The CASTOR mission

CASTOR is a proposed wide-field ( 30 ′ × 30 ′ = 0.25 deg ² ), high-resolution ( FWHM ∼ 0.15 ′′ ), 1-m-diameter space telescope that is under development by the Canadian Space Agency and the National Research Council of Canada. Optimized for UV/blue-optical wavelengths, the telescope uses dichroics to enable imaging in three channels (and up to five bands) that cover the 0.15 to 0.55 μ m spectral region, simultaneously. CASTOR will also feature low- and low-medium-resolution spectroscopic capabilities through the use of a deployable grism for low-resolution ( R ≲ 420 ) slit-less spectroscopy in its UV and u channels, and low-medium-resolution R ∼ 1400 multi-object spectroscopy in a parallel field using a digital micro-mirror device. High-speed, precision photometry will be possible using dedicated CMOS detectors in each of its three channels. We present an overview of the mission, including the optical design, instruments and detectors, payload layout, satellite bus, orbit, and ground segment. We describe the mission’s scientific capabilities and expected place within the astronomical landscape in the 2030s. The 5-year lifetime is baselined on a combination of legacy surveys, guest observer programs, and target-of-opportunity science. We summarize scientific plans for the mission in each of eight fields: cosmology, time domain and multi-messenger science, active galactic nuclei, galaxies, near-field cosmology, stellar astrophysics, exoplanets, and solar system studies. We conclude by describing ongoing development efforts, highlighting areas of particular relevance for NASA’s Habitable Worlds Observatory.