by the joint DOE/NASA design team on the Joint Dark Energy Mission—specifically the JDEM-Omega concept—and expands its scientific reach. WFIRST is based on mature technologies with technical risk that is medium low and has medium cost and schedule risk. The independent cost appraisal is $1.6 billion, not including the guest investigator program. As a telescope capable of imaging a large area of the sky, WFIRST will complement the targeted infrared observations of the James Webb Space Telescope. The small field of view of JWST would render it incapable of carrying out the prime WFIRST program of dark energy and exoplanet studies, even if it were used exclusively for this task. The recommended schedule has a launch data of 2020 with a 5-year baseline mission. An extended 10-year mission could improve the statistical results and further broaden the science program. The European Space Agency (ESA) is considering an M-class proposal, called Euclid, with related goals. Collaboration on a combined mission with the United States playing a leading role should be considered so long as the committee’s recommended science program is preserved and overall cost savings result.
WFIRST addresses fundamental and pressing scientific questions and will contribute to a broad range of astrophysics. It complements the committee’s proposed ground-based program in two key science areas: dark energy science and the study of exoplanets. It is a part of coordinated and synergistic programs in fields in which the United States has pioneered the progress to date. It presents opportunities for interagency and perhaps international collaboration that would tap complementary experience and skills. It also presents relatively low technical and cost risk, making its completion feasible within the decade, even in a constrained budgetary environment. For all these reasons it is the committee’s top-priority recommendation for a space mission.
The Explorer program supports small and medium-size missions, selected through competitive peer review, that are developed and launched on roughly 5-year timescales. The Explorer program enables rapid responses to new discoveries and provides platforms for targeted investigations essential to the breadth of NASA’s astrophysics program. Explorers have delivered a scientific return on investment at the highest level over the past two decades. The three astrophysics Medium-scale Explorer (MIDEX) missions launched to date—the Wilkinson Microwave Anisotropy Probe (WMAP), Swift, and the Wide-Field Infrared Survey Explorer (WISE)—have provided high-impact science for a combined cost significantly less than that of a single flagship mission.4 WMAP, launched just 5 years after the