The April 23 launch of the space shuttle Discovery will be a day engineers at the Space Dynamics Lab at Utah State University have been working toward for nearly 10 years.

SDL has designed and built one of the primary experiments on the shuttle payload - an infrared sensor originally scheduled for launch in 1986 - that was put on hold following the explosion of the space shuttle Challenger.S.J. Wellard, a senior engineer at SDL and flight operations leader for the USU team that will gather data during the mission, said the northern Utah lab began work on the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS) in 1982.

"Twenty-nine different launch dates have been set for us," Wellard said during a telephone interview from Houston. "This is the closest we've ever been and it's great to feel like it's really going to fly."

CIRRIS 1-A is one of five experiments being flown as part of a payload known collectively as Air Force Program-675, and according to NASA is, "the highest priority experiment being flown with AFP-675."

CIRRIS Program Manager Brent Bartschi, a senior engineer at SDL, said besides getting a vast amount of information about the upper atmosphere, the Air Force is getting a bargain with CIRRIS 1-A. Bartschi said since SDL is a relatively small, non-profit laboratory, staffers were able to design and build the instrument for far less than a large aerospace contractor could have.

Although frustrating, the delays the CIRRIS team has faced since Challenger have allowed more time to work on the project. Wellard said astronauts Guion Bluford and C. Lacy Veach, who will operate CIRRIS from the shuttle flight deck, have had more extensive training than most mission specialists have been able to receive.

Bartschi added that technological advances made in the past few years will be a real asset in handling the vast amount of data that will be collected during the flight.

"We have been making measurements of the atmosphere for years with sensors launched on rockets, aircraft and balloons," Bartschi said. "But handling the data from this mission will be a big job because the sensor is on the shuttle and will be working for such a long time, this will provide more information than all previous flights."

The data they hope to gather for the Phillips Laboratory Geophysics Directorate will be measurements of infrared emissions in the upper atmosphere from air glow, the aurora and the unique infrared signatures of objects in the atmosphere that will be useful for military systems designers, Bartschi explained.

The shuttle and its payload are on the launch pad now, festooned with bright flags that pinpoint spots to be evaluated again during some of the intensive checks before liftoff.