On-Orbit Performance & Operation of the Attitude & Pointing Control Subsystems on ASTERIA

The Arcsecond Space Telescope Enabling Research in Astrophysics (ASTERIA) is a 6U CubeSat that was deployed from the International Space Station on 20 November 2017. The underlying goal of the mission is to image and perform photometry on bright, nearby stars and possibly detect transiting exoplanets orbiting these stars. As a technology demonstration with an eye to enable this science, the payload must be pointed with a stability of 5 arcseconds RMS over 20-minute observations and a repeatability of 1 arcsecond RMS across multiple observations. A two-stage control system was employed to achieve these pointing requirements: reaction wheels control the attitude of the spacecraft bus while a piezo stage translates the focal plane array to control the pointing of the payload. This paper will present on-orbit results that demonstrate a pointing stability of 0.5 arcsecond RMS over 20 minutes and a pointing repeatability of 1 milliarcsecond RMS from observation to observation, the best pointing of a CubeSat to date. In addition, this paper will discuss the pointing achieved by the attitude control subsystem alone, pointing issues due to temporarily bright pixels, hot pixels, and reaction wheel speed reversals or zero crossings, the deployment and Sun acquisition phase, momentum management issues arising from a large residual dipole, and some of the anomalies encountered with the attitude control subsystem.