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Deep Impact (space mission)
The probe will approach the nucleus of Comet Tempel 1 on July 4, 2005, the 229th Independence Day of the United States. One section of the probe, called the impactor, will separate and plunge toward the nucleus. It will impact the nucleus 24 hours later, blowing a 100 metre-wide crater. The entire event will be photographed and studied by the remaining section, the flyby probe, as well as by Earth-based and orbital telescopes. On its journey to Tempel 1, Deep Impact will cover 431 million kilometres (268 million miles).
The flyby spacecraft contains a High Resolution Instrument (HRI) and Medium Resolution Instrument (MRI). The HRI is an imaging devices that combines a visible-light camera, infrared spectrometer, and an imaging module. It has been optimized for observing the comet's nucleus. The MRI is the backup device, and will primarily be used for navigation during the final 10-day approach. The impactor section of the spacecraft contains an instrument that is nearly identical to the MRI.
The impactor has a mass of 370 kilogram and will impact with a velocity of about 10.2 kilometers per second, thus generating 1.9 × 1010 joules of energy upon impacting with the comet, the equivalent of 4.8 tons of TNT. The impact shall produce a 300ft crater, larger than the bowl of the Roman Colosseum.
The probe was originally scheduled for launch on December 30, 2004, but NASA officials delayed its launch, in order to allow more time for testing the software. It was successfully launched from Cape Canaveral on January 12, 2005 at 1:47 p.m. EST (1847 UTC) by a Delta 2 rocket.
Deep Impact's state of health was uncertain during the first day after launch. Shortly after entering orbit around the Sun and deploying its solar panels, the probe switched itself to emergency backup mode. The exact cause and extent of the problem is not yet known, but NASA indicated that the on-board monitoring system detected an overheat problem. NASA subsequently announced that the probe was out of safe mode and healthy. 
On February 11, Deep Impact's rockets were fired as planned to correct the spacecraft's course. This correction was so precise that the next planned maneuver for March 31 was cancelled, and the spacecraft entered its "cruise phase" on March 25. This phase will continue until about 60 days before the encounter with comet Tempel 1. The cruise phase came on the heels of the "commissioning phase", in which all instruments were activated and checked out. During these tests it was found that the HRI images are not in focus after it underwent a bake-out period . Mission members are investigating the problem.
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