Stardust was a 385-kilogram robotic space probe launched by NASA on 7 February 1999. Its primary mission was to collect dust samples from the coma of comet Wild 2, as well as samples of cosmic dust, and return them to Earth for analysis. It was the first sample return mission of its kind. En route to Comet Wild 2, it also flew by and studied the asteroid 5535 Annefrank. The primary mission was successfully completed on 15 January 2006 when the sample return capsule returned to Earth. A mission extension, codenamed NExT, culminated in February 2011 with Stardust intercepting Comet Tempel 1, a small Solar System body previously visited by Deep Impact in 2005. Stardust ceased operations in March 2011. On 14 August 2014, scientists announced the identification of possible interstellar dust particles from the Stardust capsule returned to Earth in 2006.
Mission background
History Beginning in the 1980s, scientists began seeking a dedicated mission to study a comet. During the early 1990s, several missions to study Comet Halley became the first successful missions to return close-up data. However, the US cometary mission, Comet Rendezvous Asteroid Flyby, was canceled for budgetary reasons. In the mid-1990s, further support was given to a cheaper, Discovery-class mission that would study Comet Wild 2 in 2004. Stardust was competitively selected in the fall of 1995 as a NASA Discovery Program mission of low-cost with highly focused science goals. Construction of Stardust began in 1996, and was subject to the maximum contamination restriction, level 5 planetary protection. However, the risk of interplanetary contamination by alien life was judged low, as particle impacts at over 450 metres per second (1,000 mph), even into aerogel, were believed to be terminal for any known microorganism. Comet Wild 2 was selected as the primary target of the mission for the rare chance to observe a long-period comet that has ventured close to the Sun. The comet has since become a short period comet after an event in 1974, where the orbit of Wild 2 was affected by the gravitational pull of Jupiter, moving the orbit inward, closer to the Sun. In planning the mission, it was expected that most of the original material from which the comet formed would still be preserved. The primary science objectives of the mission included:
Providing a flyby of a comet of interest (Wild 2) at a sufficiently low velocity (less than 6.5 km/s) such that non-destructive capture of comet dust is possible using an aerogel collector. Facilitating the intercept of significant numbers of interstellar dust particles using the same collection medium, also at as low a velocity as possible. Returning as many high-resolution images of the comet coma and nucleus as possible, subject to the cost constraints of the mission. The spacecraft was designed, built and operated by Lockheed Martin Astronautics as a Discovery-class mission in Denver, Colorado. JPL provided mission management for the NASA division for mission operations. The principal investigator of the mission was Dr. Donald Brownlee from the University of Washington.
Spacecraft design The spacecraft bus measured 1.7 meters (5 ft 7 in) in length, and 0.66 meters (2 ft 2 in) in width, a design adapted from the SpaceProbe deep space bus developed by Lockheed Martin Astronautics. The bus was primarily constructed with graphite fiber panels with an aluminum honeycomb support structure underneath; the entire spacecraft was covered with polycyanate, Kapton sheeting for further protection. To maintain low costs, the spacecraft incorporated many designs and technologies used in past missions or previously developed for future missions by the Small Spacecraft Technologies Initiative (SSTI). The spacecraft featured five scientific instruments to collect data, including the Stardust Sample Collection tray, which was brought back to Earth for analysis.
Attitude control and propulsion The spacecraft was three-axis stabilized with eight 4.41 N hydrazine monopropellant thrusters, and eight 1 N thrusters to maintain attitude control (orientation); necessary minor propulsion maneuvers were performed by these thrusters as well. The spacecraft was launched with 80 kilograms of propellant. Information for spacecraft positioning was provided by a star camera using FSW to determine attitude (Stellar Compass), an inertial measurement unit, and two Sun sensors. The Stellar Compass software was provided by Intelligent Decisions, Inc.
Communications For communicating with the Deep Space Network, the spacecraft transmitted data across the X-band using a 0.6-meter (2 ft 0 in) parabolic high-gain antenna, medium-gain antenna (MGA) and low-gain antennas (LGA) depending on mission phase, and a 15-watt transponder design originally intended for the Cassini spacecraft.
Power The probe was powered by two solar arrays, providing an average of 330 watts of power. The arrays also included Whipple shields to protect the delicate surfaces from the potentially damaging cometary dust while the spacecraft was in the coma of Wild 2. The solar array design was derived primarily from the Small Spacecraft Technology Initiative (SSTI) spacecraft development guidelines. The arrays provided a unique method of switching strings from series to parallel depending on the distance from the Sun. A single nickel–hydrogen (NiH2) battery was also included to provide the spacecraft with power when the solar arrays received too little sunlight.
Computer The computer on the spacecraft operated using a radiation-hardened RAD6000 32-bit processor card. For storing data when the spacecraft was unable to communicate with Earth, the processor card was able to store 128 megabytes, 20% of which was occupied by the flight system software. The system software is a form of VxWorks, an embedded operating system developed by Wind River Systems.
Scientific instruments
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