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EPOXI

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Template:Infobox spacecraft

EPOXI mission patch
EPOXI mission patch

EPOXI is a NASA unmanned space mission led by the University of Maryland using the existing Deep Impact vehicle to begin a new series of observations. It first investigated extrasolar planets and, on November 4, 2010, it performed a close approach to the comet 103P/Hartley (alternately named Hartley 2).[1] The new mission was originally announced on 3 July 2007 as including flyby of comet 85P/Boethin, but Boethin was too small and faint for its orbit to be calculated accurately, so the mission was subsequently retargeted for a 103P/Hartley flyby.[2] NASA and the University of Maryland confirmed funding for the 103P/Hartley flyby in news releases issued on December 13, 2007.[3][4]

EPOXI combines two targets: the Deep Impact Extended Investigation (DIXI), and the Extrasolar Planet Observation and Characterization (EPOCh). Deep Impact will conduct both missions, the Extrasolar Planet Observation and Characterization during the cruise phase to 103P/Hartley, and the Deep Impact Extended Investigation at flyby. The spacecraft was also used as a test platform for a delay-tolerant networking transmission while at a distance of 20 million miles from Earth.[5]

NASA's Jet Propulsion Laboratory, in Pasadena, California., manages EPOXI for NASA's Science Mission Directorate, Washington. The Principal Investigator is Michael A'Hearn.[citation needed]

Mission

The Deep Impact mission was finished with the visit to comet Tempel 1. But the spacecraft still had plenty of maneuvering fuel left, so NASA approved a second mission, called Epoxi, that included a visit to a second comet. Three years ago, the mission had to shift course when the comet it was aiming for, Comet Boethin, could not be found. The backup target was Hartley 2.

"It's exciting that we can send the Deep Impact spacecraft on a new mission that combines two totally independent science investigations, both of which can help us better understand how solar systems form and evolve," said Deep Impact leader and University of Maryland astronomer Michael A'Hearn who is principal investigator for both the overall EPOXI mission and its DIXI component.[4]

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 allowed the spacecraft to use Earth's gravity to begin a new mission in a path towards another comet. The extended mission is called EPOXI (Extrasolar Planet Observation and Deep Impact Extended Investigation) and in January 2008 Deep Impact began studying the stars with several known extrasolar planets in an attempt to find other such stars nearby. The larger of the spacecraft's two telescopes attempts to find the planets using the transit method.[6]

The initial plan was for a December 5, 2008 flyby of Comet Boethin, with the spacecraft coming within 435 miles (700 kilometers). The spacecraft does not carry a second impactor to collide with the comet and would observe the comet to compare it to various characteristics found on 9P/Tempel. A'Hearn, the Deep Impact team leader reflected on the upcoming project at that time: "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."[7] He explained that the mission would provide only about half of the information collected during the collision with Tempel 1 but at a fraction of the cost.[7] (EPOXI’s low mission cost of $40 million is achieved by reusing the existing Deep Impact spacecraft.) Deep Impact will use its spectrometer to study the comet's surface composition and its telescopes for viewing the surface features.[6]

However, as the Earth gravity assist approached, astronomers were unable to locate Comet Boethin, which is too faint to be observed. Consequently, its orbit could not be calculated with sufficient precision to permit a flyby. Instead, the team decided to send Deep Impact to comet 103P/Hartley requiring an extra two years. NASA approved the additional funding required and retargeted the spacecraft.[8]

Mission controllers at the Jet Propulsion Laboratory began redirecting EPOXI on November 1, 2007. They commanded the spacecraft to perform a three-minute rocket burn that changed the spacecraft's velocity. EPOXI’s new trajectory set the stage for three Earth flybys, the first on December 31, 2007. This placed the spacecraft into an orbital "holding pattern" so that it could encounter comet 103P/Hartley in 2010.

In June 2009[9], EPOXI's spectrometer scanned the Moon on its way to Hartley, and discovered traces of "water or hydroxyl", confirming a Moon Mineralogy Mapper observation — a discovery announced in late September, 2009.[10]

The flyby of comet 103P/Hartley occurred November 4, 2010.

EPOCh

EPOXI imaged the Moon transiting the Earth on 28-29 May 2008. (Click to view animation)

Before the 2008 flyby to re-orient for the comet 103P/Hartley encounter, the spacecraft used High Resolution Instrument, the larger of its two telescopes, to perform photometric observations of previously discovered transiting extrasolar planets from January to August 2008. [11] The goal of photometric observations is to measure the quantity of light, not necessarily resolve an image. An aberration in the primary mirror of the HRI [12] allowed the HRI to spread the light from observations over more pixels without saturating the CCD, effectively obtaining better data. A total of 198,434 images were exposed. [13] EPOCh's goals were to study the physical properties of giant planets and search for rings, moons and planets[14] as small as three Earth masses.[15] It also looked at Earth as though it were an extrasolar planet to provide data that could characterize Earth-type planets for future missions, and it imaged the Earth over 24 hours to capture the Moon passing in front on 2008-05-29.[11]

Planetary systems observed
Star Constellation Distance (ly) Planet
XO-2 Lynx 486 b
Gliese 436 Leo 33.48 b
BD+36°2593 Boötes 1010 HAT-P-4b
GSC 03089-00929 Hercules 1300 TrES-3
WASP-3 Lyra 727 b
GSC 03549-02811 Draco 718 TrES-2
HAT-P-7 Cygnus 1044 b

"The search for exosolar planetary systems is one of the most intriguing explorations of our time," said Drake Deming, EPOXI deputy principal investigator at NASA's Goddard Space Flight Center, Greenbelt, Md. "With EPOXI we have the potential to discover new worlds and even analyze the light they emit to perhaps discover what atmospheres they possess."

Comet flyby

The nucleus of comet 103P/Hartley, measuring approximately 2 kilometers (1.2 miles) in length and .4 kilometers (.25 miles) at its most narrow portion or neck. Jets can be seen streaming out of the nucleus.
Another view of the comet, taken near closest approach.

The mission's closest approach to 103P/Hartley occurred at 10 am EDT on 4 November 2010, passing to within about 700 kilometers (435 miles) of the small, half-mile-wide comet. [16] The spacecraft employed the same suite of three science instruments—two telescopes and an infrared spectrometer—that the Deep Impact spacecraft used during its prime mission to guide an impactor into comet Tempel 1 in July 2005 and observe the results.

Early results of the observations show that the comet is powered by dry ice, not water vapor as was previously thought.[17] The images were clear enough for scientists to link jets of dust and gas with specific surface features.[18]

If EPOXI’s observations of 103P/Hartley show it is similar to one of the other comets that have been observed, this new class of comets will be defined for the first time. If the comet displays different characteristics, it would deepen the mystery of cometary diversity.

"When comet Boethin could not be located, we went to our backup, which is every bit as interesting but about two years farther down the road," said Tom Duxbury, EPOXI project manager at NASA's Jet Propulsion Laboratory in Pasadena, California.

"Hartley 2 is scientifically just as interesting as comet Boethin because both have relatively small, active nuclei," said Michael A'Hearn, principal investigator for EPOXI at the University of Maryland, College Park.

The craft is now in a solar orbit near to that of the Earth. It used Earth for a gentle gravity assist maneuver in Dec 2008 and again in Dec 2009. On May 30, 2010 the spacecraft successfully fired its engines for an 11.3 second trajectory correction maneuver, for a velocity change (ΔV) of 0.1 metres per second (0.22 mph), in preparation for an Earth flyby on June 27. Observations of 103P/Hartley began on September 5 and will end on November 25, 2010.[19] For a diagram of the EPOXI solar orbits see here.

References

  1. ^ http://epoxi.umd.edu/3gallery/20101021_CN.shtml
  2. ^ "NASA Gives Two Successful Spacecraft New Assignments" (Press release). NASA. July 3, 2007. Retrieved 7 August 2009.
  3. ^ "NASA Sends Spacecraft on Mission to Comet Hartley 2" (Press release). NASA. Dec. 13, 2007. Retrieved 7 August 2009. {{cite press release}}: Check date values in: |date= (help)
  4. ^ a b "Deep Impact Extended Mission Heads for Comet Hartley 2" (Press release). University of Maryland. December 13, 2007. Retrieved 7 August 2009.
  5. ^ "First test for interplanetary net". BBC News. 21 November 2008. Retrieved 7 August 2009.
  6. ^ a b "Science Daily". Deep Impact Mission: Aiming For Close-ups Of Extrasolar Planets. Retrieved June 3, 2007.
  7. ^ a b "Skymania News". Deep Impact will fly to new comet. Retrieved June 12, 2007.
  8. ^ EPOXI Mission Status, NASA/University of Maryland, December 2, 2007.
  9. ^ Deep Impact and Other Spacecraft Find Clear Evidence of Water on Moon: Thin layer of surface 'dew' appears to form, then dissipate each day
  10. ^ Science, A Whiff of Water Found on the Moon
  11. ^ a b "EPOXI Mission Status Reports". Retrieved 2009-03-07.
  12. ^ "Beyond Deep Impact: Possible Targets After Fireworks". Retrieved 2010-03-01.
  13. ^ Rieber, R., Sharrow, & Robert. (2009). The Contingency of Success: Operations for Deep Impact's Planet Hunt. IEEE Aerospace Conference. Big Sky, MT
  14. ^ "Sarah Ballard: Preliminary Results from the NASA EPOXI Mission" (Mov). http://epoxi.umd.edu/4gallery/vid_DPS08.shtml. Retrieved 2009-03-07. {{cite web}}: External link in |work= (help) (at 2 minutes 20 seconds in video)
  15. ^ "EPOXI Mission Science". Retrieved 2009-03-07.
  16. ^ http://www.nasa.gov/mission_pages/epoxi/epoxi20101104b.html
  17. ^ http://epoxi.umd.edu/7press/news/20101110.shtml
  18. ^ http://epoxi.umd.edu/7press/news/20101118.shtml
  19. ^ "NASA Spacecraft Burns for Home, Then Comet". NASA.
External image
image icon Deep Impact trajectory
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