21 December 2005

Stardust Nears Home

Image credit: NASA

We are stardust, we are golden
And we got to get ourselves back to the garden
-- Crosby, Stills & Nash


After a rendezvous with comet Wild 2 (pronounced "Vilt") in January of 2004, Stardust's cometary sample return is presently speeding back home to the garden for a highly anticipated arrival January 15th. I find this mission particularly exciting, as it offers our first opportunity to perform an Earthbound examination of materials from one of the cosmos' many time capsules. The propect of capturing invaluable cometary particles and interstellar dust may sound relatively simple. It isn't. Enter: Aerogel.

The primary objective of the Stardust mission is to capture both cometary samples and interstellar dust. Main challenges to accomplishing this successfully involve slowing down the particles from their high velocity with minimal heating or other effects that would cause their physical alteration. When the Stardust Spacecraft encounters the Comet Wild 2, the impact velocity of the particles will be up to 6 times the speed of a rifle bullet. Although the captured particles will each be smaller than a grain of sand, high-speed capture could alter their shape and chemical composition - or even vaporize them entirely.

To collect particles without damaging them, Stardust uses an extraordinary substance called aerogel. This is a silicon-based solid with a porous, sponge-like structure in which 99.8 percent of the volume is empty space. By comparison, aerogel is 1,000 times less dense than glass, which is another silicon-based solid. When a particle hits the aerogel, it buries itself in the material, creating a carrot-shaped track up to 200 times its own length. This slows it down and brings the sample to a relatively gradual stop. Since aerogel is mostly transparent - with a distinctive smoky blue cast - scientists will use these tracks to find the tiny particles.


The scientific payoff yielded by this endeavor promises to be magnificent, as noted by Stardust's Principal Investigator, Dr. Donald Brownlee:

It is widely believed that comets are the best bodies for preserving the very materials that the solar system was built from. Like a fantastic library, they have stored preserved materials and records of our formation. The gaseous emissions can be analyzed from a distance either by telescopes on or orbiting Earth or by instruments on spacecraft sent to comets. The dust and rocks are another matter. They are believed to be samples of the solid building blocks of the solar system, samples of the solids that began the process of collision and sticking in the early history of the solar system that began with dust and produced ever larger bodies, and ultimately whole solid planets like Earth, Mars and Pluto. Some information can be obtained by telescopic study of the dust but the real secrets of the material cannot be examined remotely. On scales from kilometers to microns (a hair is about 100 microns in diameter) primitive materials just look like black charcoal. They are black due to their high content of carbon and other light absorbing materials and most of their components are so small that they cannot be individually seen by the naked eye. Like books in a library, they have to be opened and read but in this case the words are small, very small. So small they can only be read by large microscopes and other instruments that are too heavy, complex and power hungry to be put onto robotic spacecraft.




Stardust's current view of home.

In September 8th of 2004, a similar sample return mission designed to directly measure the solar wind, Genesis, unfortunately experienced a nasty 193 m.p.h. (311 k.p.h.) introduction to the Utah soil. An oboard design flaw resulted in the capsule's parachutes failure to deploy. Thankfully, however, it appears the Genesis team will be able to complete some if not all of their science objectives.

The Genesis mishap prompted a thorough review of Stardust's design. Project manager Thomas Duxbury remains confident that Stardust's sample return capsule will fare much better than its predecessor.

NASA issued this press release today:

NASA Prepares for Return of Interstellar Cargo

NASA's Stardust mission is nearing Earth after a 2.88 billion mile round-trip journey to return cometary and interstellar dust particles back to Earth. Scientists believe the cargo will help provide answers to fundamental questions about comets and the origins of the solar system.

The velocity of the sample return capsule, as it enters the Earth's atmosphere at 28,860 mph, will be the fastest of any human-made object on record. It surpasses the record set in May 1969 during the return of the Apollo 10 command module. The capsule is scheduled to return on Jan. 15.

"Comets are some of the most informative occupants of the solar system. The more we can learn from science exploration missions like Stardust, the more we can prepare for human exploration to the moon, Mars and beyond," said Mary Cleave, associate administrator for NASA's Science Mission Directorate.

Several events must occur before scientists can retrieve cosmic samples from the capsule landing at the U.S. Air Force Utah Test and Training Range, southwest of Salt Lake City. Mission navigators will command the spacecraft to perform targeting maneuvers on Jan. 5 and 13. On Jan. 15 at 12:57 a.m. EST, Stardust will release its sample return capsule. Four hours later, the capsule will enter Earth's atmosphere 410,000 feet over the Pacific Ocean.

The capsule will release a drogue parachute at approximately 105,000 feet. Once the capsule has descended to about 10,000 feet, the main parachute will deploy. The capsule is scheduled to land on the range at 5:12 a.m. EST.

After the capsule lands, if conditions allow, a helicopter crew will fly it to the U.S. Army Dugway Proving Ground, Utah, for initial processing. If weather does not allow helicopters to fly, special off-road vehicles will retrieve the capsule and return it to Dugway. Samples will be moved to a special laboratory at NASA's Johnson Space Center, Houston, where they will be preserved and studied.

"Locked within the cometary particles is unique chemical and physical information that could be the record of the formation of the planets and the materials from which they were made," said Don Brownlee, Stardust principal investigator at the University of Washington, Seattle.

NASA expects most of the collected particles to be no more than a third of a millimeter across. Scientists will slice these particle samples into even smaller pieces for study.


Best wishes for a smooth return and soft landing!



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1 Comments:

Blogger Wolverine said...

Of course, the less-than-skeptical doomsday mongers on the web are already crying Chicken Little. Oh teh noes! Michael Crichton anyone? :rolls eyes:

12:51 AM CST  

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