and EUVE, is relatively small. Swift is a current real-time mission that conforms to this general model. Swift science and mission operations are handled by the PI at the Goddard Space Flight Center, with substantial efforts in both mission and science operations contracted to coinvestigators at Pennsylvania State University. The Swift data are promptly available via the High Energy Astrophysics Science Archive Research Center (HEASARC), within seconds for the gamma-ray burst detections, and are quickly accessible and archivable for longer-term analyses.
Somewhat more complicated in their mission operations are those Explorer-class space astronomy missions that are expected to have significant guest investigator involvement. Operated out of the Goddard Space Flight Center (GSFC), the Rossi X-ray Timing Explorer (RXTE) mission is an all-guest-investigator mission, without guaranteed observatory time for the scientific staff but with some guaranteed research time that a staff member can use to propose for observatory time. The RXTE science operations center is responsible for the detailed scientific planning of the mission operations, the coordination of the colocated contractor flight operations team, and postacquisition data processing. RXTE staff provide preproposal simulation software and proposal support, as well as data analysis software, to its guest investigator community.
The RXTE center also reviews proposals for guest investigations on behalf of NASA Headquarters. While NASA Headquarters has responsibility for approving the grants and contracts that are associated with guest investigations, the review of proposals (i.e., evaluating proposals for technical merit, convening teams of proposal reviewers from the scientific community for evaluating scientific merit, and making recommendations for proposal acceptance) has now been tasked to mission centers in the overall statement of work.
RXTE, much like other Explorer-class missions, is required to have an EPO plan and has a small budget and fractional staff time devoted to it.
A variation on the small mission center described above is a guest observer facility (GOF). GOFs do not have mission operations responsibilities and provide only support to guest observers. A good example is the XMM–Newton GOF at the GSFC, which provides functions specifically associated with NASA support to U.S. guest observers since XMM–Newton is a mission of the European Space Agency, whose science and mission operations are conducted in Europe. Virtually all center-provided functions are now accessed remotely, so that the NASA-specific functions are related to value-added support for proposal preparation and data analysis for U.S. guest observers. GOF provides a user guide for XMM–Newton data analysis, manages the budget proposal process for U.S. guest observers, and provides preproposal support as well as a help desk, although the GOF budget limits the extent of the support that can be provided. But, since the scientists associated with the GOF and the HEASARC are XMM–Newton users, the help-desk support is expert and the standard HEASARC analysis tools1 for XMM–Newton data are well supported and effectively utilized by the U.S. guest observer community for XMM–Newton. Similar to the XMM–Newton/HEASARC relationship, the Infrared Processing and Analysis Center (IPAC) supports U.S. users of the European Space Agency’s Infrared Space Observatory.