Accession Number:

AD0256894

Title:

GAS CONDUCTION PROBLEM WITH MULTILAYERED RADIATION SHIELDS

Descriptive Note:

Corporate Author:

LITTLE (ARTHUR D) INC CAMBRIDGE MASS

Personal Author(s):

Report Date:

1961-04-01

Pagination or Media Count:

1.0

Abstract:

ON A LONG MISSION IN SPACE, A CRYOGENIC FUEL TANK MAY REQUIRE 100 SHEETS OF LOW-EMISSIVITY METAL FOIL IF HEAT IS TRANSFERRED THROUGH THE SHIELDING ONLY BY RADIATION. If gas conduction also occurs, more foils will be needed for the same rate of fuel boil-off. For a gas pressure of .00014 mm Hg, 200 foils are required. Consequently, an adequate sealed-off, evacuated shield is difficult to construct. If outgassing of the foils and gas diffusion from the fuel tank are appreciable, it is also difficult to arrange the geometry of the shields to use the external space vacuum for pumping. In the case of pumping through the edges of a 100-cm wide shield panel, the outgassing rate should not exceed about 10 to the 9th power moleculessec from each sq cm of foil surface, if the number of foils is to remain about 100. The allowable outgassing rate for broadside pumping of optimally perforated foils is around 10 to the 10th power molecules per sec per sq cm. The allowable diffusion rate from the fuel tank is 10 to the 12th power molecules per sec per sq cm of tank surface. A basic consideration is that any geometrical arrangement of the foils that enhances pumping of the gas also reduces the effectiveness of the foils as a radiation shield, since radiation can enter by the same path by which molecules leave. As a result, only a limited number of layers of foil is useful. Author

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Distribution Statement:

APPROVED FOR PUBLIC RELEASE