Budget justification documents released recently by the U.S. Missile Defense Agency (MDA) have shed some more light on a mysterious experimental satellite that in the past has raised suspicions among opponents of space weapons.

The Near Field Infrared Experiment (NFIRE) satellite, slated for launch in late 2006 or early 2007, will help “mitigate endgame homing and guidance risk for both terrestrial … and future space-based boost phase interceptors,” according to the documents, which were sent to Congress in March.

NFIRE generated controversy last year when it was disclosed that the satellite — which the MDA said would demonstrate a sensor that can distinguish between a missile and its hot exhaust plume — would include a small projectile to be fired in the direction of a target warhead. Critics, including U.S. Rep. Loretta Sanchez (D-Calif.), charged that NFIRE was a stepping-stone to space-based weapons, and the projectile-firing subsequently was dropped from the experiment.

According to the budget justification documents, the MDA now plans to conduct three main experiments with the NFIRE satellite, which is being built by General Dynamics’ Spectrum Astro Space Systems division in Gilbert, Ariz. The first involves testing the infrared sensor’s sensitivity to targets including aircraft, missiles and space-launch vehicles at distances ranging from 100 to 1,000 kilometers, the documents show.

A second experiment will entail launching ballistic missiles that will pass within 10 kilometers of the satellite.

A third mission objective is to verify the accuracy of the NFIRE infrared sensor by using it to monitor events on the ground like forest fires and rocket-engine tests.

The MDA is requesting $13.7 million in 2006 for the NFIRE experiment, a fraction of the $68 million being spent on the effort this year.