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Robert Boyle and Francis Connors Cryogenics, Propulsion and Fluid Systems Branch NASA/Goddard Space Flight Center Greenbelt, MD 20771
John Marketon and Vincent Arillo Hughes-STX
Edward James and Richard Fink and McDonnell Douglas Corp.
Precision optical instruments with low-temperature detectors can suffer degraded performance caused by the vibration of typical Stirling cycle cryocoolers. These cryocoolers produce significant vibration at the harmonics of the drive frequency due to motor design and gas thermodynamics. A simple control system using force sensors and non-real time signal processing has been designed and tested which reduces vibration levels by as much as 50dB at the drive frequency and 30dB at the harmonics. The theory and design of the system are discussed, and test results are presented with cryocoolers built by British Aerospace, Lockheed/Lucas, Hughes, and Stirling Technology Corp. Testing of this system with position sensors shows slightly lower performance than the force sensor system at the lower harmonics, with performance rolling off at higher frequencies.Conclusions and lessons learned from the GSFC test experience are presented. These include: the stability of control parameters over time with the cooler in both the horizontal and vertical orientations; the ability to control vibration at an arbitrary number of harmonics; the effect of on-axis vibration control on the residual radial off-axis vibration; and the effect of vibration control on input power. Application of this system for space flight is discussed, and future work is described.
Cryocoolers 7; 7th International Cryocooler Conference, Phillips Laboratory Conference Proceedings, PL-CP--93-1001, Part 3, pp. 805 - 819 (1992).