(Redirected from Deep Impact (spacecraft))
'''Deep Impact''' is an ongoing
NASA space probe launched on
January 12,
2005 that was designed to study the composition of the interior of the
comet Tempel 1 by colliding a section of the spacecraft into the comet. At 5:52
UTC on
July 4,
2005, the impactor 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. The mission garnered large publicity from the media, international scientists, and amateur astronomers. The spacecraft will fly by Earth on
December 31,
2007 as it heads to a new mission to study
extrasolar planets and
Comet Boethin.
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.
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.
[3] 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 370 kg
copper-core "Smart Impactor" which impacted the comet, and the "Flyby" section, which imaged the comet from a safe distance during the encounter with Temple 1.
The Flyby spacecraft is about 3.2 meters long, 1.7 meters wide, and 2.3 meters high.
It included a solar panel, 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,
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.
[4]
The impactor's payload, dubbed the "Cratering Mass", was 100%
copper (Impactor 49% copper by mass) 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.
[5] Instead of using explosives, it was also cheaper to use copper as the payload.
The name of the mission is shared with the ''
Deep Impact'' film, 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.
[6]
Mission profile
_rocket_with_Deep_Impact.jpg)
''Deep Impact'' about to be launched with a Delta II rocket
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).
[7] 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 mph).
The impactor, a 350-kilogram (770-pound) copper projectile,
[8] delivered 1.96 × 10
10 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 wide (larger than the bowl of the Roman
Colosseum). The size of the crater was still not known one year after the impact.
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
telescopes and
orbital observatories, including the
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 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.
[9]
Mission events
Before launch
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.
[10] 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.[11] in
Boulder, Colorado, USA. Developing the software for the spacecraft took eighteen months and the application code consisted of 20,000 lines and 19 different application threads.
The total cost of developing the spacecraft and completing its mission reached $
US330 million.
Launch and commissioning phase
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.
[12] It was successfully launched from
Cape Canaveral on
January 12 2005 at 1:47 p.m. EST (1847 UTC) by a
Delta 2 rocket.
[13]
''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.
[14]
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 period.
[15] After mission members investigated the problem, on June 9, 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.
[16]
Cruise phase
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
kilometers (39.7 million miles).
[17]
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).
[18] 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."
Approach phase
The approach phase extended from 60 days before encounter (May 5) until five days before
encounter. Sixty days out was 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.
[19] The spacecraft studied the images of various distant stars to determine its current trajectory and position.
Don Yeomans, a mission co-investigator for JPL pointed out that "it takes 7½ minutes for the signal to get back to Earth, so you can't joystick this thing. You have to rely on the fact that the Impactor is a smart spacecraft as is the Flyby spacecraft. So you have to build in the intelligence ahead of time and let it do its thing."
[20] 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.
Impact phase
Deep Impact comet encounter sequence
Impact phase began nominally on June 29, five days before impact. The impactor successfully separated from the Flyby spacecraft at 6:00 (6:07 Ground UTC) July 3
UTC.
[21][22] The first images from the instrumented Impactor were seen two hours after separation.
[23]
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.
[24] The Impactor spacecraft executed three correction maneuvers in the final two hours before impact.
[25]
The impactor was maneuvered to plant itself in front of the comet, so that Tempel 1 would collide with it.
Impact occurred at 05:45 UTC (05:52 Ground UTC, +/- up to three minutes, One-Way Light Time = 7m 26s) on the morning of July 4, within one second of the expected time for impact.
The Impactor returned images as late as three seconds before impact. Most of the data captured was stored on board the Flyby spacecraft, which radioed approximately 4,500 images from the HRI, MRI, and ITS cameras to earth over the next few days.
[26][27] The energy from the collision was similar in size to exploding five tons of
dynamite and the comet shined six times brighter than normal.
[28]
Impact Phase Timeline (NASA)
Extended Mission (EPOXI)
Deep Impact Extended Investigation (DIXI) and the Extrasolar Planet Observation and Characterization (EPOCh) were combined to create EPOXI. After the flyby of Tempel 1, ''Deep Impact'' was reprogrammed to head to comet
Boethin. On
July 20,
2005, a trajectory correction maneuver was performed to place the spacecraft on a trajectory to carry it to Earth, where it would use a gravitational slingshot to reach the new target. The follow-on mission was approved
October 31,
2006.
[29]
Results
Mission team members celebrate after the impact with the comet
Mission control did not become aware of the impactor's success until five minutes later at 0157
ET.
[30] Once news of a successful impact had taken place, the mission control team members applauded and hugged each other. Don Yeomans confirmed the results for the press, "We hit it just exactly where we wanted to"
[31] and JPL Director Charles Elachi stated "The success exceeded our expectations."
[32] In the post-impact briefing at 0100
Pacific Daylight Time (08:00
UTC) on
July 4,
2005, 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 30 meters deep.
Lucy McFadden, one of the co-investigators of the impact, stated "We didn't expect the success of one part of the mission [bright dust cloud] to affect a second part [seeing the resultant crater]. But that is part of the fun of science, to meet with the unexpected."
[33] 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 250,000 tonnes of water
[34] and between 10 and 25 million kilograms of dust were lost from the impact.
[35]
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 models which had comets as loose aggregates of material. In addition, the material was finer than expected; scientists likened it to
talcum powder rather than
sand.
[36] Other materials found while studying the impact included
clays,
carbonates,
sodium, and crystalline
silicates which were found by studying the spectroscopy of the impact.
[37] Clays and carbonates usually require liquid water to form and sodium is rare in space.
[38] 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 have expressed interest in more missions to different comets to determine if they share similar compositions or if there are different materials found deeper within comets that were produced at the time of the solar system's formation.
[39]
Astronomers determined that the comet had possibly formed in the
Uranus and
Neptune Oort cloud region of the solar system. Based on its interior chemistry, astronomers were able to determine that a comet which forms farther from the Sun will have greater amounts of ices with low freezing temperatures, such as
ethane, which was present in Tempel 1. If comets have similar compositions as Tempel, astronomers believe they could have formed in the same region.
[40]
Public interest
Media coverage
This image was circulated widely in the media.
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. "All we can do now is sit back and wait," said one senior personnel. "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
Waikiki Beach.
Experts came up with a range of soundbites to summarize the mission to the public. Iwan Williams of
Queen Mary, University of London, said "It was like a mosquito hitting a
747. What we've found is that the mosquito didn't splat on the surface; it's actually gone through the windscreen."
[41] One of the NASA investigators, Dr. Jessica Sunshine, explained the mission by analogy with how a
geologist examines a rock: "He doesn't just look at it, he gets his hammer out and hits it, to find out about what it's like inside and how it's put together: is it a loose association of particles or is it solid?"
One day after the impact Marina Bay, a
Russian
astrologer, sued NASA for $300 million for the impact which "ruin[ed] the natural balance of forces in the universe."
[42] 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."
[43] 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."
[44]
Send Your Name To A Comet!
The CD containing the 625,000 names is added to the Impactor
The mission was notable for one of its promotional activities, "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.
[45] 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."
[46] The idea was credited with driving interest in the mission.
[47]
Reaction from China
Chinese researchers used ''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."
[48]
Two days after the U.S. mission succeeded in having a probe collide with a comet, China revealed a plan for what it called a "more clever" version of the mission: landing a probe on a small comet or
asteroid to push it off course.
[49] China will begin the mission after sending a probe to the
Moon.
Contributions from amateur astronomers
Since observing time on large, professional
telescopes such as
Keck or
Hubble is always scarce, the ''Deep Impact'' scientists have called on "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 is to look for "volatile outgassing, dust coma development and dust production rates, dust tail development, and jet activity and outbursts."
[50] Since 2000, amateur astronomers have submitted over a thousand
CCD images of the comet.
[51]
The comet is currently too dim to be seen with anything smaller than a large backyard telescope, but it was thought possible that the impact on July 4 could brighten the comet substantially, making it visible through binoculars toward the star
Spica (visible even to the naked eye in areas with low light pollution).
[52]
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.
[53] Another amateur published a map of the crash area from NASA images.
[54]
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 and His Comets becoming the first
rock and roll single to reach No. 1 on the recording sales charts. Within twenty-four hours of the mission's success, a two-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 and His Comets performing in 1955 and the surviving original members of The Comets performing in March 2005.
[55] The video was posted to NASA's
website for a couple of weeks afterwards.
On July 5, the surviving original members of The Comets (ranging in age from 71 to 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.
[56] Later, in February 2006, the
International Astronomical Union citation that officially named
asteroid 79896 Billhaley included a reference to the JPL concert.
[57]
Future activities
On
July 21,
2005 ''Deep Impact'' executed a trajectory correction maneuver that placed the spacecraft on course to fly past Earth on
December 31,
2007. The maneuver allows the spacecraft to use Earth's gravity to begin a new mission in a path towards another comet. The proposed $500,000 extended mission is called
EPOXI (Extrasolar Planet Observation and Deep Impact Extended Investigation) and in January 2008 will have ''Deep Impact'' begin studying the stars around several known
extrasolar planets to attempt to find other nearby extrasolar planets. The telescope on the spacecraft would attempt to find the planets using the
astrometry and
transit methods.
[58]
On
December 5,
2008, the spacecraft will come within 435 miles (700 kilometers) of
Comet Boethin. Instead of using another impactor to collide with the comet (which the spacecraft does not have), the spacecraft will observe the comet to compare it to various characteristics found on Tempel 1. Michael A'Hearn, the ''Deep Impact'' team leader reflected on the upcoming project: "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."
[59] He continued on to reveal that the mission would provide about half of the information as the collision of Tempel 1 but at a fraction of the cost.
''Deep Impact'' will use its
spectrometer to study the comet's surface composition and its telescope for viewing the surface features.
See also
★
Unmanned space mission
References
1. NASA Mission Dates.
2. NASA
3. NSSDC Master Catalog Display:Spacecraft
4. Solar System Exploration
5. NASA
6. ABC News
7. Military Embedded Systems
8. NASA Mission Profile.
9. Rosetta monitors Deep Impact
10. Solar System Exploration
11. Ball Aerospace & Technologies Corp.
12. Spaceflight Now
13. Boeing Image Gallery
14. Jet Propulsion Laboratory
15. Spaceflight Now
16. Space.com
17. Jet Propulsion Laboratory
18. Spaceref
19. Jet Propulsion Laboratory
20. Space.com
21. Deep Impact homepage
22. Bloomberg.com
23. DEEP IMPACT COMET ENCOUNTER
24. Jet Propulsion Laboratory
25. NASA
26. BBC
27. NASA
28. Wired
29. Jet Propulsion Laboratory with University of Maryland
30. CNN
31. NewsFromRussia
32. CriEnglish.com
33. NASA
34. BBC News
35. NewScientist.com
36. vigyanprasar
37. New York Times
38. Astrobiology.com
39. C&EN
40. SpaceRef.com
41. BBC News
42. MSNBC
43. BBC News
44. MosNews.com
45. NASA
46. NASA
47. Space.com
48. xinhuanet
49. The Economic Times
50. Amateur Observers' Program
51. Small Science Telescope Program
52. Comet Tempel 1
53. Google Groups
54. Jost Jahn
55. Reviews & News about Bill Haley and The Comets
56. USAToday
57. Klet Observatory
58. Science Daily
59. Skymania News
★ "Deep Impact: Our First Look Inside a Comet." June 2005 issue of ''
Sky and Telescope'' magazine, pp. 40-44.
PDF file.
★ "Deep Impact encounter press kit."
PDF file.
★ "Deep Impact: Mission Science Q&A." NASA.
[1]
External links
;Official websites
:
★
Deep Impact at JPL
:
★
Deep Impact at NASA
:
★
Deep Impact Mission Profile by
NASA's Solar System Exploration
:
★
Deep Impact at the University of Maryland, College Park
:
★
Deep Impact at Ball Aerospace & Technologies Corp.
;Additional information
:
★
''Space.com'' Technology page on Deep Impact
:
★
Watch a mini-doco about Deep Impact from Australian TV, 4 August 2005
:
★
Deep Impact Reveals Comet's Components - Scientific American
;Maps, photos, and other images
:
★
Real-time image viewer
:
★
Real-time Java viewer of Deep Impact's position
;Other languages
:
★ Croatian:
Deep Impact images and information
:
★ French:
Photos and videos of the impact
_rocket_with_Deep_Impact.jpg)
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