ExtraVehicular Activity (EVA) Operations in the Geostationary Environment

摘要

The geostationary altitude (35,786 km) at the equator is a unique altitude where the orbital rotation period is the same as the earth (24 hours), and a satellite placed at a given longitude such as a GOES weather satellite has a “viewing angle” centered at that given longitude (the diameter of the earth as seen from the satellite is approximately 17 deg). To date, there are several hundred satellites in the geostationary orbit (sometimes called a “geosynchronous orbit”), and some consideration has been given to perform human and robotic-assisted on-orbit repair and service of defunct satellites. The geostationary environment is also populated with high energy geomagnetically-trapped electrons and low energy geomagnetically-trapped protons in the outer part of the Van Allen belts. In addition, the earth’s magnetic field is very weak at this altitude and orbital latitude (0 deg) and solar protons emitted during a coronal mass ejection (CME) and galactic cosmic radiation (GCR) have easy access to the geostationary environment. In this paper space radiation analyses and exposure assessments are presented that include vehicle and EVA spacesuit shielding requirements to adequately protect the astronauts. In addition, other supplemental shielding materials, techniques, and mitigation procedures are investigated to further reduce crew exposures. A detailed discussion is also presented for the nominal radiation environment and for periods of geomagnetic and solar disturbances, and particle enhancements.