Serving as the spacecraft's primary payload, the Advanced Responsive Tactically-Effective Military Imaging Spectrometer, or ARTEMIS, will deliver processed information to the warfighter on the ground within 10 minutes, following a single-pass collection opportunity on a specified target.

Dr. Thomas Cooley, TactSat-3 program manager, explained that the ARTEMIS sensor delivers information by first measuring the spectrum for each point or pixel in an image. He said the goal of the sensor is to measure the spectral radiance that results from the reflection off of materials.

"Most materials have a color spectrum," said Dr. Cooley. "They exhibit some kind of color, not just black, white or gray, when measured across a wide spectral range as ARTEMIS does from 400 to 2,500 nanometers, which encompasses all the visible light bands into the short-wave infra red."

This type of capability is fundamentally new for DOD, said Dr. Cooley.

"There are many challenges to bring this technology to full fruition, including achieving a precise radiometric and spectral calibration of the ARTEMIS instrument and accurately correcting for atmospheric spectral features."

Developed by Raytheon Space and Airborne Systems, ARTEMIS consists of a trio of components: a telescope, a spectrometer and an onboard digital signal processor, provided by SEAKR Engineering and Space Computer Corp.

The telescope is designed for imaging application performance and contains a secondary mirror with an incorporated focus device. Because the primary function of the telescope is to collect photons or light energy and not to provide exquisite imaging performance, since the system is a spectrometer first, the performance and therefore the cost of the telescope could be relaxed from what a purely imaging system would require.

The spectrometer, developed to match the telescope interfaces, employs a single focal plane array, which simplifies both the optical system and the processing of the data over previous designs with multiple focal plane arrays.

And the onboard digital signal processor, featuring 16 gigabyte storage and reprogrammable capability, processes the measured spectra into data products and transmits the image products via a common data link to the ground.

Although there are technology hurdles associated with image spectroscopy, Dr. Cooley said Air Force research labs are well equipped to overcome the challenge.

"Many dual-use (military and civilian) applications have been developed for imaging spectroscopy using both airborne data and data from NASA's Hyperion instrument, launched in 2000, which provides 30-meter spectral resolution and approximately 220 spectral bands," he said. "The ARTEMIS payload, utilizing design lessons from previous imaging spectrometer sensors, will produce approximately 400 spectral channels and, with other design enhancements, will substantially improve the spectral performance across the entire spectral region."

TacSat-3's lift off has been scheduled for May 5 from the Mid-Atlantic Regional Spaceport, located at the NASA Wallops Flight Facility, Wallops Island, Va. Officials in DOD's Operationally Responsive Space Office are funding the launch and will be leading the military utility assessment to determine the operational utility of this type of sensor and of this low-cost spacecraft.

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