Astronomers' spirits sagged earlier this year when the Hubble Space Telescope's new infrared camera sprang a coolant leak, potentially cutting in half the instrument's planned 4-year lifetime. But now NASA is toying with an idea for a fix that might even keep the camera going longer than originally expected.
The Near Infrared Camera and Multi-Object Spectrometer (NICMOS) can peer through cosmic dust into star-forming regions as well as pick up the reddened light of very distant galaxies. But after the instrument was installed in February, NASA engineers discovered that the solid nitrogen needed to keep it cool enough to detect faint infrared signals was warming and escaping into space faster than planned.
Because there's no easy way to refill the nitrogen Dewar in zero gravity, the agency is now exploring a different solution: a high-tech heat pump being developed by the Air Force to cool infrared missile detectors. The prototype pump compresses gaseous neon, which then expands and draws heat from its surroundings. NASA engineers believe they can adapt such a system to cool the NICMOS filters and detectors to about 70 kelvins, 12 K warmer than the solid nitrogen was to keep them, but "just fine" for observations, says Hubble project scientist David Leckrone. He says engineers hope to complete a feasibility study next month.
If no major difficulties arise, astronauts could attach the unit during the next scheduled servicing mission in December 1999--shortly after the last of the solid nitrogen is expected to sublime away. In the best case, the retrofitted refrigerator might even lengthen the instrument's lifetime. Unlike a limited coolant supply, the heat pump would keep cooling indefinitely as long as it was supplied with electricity, Leckrone says.
Robert Williams, director of the Space Telescope Science Institute in Baltimore, says he's "ambivalent" about the plan, because NASA might siphon funds from other Hubble research to pay for the repairs. But Leckrone says the project might attract funding from outside sources interested in using heat pumps in space, such as the Air Force.