The WFIRST CGI Integral Field Spectrograph: Requirements and Performance Predictions

The WFIRST coronagraphic instrument (CGI) will
demonstrate exoplanet spectroscopy using an integral field spectrograph
(IFS). The CGI IFS, being designed and built at
Goddard Space Flight Center, has a spectral resolution of R50
and is designed to accommodate a 20% bandpass spanning 600-
970 nm. The IFS is principally targeting the abundance of
Methane features, with the primary coronagraph band being
centered around 770nm. Key to the performance estimates
are the achievable signal-to-noise (SNR) ratios and the stability
of the microspectra over the course of tens and hundreds of
hours. As a technology demonstration for CGI, the ability to
close a wavefront control loop around the IFS, maintain a stable
dark hole, and provide time resolved data that simultaneously
spans spatial and spectral dimensions are crucial demonstrations
for future observatories. The IFS is optimized both for
coronagraphs and science observations with a potential future
starshade. We highlight how the long duration observations,
and requirements for both starshades and coronagraphs drive
the IFS requirements and the calibrations required both onorbit
and on the ground. We also provide further detail on
the optomechanical design, its stability based on thermal and
structural predictions, anticipated performance, and operations
concept of the CGI IFS. The impact of these performance metrics
are projected into simulated data products, demonstrating
cube extraction of noisy images and the subsequent planet spectrum
that can be extracted from them. These demonstrations
and performance predictions are key to future missions such
as LUVOIR and HabEx, whose principal science case relies on
efficient spectroscopy of exoplanets.