The wide field instrument provides the Wide Field imaging and slitless spectroscopic capabilities required to perform the Dark Energy, Exoplanet Microlensing, and NIR surveys while the coronagraph instrument supports the Exoplanet high contrast imaging and spectroscopicy science. The wide field instrument includes filters that provide an imaging mode covering 0.48 — 2.0 μm, and two slitless spectroscopy modes. The spectroscopy modes cover 1.0 — 1.93 μm with resolving power 450-850, and .8-1.8 μm (not yet final) with resolving power of 70-140. The wide field focal plane uses 4k x 4k HgCdTe detectors with 10 μm pixels. The HgCdTe detectors are arranged in a 6x3 array, providing an active area of 0.281 deg2. The instrument provides a sharp point spread function, precision photometry, and stable observations for implementing the Dark Energy, Exoplanet Microlensing, and NIR surveys.
The Coronagraph Instrument (CGI) will be the first instrument on a space telescope to make use of numerically optimized, precision-fabricated coronagraph masks; large-format deformable mirrors for high-order wavefront control; a low-order wavefront sensing and control system; and electron-multiplying CCD (EMCCD) detectors for low-flux photon counting.
In order to execute a compelling demonstration of its critical technologies on astrophysical sources, CGI will have the capability to switch between three observing modes: (i) broadband imaging with a Hybrid Lyot Coronagraph with inner working angle 3 λ/D (150 mas) in a 546—604 nm bandpass; (ii) a Shaped Pupil Coronagraph for spectroscopic imaging with a lenslet-based integral field spectrograph, at spectral resolving power R=50 in a 675—785 nm bandpass; (iii) a Shaped Pupil Coronagraph for broadband imaging of debris disks at separations ranging 6—20 λ/D in a 784—866 nm bandpass. All of these observing modes are designed to reach a flux ratio sensitivity requirement of 5´10-8 including margins and model uncertainty factors. Error budget predictions indicate CGI may reach flux ratio sensitivities down to 5´10-10 in imaging (100 hr, V=5), and 4´10-9 in spectroscopy (400 hr, V=5).
WFIRST will be at the L2 Sun-Earth orbit, about 1 million miles from Earth. The gravitational forces between the sun and Earth at this point are equal, allowing for a stable satellite orbit.
The WFIRST Design Reference Mission (DRM) uses existing 2.4-meter telescope hardware, along with heritage instrument, spacecraft, and ground system architectures and hardware to meet the WFIRST science requirements. The current WFIRST observatory will be flying at the second Sun-Earth Lagrange point (SEL2). The orbit isn't a Halo, as it doesn't pass through the exact same points every 6 months. It is evolving and opening in a quasi-periodic fashion, and hence is called a Quasi-Halo.