Cometary Encounter Closer

Image of Borrelly taken by Deep Space 1.
This was the final image of the nucleus of comet Borrelly, taken just 160 seconds before Deep Space 1′s closest approach to it. Smooth, rolling plains containing brighter regions are present in the middle of the nucleus and seem to be the source of dust jets seen in the coma.
Credit: NASA/JPL

NASA’s Deep Impact spacecraft completed the commissioning phase of the mission and has moved into the cruise phase.

Deep Impact mission planners have separated the spacecraft’s flight operations into five mission phases. Cruise phase will continue until about 60 days before the encounter with comet Tempel 1 on July 4, 2005.

Soon after launch on Jan. 12, 2005, Deep Impact entered the commissioning phase. During that phase, the mission team verified the basic state of health of all subsystems and tested the operation of science instruments. The spacecraft’s autonomous navigation system was activated and tested using the moon and Jupiter as targets.

The spacecraft’s high gain antenna, which will relay images and data of the cometary collision, was activated and is operating properly. A trajectory correction maneuver was performed, refining the spacecraft’s flight path to comet Tempel 1. The maneuver was so successful that a second one planned for March 31 was cancelled.

Another event during commissioning phase was the bake-out heating of the spacecraft’s High Resolution Instrument (HRI) to remove normal residual moisture from its barrel. The moisture was a result of absorption into the structure of the instrument during the vehicle’s last hours on the launch pad and its transit through the atmosphere to space.

dust_particle
Comet Halley imaged by European flyby.
Credit: ESA

At completion of the bake-out procedure, test images were taken through the HRI. These images indicate the telescope has not reached perfect focus. A special team has been formed to investigate the performance and to evaluate activities to bring the telescope the rest of the way to focus. Future calibration tests will provide additional information about the instruments’ performance.

The Deep Impact spacecraft has four data collectors to observe the effects of the collision: a camera and infrared spectrometer comprise the High Resolution Instrument; a Medium Resolution Instrument (MRI); and a duplicate camera on the Impactor Targeting Sensor (ITS). They will record the vehicle’s final moments before it is run over by comet Tempel 1 at approximately 23,000 mph. The MRI and ITS are performing as expected.

Eros_surface
The rocks inside a crater on the Asteroid Eros, as imaged before impact with the NEAR spacecraft. Numerous small impacts on the asteroid show brown boulders visible interior to the less exposed (white) lip of the crater. False-color for emphasis.
Image Credit: NASA/Eros

"This in no way will affect our ability to impact the comet on July 4," said Rick Grammier, Deep Impact project manager at NASA’s Jet Propulsion Laboratory (JPL), Pasadena, Calif. "Everyone on the science and engineering teams is getting very excited and looking forward to the encounter."

Dr. Michael A’Hearn of the University of Maryland, College Park, Md., added, "We are very early in the process of examining the data from all the instruments. It appears our infrared spectrometer is performing spectacularly, and even if the spatial resolution of the High Resolution Instrument remains at present levels, we still expect to obtain the best, most detailed pictures of a comet ever taken."

Deep Impact is comprised of two parts, a flyby spacecraft and a smaller impactor. The impactor will be released into the comet’s path for the planned high-speed collision. The crater produced by the impactor is expected to range from the width of a house up to the size of a football stadium and be from two to 14 stories deep. Ice and dust debris will be ejected from the crater revealing the material beneath.

Along with the imagers aboard the spacecraft, NASA’s Hubble, Spitzer and Chandra space telescopes, along with the largest telescopes on Earth, will observe the effects of the material flying from the comet’s newly formed crater.

An intimate glimpse beneath the surface of a comet, where material and debris from the formation of the solar system remain relatively unchanged, will answer basic questions about the formation of the solar system. The effects of the collision will offer a better look at the nature and composition of these celestial travelers.