3.4 Assessment of Recent Changes in the Explorer Program

A Report of the Panel to Review the Explorer Program1


Since the 1960s, the Explorer program at the Goddard Space Flight Center (GSFC) has been of crucial importance for the disciplines of space physics and space astronomy. Level-of-effort funding for the Explorer program enabled these disciplines to develop many relatively small, Earth- and moon-orbiting missions that allowed these disciplines to progress, to develop new technologies and instruments, and to foster a substantial body of talented investigators. In the 1980s, Explorer began to depart from its small-and-frequent character and to put its resources into a few larger missions; for example, the X-ray Timing Explorer (XTE) and the Far-Ultraviolet Spectroscopic Explorer (FUSE) each cost in the $200 million range. As the 1990s progressed, however, budget and scientific community pressure mounted for smaller and more frequent missions, forcing a reappraisal of NASA’s general approach to space science missions.

In 1994, the downscoping and restructuring of the FUSE mission signaled the end of the Delta-class Explorers. The new Explorer program consisted of a Mid-class Explorer (MIDEX; capped at $70 million per mission), the existing Small Explorer (SMEX; capped at $35 million per mission), and the University Explorer (UNEX; capped at $5 million). The cap refers to the charge to the Explorer budget line. In March 1995, NASA conducted the first competition for the MIDEX program, with selections made the following spring.

Following this first round of MIDEX selections, NASA’s Office of Space Science requested that the Space Studies Board assess the solicitation and selection process recently concluded in terms of the program’s objectives to optimize science value through a competitive, community-based program of frequent flight opportunities in astronomy and space physics. The Discovery program for solar system exploration was identified as a model for future evolution of the Explorer program. In order to carry out the assessment, which was to consider involvement of the science community, NASA centers, and industry as well as overall scientific effectiveness, the Board established the Panel to Review the Explorer Program. The panel met on September 12–14 to be briefed on the program to date and to evaluate its progress in the terms requested. Following are the findings of the panel and a number of recommendations based on these findings and information provided.

General Finding. The panel believes that most of the perceived problems brought to light after the first MIDEX AO were due to the “dual mode option”2 and the lack of full cost accounting for government contributions. In addition, debriefing of unsuccessful proposal teams was not adequate. While the AO and the selection process both need improvement, and while interaction with the science community also needs to be strengthened, the panel believes that the program is now on the right path and that the new Explorer program should be excellent if properly administered. The perception will probably continue that GSFC and its scientists have an advantage, but the panel is satisfied that the Explorer program management is addressing this issue and that elimination of the recognized flaws will bring about a level playing field for both scientists and industry. Given time and continuing effort, it is the belief of the panel that the astronomy and space physics communities will strongly support the program.

Finding 1. The panel supports use of the “PI mode” by NASA. It brings new vigor to the program at a time when diminishing opportunities could lead to disillusionment amongst the science community. It is an open process that appears to be intrinsically fair. It has exposed a reservoir of ideas for focused science under a cost cap.

Finding 2. The panel believes that the new Explorer program cannot succeed without a high level of support by the science community. In the first (1995) MIDEX solicitation the most readily avoidable errors were failure to consult


“Executive Summary” reprinted from Assessment of Recent Changes in the Explorer Program, National Academy Press, Washington, D.C., 1996, pp. 1–3.


The first MIDEX Announcement of Opportunity (AO), released on March 27, 1995, offered two options for structuring the management approach of a proposal: a more traditional approach in which a flight project would be managed by GSFC, with Principal Investigator (PI) responsibility limited to instrumentation (“NAS A-provided spacecraft mode”), and a Discovery-like approach in which a PI would assume total responsibility for the mission, possibly including delegation of project management functions to industry or to a NASA field center (“PI mode”).

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