NASA Spacecraft Photographs Hartley 2 CometNASA Spacecraft Photographs Hartley 2 Comet

Hartley 2 Comet

NASA used two imaging instruments on a spacecraft that flew within 435 miles of the comet Hartley 2 to capture some of the most detailed photos ever of the celestial phenomenon.

The space agency began the EPOXI mission to send a craft called Deep Impact to Hartley 2 -- a comet 23 million miles away from earth -- in late 2007. Hartley was photographed a few weeks after it had passed 11 million miles away from Earth, relatively close in astronomical terms.

The comet -- discovered in 1985 by British astronomer Malcolm Hartley -- became only the fifth comet ever to have been photographed by a spacecraft. Comets are collections of dust, rocks and ice that travel through the solar system.

The Deep Impact craft is so named because of a previous mission it flew to a comet called Tempel 1. The craft fired a missile into the comet, causing an explosion and creating a crater.

Two imaging instruments on Deep Impact are responsible for the pictures NASA now has of Hartley 2; each instrument had its own specific capability and purpose, according to NASA.

The high-resolution instrument features a 30-centimeter-diameter telescope that delivers light simultaneously to both a multispectral camera and an infrared spectrometer, according to NASA. The camera is one of the largest to date to fly on a planetary mission, which is why it was able to take such detailed shots of the comet, the agency said.

There was one problem with the high-resolution camera that engineers didn't anticipate, however, according to NASA. Tests done after Deep Impact was already on its way to Hartley 2 found that the focus of the camera was not as clear as expected.

The imaging team corrected the problem by using an image-processing technique called deconvolution, which was also used to improve images from the Hubble Space Telescope before its second camera instrument was installed, according to NASA.

The other imager on Deep Impact -- a medium-resolution instrument -- took photos of the stars and the comet for guidance and navigation, according to NASA. It also collected visible images with a wide field of view of material ejected from the comet, as well as the comet nucleus itself. NASA scientists will study the images for scientific purposes.

The main computer flying Deep Impact is based on a Rad 750 chip, a radiation-hardened version of a PowerPC processor, according to NASA. The craft's power comes from a fixed solar array of 7.5 square meters, with a rechargeable 16-amp-hour nickel hydrogen battery that provides power during a solar eclipse. A hydrazine-fueled propulsion system powers its flight through space.

NASA is now evaluating the photos, which provide detail about material that has not changed for more than 4 billion years, to determine what it can learn about the solar system.