Stardust (spacecraft)

Stardust
Artist's conception of the Stardust spacecraft
Organization	NASA Jet Propulsion Laboratory
Major contractors	Lockheed Martin
Mission type	Fly-by, sample collection
Satellite of	Sun
Orbital insertion date	January 2, 2004
Launch date	February 7, 1999 21:04:15 UTC
Launch vehicle	Delta II booster
Mission duration	7 years
COSPAR ID	1999-003A
Home page	Stardust homepage
Mass	300 kg
Power	330 W

Stardust is an American interplanetary mission of the NASA Jet Propulsion Laboratory, whose primary purpose was to investigate the makeup of the comet Wild 2 and its coma. It was launched on February 7, 1999 by NASA, travelled nearly 3 billion miles (5·10 km), and returned to Earth on January 15, 2006 to release a sample material capsule. It is the first sample return mission to collect cosmic dust and return the sample to Earth. On July 3, 2007 a second mission was approved to revisit the comet Tempel 1.

Primary mission

NASA began construction of the Stardust spacecraft in 1996. After launch in 1999, the Stardust spacecraft travelled in an initial orbit beyond — but intersecting — Earth's orbit. The Delta II booster did not have enough energy to reach Wild 2 directly. The Stardust spacecraft then approached Earth in January 2001 for a gravity assist maneuver. The encounter with Earth enlarged the spacecraft's orbit to intersect that of Wild 2.

On the second orbit, Stardust flew by the comet Wild 2 on January 2, 2004. During the flyby it collected dust samples from the comet's coma and took detailed pictures of its icy nucleus. Additionally, the spacecraft accomplished several other goals. It passed within 3300 km of the asteroid 5535 Annefrank on November 2, 2002 and took several photographs. The aerogel collector also acquired interstellar dust. In March-May 2000 and July-December 2002, the spacecraft angled itself into a dust stream believed to originate outside the solar system. The reverse side of the aerogel collector then caught a sample of such particles.

The sample material capsule from Stardust returned to Earth at approximately 10:10 UTC on January 15, 2006 in Utah's Great Salt Lake desert, near the U.S. Army Dugway Proving Ground, to deliver the sample material. The landing coordinates were 40°21.9′N 113°31.25′W / 40.365°N 113.52083°W. Winds had blown the capsule a few miles off its ballistic trajectory, but it was within the target area. On arrival, the capsule was traveling in a nearly flat trajectory, at 12.9 km/s (28,900 miles per hour), which is the fastest re-entry speed into Earth's atmosphere ever achieved by a man-made object. As a point of comparison, NASA stated it would be able to travel from Salt Lake City, Utah to New York City, New York in less than six minutes. A large fire ball and sonic boom were observed in western Utah and eastern Nevada.

The Stardust mothership had been put into a "divert maneuver" to keep the hardware from hitting Earth. Under twenty kilograms of fuel remain onboard after the maneuver. On January 29, the craft was put in hibernation mode with only its solar panels and receiver still active in a three-year heliocentric orbit that will return it to Earth's vicinity on January 14, 2009.

Donald Brownlee, from the University of Washington, was the Principal Investigator for the Stardust mission. Ken Atkins of the Jet Propulsion Laboratory managed the project during development. Joe Vellinga was the Program Manager at the spacecraft contractor, Lockheed Martin. The Project Manager during Stardust operations and the current Project Manager for the NExT secondary mission is Tom Duxbury of the Jet Propulsion Laboratory.

Secondary mission: exploration of Tempel 1 (NExT)

On 19 March, 2006 Stardust scientists announced that they were considering the possibility of redirecting the spacecraft on a secondary mission to photograph Tempel 1, the comet that was impacted by the Deep Impact spacecraft in 2005. This possibility is important because Deep Impact did not succeed in capturing a good image of the crater formed on Tempel 1, due to obscuring dust from the impact.

In July 3, 2007 this extended mission was approved, under the designation of New Exploration of Tempel 1 (NExT). This investigation will provide the first look at the changes to a comet nucleus produced after its close approach to the sun. NExT also will extend the mapping of Tempel 1, making it the most mapped comet nucleus to date. This mapping will help address the major questions of comet nucleus "geology" raised by images of areas where it appears material might have flowed like a liquid or powder. NExT is scheduled to fly by Tempel 1 on February 14, 2011.

The craft

The mission spacecraft is derived from the Space probe deep space bus developed by Lockheed Martin Astronautics. This new lightweight spacecraft incorporates components, virtually all of which are either currently operating in space or are flight qualified and manifested to fly on upcoming missions. Several components have heritage from the Cassini mission; some were developed under the Small Spacecraft Technologies Initiative (SSTI).

Being a sample return mission, Stardust is subject to the maximum contamination restrictions, classified under level 5 planetary protection. However, the risk of interplanetary contamination by alien life was judged low, for instance particle impacts at over 1000 miles per hour — even into aerogel — would destroy any known microorganism.

The total weight of the spacecraft, including the hydrazine propellant needed for deep space maneuvers, is 380 kilograms. The overall length of the main bus is 1.7 meters, about the size of a refrigerator or an average office desk. It appears orange-brown due to the blankets of Kapton film.

At one end of the spacecraft is the sample return capsule; the capsule contains the aerogel tray, and an arm to extend the tray. The opposite end of the spacecraft has the main dust shield, and the interface to the launch vehicle. Two sides of the spacecraft body hold solar arrays. Unlike most other missions, the silicon arrays do not articulate to track the sun after their initial deployment. The spacecraft is fairly passive and generates adequate power during the lengthy cruise portions of the mission. The encounter phase, when Stardust must orient the collector and dust shields at Wild 2 regardless of solar illumination, is relatively brief. Each array also has a dust shield. The remaining sides of the spacecraft contain the communications dish and scientific instruments.

Science payload

Aerogel sample collectors

Comet and interstellar particles are collected in ultra low density aerogel. More than 1,000 square centimeters of collection area is provided for each type of particle (cometary and interstellar). The collector tray contains ninety blocks of aerogel in a metal grid. The appearance of the grid has been likened to an ice cube tray; the round collector is about the size of a tennis racket.

When the spacecraft flew past the comet, the impact velocity of the particles in the coma as they were captured was 6100 metres per second, up to nine times the speed of a bullet fired from a rifle. Although the captured particles were each smaller than a grain of sand, high-speed capture could have altered their shape and chemical composition — or vaporized them entirely.

To collect the particles without damaging them, a silicon-based solid with a porous, sponge-like structure is used in which 99.9 percent of the volume is empty space. Aerogel is 1,000 times less dense than glass, 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, as it slows down and comes to a stop — like an airplane setting down on a runway and braking to reduce its speed gradually. Since aerogel is mostly transparent — a property earning it the nickname "solid smoke" or "blue smoke" — scientists will use these tracks to find the tiny particles.

The aerogel was packed in a Sample Return Capsule (SRC) which was released from the spacecraft just before reentry, for a separate landing on a parachute, while the rest of the spacecraft fired its engines, putting it into orbit around the sun.

While there was some concern about this landing, as the capsule shares a parachute design with Genesis, a solar probe whose parachute did not deploy properly in 2004 due to an assembly and integration error, the Utah landing saw the spacecraft arrive intact and within a minute of estimates.

To analyse the aerogel for interstellar dust, about one million photographs will be taken, each one of a very small section of the gel. These will be distributed to home computer users who will be credited for any particles found, in a program called Stardust@home modeled after SETI@home and Mars Clickworkers.

Primary mission

Secondary mission: exploration of Tempel 1 (NExT)

The craft

Science payload

Aerogel sample collectors

Comet and Interstellar Dust Analyzer (CIDA)

External links