NASA Press Release: 

Mission: AIM (Aeronomy of Ice in the Mesosphere)
Launch Pad: Vandenberg Air Force Base, Calif.
Launch Vehicle: Pegasus XL (Orbital Sciences)
Launch Date: April 25, 2007
Launch Time: 1:26:49 p.m. PDT

Since NASA's AIM spacecraft arrived at Vandenberg Air Force Base, Calif., on March 10, the prelaunch processing has gone well and is on schedule. A critical milestone was achieved when technicians performed a partial deployment of the solar array and successfully conducted an illumination test. Instrument cleaning and calibration is currently under way. The spacecraft separation system is scheduled to be installed this weekend. Mating of the AIM spacecraft to the Pegasus XL rocket is targeted for April 3.

The mating of the three stages of the Pegasus XL is complete. A flight simulation successfully tested the launch vehicle, including testing of the reaction control system pneumatic thrusters. Next week, prior to mating the AIM spacecraft to the Pegasus XL, the spacecraft will be electrically connected to the launch vehicle for a flight simulation. Another flight simulation will be conducted during the second week of April, after AIM is mechanically mated and electrically integrated onto the Pegasus rocket.