Spacecraft Design and Instrumentation
The spacecraft consists of two main sections, the 370-kg (815-lb) copper-core "Smart Impactor" that impacted the comet, and the "Flyby" section, which imaged the comet from a safe distance during the encounter with Tempel 1.
The Flyby spacecraft is about 3.2 meters (10.5 ft) long, 1.7 meters (5.6 ft) wide and 2.3 meters (7.5 ft) high. It includes two solar panels, a debris shield, and several science instruments for imaging, infrared spectroscopy, and optical navigation to its destination near the comet. The spacecraft also carried two cameras, the High Resolution Imager (HRI), and the Medium Resolution Imager (MRI). The HRI is an imaging device that combines a visible-light camera with a filter wheel, and an imaging infrared spectrometer called the "Spectral Imaging Module" or SIM that operates on a spectral band from 1.05 to 4.8 micrometres. It has been optimized for observing the comet's nucleus. The MRI is the backup device, and was used primarily for navigation during the final 10-day approach. It also has a filter wheel, with a slightly different set of filters.
The Impactor section of the spacecraft contains an instrument that is optically identical to the MRI, called the Impactor Targeting Sensor (ITS), but without the filter wheel. Its dual purpose was to sense the Impactor's trajectory, which could then be adjusted up to four times between release and impact, and to image the comet from close range. As the Impactor neared the comet's surface, this camera took high-resolution pictures of the nucleus (as good as 0.2 metre per pixel) that were transmitted in real-time to the Flyby spacecraft before it and the Impactor were destroyed. The final image taken by the impactor was snapped only 3.7 seconds before impact.
The impactor's payload, dubbed the "Cratering Mass", was 100% copper (impactor 49% copper by mass) to reduce debris interfering with scientific measurements of the impact. Since copper was not expected to be found on a comet, scientists could eliminate copper from the spectrometer reading. Instead of using explosives, it was also cheaper to use copper as the payload.
The name of the mission is shared with the 1998 Deep Impact film, in which a comet strikes the Earth. This is coincidental, however, as the scientists behind the mission and the creators of the film devised the name independently of each other at around the same time.
Read more about this topic: Deep Impact (spacecraft)
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