Missions Evaluated by the Small Satellite Cost Model
	Launched in February 1999, Stardust is journeying to the comet Wild-2. It will arrive in 2004 and, during a slow flyby, will collect samples of dust and gas in a low-density material called aerogel. The samples will be returned to Earth for analysis in 2006. Stardust will also photograph the comet and do chemical analysis of particles and gases. The JPL/Lockheed Martin-built spacecraft is one of NASA's Discovery Program missions. It is the first NASA mission dedicated to exploring a comet and the first U.S. mission launched to robotically obtain samples in deep space.
	NEAR was launched in February 1996. Its objective was to orbit the asteroid Eros for one year starting in January 1999, collecting scientific data. Developed in 29 months at JHU/APL, NEAR was part of the NASA Discovery Program. Its payload was composed of a multispectral imager, a laser rangefinder, an X-ray/gamma-ray spectrometer, and a magnetometer. A software-error-induced burn abort that occurred in December 1998 resulted in delaying the rendezvous and subsequent data acquisition until February 2000.
	The Lunar Prospector, a NASA-sponsored lunar polar orbiting probe developed by Lockheed Martin, was launched aboard Athena II in January 1998. Its primary mission was to map the moon's chemical, gravitational, and magnetic properties. Data from instruments, including a gamma-ray spectrometer, a neutron spectrometer, an alpha particle spectrometer, a magnetometer, and an electron reflectometer, were used to construct a map of the surface composition of the moon.
	Mars Pathfinder, the second launch in the Discovery Program developed by JPL, consists of a cruise stage, entry vehicle, and lander. The mission of Mars Pathfinder was to test technologies in preparation for future Mars missions, as well as to collect data on the Martian atmosphere, meteorology, surface geology, and rock and soil composition. On July 4, 1997, Mars Pathfinder successfully landed on Mars and subsequently rolled out the Sojourner rover to analyze native rock composition.
	The ACE (Advanced Composition Explorer) spacecraft carried six high-resolution sensors, mainly spectrometers, and three monitoring instruments. It collected samples of low-energy solar and high-energy galactic particles and measured conditions of solar wind flow and particle events. An Explorer mission sponsored by the NASA Office of Space Science and built by JHU/APL, ACE orbits the L1 libration point, a location 900,000 miles from Earth where the gravitational effects of Earth and the sun are balanced, to provide near-real-time solar wind information.
	SWAS (Submillimeter Wave Astronomy Satellite) was the third NASA Small Explorer mission. It was launched aboard a Pegasus XL rocket in December 1998. The overall goal of the mission was to understand star formation by using a passively cooled Cassegrain telescope to determine the composition of interstellar clouds and establish the means by which these clouds cool as they collapse to form stars and planets. SWAS observed water, molecular oxygen, isotopic carbon monoxide, and atomic carbon.
	Launched in October 1998, DS1 (Deep Space 1) was a NASA New Millennium Program mission. Its objective was to validate several technologies in space including solar electric propulsion and autonomous navigation. Instruments on board included a solar concentrator array and a miniature integrated camera and imaging spectrometer. The spacecraft, built by JPL and Spectrum Astro, was designed to monitor solar wind and measure the interaction with targets during flybys of an asteroid and a comet.
	The primary mission objectives of the Clementine lunar orbiter, launched in January 1994 aboard Titan IIG, were to investigate long-term effects of the space environment on sensors and spacecraft components and to take multispectral images of the moon and the near-Earth asteroid Geographos. The Naval Research Laboratory-built spacecraft incorporated advanced technologies, including Lawrence Livermore National Laboratory lightweight sensors. After Clementine completed lunar mapping, its onboard computer malfunctioned on departure from lunar orbit and depletion of onboard fuel resulted.
(Illustrations courtesy of NASA)

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