12-04, 11:20–11:40 (Europe/Luxembourg), Banquet Room
Background
Interstellar spacecraft need to know their position and velocity at various points in their mission in order to make course corrections, and to switch on/off propulsion, instruments, or communications. Given their large distances from Earth, spacecraft must be able to navigate autonomously.
Objective
I develop a model to determine the 3D position and 3D velocity of a spacecraft using measurements of the angular separations of stars.
Methods
The Gaia survey has provided accurate stellar positions and velocities relative to the solar system barycentre (SSB). A spacecraft at some other arbitrary position and velocity can observe the same stars, but at different angular positions due to parallax, aberration, and proper motion. This can be inverted: By measuring the relative angular positions of the stars, the 3D position and 3D velocity of the spacecraft relative to the SSB can be inferred, here using a Monte Carlo approach. The model requires measurements of only the angular separations between pairs of stars (no absolute measurements), as done historically with a sextant. The model takes into account special relativity and light travel time. An accurate onboard clock is not required as the approximate SSB time is also inferred. Stellar radial velocity measurements may be used in addition or instead to achieve similar results. I demonstrate the performance using simulated spacecraft data together with real astrometric data.
Results
Using 20 bright, nearby stars and assuming an angular measurement accuracy of 10 mas, the position of a spacecraft can be determined to within 0.03 au and its velocity to 20 m/s. The accuracy improves linearly with the accuracy of the angular separation measurements. Increasing the number of stars or taking multiple measurements over time improves the determination further.
Conclusions
While not as accurate as pulsar navigation in the solar vicinity, the astrometric method works in deep space many parsecs from the Sun, where pulsar navigation would also have to accommodate parallaxes. Astrometric navigation can also be used for initialization, combined with pulsar navigation, or used as a backup system.
This work builds on that published by the author in PASP 133:074502 (2021).
Coryn Bailer-Jones is a staff scientist and group leader at the Max Planck Institute for Astronomy in Heidelberg. He works on machine learning and statistical data analysis methods for inference in large astronomical data sets, and leads a group working on the development and application of these for the ESA Gaia mission. He also teaches physics, astronomy, and statistics at Heidelberg University. His interests include, among other things, exoplanets, nearby stars, the impact of astronomical phenomena on the Earth, and the physics of interstellar travel.