Deep Impact (EPOXI)
Launch Date Jan. 12, 2005 | 18:47:08.574 UT
Launch Site Cape Canaveral, Florida, USA
Destination Comets, Earth, Earth’s Moon, Beyond Our Solar System
Type Flyby, Impact
Status Successful
Nation United States
Alternate Names 2005-001A, EPOXI, Deep Impact, DIF, Deep Impact Flyby Spacecraft, 28517, DIXI


Deep Impact's primary mission was to probe beneath the surface of a comet. The spacecraft delivered a special impactor into the path of Tempel 1 to reveal never before seen materials and provide clues about the internal composition and structure of a comet.


After almost nine years in space that included an unprecedented 4th of July impact and subsequent flyby of a comet, an additional comet flyby, and the return of approximately 500,000 images of celestial objects, NASA's Deep Impact mission ended in September 2013.

Deep Impact, history's most traveled deep-space comet hunter, provided many significant results for the science community. Here are the mission team's top five:

  1. First determination that a comet's surface layer (few to 10 meters or so) is very porous (greater than 75 percent empty space)
  2. First direct evidence showing chemical diversity of outgassing associated with different parts of the cometary nucleus
  3. Discovered that hyperactive comets (5-10 percent of all comets) are driven by carbon dioxide and that the observed excess water is from icy grains in the coma. The processes of hyperactive comets are very different from those in normal comets.
  4. Observations led to re-thinking where in the solar system comets formed. Contrary to all thinking for the last half century, the Jupiter family comets must have formed closer to the sun than did the Oort cloud comets.
  5. Enabled the subsequent exciting results from the Stardust NExT mission that changes theories on how comets evolve.

Key Dates

Jan. 12, 2005 | 18:47:08.574 UT: Launch

July 1, 2005: Comet P/Tempel 1 Rendezvous

July 4, 2005 | 5:52 UT: Comet Impact

August 2005: End of Primary Mission

Nov. 4, 2010: 103P/Hartley 2 Flyby


Launch Vehicle: Delta II

Spacecraft Mass: 1,433 pounds (650 kilograms)

Spacecraft Instruments:

The High-Resolution Instrument is the main scientific instrument on the Deep Impact flyby spacecraft. It features a 30-centimeter-diameter (11.8-inch) telescope that delivers light simultaneously to both a multispectral camera and an infrared spectrometer. When the flyby spacecraft comes within 700 kilometers (420 miles) of the comet's nucleus, the camera will image parts of the comet with a scale better than 2 meters (about 6 feet) per pixel. This camera is one of the largest instruments flown to date on a planetary mission.

The Medium-Resolution Instrument is the other scientific instrument on the flyby spacecraft. It is a smaller telescope with a diameter of 12 centimeters (4.7 inches). Due to its wider field-of-view, it can observe more of the field of ejected material as well as the crater created by the impact event. It can also observe more stars around the comet and is therefore slightly better at navigation during the final 10 days of approach to the comet. When the flyby spacecraft comes within 700 kilometers (420 miles) of the comet's nucleus, this instrument can image the entire comet with a resolution of about 10 meters (about 33 feet) per pixel.

The impactor spacecraft weighs a total of 372 kilograms (820 pounds), with 113 kilograms (249 pounds) of that being "cratering mass" -- dead weight designed to help the impactor make a substantial crater in the cometary nucleus. The cratering mass is made up of copper plates at the impact end of the impactor. The copper plates are machined to form a spherical shape.

The impactor is powered during its brief solo flight by a single 250-amp-hour battery. The computer and avionics interface box are similar to those on the flyby spacecraft; star trackers, inertial reference units and many propellant subsystem components are the same on both spacecraft. Like the flyby spacecraft, the impactor has a group of thrusters to refine its flight path. Because of its brief mission, the impactor does not have redundant backups as does the flyby spacecraft. The impactor's single scientific instrument, called the impactor targeting sensor, is an imaging system identical to the medium-resolution instrument on the flyby spacecraft, but without a filter wheel. A 12-centimeter-diameter (4.7-inch) telescope provides navigation images as well as closeup scientific images of the comet just before impact.

Additional Resources

NASA Deep Impact Mission Profile

NASA Jet Propulsion Laboratory: Deep Impact Page

Selected References

Siddiqi, Asif A. Deep Space Chronicle: A Chronology of Deep Space and Planetary Probes 1958-2000, NASA, 2002.

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