This is an interesting article on Winning NASA Space Mission Proposals
NASA’s robotic space missions are awarded through a competitive proposal process. These missions can cost from $100 to $750 million dollars, not including launch services and inflight propulsion devices. They are presented to the public first as planning documents and later as announcements of opportunity, or AOs. These AOs are released by NASA’s Science Mission Directorate about once per year for cheaper missions and every few years for higher cost missions.
Announcements of opportunity are usually released in draft form about six months from the due-at-NASA date and in final form about three months from the due-at-NASA date. A month or so before the draft release, there will usually be a heads up announcement citing the particulars of the release—schedule, cost cap, etc. These announcements are posted in the NEWS page on each mission’s home page.
Explorer Class—usually capped at $200 million although Small Explorers (SMEX) can come in at $120 million. They usually focus on astrophysics and heliophysics and are released every year or so. Since 1958 there have been 92 Explorer missions.
Discovery Class—The next Discovery release in fall of 2012 is expected to be capped at $500 million. They usually focus on planetary science and are released ever 1-3 years. Since 1995 there have been 11 Discovery missions.
New Frontiers Class—A spin-off of the Discovery program, they are usually capped at $650 million. New Frontiers usually focus on planetary science.
Flagship Class missions usually cost several billion dollars and are typically the
product of study groups such as the Mars Exploration Program Analysis Group
(MEPAG) or the Venus Exploration Analysis Group (VEXAG). They are
generally not announced through AOs.
More information is available at