Over the next two years an APL team will design and build the $17.6 million Compact Reconnaissance Imaging Spectrometer for Mars, or CRISM, which will search for mineral residues of past or recent water on the Martian surface.

As the orbiter flies over a given area, CRISM's scanning mechanism allows the instrument's visible and infrared spectrometers to track a targeted region on the surface and map it from different angles as the orbiter passes overhead. CRISM uses the spectrum of reflected sunlight to determine the mineralogy of surface materials at scales as small as 82 feet (25 meters).

"By looking at the different spectra of reflected sunlight, the instrument will pick up the 'fingerprints' of different minerals," says CRISM Principal Investigator Dr. Scott Murchie of the Applied Physics Laboratory. "Finding certain minerals on the surface tells you that water has been there. The exact combination of minerals tells you about the climatic conditions at the surface when the water flowed as liquid."

Between its targeted, high-resolution observations, CRISM will search the planet at a reduced set of wavelengths to find new sites of interest not previously suspected. "Many of the oldest rocks will be battered by craters so that ancient lakes and springs wouldn't be obvious just from pictures. This survey capability will help us find places for future landings that wouldn't otherwise be recognized."

Set to launch in August 2005, the Mars Reconnaissance Orbiter is the latest mission in NASA's long-term Mars exploration program. The craft will analyze the surface at new scales to follow hints of water detected in images from the Mars Global Surveyor spacecraft, and to bridge the gap between surface observations and measurements from orbit.

The MRO high-resolution imager, also selected by NASA at the same time as CRISM, will return the sharpest images of the Martian surface ever taken by Mars-circling orbiters - at resolutions high enough to spot rocks the size of beach balls. The mission will identify ideal locations for future landers to touch down on Mars.

Though CRISM is the first APL-developed science tool on a Mars mission, the Laboratory has built 59 spacecraft and provided 136 instruments for a variety of Earth-orbiting and deep space satellites over the past 40 years. APL managed NASA's Near Earth Asteroid Rendezvous (NEAR) mission, which included the first spacecraft to orbit and land on an asteroid.

Other APL-managed NASA missions include the Comet Nucleus Tour (CONTOUR), which launches in July 2002 for a comprehensive study of at least two comets, and MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER), a Mercury orbiter set to launch in 2004.

In fact, CRISM derives much of its design from the high-resolution camera and spectral mapper on the CONTOUR spacecraft, currently under construction at APL. "The requirements for making these kinds of observations on Mars are similar to those for mapping the nucleus of a comet," says Dennis Fort, CRISM systems engineer.

"The approach used on CONTOUR for tracking a comet and acquiring high resolution spectra adapts nicely to prospecting for small mineral deposits on the surface of Mars from orbit." Other components of CRISM are adapted from the similarly scannable imaging system on the MESSENGER Mercury orbiter, also currently under development at APL.

APL provided the ultra-stable oscillator - a super-precise timekeeping device - for Mars Global Surveyor, which has been essential to mapping atmospheric structure and circulation patterns on Mars for the past four years.

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