Active Reduction of Cryocooler Induced Vibration Using Smart Materials And Adaptive Controls

Abstract

At DLR Berlin – Adlershof Research Center, the BIRD (BERLIN INFRARED DETECTOR) satellite is currently being designed, fabricated and tested for launch in late 1999. This small satellite is planned to weight about 80 kg. and measure about 500 mm on each side before the deployment of antennas and solar panels. As the primary payload, the satellite will be carrying two infrared detectors for the purpose of earth observation. The cameras will be independently mounted but observing the same field of view with a slight overlap. Due to the severe weight and volume restrictions, it is planned to use cryocoolers to ensure the necessary operating temperatures for the infrared sensors. The initially selected cryocoolers model induces significant uniaxial vibration into the satellite due to a moving piston arm and an additional pumping action. The coupling of the oscillating cooling arm to the sensor head brings the danger that the sensors’ orientation will not be fixed to the desired accuracy which would result in potential reductions of the quality of the scientific results. Due to volume constraints the standard approach of employing a cryostat cannot be applied, nor is it suitable to mount the cryocoolers back to back since each cryocooler is used separately for the individual infrared sensor. In the present paper an adaptive solution to counteract induced forces and resulting vibrations at the sensors’ heads with respect to the operational boundary conditions in space will be discussed. For this, an adaptive microvibration control system based on piezoceramic actuators and sensors is presented. Adaptive signal processing is used for the adjustment of the actuator driving signals. Digital transversal filter types combined with recursive adaptation algorithms allow self-optimizing controllers. The design of a demonstration structure and the performance of adequate experiments will be described.