QuikScat will fire its four onboard thrusters today in a "cluster" of five separate burns. The thrusters will fire for about 10 minutes beginning at 1 p.m. PDT, then will rest while the satellite orbits Earth twice, then fire again, continuing until the thrusters have fired a total of five times today.

The thruster firings are designed to begin circularizing QuikScat's orbit and raise the perigee, or the closest point in its orbit to Earth. Each of the thrusters puts out 4.4 newtons (1 pound) of force.

Commands to carry out the "cluster burn" have been generated at the University of Colorado's Laboratory for Atmospheric and Space Physics, Boulder, CO, which conducts satellite operations under the direction of engineers from Ball Aerospace & Technologies Corp., Boulder, CO, which built the satellite.

The command sequence was to be sent early this morning to a station of NASA's Deep Space Network in Canberra, Australia, for transmission to the satellite.

Today's series of firings will be the largest of five such cluster burns scheduled over the next week and a half. Following launch, QuikScat has followed an orbit that takes it as close as 290 kilometers (180 miles) to Earth's north pole; after today's firings, the satellite will pass within about 420 kilometers (260 miles) of the north pole.

Today's cluster of firings will increase QuikScat's velocity by about 44 meters per second (100 miles per hour), causing the satellite to complete one orbit of Earth every 97 minutes at a speed of about 7.4 kilometers per second (16,500 miles per hour).

Later cluster burns will continue to adjust QuikScat's orbit until the satellite is circling Earth at a fixed altitude of 800 kilometers (500 miles).

They will change the orbit by progressively smaller amounts as the pressure in the satellite's propellant tank declines and thruster performance decreases.

Later cluster burns are tentatively scheduled for about the same time of day on June 27, June 29, July 1 and July 3. Once the burns have circularized QuikScat's orbit, two or three small burns will be performed to perfect the final orbit size, shape and orientation for the start of the ocean-mapping mission.

All satellite systems are operating normally. The satellite's scatterometer radar instrument is scheduled to be turned on and begin collecting and transmitting data on July 7.

Members of the science team will spend about 13 days calibrating initial data before the primary mission of mapping ocean winds begins on July 19.