Stardust (spacecraft)

Launched by NASA on February 7, 1999, the 385-kilogram robotic probe Stardust became the first mission to return samples from a comet. Its main goal was to gather dust from the coma of Comet Wild 2, along with cosmic dust, and bring those samples back to Earth for study. Along the way, it also passed and examined asteroid 5535 Annefrank. The primary mission ended successfully on January 15, 2006, when the sample return capsule landed on Earth.

An extended mission called NExT saw Stardust intercept Comet Tempel 1 in February 2011, a comet previously visited by Deep Impact in 2005. The spacecraft stopped operating in March 2011. On August 14, 2014, scientists reported that they had identified possible interstellar dust particles from the capsule that returned in 2006.

Interest in a dedicated comet mission grew in the 1980s. In the early 1990s, missions to Comet Halley returned the first close-up data, but the U.S. Comet Rendezvous Asteroid Flyby mission was canceled due to budget issues. By the mid-1990s, support shifted to a cheaper Discovery-class mission targeting Comet Wild 2 in 2004. Stardust was chosen in fall 1995 as a low-cost, highly focused NASA Discovery mission. Construction began in 1996 under strict level 5 planetary protection, though the risk of contaminating other worlds was considered low because particle impacts at over 1000 mph, even into aerogel, would kill any known microorganism.

Comet Wild 2 was chosen because it offered a rare chance to study a long-period comet that had recently moved closer to the Sun. In 1974, Jupiter’s gravity altered the comet’s orbit, making it a short-period comet. Scientists expected that much of the comet’s original material would still be intact. The mission’s science goals included: flying by Wild 2 at a speed low enough (under 6.5 km/s) to capture dust nondestructively with an aerogel collector; intercepting interstellar dust particles at similarly low speeds; and returning as many high-resolution images of the comet’s coma and nucleus as possible within the mission’s budget.

Lockheed Martin Astronautics in Denver designed, built, and operated the spacecraft. JPL managed the mission for NASA. The principal investigator was Dr. Donald Brownlee from the University of Washington.

The spacecraft bus measured 1.7 meters long and 0.66 meters wide, adapted from Lockheed Martin’s SpaceProbe deep space bus. It was built from graphite fiber panels over an aluminum honeycomb support, covered with polycyanate and Kapton sheeting. To keep costs down, it reused designs and technologies from past missions and from the Small Spacecraft Technologies Initiative (SSTI). It carried five scientific instruments, including the sample collection tray that returned to Earth.

For attitude control and propulsion, the spacecraft used eight 4.41 N hydrazine monopropellant thrusters and eight 1 N thrusters, with 80 kilograms of propellant at launch. Positioning data came from a star camera with flight software (Stellar Compass), an inertial measurement unit, and two Sun sensors. The Stellar Compass software was provided by Intelligent Decisions, Inc.

Communications with the Deep Space Network used X-band, via a 0.6-meter parabolic high-gain antenna, a medium-gain antenna, and low-gain antennas, depending on the mission phase, along with a 15-watt transponder originally designed for Cassini.

Power came from two solar arrays that averaged 330 watts. They included Whipple shields to protect against cometary dust. The array design followed SSTI guidelines and could switch strings from series to parallel based on distance from the Sun. A single nickel-hydrogen battery provided power when sunlight was insufficient.

The onboard computer used a radiation-hardened RAD6000 32-bit processor. It stored 128 megabytes of data, 20% of which was taken up by flight system software. The operating system was VxWorks from Wind River Systems.