Миссия Deep Impact: столкновение с кометой Темпеля 1

NASA space probe launched in 2005

The Deep Impact mission was planned to help answer fundamental questions about comets, which included what makes up the composition of the comet's nucleus, what depth the crater would reach from the impact, and where the comet originated in its formation. By observing the composition of the comet, astronomers hoped to determine how comets form based on the differences between the interior and exterior makeup of the comet. Observations of the impact and its aftermath would allow astronomers to attempt to determine the answers to these questions. The mission's Principal Investigator was Michael A'Hearn, an astronomer at the University of Maryland. He led the science team, which included members from Cornell University, University of Maryland, University of Arizona, Brown University, Belton Space Exploration Initiatives, JPL, University of Hawaii, SAIC, Ball Aerospace, and Max Planck Institut für extraterrestrische Physik.

The spacecraft consists of two main sections, the 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 long, wide and high. The Impactor's payload, dubbed the "Cratering Mass", was 100% copper, with a weight of 100 kg. Including this cratering mass, copper formed 49% of total mass of the Impactor (with aluminium at 24% of the total mass); this was to minimize interference with scientific measurements. Since copper was not expected to be found on a comet, scientists could ignore copper's signature in any spectrometer readings. The mission coincidentally shared its name with the 1998 film, Deep Impact, in which a comet strikes the Earth.

Following its launch from Cape Canaveral Air Force Station pad SLC 17B at 18:47 UTC on January 12, 2005, the Deep Impact spacecraft traveled in 174 days to reach comet Tempel 1 at a cruising speed of .

A comet impact mission was first proposed to NASA in 1996, but at the time, NASA engineers were skeptical that the target could be hit. 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 in Boulder, Colorado. Developing the software for the spacecraft took 18 months and the application code consisted of 20,000 lines and 19 different application threads. It was successfully launched from Cape Canaveral on January 12, 2005, at 1:47 pm EST (1847 UTC) by a Delta II rocket. Deep Impact 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 thruster catalyst beds. The spacecraft's thrusters were used to detumble the spacecraft following third stage separation. On January 13, 2005, NASA announced that the probe was out of safe mode and healthy. On February 11, 2005, Deep Impact rockets were fired as planned to correct the spacecraft's course. This correction was so precise that the next planned correction maneuver on March 31, 2005, was unnecessary and canceled. The "commissioning phase" verified that 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 period. After mission members investigated the problem, on June 9, 2005, it was announced that by using image processing software and the mathematical technique of deconvolution, the HRI images could be corrected to restore much of the resolution anticipated.

The "cruise phase" began on March 25, 2005, immediately after the commissioning phase was completed. This phase continued until about 60 days before the encounter with comet Tempel 1. On April 25, 2005, the probe acquired the first image of its target at a distance of
On May 4, 2005, the spacecraft executed its second trajectory correction maneuver. Burning its rocket engine for 95 seconds, the spacecraft speed was changed by Rick Grammier, the project manager for the mission at NASA's Jet Propulsion Laboratory, reacted to the maneuver stating that "spacecraft performance has been excellent, and this burn was no different it was a textbook maneuver that placed us right on the money." The spacecraft studied the images of various distant stars to determine its current trajectory and position. On June 23, 2005, the first of the two final trajectory correct maneuvers (targeting maneuver) was successfully executed. A velocity change was needed to adjust the flight path towards the comet and target the Impactor at a window in space about wide.

Impact phase began nominally on June 29, 2005, five days before impact. The Impactor successfully separated from the Flyby spacecraft on July 3 at 6:00 UTC (6:07 UTC ERT). The first images from the instrumented Impactor were seen two hours after separation. The Flyby spacecraft performed one of two divert maneuvers to avoid damage. A 14 minute burn was executed which slowed down the spacecraft. It was also reported that the communication link between the Flyby and the Impactor was functioning as expected. The Impactor was maneuvered to plant itself in front of the comet, so that Tempel 1 would collide with it. The energy from the collision was similar in size to exploding five tons of dynamite and the comet shone six times brighter than normal. A mission timeline is located at Impact Phase Timeline (NASA).

Mission control did not become aware of the Impactor's success until five minutes later at 05:57 UTC. Don Yeomans confirmed the results for the press, "We hit it just exactly where we wanted to" and JPL Director Charles Elachi stated "The success exceeded our expectations." In the post impact briefing on July 4, 2005, at 08:00 UTC, the first processed images revealed existing craters on the comet. NASA scientists stated they could not see the new crater that had formed from the Impactor, but it was later discovered to be about 100 meters wide and up to deep. Analysis of data from the Swift X ray telescope showed that the comet continued outgassing from the impact for 13 days, with a peak five days after impact. A total of of water and between of dust were lost from the impact. Initial results were surprising as the material excavated by the impact contained more dust and less ice than had been expected. The only models of cometary structure astronomers could positively rule out were the very porous ones which had comets as loose aggregates of material. In addition, the material was finer than expected; scientists compared it to talcum powder rather than sand. Other materials found while studying the impact included clays, carbonates, sodium, and crystalline silicates which were found by studying the spectroscopy of the impact. Clays and carbonates usually require liquid water to form and sodium is rare in space. Observations also revealed that the comet was about 75% empty space, and one astronomer compared the outer layers of the comet to the same makeup of a snow bank. Astronomers hypothesized, based on its interior chemistry, that the comet formed in the Uranus and Neptune Oort cloud region of the Solar System. A comet which forms farther from the Sun is expected to have greater amounts of ices with low freezing temperatures, such as ethane, which was present in Tempel 1. Astronomers believe that other comets with compositions similar to Tempel 1 are likely to have formed in the same region.

Because the quality of the images of the crater formed during the Deep Impact collision was not satisfactory, on July 3, 2007, NASA approved the New Exploration of Tempel 1 (or NExT) mission. The mission utilized the already existing Stardust spacecraft, which had studied Comet Wild 2 in 2004. Stardust was placed into a new orbit so that it passed by Tempel 1 at a distance of approximately on February 15, 2011, at 04:42 UTC. This was the first time that a comet was visited by two probes on separate occasions (1P/Halley had been visited by several probes within a few weeks in 1986), and it provided an opportunity to better observe the crater that was created by Deep Impact as well as observing the changes caused by the comet's latest close approach to the Sun. On February 15, NASA scientists identified the crater formed by Deep Impact in images from Stardust. The crater is estimated to be in diameter, and has a bright mound in the center likely created when material from the impact fell back into the crater.

The impact was a substantial news event reported and discussed online, in print, and on television. There was a genuine suspense because experts held widely differing opinions over the result of the impact. Various experts debated whether the Impactor would go straight through the comet and out the other side, would create an impact crater, would open up a hole in the interior of the comet, and other theories. However, twenty four hours before impact, the flight team at JPL began privately expressing a high level of confidence that, barring any unforeseen technical glitches, the spacecraft would intercept Tempel 1. One senior personnel member stated "All we can do now is sit back and wait. Everything we can technically do to ensure impact has been done." In the final minutes as the Impactor hit the comet, more than 10,000 people watched the collision on a giant movie screen at Hawaii's Waikīkī Beach. One day after the impact, Marina Bay, a Russian astrologer, sued NASA for for the impact which "ruin[ed] the natural balance of forces in the universe." Her lawyer asked the public to volunteer to help in the claim by declaring "The impact changed the magnetic properties of the comet, and this could have affected mobile telephony here on Earth. If your phone went down this morning, ask yourself Why? and then get in touch with us." On August 9, 2005, the Presnensky Court of Moscow ruled against Bay, although she did attempt to appeal the result. One Russian physicist said that the impact had no effect on Earth and "the change to the orbit of the comet after the collision was only about 10 cm (3.9 in)."

The mission was notable for one of its promotional campaigns, "Send Your Name To A Comet!". Visitors to the Jet Propulsion Laboratory's website were invited to submit their name between May 2003 and January 2004, and the names gathered—some 625,000 in all—were then burnt onto a mini CD, which was attached to the Impactor. Dr. Don Yeomans, a member of the spacecraft's scientific team, stated "this is an opportunity to become part of an extraordinary space mission  when the craft is launched in December 2004, yours and the names of your loved ones can hitch along for the ride and be part of what may be the best space fireworks show in history." The idea was credited with driving interest in the mission.

Chinese researchers used the Deep Impact mission as an opportunity to highlight the efficiency of American science because public support ensured the possibility of funding long term research. By contrast, "in China, the public usually has no idea what our scientists are doing, and limited funding for the promotion of science weakens people's enthusiasm for research." Two days after the US mission succeeded in having a probe collide with a comet, China revealed a plan: landing a probe on a small comet or asteroid to push it off course. China said it would begin the mission after sending a probe to the Moon.

Since observing time on large, professional telescopes such as Keck or Hubble is always scarce, the Deep Impact scientists called upon "advanced amateur, student, and professional astronomers" to use small telescopes to make long term observations of the target comet before and after impact. The purpose of these observations was to look for "volatile outgassing, dust coma development and dust production rates, dust tail development, and jet activity and outbursts." By mid 2007, amateur astronomers had submitted over a thousand CCD images of the comet. One notable amateur observation was by students from schools in Hawaii, working with US and UK scientists, who during the press conference took live images using the Faulkes Automatic Telescope in Hawaii (the students operated the telescope over the Internet) and were one of the first groups to get images of the impact. One amateur astronomer reported seeing a structureless bright cloud around the comet, and an estimated 2 magnitude increase in brightness after the impact. Another amateur published a map of the crash area from NASA images.

The Deep Impact mission coincided with celebrations in the Los Angeles area marking the 50th anniversary of "Rock Around the Clock" by Bill Haley & His Comets becoming the first rock and roll single to reach No. 1 on the recording sales charts. Within 24 hours of the mission's success, a 2 minute music video produced by Martin Lewis had been created using images of the impact itself combined with computer animation of the Deep Impact probe in flight, interspersed with footage of Bill Haley & His Comets performing in 1955 and the surviving original members of The Comets performing in March 2005. The video was posted to NASA's website for a couple of weeks afterwards. On July 5, 2005, the surviving original members of The Comets (ranging in age from 71–84) performed a free concert for hundreds of employees of the Jet Propulsion Laboratory to help them celebrate the mission's success. This event received worldwide press attention. In February 2006, the International Astronomical Union citation that officially named asteroid 79896 Billhaley included a reference to the JPL concert.

Deep Impact embarked on an extended mission designated EPOXI (Extrasolar Planet Observation and Deep Impact Extended Investigation) to visit other comets, after being put to sleep in 2005 upon completion of the Tempel 1 mission.

Its first extended visit was to do a flyby of Comet Boethin, but with some complications. On July 21, 2005, Deep Impact executed a trajectory correction maneuver that allows the spacecraft to use Earth's gravity to begin a new mission in a path towards another comet. The original plan was for a December 5, 2008, flyby of Comet Boethin, coming within of the comet. Michael A'Hearn, the Deep Impact team leader, explained "We propose to direct the spacecraft for a flyby of Comet Boethin to investigate whether the results found at Comet Tempel 1 are unique or are also found on other comets." The $40 million mission would provide about half of the information as the collision of Tempel 1 but at a fraction of the cost. Deep Impact would use its spectrometer to study the comet's surface composition and its telescope for viewing the surface features. On May 28, 2010, a burn of 11.3 seconds was conducted, to enable the June 27 Earth fly by to be optimized for the transit to Hartley 2 and fly by on November 4. The velocity change was
On November 4, 2010, the Deep Impact extended mission (EPOXI) returned images from comet Hartley 2.

At the end of 2011, Deep Impact was re targeted towards asteroid (163249) 2002 GT which it would reach on January 4, 2020. At the time of re targeting, whether or not a related science mission would be carried out in 2020 was yet to be determined, based on NASA's budget and the health of the probe. A 71 second engine burn on October 4, 2012, changed the probe's velocity by to keep the mission on track. Also, there was a 140 second burn on November 24, 2011. Distance of a flyby would not be more than 400 kilometers.

In February 2013, Deep Impact observed Comet ISON. The comet remained observable until March 2013.

On September 3, 2013, a mission update was posted to the EPOXI mission status website, stating "Communication with the spacecraft was lost some time between August 11 and August 14 The last communication was on August 8. the team on August 30 determined the cause of the problem. The team is now trying to determine how best to try to recover communication." On September 20, 2013, NASA abandoned further attempts to contact the craft. According to chief scientist A'Hearn, the reason for the software malfunction was a Y2K like problem. August 11, 2013, 00:38:49.6, was 232 tenth seconds (deciseconds) from January 1, 2000, leading to speculation that a system on the craft tracked time in one tenth second increments since January 1, 2000, and stored it in an unsigned 32 bit integer, which then overflowed at this time, similar to the Year 2038 problem.