About Deep Impact
On the evening of July 3, 2005, Deep Impact, a NASA Discovery Mission, performed an incredibly complex experiment in space to probe beneath the surface of a comet and reveal the secrets of its interior. As a larger “flyby” spacecraft released a smaller “impactor” spacecraft into the path of comet Tempel 1, the experiment became one of a cometary bullet chasing down a spacecraft bullet while a third spacecraft bullet sped along to watch.
Deep Impact was launched aboard a Delta II rocket on January 12 2005. Five months later, it started collecting images of the comet before the impact. In early July 2005, 24 hours before impact, the flyby spacecraft pointed its high-precision tracking telescopes at the comet and released the impactor on a course to hit the comet's sunlit side.
The impactor was a battery-powered spacecraft that operated independently of the flyby spacecraft for just one day. It is called a "smart" impactor because, after its release, it took over its own navigation and maneuvered into the path of the comet. A camera on the impactor captured and relayed images of the comet's nucleus just seconds before collision. The impactor spacecraft was composed mainly of copper, which is not expected to appear in data from a comet's composition. For its short period of operation, the impactor used simpler versions of the flyby spacecraft's hardware and software - and fewer backup systems. The impact was not forceful enough to make an appreciable change in the comet's orbital path around the Sun.
After release of the impactor, the flyby spacecraft maneuvered to a new path that, at closest approach passed 500 km from the comet. The flyby spacecraft observed and recorded data about the impact, the ejected material blasted from the crater, and the structure and composition of the crater's interior. After its shields protected it from the comet's dust tail passing overhead, the flyby spacecraft turned to look at the comet again. The flyby spacecraft collected additional data from the other side of the nucleus and observed changes in the comet's activity. While the flyby spacecraft and impactor did their jobs, professional and amateur astronomers at large and small telescopes on Earth observed the impact and its aftermath, and results were broadcast live over the Internet.
Two instruments on the flyby spacecraft observed the impact, crater and debris with optical imaging and infrared spectral mapping. The flyby spacecraft uses an X-band radio antenna (transmission at about eight gigahertz) to communicate to Earth as it also listened to the impactor on a different frequency. For most of the mission, the flyby spacecraft communicates through the 34-meter antennae of NASA's Deep Space Network. During the short period of encounter and impact, when there was a huge increase in volume of data, overlapping antennas around the world were used. Primary data was transmitted immediately and other data was transmitted over the following week.
Image and Text Credit: NASA/JPL-Caltech/UMD