), as summarized in Fig. 1 [3].…”