Design of Space Stations for Low Atmospheric Leakage

Abstract

N[ important consideration in the design and use of a long-duration Earth-orbiting Space Station is leakage of atmosphere from its pressurized compartments. The gases comprising the original atmosphere are, of course, launched with the Space Station. Compensation for atmosphere that has escaped is accomplished with an onboard supply which is periodically replenished, as required, with the Earth-to-orbit logistics system. The amount of leakage is then directly related to the demand on the logistics system and if the leakage is excessive, it contributes to the problems of contamination of the local (near the station) space environment and to maintaining effective thermal control. The authors found in researching applicable leakage test data and in discussions with various engineers in the aerospace industry, that a wide range of estimates for spacecraft leakage rates exists. Primarily this has resulted because no real effort has been made to design manned spacecraft to meet the stateof-the-art design and fabrication for low leakage. This paper presents an assessment of the atmospheric leakage (approximately 0.002 Ib/day) for a typical Space Station concept.1 The Space Station has been designed to provide a research facility that can accommodate a 12 man scientific crew over an orbital lifetime of at least 10 yr. The internal atmosphere is a mixture of O2 and N2 at a pressure of 14.7 psia; this constitutes approximately 2,000 pounds of gas. The paper begins by identifying the potential sources of atmospheric losses that are of particular concern to the designer. Meteoroid and accidental punctures of the pressure shell are shown to present special problems and, hence, require special solutions. Considerations of long-term leakage are then limited to known penetrations of the pressure shell. Data are presented to show that leakage through these joints can be reduced to that which passes through the sealant material itself. Test data are reviewed and the most applicable data used to derive a basis for estimating Space Station leakage. An effective design for leakage monitoring and control is also presented. Finally, design requirements are presented, which would result in spacecraft designs that leak orders-of-magnitudes less than anything previously flown.