Mitigation of Thruster Plume Erosion of International Space Station Solar Array Coatings

摘要

Optically sensitive surfaces on the International Space Station (ISS) can be damaged (or eroded/pitted) when impacted by high-velocity particles from unburned liquid propellant present in bipropellant thruster plumes. Surfaces with thin optical coatings, such as solar arrays and radiators, are of primary concern. Thruster plume-induced erosion/pitting of sensitive surfaces has been observed on space shuttle flight experiments. The Boeing ISS Environments Team in Houston has developed an approach to modeling thruster plume-induced erosion/pitting of ISS surface materials. The Boeing team has conducted analyses simulating bipropellant thruster particles impacting sensitive ISS surfaces for various assembly stages. Thruster firings for ISS reboost/attitude control, as well as visiting vehicle thruster firings during approach or separation to ISS docking ports, were simulated. The results of these analyses show that particle impingement angle greatly affects surface damage, with normal impacts being the most severe. Particles with highly oblique impact angles (～75 deg off normal), however, will essentially skid off surfaces without causing any erosion/pitting. A mitigation technique has been developed to prevent plume erosion/pitting of solar array coatings. Before a thruster-firing event, solar arrays may be rotated to a preestablished position that will eliminate plume particle impact damage to the surface. The preestablished positions are defined based on the geometry of the ISS thrusters relative to the solar array panels to ensure that plume particles will impinge at highly oblique angles (greater than 75 deg off normal). Upcoming ISS milestones will introduce new sensitive surfaces and thrusters, making 2005 a critical year for establishing operational constraints to mitigate thruster plume erosion. Some of these milestones include the space shuttle return to flight, the deployment of new ISS solar arrays, and the maiden voyage of ESA's automated transfer vehicle. Operational constraints for plume erosion mitigation are being coordinated with other solar array operational constraints such as power, thermal, and plume-induced structural loads. An integrated operational solution is being implemented to support the ISS assembly flight sequence. This paper will discuss plume erosion analyses and the implementation of operational mitigation as well as ongoing testing to better characterize plume erosion effects.