NinjaSat: Astronomical X-ray CubeSat Observatory

Abstract

NinjaSat is a 6U X-ray CubeSat that was funded at RIKEN in April 2020 and launched into a 530-km Sun-synchronous orbit on November 11, 2023. The mission is dedicated to pointed observations of X-ray sources, aiming to monitor newly emerging bright X-ray transients as well as conduct long-term observations of known objects. The satellite carries two non-imaging gas proportional counters (Gas Multiplier Counters; GMCs) with a total effective area of 32 cm^2 at 6 keV, providing photon-event time tags with a resolution of 61 microseconds. To monitor the space radiation environment, NinjaSat is also equipped with two Si-PIN radiation belt monitors (RBMs). [Ref.1]

Scientific operations began on February 23, 2024, and continued until re-entry on September 18, 2025, during which NinjaSat successfully observed 32 X-ray targets. In this talk, I will describe the mission design, instrumentation, operations, and scientific results obtained with NinjaSat. In addition to its primary astronomical objectives, NinjaSat produced valuable byproducts, including demonstrations of X-ray pulsar navigation and atmospheric density measurements. I will also introduce the follow-up mission, NinjaSat2, currently planned for launch in 2028.

[Ref. 1] https://doi.org/10.1093/pasj/psaf014