5.7 Report Series: Committee on Astronomy and Astrophysics: Small Explorer Missions
A Report of the SSB ad hoc Committee on Astronomy and Astrophysics
Introduction
The 2010 astronomy and astrophysics decadal survey, New Worlds, New Horizons in Astronomy and Astrophysics (hereafter NWNH),1 laid out an exciting portfolio of recommended activities to guide the agencies’ research programs over the period 2012-2021. The newly constituted Committee on Astronomy and Astrophysics (CAA) is tasked with monitoring the progress of the survey’s recommended priorities.
The CAA met in conjunction with Space Science Week 2017 in Washington, D.C., on March 28-30, 2017. This was the first meeting at which the CAA could produce a report, and in advance of that meeting, the CAA received a question from NASA about an upcoming Small Explorer (SMEX) mission call.2,3 In response, the National Academies of Sciences, Engineering, and Medicine issued a charge to the committee, which is given in Appendix A. The primary task to the CAA in the charge is for the CAA to “write a brief report addressing whether there may or may not be sufficient compelling science motivations for a SMEX-sized mission to justify a SMEX Announcement of Opportunity (AO) in 2018 or 2019 (as is currently planned).” The CAA was also asked to “comment on the potential impact of any change to the planned 2018/19 SMEX AO on the NWNH-recommended program.” The 2018/19 SMEX AO will be for the astrophysics program.
The CAA decided to solicit community input (see Appendix B) via the American Astronomical Society and through direct e-mail to former and current SMEX principal investigators (PIs). Responses received from the community are compiled in Appendix C. The CAA also requested from NASA statistical and other information about the SMEX program’s history, and NASA’s response is also included in Appendix C.
Astronomy is a vibrant and dynamic field, and enabling a range of “unscripted” opportunities for discovery, alongside multi-decade strategic planning, has proven to be a remarkably productive methodology. The CAA reiterates the points made in NWNH about SMEXs:
NWNH, p. 18:
Small Explorer (SMEX) missions, as well as Mission of Opportunity contributions to non-NASA missions, have made essential advances in understanding of phenomena ranging from the explosive release of energy in flares on the Sun (with the Reuven Ramaty High Energy Solar Spectroscopic Imager) to the assembly of galaxies (with the Galaxy Evolution Explorer). The promise of future Explorer missions is as great as ever, and this program will be essential to enabling new opportunities, and to maintaining breadth and vibrancy in NASA’s astrophysics portfolio in a time of budgetary stress.
NWNH, p. 150:
The GALEX Small Explorer (SMEX) ultraviolet mission is changing our understanding of how stars formed and how galaxies evolved over the past 10 billion years of cosmic history, and it is now supporting an active guest investigator program.
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NOTE: “Introduction” reprinted from Report Series: Committee on Astronomy and Astrophysics: Small Explorer Missions, The National Academies Press, Washington, D.C., 2017, p. 1.
1 National Research Council, New Worlds, New Horizons in Astronomy and Astrophysics, The National Academies Press, Washington, D.C., 2010.
2 A SMEX mission is currently defined by two constraints: (1) a cost cap, which was $125 million in the 2014 AO, and (2) the launch capability, which at present is Pegasus-class.
3 Small Explorer (SMEX) missions are part of the Explorers program, which serves both the NASA astrophysics and heliophysics research programs.
NWNH, p. 208:
Priority 2 (Large, Space). Explorer Program
The Explorer program’s Small Explorer (SMEX) and Medium-scale Explorer (MIDEX) missions, developed and launched on few-year timescales, enable rapid response to new discoveries and provide platforms for targeted investigations essential to the breadth of NASA’s astrophysics program. From the WMAP MIDEX measurements of the age and content of the universe accomplished through its mapping of the cosmic microwave background (see Figures 2.4 and 2.5 in Chapter 2), to the GALEX SMEX contributions to understanding of the evolution of galaxies, Explorers are on the forefront of scientific discovery (Figure 7.4). With multiple missions launched per decade for a cost substantially less than that of a single flagship mission, the Explorer program is unique in the world for its versatility and scientific return for the investment. The Explorer program also offers highly leveraged Missions of Opportunity (MoOs), which enable U.S. scientists to make scientific and hardware contributions to non-NASA missions, and which provide a mechanism to develop large suborbital experiments. The frequent opportunity to deploy SMEX (currently $160 million) and MIDEX (currently $300 million) experiments on timescales significantly less than a decade has enabled the United States to seize scientific opportunities, exploit new technologies and techniques, and involve university groups, including students and postdoctoral scholars, in significant development roles.
The Midterm Assessment Report recommended the following:
NASA’s Astrophysics Division should execute its current plan, as presented to the committee, of at least four Explorer Announcements of Opportunity during the 2012-2021 decade, each with a Mission of Opportunity call, and each followed by mission selection.4
This plan included the SMEX round that is the subject of this report.
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4 National Academies of Sciences, Engineering, and Medicine, New Worlds, New Horizons: A Midterm Assessment, The National Academies Press, Washington, D.C., 2016, p. 10.
