In-orbit Demonstration of X-ray Pulsar Navigation with NinjaSat

TL;DR

This paper demonstrates the feasibility of using a CubeSat-based X-ray observatory for pulsar navigation, achieving position accuracy within a few hundred kilometers through the SEPO method and Crab Pulsar observations.

Contribution

First experimental verification of pulsar navigation using a CubeSat X-ray observatory with the SEPO method, showing practical navigation accuracy.

Findings

Position constrained within ~40 km along Crab line of sight

3D position error ranged from 27 to 370 km

Navigation accuracy depends on seasonal geometry

Abstract

This study demonstrated the pulsar navigation capability of the CubeSat X-ray observatory NinjaSat, which is equipped with two Gas Multiplier Counters (GMCs). The GMCs are sensitive to the 2-50 keV energy band and have an effective area of 16 cm^2 per module at 6 keV. We verified the timing accuracy by observing the Crab Pulsar and confirmed stable timing performance within 100 microseconds. To demonstrate pulsar navigation, we applied a method that optimizes orbital parameters to maximize the significance of the pulsar X-ray pulse profile, known as the Significance Enhancement of Pulse-profile with Orbit-dynamics (SEPO) method. We observed the Crab Pulsar with a total exposure of approximately 100 ks at different epochs and analyzed the data transmitted to the ground. By comparing the optimized orbit with the satellite position derived from Global Positioning System data, we quantitatively evaluated the navigation performance. The results show that the position component along the Crab line of sight was consistently constrained within approximately 40 km, and the three-dimensional position error ranged from 27 to 370 km depending on the observation epoch. These results demonstrate the feasibility of applying a CubeSat-class X-ray observatory to pulsar navigation and 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.