In-orbit demonstration of X-ray pulsar navigation with NinjaSat

We demonstrate the pulsar navigation capability of a CubeSat X-ray observatory, NinjaSat, equipped with two sets of gas multiplier counters (GMCs). GMCs are sensitive to the 2 to 50 keV band with an effective area of 16 cm2 per module at 6 keV. We verified the timing accuracy by observing Crab Pulsar and confirmed that a stable timing measurement performance is stable within 100 μs. To demonstrate the pulsar navigation, we applied a method that optimizes orbital parameters to maximize the significance of the pulse profile of X-rays from a pulsar using “Significance Enhancement of Pulse-profile with Orbit-dynamics (SEPO).” We observed Crab Pulsar with an exposure time of ∼100 ks at different epochs and analyzed the data downlinked to the ground. By comparing the optimized orbit with the satellite position derived from Global Positioning System data, we quantitatively evaluated the pulsar navigation performance. The results showed that the position component along the Crab line of sight was consistently constrained within ∼40 km, and the range of three-dimensional error varied between 27 and 370 km depending on the observation epoch. We demonstrate the feasibility of applying a CubeSat-class X-ray observatory to pulsar navigation and also provide the first experimental verification that the accuracy of the SEPO method depends on the seasonal geometry between the orbital plane and the pulsar direction.