Distant Supernovae and the NICMOS Cryocooler (NCS) Initiative

One of the most important discoveries in physics and astronomy in the last century was that the universe is not only expanding but that its expansion rate is accelerating. To study the evolution of this expansion, astronomers use distant supernovae as standard candle light sources to see how the universe behaved at early times.

Hubble is the only telescope that can measure supernovae from the time the universe was younger than about half its present age. Most of the light from these supernovae is Doppler-shifted to infrared wavelengths by the expansion of the universe. Hubble has been able to study these supernovae with the Near Infrared Camera and Multi-Object Spectrometer (NICMOS.) Unfortunately, NICMOS ceased working in 1998, because of a mechanical failure in the insulation that kept its detectors cold.

The Hubble project team at the Goddard Space Flight Center invented a method to restore NICMOS for science operations by mounting a mechanical refrigerator on the instrument. The NICMOS Cryocooler System (NCS) was designed to cool the detectors by circulating cold gas into the NICMOS insulating container to carry heat to the outside of the telescope, http://archive.stsci.edu/prepds/udf/udf_hlsp.html.

The NCS was an experimental concept with no track record in space. NASA planned to install it on the second flight of the third servicing mission, SM3b, in 2002. Just prior to the flight, however, one of HubbleÕs gyroscopes failed and another began to operate erratically. Because of the limited number of spacewalks (EVAÕs for Extra-Vehicular Activity) available for astronaut work during the servicing mission, there was not enough time to mount the NCS and replace the gyroscopes. NASA planned to drop the NCS installation to allow new gyroscopes to be installed.

Steve worked with Dave Leckrone, Hubble Project Scientist, to change that decision. Together, they convinced NASA that the science benefit from restoring NICMOS to operation would outweigh the risk of further gyroscope failure and loss of science. NASA concurred, and the NCS was installed on SM3b, restoring NICMOS to full operational status.

Since NICMOS has been revived, two large programs to discover supernovae and measure the history of universal expansion have been carried out with Hubble. The Piggyback survey and the PANS project, both under the direction of Adam Riess. These surveys have uncovered more than 20 supernovae from the time when the universe was only a few billion years old and have refined our knowledge of dark energy characteristics by more than a factor of eight. Hubble is now one of the most important observatories for research on the early universe owing to NICMOS and its infrared view of the heavens.