Stardust (spacecraft)
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Stardust is an American interplanetary spacecraft launched on February 7, 1999. Its purpose is to investigate the makeup of the comet Wild 2 and its coma.
Stardust flew by 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. Stardust is now on its way back to Earth and will arrive at Earth in 2006, to deliver the sample material in a capsule.
Additionally, the spacecraft passed within 3300 km of the asteroid 5535 Annefrank on November 2, 2002 and took several photographs.
Donald Brownlee, from the University of Washington, is the Principal Investigator for the Stardust mission.
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The craft
The mission spacecraft is derived from the SpaceProbe 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.
The total weight of the spacecraft including the propellant needed for deep space maneuvers is 380 kilograms. The overall length of the main bus is 1.7 meters, about the size of an average office desk.
Stardust runs a VxWorks embedded operating system.
Science payload
Aerogel sample collectors
Stardust_Dust_Collector_with_aerogel.jpg
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).
When the spacecraft flew past the comet, the impact velocity of the particles they are captured was 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 alter their shape and chemical composition - or vaporize them entirely.
To collect the particles without damaging them, a silicon-based solid with a porous, sponge-like structure is used in which 99 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 will bury 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 - sometimes called "blue smoke" - scientists will use these tracks to find the tiny particles.
The aerogel is packed in a Sample Return Capsule (SRC) which will be released from the spacecraft just before reentry, for a separate landing on a parachute, while the rest of the spacecraft is destroyed in the atmosphere.
There is 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 design error.
Comet and Interstellar Dust Analyzer (CIDA)
Stardust_CIDA.jpg
The CIDA instrument is a time-of-flight mass spectrometer that determines the composition of individual dust grains which collide with a silver impact plate.
The purpose of the Cometary and Interstellar Dust Analyzer (CIDA) instrument on Stardust is to intercept and perform real-time compositional analysis of dust as it is encountered by the spacecraft for transmission back to Earth.
The CIDA separates ions' masses by comparing differences in their flight times. The operating principle of the instrument is the following: when a dust particle hits the target of the instrument, ions are extracted from it by the electrostatic grid. Depending on the polarity of the target positive or negative ions can be extracted. The extracted ions move through the instrument, are reflected in the reflector, and detected in the detector. Heavier ions take more time to travel through the instrument than lighter ones, so the flight times of the ions are then used to calculate their masses.
The CIDA is the same instrument design as flew on Giotto and two Vega spacecraft where it obtained unique data on the chemical composition of individual particulates in Halley's coma. It consists of an inlet, a target, an ion extractor, a time-of-flight (TOF) mass spectrometer (MS) and an ion detector.
The co-investigator in charge of the CIDA is Jochen Kissel of Max-Planck-Institut für extraterrestrische Physik in Garching, Germany where the instrument has been developed. Electronics hardware has been built by von Hoerner & Sulger GmbH in Schwetzingen, Germany. Software for the CIDA instrument is being developed by The Finnish Meterological Institute.
Navigation camera (NavCam)
The Navigation camera is used for targeting the flyby of the Wild 2 nucleus, but also provides high-resolution science images of the comet.
The Navigation Camera (NC), an engineering subsystem, was used to optically navigate the spacecraft upon approach to the comet. This allowed the spacecraft to achieve the proper flyby distance, near enough to the nucleus, to assure adequate dust collection. The camera also served as an imaging camera to collect science data. The data includes high-resolution color images of the comet nucleus, on approach and on departure, and broadband images at various phase angles while nearby. These images will be used to construct a 3-D map of the nucleus in order to better understand its origin, morphology, and mechanisms, to search for mineralogical inhomogeneities on the nucleus, and potentially to supply information on the nucleus rotation state. The camera will provide images, taken through different filters, that will give information on the gas and dust coma during approach and departure phases of the mission. These images will provide information on gas composition, gas and dust dynamics, and jet phenomena, if they exist.
Dust shield and monitors
Whipple shield
The Whipple shield is designed to shadow the spacecraft to protect it during the high speed encounter with particles in the cometary coma. Bumper shields are composite panels which disrupt particles as they impact.
Nextel blankets of ceramic cloth further dissipate and spread the particle debris. Three blankets are used in the main body shield, and two are used in the solar array shields. The composite catcher absorbs all of the debris for solid particles up to 1 cm in diameter for the shield protecting the spacecraft main body.
Dust Flux Monitors (DFM)
The DFM instrument, mounted on the front of the Whipple shield, monitors the flux and size distribution of particles in the environment.
Developed under the direction of Tony Tuzzalino at the University of Chicago, the DFMI is a highly sensitive instrument designed to detect particles as small as a few micrometres. It is based on a very special polarized plastic (PVDF) that generates electrical pulses when impacted or penetrated by small high speed particles.
The Dust Flux Monitor Instrument (DFMI) consists of a Sensor Unit (SU), Electronics Box (EB), and the two acoustic sensors mounted to the Stardust spacecraft. The SU is mounted to the Whipple shield, and the EB is mounted internally to the spacecraft enclosure.
External link
- Stardust Project web page (http://stardust.jpl.nasa.gov/Home.html)