Thermal Performance of the Cosmic Background Explorer Superfluid Helium Dewar, as Built and with an Improved Support System
Launch of the Cosmic Background Explorer (COBB) is planned for 1990. A critical element of the COBE is the 650 L superfluid helium dewar that will maintain the cryogenic instrument assembly at ~2 K for an estimated 14 months. Life testing of the dewar was completed in the autumn of 1985. The support system heat conduction is a major part of the overall heat load to the cryogen. The COBE dewar uses a tension strap system made of fiberglass/epoxy; this is the most thermally efficient system used to date in flight hardware. However, the thermal efficiency of the COBE support system could be considerably improved by using a more optimized orientation of straps and a newly-developed composite material instead of the fiberglass/epoxy. A thermally optimized tension strap support system is defined based on recent fatigue testing of alumina/epoxy straps. This material has a modulus of elasticity over twice that of fiberglass/epoxy, and therefore displays greater fatigue strength. A support system using alumina/epoxy can have both smaller strap size and greater stiffness than a fiberglass system. The thermal conductivity is somewhat higher than that of fiberglass/epoxy. The more optimized strap orientation provides considerably greater strap length and thermal resistance, and the alumina material provides about 50 percent higher resonance frequency. Thermal performance predictions are compared for the COBE dewar (1) as built, (2) with fiberglass/epoxy straps in an optimized configuration, and (3) with alumina/epoxy straps in an optimized configuration. The optimized support designs provide a predicted cryogen lifetime improvement of about 50 percent.
KeywordsFatigue Strength Cosmic Background Flight Hardware Cryogen Tank Tension Strap
Unable to display preview. Download preview PDF.
- 1.R. A. Hopkins and S. H. Castles, Design of the superfluid helium dewar for the Cosmic Background Explorer, in: “Proceedings of SPIE,” Vol. 509, August 1984.Google Scholar
- 2.R. A. Hopkins and D. A. Payne, Optimized support systems for space-borne dewars, in: “Cryogenics,” Vol. 27, No. 4, April 1987.Google Scholar
- 3.Space Shuttle System Payload Accommodations,“ JSC07700, Vol. XIV, p. 3–24.Google Scholar
- 4.R. A. Hopkins and D. A. Payne, Next-generation tension strap supports for spaceborne dewars, in: “AIAA 22nd International Thermo-physics Conference,” June 1987.Google Scholar
- 5.M. Takeno, S. Nishijima and T. Okada, Thermal and mechanical properties of advanced composite materials at low temperatures, in: “Advances in Cryogenic Engineering,” Vol. 30, 1986.Google Scholar
- 6.J. G. Hust, Thermal conductivity of glass fiber/epoxy composite support bands for cryogenic dewars, Phase II, NBS Report 773.30–83–1, June 1983.Google Scholar
- 7.R. A. Hopkins and M. G. Ryschkewitsch, Measured ground performance and predicted orbital performance of the superfluid helium dewar for the Cosmic Background Explorer, in: “Proceedings of SPIE,” Vol. 619, January 1986.Google Scholar