A cooperative NASA/USAF investigation of spacecraft charging in the magnetosphere
- Paper ID
1977-IAF-188
- author
- company
Los Angeles Air Force Station
- country
U.S.A.
- year
1977
- abstract
Electrons with energies from 1 to 20 KeV, injected from the plasma sheet during geomagnetic substorms, can charge spacecraft surfaces to potentials in the kilovolt range (ATS-6 measurements: -19,000 volts). Subsequent photo-emission from metallic surfaces exposed to sunlight drive them to a less negative potential, producing differentiallycharged surfaces on the spacecraft. Dielectric surfaces can become charged as large capacitors. Electrostatic discharges occurring between the differentially-charged surfaces or as a result of dielectric breakdown generate spurious structural currents, electromagnetic interference (EMI), and possible material degradation. If spacecraft materials such as thermal blankets, solar cell cover glasses and first-surface reflectors react to the charging environment as they have in laboratory simulation experiments conducted by numerous international research laboratories, then the hundreds of instances of electrical, thermal and mechanical anomalies identified in more than 20 international satellite systems may be related to this differential charging phenomenon. Anomalous events are often viewed as unexplainable primarily due to a lack of in situ data. The lack of a data base could result in an overdesign of space systems in order to meet engineering and environmental specifications which are inadequate. A cooperative program has, therefore, been established through formal agreements between the NASA and the USAF to provide design criteria as well as techniques and test methods to ensure control of absolute and differential charging of spacecraft surfaces. The program consists of efforts aimed at understanding the spacecraft charging/discharging/ coupling phenomena and relating spaceflight data tc ground test results by means of the following: analytical programs to define the space environment and to model the spacecraft interaction with the environment, experimental programs to develop ground facilities for simulating this environment and to determine the response of spacecraft materials to this environment, a development program to prepare new or modified materials, and flight programs to obtain space environment data for verification of models and calibration of ground facilities.