The Muscle and Mind Behind the Mission
The Deep Impact spacecraft consisted of two parts, the flyby spacecraft and the impactor, and was about the size of a sport utility vehicle. The flyby carries a High Resolution Instrument (HRI) and a Medium Resolution Instrument (MRI) for imaging, infrared spectroscopy and optical navigation. It uses a fixed solar array and an NiH2 battery to power itself. The impactor remained attached to the flyby until 24 hours before it impacted Tempel 1.
Once released, the impactor guided itself into the path of the comet using a high-precision star-tracker (which navigates by looking at the stars), the Impactor Target Sensor (ITS) and auto-navigation algorithms specially developed for this mission. The impactor also contained a small hydrazine propulsion system for more precise trajectory and attitude control. The HRI, MRI and ITS worked together to guide the flyby spacecraft to the comet and record scientific data before, during and after the impact.
The complete flight system was launched as a payload on a Boeing Delta II rocket (see How Rocket Engines Work) in January 2005. It encountered Tempel 1 in early July 2005. Twenty-four hours before impact, the impactor detached itself from the flyby spacecraft. At this point, the flyby slowed down and positioned itself to observe the impact as it passes by the comet.
Once the impactor left the flyby spacecraft, it positioned itself to impact the comet on the sunlit side, allowing for better-quality images.
The flyby's imaging equipment observed the nucleus for more than 10 minutes after the impact, imaging the impact, the crater development and the crater interior. The flyby also acquired spectrometry of the nucleus and the crater site. It sent all of the images and spectrometry back to the Deep Space Network on the ground.