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''Deep Impact'' is a on July 4 2005 , one section of the ''Deep Impact'' probe successfully impacted the comet's Nucleus , excavating debris from the interior of the nucleus. Photographs of the impact showed the comet to be more dusty and less icy than expected. The impact generated a large, bright dust cloud that obscured the hoped-for view of the impact crater. Previous space missions to comets, such as Giotto and Stardust , were fly-by missions, only able to photograph and examine the surfaces of cometary nuclei from a distance. The ''Deep Impact'' mission was the first to eject material from a comet's surface. MISSION PROFILE Following its launch on January 12 2005 , the ''Deep Impact'' spacecraft traveled 429 million kilometers in 174 days to reach Comet Tempel 1 at a cruising speed of 28.6 km/s (103,000 km/h or 64,000 mph). Once the spacecraft reached the vicinity of the comet on July 3 2005 , it separated into two portions, an impactor and a flyby probe. The impactor used its thrusters to move into the path of the comet, impacting 24 hours later at a relative speed of 10.3 km/s (37,000 km/h or 23,000 mi/h). The impactor, with its Mass of 370 Kilogram s (814 pounds), delivered 1.96 × 1010 Joule s of Kinetic Energy - the equivalent of 4.5 Ton s of TNT . Scientists believe that the energy of this high-velocity collision was sufficient to excavate a crater up to 100 m wide (larger than the bowl of the Roman Colosseum ), although the crater has not yet been spotted in post-impact images as the cloud of debris resulting from the impact is obscuring the view. Just minutes after the impact, the flyby probe passed by the nucleus at a close distance of 500 km, taking pictures of the crater position, the ejecta plume, and the entire cometary nucleus. The entire event was photographed by Earth -based Telescope s and Orbital Observatories , including the Hubble , Chandra , Spitzer and XMM-Newton . The impact was also observed by Camera s and Spectroscope s on board Europe 's Rosetta spacecraft, which was about 80 million km from the comet at the time of impact. Rosetta should determine the composition of the gas and Dust cloud kicked up by the impact.1 After this flyby of Tempel 1, it could be possible to retarget Deep Impact to comet Boethin , pending on budget availability. On July 20 2005 a trajectory correction maneuver was performed to place the spacecraft on a trajectory to carry it to the Earth and use a gravitational slingshot to target another comet.2 SCIENTIFIC GOALS The mission's Principal Investigator is Michael A'hearn , an astronomer at the University Of Maryland . The Deep Impact mission will help answer fundamental questions about comets, such as:
Scientists hope that these questions will be answered, at least in part, by data from the Deep Impact mission. For example, the size and shape of the crater produced by the impact will tell scientists how well-packed the cometary material is. SPACECRAFT DESIGN AND INSTRUMENTATION The spacecraft consists of two main sections, the 370 kg Copper -core "Smart Impactor" which impacted the comet, and the "Flyby" section, which imaged the crater created by the impactor. The flyby section carries 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, Infrared Spectrometer , and an imaging module. It has been optimized for observing the comet's nucleus. The MRI is the backup device, and was primarily used for navigation during the final 10-day approach. The impactor section of the spacecraft contains an instrument that is optically identical to the MRI, called the Impactor Targeting Sensor (ITS). Its dual purpose was to sense the Impactor's trajectory, which could then be trimmed (adjusted) up to four times, 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 meters 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.3 The Impactor's payload, dubbed the "Cratering Mass" was 49% Copper to reduce debris interfering with scientific measurements of the impact. Since copper was not expected to be found on a comet, scientists can eliminate copper from the spectrometer reading. If the impactor was loaded with other materials such as explosives, it would create a significant amount of organic vapor. MISSION EVENTS Before launch and the Deep Impact impactor, simulated by A comet-impact mission was first proposed to NASA in 1996 . However, NASA engineers were skeptical that the target could be hit.4 In 1999 , a revised and technologically-upgraded mission proposal, dubbed Deep Impact, was accepted and funded as part of NASA's Discovery Program of low-cost spacecraft. The two spacecraft (Impactor and Flyby) and the three main instruments were built and integrated by Ball Aerospace & Technologies Corp. in Boulder, Colorado, USA. The name of the mission is shared with the '' Deep Impact '' movie, in which a comet strikes the Earth; but this is coincidental, as the scientists behind the mission and the creators of the movie devised the name independently of each other, at around the same time. ABC News article - link broken as of 2006-03-02 Launch and commissioning phase The probe was originally scheduled for launch on 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 Safe Mode . The cause of the problem was simply an incorrect temperature limit in the fault protection logic for the spacecraft's RCS thrusters. The spacecraft's thrusters were used to detumble the spacecraft following third stage separation. NASA subsequently announced that the probe was out of safe mode and healthy.5 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 canceled. During the "commissioning phase" all instruments were activated and checked out. During these tests it was found that the HRI images were not in focus after it underwent a bake-out period6. Mission members are investigating the problem. On June 9 , as part of a mission briefing, it was announced that by using image processing software and the mathematical technique of Deconvolution , the HRI images could be corrected to provide the resolution anticipated.7 Cruise phase imaged on April 25 by the Deep Impact spacecraft]] The "cruise phase" began on March 25 , immediately after the commissioning phase was completed. This phase continued until about 60 days before the encounter with comet Tempel 1. On April 25 the probe acquired the first image of its target at a distance of 64 million Km (39.7 million miles).8 On May 4 it executed its second trajectory correction maneuver. Burning its rocket engine for 95 seconds the spacecraft speed was changed by 18.2 kilometers per hour (11.3 miles per hour). Approach phase The approach phase extends from 60 days before encounter ( May 5 ) until five days before encounter. Sixty days out was about the earliest time that the ''Deep Impact'' spacecraft was expected to detect the comet with its MRI camera. In fact, the comet was spotted ahead of schedule, sixty-nine days before impact (see Cruise Phase above). This milestone marks the beginning of an intensive period of observations to refine knowledge of the comet's orbit and study the comet's rotation, activity and dust environment. On June 14 and June 22 Deep Impact observed two outbursts of activity from the comet, the latter being six times larger than the former.9 On June 23 , the first of the two final trajectory correct maneuvers (targeting maneuver) was successfully executed. A 6 m/s (13.4 mph) velocity change was needed to adjust the flight path towards the comet and target the impactor at a window in space about 100 kilometers wide. |
Image:Deep Impact Approach 2jpgThe Moment Of Impact, As Shown On
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