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A modification to the multipactor electron source used in the study of the behavior of spacecraft insulating materials is described. The electron accelerating system was included within the source, freeing the region between the source and the target of fields produced by the source electrodes.
Conditions and causes of multipactor breakdown and discharge in spacecraft electronic systems and equipment
Harmonic and noise current measurements, and intermodulation distortion coefficients for studying multipactor radio frequency discharge in space electronic systems
Study of multipactor breakdown in space electronic systems and measurement of harmonic content in typical discharge
This report supplies the technical background and design techniques needed by an engineer who is designing electrical insulation for high-voltage, high-power components, equipment, and systems on spacecraft. The data in this volume is in addition to the material in Volume 4 of the final report "High Voltage Design Guide: Aircraft' which is common to the electrical insulation design for both aircraft and spacecraft equipment. The common data includes testing, tracking, partial discharges and corona. Unique material involves the semi vacuum environment, spacecraft charging, and multipactor.
Shuttle polar orbit missions are being planned in which astronaut extravehicular activities (EVA) will eventually include external operations or repair and refurbishment of satellites. Recent satellite data and model calculations show that significant spacecraft charging and differential charging occurs in that environment and could endanger equipment and personnel involved in the EVA. These spacecraft charging events take place in response to an intense flux of high energy electrons accompanied by a large drop in the ambient plasma density. The extent of which the auroral environment can be simulated in a large vacuum chamber are determined so that conditions which lead to significant charging and discharging may be observed and controlled. A large chamber would be required in order to simulate the effects of an aurora-like, large cross-section, energetic electron precipitation on a target system the size of an astronaut with a life support system. The precipitating electrons can be simulated with an array of multipactor sources and the background ionization produced by the beam can be limited to the range of the auroral density if the chamber pressure is not significantly above 1 x .000001 Torr. Some small chamber work has shown that the plasma in the beam will diffuse radially at a rate determined by the Bohm diffusion coefficient.
The Assembly and Contingency Radio Frequency Group (ACRFG) onboard the International Space Station (ISS) is used for command and control communications and transmits (45 dBm or 32 watts) and receives at S-band. The system is nominally pressurized with gaseous helium (He) and nitrogen (N2) at 8 pounds per square inch absolute (psia). MacDonald, Dettwiler and Associates Ltd. (MDA) was engaged to analyze the operational characteristics of this unit in an effort to determine if the anomalous behavior was a result of a corona event. Based on this analysis, MDA did not recommend continued use of this ACRFG. The NESC was requested to provide expert support in the area of high-voltage corona and multipactoring in an S-Band RF system and to assess the probability of corona occurring in the ACRFG during the planned EVA. The NESC recommended minimal continued use of S/N 002 ACRFG until a replacement unit can be installed. Following replacement, S/N 002 will be subjected to destructive failure analysis in an effort to determine the proximate and root cause(s) of the anomalous behavior.