"I see so if you wanted to actually build the space craft you would work for probably a private company."<br /><br />The short answer is, "Yes!" A customer, whether a U.S. Government agency (NASA, USAF, Navy, Army, etc.) or a private satellite T.V. company, etc., usually places a Request For Proposal out to one or more prime contractors (due to mergers and such, it is to the point where there IS only ONE prime contractor in this country!). A proposal is prepared, and if there are more than one company bidding, a bidder is selected. The contract that is signed may be for the complete package, including building the spacecraft, launching, and possibly subsequent support and operation. Some commercial satellite companies contract the actual operation of the orbiting spacecraft. In other instances, such as spy satellites and the like, the agency buying the "bird" will do the operating...especially if classified operations are involved.<br /><br />In the case of the Constellation programs, the overall program including basic design is being handled by NASA, with the actual design and build of the spacecraft, boosters, etc., being done by the large contractors. They in turn will subcontract many components to specialized outfits.<br /><br />As an (old, but typical) example, take the Space Shuttle Solid Rocket Boosters...please! (Oh, that Henny Youngman! <img src="/images/icons/laugh.gif" /> ) United Space Boosters, Inc. (USBI) was the prime contractor for the boosters during the Design, Development, Test & Evaluation (DDT&E) phase, up through STS-4, and for quite awhile later. They were located in Huntsville, AL, and reported directly to the NASA office at Marshall SFC. But USBI didn't build the boosters. That was contracted to (then) Morton-Thiokol (now ATK Space Launch Systems or some corporate name). USBI was in charge of booster integration and management...EXCEPT for the SRB Decelerator Subsystem (parachute recovery system). That was contracted with (the