NinjaSat is an X-ray CubeSat designed for agile, long-term continuous observations of bright X-ray sources, with the size of 6U ( 112 . 7 × 237 . 1 × 340 . 5 mm 3 ) and a mass of 8 kg. NinjaSat is capable of pointing at X-ray sources with an accuracy of less than 0 . ◦1 ( 2 σ confidence le v el ) with three-axis attitude control. The satellite bus is a commercially a v ailable NanoAvionics M6P, equipped with two non-imaging gas X-ray detectors co v ering an energy range of 2–50 keV. A total effective area of 32 cm 2 at 6 keV is capable of observing X-ray sources with a flux of approximately 10 −10 erg cm −2 s −1 . The arrival time of each photon can be tagged with a time resolution of 61 μs. The two radiation belt monitors continuously measure the fluxes of protons above 5 MeV and electrons above 200 keV trapped in the geomagnetic field, alerting the X-ray detectors when the flux e x ceeds a threshold. T he NinjaSat project started in 2020. Fabrication of the scientific payloads was completed in 2022 August, and satellite integration and tests were completed in 2023 July. NinjaSat was launched into a Sun-synchronous polar orbit at an altitude of about 530 km on 2023 No v ember 11 b y the SpaceX Transporter-9 mission. After about three months of satellite commissioning and pa yload v erification, w e observed the Crab Nebula on 2024 February 9 and successfully detected the 33.8262 ms pulsation from the neutron st ar. W ith this observation, NinjaSat met the minimum success criterion and stepped f orw ard to scientific observations as initially planned. By the end of 2024 November, w e successfully observ ed 21 X-ra y sources using NinjaSat. T his achie v ement demonstrates that, with careful target selection, we can conduct scientific observations effectively using CubeSats, contributing to time-domain astronomy.
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