The on-orbit performance of the Colorado Ultraviolet Transit Experiment (CUTE) Mission

We present the on-orbit performance of the Colorado Ultraviolet Transit Experiment ($CUTE$). $CUTE$ is a 6U CubeSat that launched on September 27th, 2021 and is obtaining near-ultraviolet (NUV, 2480 A – 3306 A) transit spectroscopy of short-period exoplanets. The instrument comprises a 20 cm $\times$ 8 cm rectangular Cassegrain telescope, an NUV spectrograph with a holographically ruled aberration-correcting diffraction grating, and a passively cooled, back-illuminated NUV-optimized CCD detector. The telescope feeds the spectrograph through an 18${}^{\mathrm{\prime }}$ $\times$ 60${}^{\mathrm{\prime }\mathrm{\prime }}$ slit. The spacecraft bus is a Blue Canyon Technologies XB1, which has demonstrated $\le$ 6${}^{\mathrm{\prime }\mathrm{\prime }}$ jitter in 56% of $CUTE$ science exposures. Following spacecraft commissioning, an on-orbit calibration program was executed to characterize the $CUTE$ instrument’s on-orbit performance. The results of this calibration indicate that the effective area of $CUTE$ is $\approx$ 19.0 – 27.5 cm${}^2$ and that the average intrinsic resolution element is 2.9 A across the bandpass. This paper describes the measurement of the science instrument performance parameters as well as the thermal and pointing characteristics of the observatory.