— Ch. 1 · Mission Genesis And Design —
Deep Impact (spacecraft).
~6 min read · Ch. 1 of 6
A comet-impact mission first appeared on NASA's desk in 1996. Engineers at the agency were skeptical that a probe could hit such a moving target. They needed to prove the concept before committing resources. A revised proposal arrived three years later, in 1999. This version won funding under NASA's Discovery Program for low-cost spacecraft. The total cost of developing the spacecraft and completing its mission reached an unspecified amount, but it was designed to be affordable compared to other deep space projects.
Ball Aerospace & Technologies built the two main sections in Boulder, Colorado. One part was the copper-core Smart Impactor. It weighed 372 kg and contained a payload called the Cratering Mass. This mass was 100% copper and weighed 113 kg. Copper formed 49% of the total mass of the Impactor. Scientists chose this metal because they did not expect to find copper on a comet. Using copper meant they could ignore its signature in spectrometer readings. The other section was the Flyby spacecraft. It measured about 1 meter long, 1 meter wide, and 1 meter high. It carried solar panels and science instruments for imaging and navigation.
The software took 18 months to develop. The application code consisted of 20,000 lines spread across 19 different threads. Rick Grammier served as the project manager at NASA's Jet Propulsion Laboratory. He oversaw the integration of these complex systems. The mission required precise calculations to ensure the probe would reach its destination.
The Tempel 1 Impact Event
Deep Impact launched from Cape Canaveral Air Force Station pad SLC-17B at 18:47 UTC on the 12th of January 2005. A Delta II rocket carried it into space. The spacecraft traveled 174 days to reach comet Tempel 1. On the 3rd of July 2005, it separated into the Impactor and Flyby sections. The Impactor used thrusters to move into the path of the comet. It impacted 24 hours later at a relative speed of 10.2 km/s.
Impact occurred at 05:52 UTC on the morning of the 4th of July 2005. The energy from the collision was similar in size to exploding five tons of dynamite. Most data captured was stored on board the Flyby spacecraft. It radioed approximately 4,500 images from the HRI, MRI, and ITS cameras to Earth over the next few days. Mission control did not become aware of the success until five minutes later at 05:57 UTC. Don Yeomans confirmed the results for the press, stating they hit the target exactly where planned.
The impact generated an unexpectedly large and bright dust cloud. This cloud obscured the view of the new crater. Photographs taken by the spacecraft showed the comet to be more dusty and less icy than expected. The entire event was also photographed by Earth-based telescopes including Hubble and Chandra. Cameras aboard Europe's Rosetta spacecraft observed the gas and dust cloud kicked up by the impact.