Abstract
Vacuum conditions to be encountered in the wakes of high altitude unmanned space vehicles are calculated in order to demonstrate possibilities for conducting experiments using the high pumping speeds and very high vacuum (down to 10 to the -15th torr) attainable. The flux of ambient particles backscattered by emissions from spacecraft surfaces is modelled for an idealized Long Duration Exposure Facility spacecraft structure in an orbit of 550 km altitude. The total backscattered fluxes are found to be between 3 x 10 to the 4th and 3 x 10 to the 5th per sq cm sec for H and between 10 to the 6th and 10 to the 7th per sq cm sec for He and O, depending on the angle with respect to the wake axis. It is found that the direct ambient hydrogen flux is an order of magnitude greater than the backscattered flux, while the backscattered fluxes of He and O are greater than the direct fluxes. It is pointed out that care should be taken in designing space experiments to enable these theoretical conditions to be met.
Published Version
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