Deep Impact's comet-watching telescope is blurred
BY JUSTIN RAY
Posted: March 25, 2005
The largest telescope ever launched into deep space is out of focus, NASA acknowledged Friday, but scientists say it still should collect the sharpest pictures of a comet's icy heart during a violent encounter July 4.
The 11.8-inch telescope is flying aboard the Deep Impact spacecraft, which will fire an 800-pound projectile into the nucleus of Comet Tempel 1 to burst through the crust coating the comet's core, form a stadium-sized crater and offer an unprecedented glimpse at ancient ices packed beneath the surface.
Known as the High-Resolution Instrument, the telescope will deliver light simultaneously to both a multispectral camera and an infrared spectrometer to photograph the crater and study the gases and dusts blown out of the comet during the impact.
As part of this commissioning, the High-Resolution Instrument underwent so-called "bake-out heating" in a bid to remove residual moisture from its telescope 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," NASA said in a statement Friday.
"At completion of the bake-out procedure, test images were taken through the HRI. These images indicate the telescope has not reached perfect focus."
The space agency says a special team has been formed to investigate ways to achieve the proper focus. Upcoming calibration tests will provide additional information about the instruments' performance, officials said.
"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. "Everyone on the science and engineering teams is getting very excited and looking forward to the encounter."
"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," said Dr. Michael A'Hearn of the University of Maryland.
Deep Impact consists of the main spacecraft, or mothership, and the impactor. The mothership carries the HRI telescope and a medium-resolution camera package to watch the impact and study the aftermath.
The impactor is a stubby-nosed, washing machine-sized bullet about two-and-a-half feet tall and three feet in diameter and sports a manhole cover-sized disc of copper with even more copper mass behind it to penetrate as deep into the comet as possible. The impactor also has cameras to photograph the comet until moments before slamming into the nucleus 23,000 mph, releasing the energy equivalent of 4.5 tons of exploding TNT.
The mothership has less than 14 minutes to make its observations while zooming toward the comet before passing by Tempel 1 at a distance of 300 miles. Scientists expect the materials thrown out of the freshly bored hole will settle within a few minutes, permitting good visibility into the crater.
The pristine building blocks buried inside comets will tell astronomers what conditions were like when the solar system was spawning planets. Uncovering the compositional fingerprints of comets has become a priority for scientists because these objects peppered the young Earth, possibly delivering the organic materials needed for the rise of life, the water for our oceans and even playing a role in generating the atmosphere.
Once the July 4 rendezvous is completed, astronomers have hoped to divert the Deep Impact mothership to other comets to use the HRI telescope for up-close encounters with other rocky snowballs over the next few years.
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