Many proposed space based observations will rely on the use of closed
cycle and passive cooling systems to provide the thermal environment f
or high sensitivity. The use of closed cycle mechanical coolers on spa
ce telescopes poses particular integration problems; some of these dif
ficulties are discussed in this paper. One of the major problems envis
aged is that of exported vibration. This problem, and that of the heat
sinking required, can be alleviated by siting the compressors of the
Stirling cycle precooler further from the displacer unit. The effect o
f the separation between the compressors and the displacer on the perf
ormance of the Stirling cycle precooler has been measured. Increasing
the separation from 170 mm to 565 mm decreases the cooling power at 25
K from 220 mW to 180 mW. In most applications this would be acceptabl
e. The pre-cooler provides cooling at a single point. In situations wh
ere refrigeration of extended objects (e.g. telescope mirrors) is requ
ired, some distribution method has to be found. A scheme for achieving
this is presented together with preliminary calculations on such a sy
stem. Temperatures in the region of 2.5 to 4 K are required to meet th
e requirements for long wavelength detectors. We have demonstrated how
these temperatures can be achieved in a continuously operating closed
cycle cooler that has been engineered for space applications. This co
oler consists of a two-stage Stirling cycle precooling a closed cycle
Joule-Thomson (JT) stage. Temperatures in the region of 4 K are achiev
ed by the use of helium-4 in the JT system. The lighter isotope of hel
ium is used to obtain temperatures down to 2.5 K. Under no-load condit
ions the precooler reaches a base temperature of 11.3 K. The JT system
achieves 4.3 K with a 10mW heat load and 2.5 K with a heat load of ov
er 3 mW. The input power to the cooler is approximately 126 W. The tem
perature stability of the cooler at low temperatures is important to k
eep detector drift to a minimum. The temperature of the JT stage has b
een measured in uncontrolled laboratory conditions and found to vary b
y only 30 mK over a seventy hour period. The pre-cooler temperature va
ried by approximately 0.6 K during these measurements.