The WFIRST Observatory uses an existing 2.4m AFTA (Astrophysics-Focused Telescope Assets) telescope, donated to NASA by another agency. The design reference mission described in the Final Report of the WFIRST-AFTA Science Definition Team has two instruments to execute the mission science program:
A high-latitude WFI galaxy survey (HLS) will be performed, taking a total of up to 2 years of observations. The HLS will cover over 2,200 square degrees with imaging and low-resolution (grism) spectroscopy. The imaging, in four NIR bands (Y, J, H, and F184), will reach J=26.7 AB for point sources. The spectroscopy will measure redshifts for over 15 million sources at redshift 1.1 to 2.8. Imaging and spectroscopy will support dark energy weak lensing and baryon acoustic oscillation measurements, respectively, and form an invaluable survey for Archival Guest Investigator studies of General Astrophysics topics.
A three-tiered WFI supernova survey will perform both imaging and IFC spectroscopy, taking a total of approximately 0.6 years. The imaging survey is designed in three tiers, shallow, medium, and deep, to find supernovae at redshift < 0.4, < 0.8, and < 1.7, respectively. The three tiers will cover approximately 27, 9, and 5 square degrees, respectively, with observations repeated with a cadence of 5 days, in filters Y and J for the shallow tier, and J and H for the medium and deep tier. IFC spectrophotometric observations will be used to fully characterize the type and light curve of a subset of 2700 supernovae, chosen to sample the full redshift range. These survey data will also be useful for Archival Guest Investigator studies of General Astrophysics topics.
A WFI microlensing survey of the Milky Way Bulge will be performed with the WFI, taking a total of approximately 1 year. Ten fields will be imaged every 15 minutes over contiguous 72-day periods ("seasons"), to create highly-sampled light curves of 56 million stars brighter than H=21.6 (AB). Six such seasons will be executed over the mission lifetime, resulting in the expected discovery of over 2000 bound planets in the range 0.1-1000 Earth masses and orbital major axes from 0.03 to 30 AU through their microlensing signature. About 20,000 giant planets in short-period orbits will be detected from their transit signature. These survey data will also be useful for Archival Guest Investigator studies of General Astrophysics topics.
A coronagraphic observing program will be performed as part of the Technology Demonstration. Initial observations will focus on discovery and characterization of planets around pre-selected target stars. When a previously known or unknown planet is detected, additional observations will be made for longer time periods, with full spectral resolution for planet characterization. Dozens of planets will be targeted in this manner.
A WFI GO program will also be implemented during the 5-year baseline mission. Observations covering all areas of astrophysics will be competitively selected through peer review, in the same spirit as for other NASA Great Observatories. Also, the CGI will have a Participating Scientist Program upon successful completion of the Technology Demonstration.