Aerojet will begin work on the program in January, leading up to launch of the unmanned spacecraft in spring 2004. Aerojet's contract with Johns Hopkins University's Applied Physics Laboratory also includes spacecraft integration support and launch site operations.

"We are proud to utilize our mission-proven expertise in spacecraft propulsion systems on this exciting, historic mission," said Bob Harris, Aerojet vice president of Strategic and Space Propulsion.

Aerojet's propulsion system will consist of an integrated set of one- and five-pound thrusters fueled by hydrazine, and a single 150-pound bipropellant main engine. After Messenger is launched into space, the propulsion system will take over. Thrusters will fire periodically to control the spacecraft's velocity, direction and stability for more than five years as it swings by Venus twice and Mercury twice prior to entering Mercury orbit in late September 2009.

Messenger's seven instruments will transmit global images of Mercury as well as other data for the following year. The $286 million Messenger (MErcury: Surface, Space ENvironment, GEochemistry and Ranging) is part of NASA's Discovery Program, which emphasizes lower-cost, highly-focused scientific missions.