Encyclopedia Astronautica
Deep Impact

Deep Impact
Credit: NASA
Deep Impact
Credit: NASA
American comet probe. One launch, 2005.01.12. Studied interior composition of Comet Tempel 1. The flyby spacecraft carried a smaller impactor which it released, allowing it to study the plume from the collision with the comet on 2005.07.04.

Comet Tempel 1 was discovered in 1867 and orbits the Sun every 5.5 years. Planning and design for the Deep Impact mission ran from November 1999 through May 2001. This was followed by the building and testing of the two-part spacecraft. The larger flyby spacecraft was designed to carry a smaller impactor to Comet Tempel 1 and release it into the comet's path for a collision on July 4, 2005.

In January 2005, a Delta II rocket launched the combined Deep Impact spacecraft toward the comet. The combined spacecraft was to approach Tempel 1 and collect images of the comet before the impact. In early July 2005, 24 hours before impact, the flyby spacecraft would point its high-precision tracking telescopes at the comet and release the impactor on a course to hit the comet's sunlit side.

The impactor was a battery-powered spacecraft that would operate independently of the flyby spacecraft for just one day. After its release, it was to take over its own navigation and maneuvers into the path of the comet. A camera on the impactor would capture and relay images of the comet's nucleus just seconds before collision. After release of the impactor, the flyby spacecraft was to maneuver to a path with a closest approach of 500 km from the comet.

On July 4, 2005, the 370-kg impactor would hit the comet. On impact, a crater was produced expected to range in size from 10 to 100 m across. Ice and dust debris would be ejected, hopefully revealing fresh material beneath.

After release of the impactor, the flyby spacecraft was to maneuver to a path with a closest approach of 500 km from the comet. The flyby spacecraft would observe and record data on the impact, the ejected material blasted from the crater using cameras and a spectrometer. This should reveal the structure and composition of the crater's interior. A shield was to protect it as it passed through the comet's dust tail. Thereafter the flyby spacecraft would turn to look at the comet again, recording additional data from the other side of the nucleus and observing changes in the comet's activity.

The flyby spacecraft carried a set of instruments and the smart impactor. Two instruments on the flyby spacecraft observed the impact, crater and debris with optical imaging and infrared spectral mapping. The flyby spacecraft used an X-band radio antenna (transmission at about eight gigahertz) to communicate to Earth while monitoring the impactor on a different frequency. For most of the mission, the flyby spacecraft communicated through the 34-meter antennae of NASA's Deep Space Network. During the short period of encounter and impact, when there was an increase in volume of data, overlapping antennas around the world were used. Primary data would be transmitted immediately and other data stored and transmitted over the following week. The impactor spacecraft was composed mainly of copper, which was not expected to appear in data from a comet's composition. For its short period of operation, the impactor used simpler versions of the flyby spacecraft's hardware and software - and fewer backup systems.

The Deep Impact mission was a partnership between the University of Maryland (UMD), the California Institute of Technology's Jet Propulsion Laboratory (JPL) and Ball Aerospace and Technology Corp. The scientific leadership of the mission was based at UMD. Engineers at Ball Aerospace designed and built the spacecraft under JPL's management. Engineers at JPL controlled the spacecraft after launch and relayed data to scientists for analysis. The entire team consisted of more than 250 scientists, engineers, managers, and educators. Deep Impact was a NASA Discovery Mission, eighth in a series of low-cost, highly focused space science investigations.

Technical Description

The Flight System was about 3.3m long, 1.7m wide, and 2.3m high. It consisted of two spacecraft: the flyby spacecraft and the impactor. Each spacecraft had its own instruments and capabilities to receive and transmit data.

Flyby Spacecraft

The flyby spacecraft carried the primary imaging instruments (the HRI and MRI telescopes) and the impactor (with an ITS telescope) to the vicinity of the comet nucleus. It released the impactor, received impactor data, supported the instruments as they imaged the impact and resulting crater, and then transmitted the science data back to Earth. The flyby spacecraft featured a high throughput RAD750 CPU with 1553 data bus-based avionics architecture, and a high stability pointing control system. The flyby spacecraft was three-axis stabilized and used a fixed solar array and a small NiH2 battery for its power system. The structure was aluminum and aluminum honeycomb construction. Blankets, surface radiators, finishes, and heaters passively controlled the temperature. The propulsion system employed a simple blowdown hydrazine design that provided 190 m/s of delta V. The flyby spacecraft mass was 650 kg.

The primary instruments on the flyby spacecraft were the High Resolution Instrument (HRI) and the Medium Resolution Instrument (MRI). The HRI, one of the largest space-based instruments built specifically for planetary science, was the main science camera for Deep Impact. It provided the highest resolution images via a combined visible camera, an infrared spectrometer, and a special imaging module. The HRI was optimally suited to observe the comet's nucleus. The HRI had a diameter of 30 cm, a focal length of 10.5 m, a field of view of 0.118 degrees, and an expected resolution of 1.4 m at 700 km from the comet in the visible spectrum. Its infrared imager would provide lower-resolution images in the 1.05 - 4.8 micrometer band.

The MRI served as the functional backup for the HRI, and was slightly better at navigation for the last 10 days of travel before impact due to its wider field of view, which allowed it to observe more stars around the comet. The difference between the two was the telescope, which sets the field of view (FOV) and the resolution of each. The MRI had a diameter of 12 cm, a focal length of 2.1 m, a field of view of 0.587 degrees, and a resolution of 7 m at 700 km range.

Flyby Spacecraft Technical Summary

  • Payload Power: 92 W average during engagement
  • Payload Mass: 370 kg impactor, 90 kg instruments
  • Payload Total Data Volume: 309 Mbytes
  • Payload Data Downlinked: 309 Mbytes
  • Pointing Accuracy: 200 microradian (inst. boresight orientation)
  • Pointing Knowledge: 65 microradian 3 axes 3-sigma
  • Telecom Band to Earth: X-band
  • Uplink/Downlink Rates: 125 bps/175 Kbps (exclusive of Reed-Solomon encoding)
  • Telecom Band to Impactor: S-band
  • Data Rate to Impactor: 64 Kbps @ max range (8,700 km)
  • Propulsion/RCS: 190 m/s divert; 5000 N-s RCS total impulse


The impactor guided itself to hit the comet nucleus on the sunlit side. The energy from the impact was to excavate a crater approximately 100 m wide and 28 m deep. The impactor separated from the flyby spacecraft 24 hours before it impacted the surface of Tempel 1. The impactor delivered 19 Gigajoules (equivalent to 4.8 tons of TNT) of kinetic energy to excavate the crater. This kinetic energy was generated by the combination of the mass of the impactor (370 kg) and its velocity when it impacted (10.2 km/s). Targeting and hitting the comet in a lit area was one of the mission's greatest challenges since the impactor would be traveling at 10 km per second and it must hit an area less than 6 km in diameter from about 864,000 km away. To accomplish this feat, the impactor used a high-precision star tracker, the Impactor Target Sensor (ITS), and Auto-Navigation algorithms (developed by Jet Propulsion Laboratory for the DS-1 mission) to guide it to the target. Minor trajectory corrections and attitude control were available by using the impactor's small hydrazine propulsion system. The impactor was made primarily of copper (49%) as opposed to aluminum (24%) because it minimized corruption of spectral emission lines that were used to analyze the nucleus.

The impactor was mechanically and electrically attached to the flyby spacecraft for all but the last 24 hours of the mission. Only during the last 24 hours would the impactor run on internal battery power. The propulsion system used hydrazine provided 25 m/s of delta-V for targeting.

The ITS on the impactor was nearly identical to the MRI on the flyby spacecraft. It differed only in that it lacked the filter wheel. The ITS had a diameter of 12 cm, a focal length of 2.1 m, and a field of view of 0.587 degrees. Expected resolution in the last image before impact was expected to be 20 cm at 20 km from the comet.

Impactor Technical Summary

  • Image Data Volume: Approximately 17 Mbytes (about 35 images) total
  • Pointing Accuracy: 2 mrad 3-sigma (targeting sensor boresight orientation)
  • Pointing Knowledge: 150 microradian 3 axes 3-sigma
  • Targeting Accuracy: 300 m 3-sigma WRT nucleus center of brightness
  • Telecom Band: S-Band
  • Data Rate to S/C: 64 Kbps @ max range (8,700 km)
  • Command Rate: 16 Kbps
  • Energy Storage: 2.8 Kw-hr for baseline 24 hr mission
  • Propulsion/RCS: 25 m/s divert; 1750 N-s RCS impulse


Spacecraft delta v: 190 m/s (620 ft/sec). Electric System: 0.92 average kW.

Gross mass: 1,020 kg (2,240 lb).
First Launch: 2005.01.12.
Number: 1 .

More... - Chronology...

Associated Countries
See also
  • Delta The Delta launch vehicle was America's longest-lived, most reliable, and lowest-cost space launch vehicle. Development began in 1955 and it continued in service in the 21st Century despite numerous candidate replacements. More...

Associated Launch Vehicles
  • Delta American orbital launch vehicle. The Delta launch vehicle was America's longest-lived, most reliable, and lowest-cost space launch vehicle. Delta began as Thor, a crash December 1955 program to produce an intermediate range ballistic missile using existing components, which flew thirteen months after go-ahead. Fifteen months after that, a space launch version flew, using an existing upper stage. The addition of solid rocket boosters allowed the Thor core and Able/Delta upper stages to be stretched. Costs were kept down by using first and second-stage rocket engines surplus to the Apollo program in the 1970's. Continuous introduction of new 'existing' technology over the years resulted in an incredible evolution - the payload into a geosynchronous transfer orbit increasing from 68 kg in 1962 to 3810 kg by 2002. Delta survived innumerable attempts to kill the program and replace it with 'more rationale' alternatives. By 2008 nearly 1,000 boosters had flown over a fifty-year career, and cancellation was again announced. More...
  • Delta 7925-9.5 American orbital launch vehicle. Four stage vehicle consisting of 9 x GEM-40 + 1 x EELT Thor/RS-27A + 1 x Delta K + 1 x Star 48B with 2.9 m (9.5 foot) diameter fairing) More...

Associated Manufacturers and Agencies
  • NASA American agency overseeing development of rockets and spacecraft. National Aeronautics and Space Administration, USA, USA. More...
  • Ball American manufacturer of spacecraft. Ball Aerospace and Technology, Boulder, Colorado, USA. More...

Associated Programs
  • Discovery The Discovery program was begun by NASA in the early 1990s as the planetary counterpart to the Explorer program. More...

  • McDowell, Jonathan, Jonathan's Space Home Page (launch records), Harvard University, 1997-present. Web Address when accessed: here.
  • NASA Report, Deep Impact Launch Press Kit, Web Address when accessed: here.
  • NASA Report, Deep Impact Fact Sheet, Web Address when accessed: here.
  • NASA Report, Deep Impact: Mission Design Approach for a New Discovery Mission, Web Address when accessed: here.
  • NASA Report, Deep Impact Encounter, Web Address when accessed: here.

Associated Launch Sites
  • Cape Canaveral America's largest launch center, used for all manned launches. Today only six of the 40 launch complexes built here remain in use. Located at or near Cape Canaveral are the Kennedy Space Center on Merritt Island, used by NASA for Saturn V and Space Shuttle launches; Patrick AFB on Cape Canaveral itself, operated the US Department of Defense and handling most other launches; the commercial Spaceport Florida; the air-launched launch vehicle and missile Drop Zone off Mayport, Florida, located at 29.00 N 79.00 W, and an offshore submarine-launched ballistic missile launch area. All of these take advantage of the extensive down-range tracking facilities that once extended from the Cape, through the Caribbean, South Atlantic, and to South Africa and the Indian Ocean. More...
  • Cape Canaveral LC17B Delta launch complex. Part of a dual launch pad complex built for the Thor ballistic missile program in 1956. Upgraded over the decades for use with Thor, Delta, Delta II, and Delta III launch vehicles, it remained in use for over half a century. More...

Deep Impact Chronology

2005 January 12 - . 18:47 GMT - . Launch Site: Cape Canaveral. Launch Complex: Cape Canaveral LC17B. Launch Pad: SLC17B. LV Family: Delta. Launch Vehicle: Delta 7925-9.5. LV Configuration: Delta 7925-9.5 D311.
  • Deep Impact - . Payload: Discovery 7. Mass: 601 kg (1,324 lb). Nation: USA. Agency: Seal Beach. Program: Discovery. Class: Comet. Type: Comet probe. Spacecraft: Deep Impact. USAF Sat Cat: 28517 . COSPAR: 2005-001A. Launched into a 0.981 AU x 1.628 AU solar orbit inclined 0.6 deg to the ecliptic. Deep Impact was to fly by Comet 9P/Tempel-1 on 3 July 2005. An impacter it released was to hit the comet on 4 July at 10.2 km/s, producing a crater and ejecta plume that would allow the flyby spacecraft to determine the composition and structure of the comet's nucleus.

2005 July 3 - .
  • Deep Impact, Impactor Release, Successful - . Nation: USA. Spacecraft: Deep Impact.

2005 July 4 - .
  • Deep Impact, Comet Tempel 1 Impact/Flyby, Successful - . Nation: USA. Spacecraft: Deep Impact.

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