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Recommendations for New Space Activities—Large Projects
Priority 1 (Large, Space) Wide Field Infrared Survey Telescope (WFIRST)
WFIRST 13 is a wide-field-of-view near-infrared imaging and low-resolution spectroscopy
observatory that will tackle two of the most fundamental questions in astrophysics: Why is the expansion
rate of the universe accelerating And are there other solar systems like ours, with worlds like Earth In
addition, WFIRST’s surveys will address issues central to understanding how galaxies, stars, and black
holes evolve. WFIRST will carry out a powerful extrasolar planet search by monitoring a large sample of
stars in the central bulge of the Milky Way for small deviations in brightness due to microlensing by
intervening solar systems. This census, combined with that made by the Kepler mission, will determine
how common Earth-like planets are over a wide range of orbital parameters. To measure the properties of
dark energy, WFIRST will employ three different techniques: it will image about 2 billion galaxies and
carry out a detailed study of weak lensing that will provide distance and rate-of-growth information; it
will measure spectra of about 200 million galaxies in order to monitor distances and expansion rate using
baryon acoustic oscillations; and finally, it will detect about 2,000 distant supernova explosions, which
can be used to measure distances. WFIRST provides the space-unique measurements that, combined with
those from LSST (the committee’s highest-priority ground-based project), are essential to advance
understanding of the cause of cosmic acceleration. In addition, WFIRST will survey large areas of sky to
address a broad range of Astro2010 science questions ranging from understanding the assembly of
galaxies to the structure of the Milky Way. WFIRST will also offer a guest investigator program
supporting both key projects and archival studies to address a broad range of astrophysical research
topics.
WFIRST is a 1.5-meter telescope that will orbit the second Lagrange point (L2), 1.5 million km
from Earth. It will image the sky at near-infrared wavelengths and perform low-resolution infrared
spectroscopy. The spacecraft hardware that was used as a template for studying WFIRST was one of the
two JDEM proposals that were submitted to the committee—the JDEM-Omega proposal (Figure 7.3).
This was used as a basis for the cost and technical evaluation assessment. Undoubtedly, design
improvements are possible, but its capabilities are essentially identical to those envisaged for WFIRST.
In a 5-year baseline mission, its observations would emphasize the planet census and dark-energy
measurements, while accommodating a competed general investigator program for additional surveys that
would exploit WFIRST’s unique capabilities using the same observation modes. The powerful
astronomical survey data collected during all of the large-area surveys would be utilized to address a
broader range of science through a funded investigator program. An extended mission, subject to the
usual senior review process, could both improve the statistical results for the main science drivers and
broaden the general investigator program.
The independent cost and readiness assessment found that WFIRST is based on mature
technologies and has relatively low technological risk. The three primary challenges identified—
achieving the image quality over the focal plane necessary for the weak lensing study, providing adequate
telemetry bandwidth from L2, and designing a focal plane that would jointly optimize the exoplanet and
dark energy science—do not present high risk. At the 70 percent confidence level the appraised cost is
$1.6 billion, with a time from project start to launch of 82 months. The enhanced observing plan relative
to JDEM, to include both microlensed planet and dark energy surveys, is not expected to be a serious cost
or schedule driver. The additional cost of a guest investigator program was not included in the cost and
risk assessment. The committee considers the general investigator program to be an essential element of
13 Adopted by the committee, the name WFIRST was suggested by the Electromagnetic Observations from
Space (EOS) Program Prioritization Panel when the panel recognized a compelling opportunity in three separate
inputs to Astro2010 (JDEM-Omega, the Microlensing Planet Finder, and the The Near-Infrared Sky Surveyor )
which, together, form the highest-priority activity.
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