  PolarLight is a compact soft X-ray polarimeter onboard a CubeSat, which was
launched into a low-Earth orbit on October 29, 2018. In March 2019, PolarLight
started full operation, and since then, regular observations with the Crab
nebula, Sco X-1, and background regions have been conducted. Here we report the
operation, calibration, and performance of PolarLight in the orbit. Based on
these, we discuss how one can run a low-cost, shared CubeSat for space
astronomy, and how CubeSats can play a role in modern space astronomy for
technical demonstration, science observations, and student training.
