# Engineering:Deep Impact (spacecraft)

Short description: NASA space probe launched in 2005, designed to study and impact the comet Tempel 1
Mission type Artist's impression of the Deep Impact space probe after deployment of the Impactor. Flyby · impactor (9P/Tempel) NASA · JPL 2005-001A 28517 www.jpl.nasa.gov/missions/deep-impact/ Final: 8 years, 6 months, 26 days Ball Aerospace · University of Maryland Spacecraft: 601 kg (1,325 lb)[3] Impactor: 372 kg (820 lb)[3] 3.3 × 1.7 × 2.3 m (10.8 × 5.6 × 7.5 ft)[3] 92 W (solar array / NiH2 battery)[3] January 12, 2005, 18:47:08 UTC Delta II 7925 Cape Canaveral Air Force Station SLC-17B Boeing Contact lost August 8, 2013 July 4, 2005, 06:05 UTC 575 km (357 mi) July 4, 2005, 05:52 UTC December 31, 2007, 19:29:20 UTC 15,567 km (9,673 mi) December 29, 2008 43,450 km (27,000 mi) June 27, 2010, 22:25:13  UTC 30,496 km (18,949 mi) November 4, 2010, 13:50:57 UTC 694 km (431 mi) Official insignia of the Deep Impact mission Discovery programDawn →

Deep Impact was a NASA space probe launched from Cape Canaveral Air Force Station on January 12, 2005.[4] It was designed to study the interior composition of the comet Tempel 1 (9P/Tempel), by releasing an impactor into the comet. At 05:52 UTC on July 4, 2005, the Impactor successfully collided with the comet's nucleus. The impact excavated debris from the interior of the nucleus, forming an impact crater. Photographs taken by the spacecraft showed the comet to be more dusty and less icy than had been expected. The impact generated an unexpectedly large and bright dust cloud, obscuring the view of the impact crater.

Previous space missions to comets, such as Giotto, Deep Space 1, and Stardust, were fly-by missions. These missions were able to photograph and examine only the surfaces of cometary nuclei, and even then from considerable distances. The Deep Impact mission was the first to eject material from a comet's surface, and the mission garnered considerable publicity from the media, international scientists, and amateur astronomers alike.

Upon the completion of its primary mission, proposals were made to further utilize the spacecraft. Consequently, Deep Impact flew by Earth on December 31, 2007 on its way to an extended mission, designated EPOXI, with a dual purpose to study extrasolar planets and comet Hartley 2 (103P/Hartley).[5] Communication was unexpectedly lost in August 2013 while the craft was heading for another asteroid flyby.

## Scientific goals

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.[6][7] 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.[8] 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.

## Spacecraft design and instrumentation

Spacecraft overview

The spacecraft consists of two main sections, the 372-kilogram (820 lb) copper-core "Smart Impactor" that impacted the comet, and the 601 kg (1,325 lb) "Flyby" section, which imaged the comet from a safe distance during the encounter with Tempel 1.[3][9][10]

The Flyby spacecraft is about 3.3 meters (10.8 ft) long, 1.7 meters (5.6 ft) wide and 2.3 meters (7.5 ft) high.[3][6] 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 meters per pixel [7.9 in/px]) 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.[11]

The Impactor's payload, dubbed the "Cratering Mass", was 100% copper, with a weight of 100 kg.[12] Including this cratering mass, copper formed 49% of total mass of the Impactor (with aluminium at 24% of the total mass);[13] 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.[12] Instead of using explosives, it was also cheaper to use copper as the payload.[7]

Explosives would also have been superfluous. At its closing velocity of 10.2 km/s, the Impactor's kinetic energy was equivalent to 4.8 tonnes of TNT, considerably more than its actual mass of only 372 kg.[14]

The mission coincidentally shared its name with the 1998 film, Deep Impact, in which a comet strikes the Earth.[15]

## Mission profile

Cameras of the Flyby spacecraft, HRI at right, MRI at left
Deep Impact prior to launch on a Delta II rocket

Following its launch from Cape Canaveral Air Force Station pad SLC-17B at 18:47 UTC on January 12, 2005,[4] the Deep Impact spacecraft traveled 429 million km (267 million mi) in 174 days to reach comet Tempel 1 at a cruising speed of 28.6 km/s (103,000 km/h; 64,000 mph).[6] Once the spacecraft reached the vicinity of the comet on July 3, 2005, it separated into the Impactor and Flyby sections. 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; 23,000 mph).[6] The Impactor delivered 1.96×1010 joules of kinetic energy—the equivalent of 4.7 tons of TNT. Scientists believed that the energy of the high-velocity collision would be sufficient to excavate a crater up to 100 m (330 ft) wide, larger than the bowl of the Roman Colosseum.[6] The size of the crater was still not known one year after the impact.[16] The 2007 Stardust spacecraft's NExT mission determined the crater's diameter to be 150 meters (490 ft).

Just minutes after the impact, the Flyby probe passed by the nucleus at a close distance of 500 km (310 mi), taking pictures of the crater position, the ejecta plume, and the entire cometary nucleus. The entire event was also photographed by Earth-based telescopes and orbital observatories, including Hubble, Chandra, Spitzer, and XMM-Newton. The impact was also observed by cameras and spectroscopes on board Europe's Rosetta spacecraft, which was about 80 million km (50 million mi) from the comet at the time of impact. Rosetta determined the composition of the gas and dust cloud that was kicked up by the impact.[17]

## Mission events

Animation of Deep Impact's trajectory from January 12, 2005, to August 8, 2013
Deep Impact ·   Tempel 1 ·   Earth ·   103P/Hartley

### Send Your Name To A Comet campaign

The CD containing the 625,000 names is added to the Impactor
Deep Impact participation certificate of Mathias Rex

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.[52] 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."[53] The idea was credited with driving interest in the mission.[54]

### Reaction from China

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."[55]

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.[56]

### Contributions from amateur astronomers

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."[57] By mid-2007, amateur astronomers had submitted over a thousand CCD images of the comet.[58]

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.[59] Another amateur published a map of the crash area from NASA images.[60]

### Musical tribute

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.[61] 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.[62] In February 2006, the International Astronomical Union citation that officially named asteroid 79896 Billhaley included a reference to the JPL concert.[63]

## Extended mission

Main page: Astronomy:EPOXI

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.[64]

### Comet Boethin plan

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.[65]

The original plan was for a December 5, 2008, flyby of Comet Boethin, coming within 700 kilometers (430 mi) 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."[66] The \$40 million mission would provide about half of the information as the collision of Tempel 1 but at a fraction of the cost.[66][67] Deep Impact would use its spectrometer to study the comet's surface composition and its telescope for viewing the surface features.[65]

However, as the December 2007 Earth gravity assist approached, astronomers were unable to locate Comet Boethin, which may have broken up into pieces too faint to be observed.[68] Consequently, its orbit could not be calculated with sufficient precision to permit a flyby.

### Flyby of Comet Hartley 2

Comet Hartley 2 on November 4, 2010

In November 2007 the JPL team targeted Deep Impact toward Comet Hartley 2. However, this would require an extra two years of travel for Deep Impact (including earth gravity assists in December 2007 and December 2008).[68] 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 0.1 m/s (0.33 ft/s).[69]

On November 4, 2010, the Deep Impact extended mission (EPOXI) returned images from comet Hartley 2.[64] EPOXI came within 700 kilometers (430 mi) of the comet, returning detailed photographs of the "peanut" shaped cometary nucleus and several bright jets. The probe's medium-resolution instrument captured the photographs.[64]

### Comet Garradd (C/2009 P1)

Deep Impact observed Comet Garradd (C/2009 P1) from February 20 to April 8, 2012, using its Medium Resolution Instrument, through a variety of filters. The comet was 1.75–2.11 astronomical unit|AU (262–316 million km) from the Sun and 1.87–1.30 astronomical unit|AU (280–194 million km) from the spacecraft. It was found that the outgassing from the comet varies with a period of 10.4 hours, which is presumed to be due to the rotation of its nucleus. The dry ice content of the comet was measured and found to be about ten percent of its water ice content by number of molecules.[70][71]

### Possible mission to asteroid (163249) 2002 GT

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.[72] A 71-second engine burn on October 4, 2012, changed the probe's velocity by 2 m/s (6.6 ft/s) to keep the mission on track.[73] Also, there was a 140-second burn on November 24, 2011. Distance of a flyby would not be more than 400 kilometers.

### Comet C/2012 S1 (ISON)

In February 2013, Deep Impact observed Comet ISON. The comet remained observable until March 2013.[74][75]

### Contact lost and end of mission

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."[71]

On September 10, 2013, a Deep Impact mission status report explained that mission controllers believe the computers on the spacecraft are continuously rebooting themselves and so are unable to issue any commands to the vehicle's thrusters. As a result of this problem, communication with the spacecraft was explained to be more difficult, as the orientation of the vehicle's antennas is unknown. Additionally, the solar panels on the vehicle may no longer be positioned correctly for generating power.[76]

On September 20, 2013, NASA abandoned further attempts to contact the craft.[77] According to chief scientist A'Hearn,[78] the reason for the software malfunction was a Y2K-like problem. August 11, 2013, 00:38:49.6, was 232 tenth-seconds 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.[79]

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