Autonomous Initial Orbit Determination Using Sequential Range-Rate Measurements

We introduce an initial orbit determination technique that uses only sequential range-rate measurements along fixed lines of sight and time between measurements. Compared to existing velocity-based initial orbit determination methods which impose additional requirements such as concurrent observations, our method may reduce the number of sensors required for a spacecraft to perform autonomous, or onboard, initial orbit determination. The measurements required may be obtained by a single range-rate sensor, such as an X-ray detector observing X-ray pulsars, and an onboard clock. The accuracy of our algorithm is compared with existing techniques for a variety of orbits. Orbit determination errors, in terms of estimated position, are characterized with Monte Carlo simulation techniques. Results indicate that our method achieves better performance compared to an initial orbit determination method utilizing velocity vectors and time of flight. The position error of our technique increases for lower velocities and shorter measurement times, which is consistent with existing velocity-based initial orbit determination methods.