Electronic Design

NASA Probe Crashes Comet’s Fourth Of July Party

This weekend’s biggest fireworks will take place 83 million miles away. NASA’s Deep Impact spacecraft will launch a probe at comet Tempel 1 on July 3. At approximately 1:52 a.m. EDT on the Fourth of July, the 39-in. wide probe will hit the comet, which is about half the size of Manhattan, at 23,000 miles/hour.

The inevitable crater could range in size from a large house to a football stadium two to 14 stories deep. The impact will eject ice and dust, revealing the material beneath the surface. The Deep Impact spacecraft, about 310 miles away from the collision, will have 13 minutes to take images and spectra of the event before it’s enveloped in debris. Observations will resume once the spacecraft clears the debris zone, giving researchers a view of the comet’s core.

“The last 24 hours of the impactor’s life should provide the most spectacular data in the history of cometary science,” said Deep Impact principal investigator Dr. Michael A’Hearn. “We know so little about the structure of cometary nuclei that almost every moment we expect to learn something new.”

Researchers say that under the comet’s surface, they will find material that dates back to the formation of the solar system—unchanged even after billions of years. This project should answer some basic questions about the formation of the solar system by offering a better look at these materials.

The Deep Impact spacecraft has four data collectors. The flyby spacecraft houses a camera and infrared spectrometer, which comprise the High Resolution Instrument, and a Medium Resolution Instrument. The impactor houses a duplicate Medium Resolution Instrument, which will record the vehicle’s final moments before impact.

Due to the speed of the experiment and the distance from Earth, the spacecraft will rely on its “autonav” software, firing thrusters to adjust flight path and orientation as necessary. This software also will take pictures and perform image processing for broadcast back to Earth. It’s based on technology from the Deep Space 1 mission and the Stardust spacecraft, earlier comet explorers.

Deep Impact’s main computer is based around a Rad 750 chip, a radiation-hardened version of a PowerPC processor used in different consumer computers. The flyby spacecraft has two redundant computers with a total memory of 1024 Mbytes. It also uses X-band radio to transmit to Earth at a frequency of about 8 GHz. Power is drawn from a fixed, 80-ft.2 solar array and a rechargeable 16-A/hr. nickel-hydrogen battery.

Those of us still on Earth during the experiment have no need to worry, though. Despite the apparent force of the collision, researchers say it won’t be powerful enough to knock the comet out of its orbit and into a more dangerous path. For details, go to the NASA web site.

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