The NICMOS Cooler was installed on the Hubble Space Telescope during a Shuttle mission STS-109 (also called Hubble Servicing Mission 3B) in March 2002. The cooler replaced NICMOS's solid nitrogen coolant, which was lost faster than was expected.
The NICMOS mechanical cooler got its first test in space on STS-95, the same Shuttle flight that John Glenn will flew on.
NICMOS (Near-Infrared Camera and Multi-Object Spectrometer) is one of the instruments currently on the Hubble Space Telescope (HST). Cooling for NICMOS's infra-red sensors came originally from a supply of solid nitrogen coolant. That solid nitrogen was loaded before the instrument was launched and has now been exhausted. The NICMOS cooler will replace the now-depleted solid nitrogen coolant. This flight test cleared the way for the cooler's installation in Hubble during Shuttle flight STS-109, March 2002.
The NICMOS cooler flew on Shuttle flight STS-95 as part of the HST Orbital Systems Test (HOST) payload. Here are some details of the orbital performance from one of the people involved in the cooler program.
The NICMOS Cryocooler (NCC) was launched October 29, 1998 aboard the Space Shuttle Discovery on STS-95 as part of the Hubble Space Telescope Orbital Systems Test (HOST). The HOST experiment is a package of instruments intended to be installed on the Hubble Space Telescope during the HST Third Servicing Mission (SM-3) scheduled for May, 2000. (Actual date of installation was March 2002, on STS-109, Hubble Servicing Mission 3B. Ed.)
A primary mission goal was to operate the NCC through at least one complete cycle of cooldown and warmup. Secondary goals were to measure the performance of the cryocooler at or near the design cold plate temperatures with design heat loads, to operate in a reduced power mode, and to perform cold starts of the turbomachines. The NCC met each of these goals with no anomalies and verified that the performance during space flight was essentially identical to results obtained from ground-based tests. The NCC operated for approximately 180 hours with no anomalies. Warmer that predicted orbiter pointing attitudes resulted in slower cooldown rates and higher temperature stabilization points than originally hoped for; however, mission results proved that the cooler could meet the temperature and thermal stability requirements presented by the NICMOS scientists.
Several steady state points between 72.9 Kelvin to 78.2 Kelvin were obtained during the mission. Temperatures were maintained for a minimum of one hour within 0.1 Kelvin, accomodating variations in the thermal environment presented during any orbit as well as intentionally applied 20 milliWatt and 400 milliWatt increases in the heat load. Radiator temperatures changed by as much as 10 Celsius without affecting the temperature stability.
The NCC team is now preparing for the return of HOST from KSC to perform additional ground testing and make minor modifications that will allow greater efficiency in the system for the HST. (All needed modifications have been made, and the cooler has now been installed on the Hubble Space Telescope. Ed.)
There are 3 main types of cooling system used in satellites today:
Passive cooling simply allows the satellite to come into equilibrium with its surroundings. A simple earth-bound example of passive cooling is putting something hot out of doors on a cold day. The hot object would cool off till it matched the temperature of the surroundings.
Passive cooling on a satellite is a little more complicated than that. Satellites use sunshades or reflective coatings on the side towards the sun, and radiators on the side away from the sun. The big advantage of passive cooling is its simplicity. The disadvantage is that its cooling ability is limited.
Stored cryogens are cold substances such as liquid helium or solid nitrogen which are stored on board the satellite. A simple earth-bound example of a stored cryogen cooler is an ice cube. The advantage of an ice cube is that it's simple to use. The disadvantage is that it eventually melts.
Stored cryogen coolers on spacecraft, like the ice cube in your drink, eventually melt, evaporate, or sublime away. But while the supply of coolant lasts, they're straightforward and simple to use.
Mechanical coolers are machines that cool. A simple earth-bound example is the refrigerator in your kitchen. The big advantage of a mechanical cooler is that, unlike the stored cryogen cooler, it doesn't stop cooling as soon as its supply of cryogen melts or evaporates. That advantage is why people use electrically powered refrigerators in their kitchens, instead of the old-fashioned "ice box", which was simply a storage chest cooled by a block of ice.
Along with that advantage, mechanical coolers do have some potential disadvantages as far as their use in spacecraft is concerned.
Spacecraft designers try to select the cooling system or systems that best fit particular spacecraft. For the NICMOS instrument, designers chose a stored cryogen system using solid nitrogen. Unfortunately, the solid nitrogen melted faster than ground tests indicated that it would. Therefore, the Hubble team decided to add a mechanical cooler, to replace the solid nitrogen. The cooler chosen is a turbo Brayton cooler, which is designed to run with essentially no vibration. This cooler was tested on STS-95, the shuttle flight with John Glenn. As described above, the cooler performed well, so the Hubble team decided to go ahead with the cooler installation, completed in March 2002 by Shuttle Mission STS-109 (Hubble Servicing Mission 3B).
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