Autonomous Orbit Determination

Autonomous Orbit Determination (AOD) is the process by which a spacecraft independently computes its own orbital state vector - position r(t), velocity v(t), and optionally attitude q(t) - without receiving tracking data from ground stations, GPS satellites, or any external infrastructure.

Traditional orbit determination relies on NASA's Deep Space Network (DSN), NORAD's Space Surveillance Network, or the European Space Operations Centre (ESOC) to measure range, range-rate (Doppler), and angular position of spacecraft from ground-based antennas. These measurements are processed in ground-based orbit determination software (e.g., GMAT, STK) and the resulting ephemeris is uploaded to the spacecraft. This architecture creates a hard dependency on ground communication - a bottleneck that limits constellation size, mission autonomy, and operations in denied environments.

Kepler Nav's approach to autonomous orbit determination uses the UNIF-PNT algorithm framework, which fuses three independent measurement sources onboard the spacecraft:

1. Signals of Opportunity (SOOP): Doppler and phase-curvature measurements from LEO communication satellites provide Earth-relative positioning.

2. Photonic Star Tracking: Optical measurements of stellar positions provide inertial attitude and coarse position via stellar aberration.

3. X-Ray Pulsar Timing (XNAV): Millisecond pulsar timing provides solar-system-barycentric position fixes for deep space operations.

These measurements feed into the Lie Group manifold navigation filter on the SE₂(3) manifold, which has been mathematically proven to achieve full observability (rank(O) = 6) - meaning the complete orbital state is recoverable from ambient measurements alone, with no ground input required.