Satellites at the beck and call of ground troops.

• Author: Jean, Grace V.
• Position: INSIDE SCIENCE + TECHNOLOGY

Military leaders for years have been asking for a capability that would allow ground units to commandeer satellites to obtain imagery of their surroundings. To realize that vision, the Defense Department has developed a system that may one day end up in the hands of troops.

The technology, a new hyperspectral imager, is orbiting Earth aboard an experimental spacecraft called Tactical Satellite-3. The Advanced Responsive Tactically Effective Military Imaging Spectrometer, or ARTEMIS for short, consists of a trio of components: a telescope, a spectrometer and an onboard digital signal processor.

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Using a portable device, a tactical commander would be able to communicate with the satellite directly and "call up" a mission for ARTEMIS to look at a particular location. The next time the satellite passed over the area, the sensor would take the images and send him the requested targeting data within 10 minutes.

"That's actionable information that he can use," says Ed Gussin, program manager of ARTEMIS at Raytheon Co. The company developed the $15 million sensor in 15 months for the Air Force Research Laboratory as part of the Defense Department's operationally responsive space effort. Under the initiative, small satellites carrying payloads designed for specific missions would be launched within days of Pentagon requests--a paradigm that is still considered quite ambitious for an industry that normally launches spacecraft in a period spanning years. TacSat-3 is part of a series of spacecraft that are testing and evaluating technologies to validate the concept.

Aboard TacSat-3, ARTEMIS is one such technology. "It can see what other sensors can't," explains Peter Wegner, director of the Pentagon's operationally responsive space office. Hyperspectral data provides a large step forward in multispectral imaging, which typically captures several different frequencies within the visible and infrared spectrum, Gussin says. With finer spatial resolution and better signal-to-noise ratio, hyperspectral sensors can collect significantly more information.

In ARTEMIS's case, the sensor peers at the ground and gathers more than 400 different spectra for each pixel. The resulting data is so accurate that the sensor can determine the chemical composition of materials. For example, multispectral imagers might snap a picture of a tree with a dark green shadow beneath it. A hyperspectral sensor aimed at the same location could discern a tank...