Traditional orbit determination during the cruise phase of a deep-space exploration mission relies on Earth-based tracking, using radiometric observations, such as range and Doppler observations. In recent years, ground station networks for deep-space applications, such as the DSN or ESTRACK have been oversubscribed, with demand expected to increase in the future. At the same time, the need for autonomous operations has increased to allow for faster response times to off-nominal events, and remove the human in the loop to reduce costs during operations. In 1999, NASA's Deep Space 1 mission demonstrated autonomous interplanetary navigation using optical images of asteroids taken from the spacecraft, paving the way for autonomous cruise phase operations. With an increasing number of interplanetary missions launched, autonomous cruise phase operations are important to reduce the strain on ground station networks as well as mission costs.

This work explores celestial navigation using optical observations of natural beacons, considering the Emirates Mission to the Asteroid Belt (EMA) as an application scenario. The work is split in two parts: first, the necessary conditions and performance of beacon navigation are assessed using a kinematic approach. In the second part, the performance of the beacon navigation technique is analyzed using a covariance analysis, at the example of the EMA trajectory and camera hardware. The covariance analysis is implemented using a sequential single-arc approach, replicating a weekly operational cycle, and including uncertainty of the low-thrust propulsion system. The sensitivity of the beacon navigation solution is investigated through a parameter analysis of the model parameters, such as the number of observed beacons per tracking window, or the image processing uncertainty. The beacon navigation solution is then compared to the radiometric baseline setup. Lastly, a solution combining radiometric observations and beacon observations is explored.

In the kinematic analysis, a modified beacon selection strategy is proposed, which improves the kinematic position uncertainty by up to 20% at observer locations below 2AU, and up to 10% at observer locations between 2 and 4AU, compared to state-of-the-art strategies proposed in literature. The number of observable beacons is determined based on the camera hardware, and image processing assumptions. When considering the EMA Narrow Angle Camera (NAC), between 80 and 120 asteroid beacons are observable while the spacecraft is within 2.5 AU of the Sun, beyond that, the number of observable asteroid beacons drops to 30. Additionally, the ephemeris uncertainty of the observed beacons is quantified and related to the image processing uncertainty.

The performance of the beacon navigation solution is found to vary depending on the segment of the EMA trajectory. Within the main asteroid belt, the beacon navigation method achieves 3-sigma position formal errors in the range of 100 to 300km, while for trajectory segments outside the main asteroid belt, the position formal errors reach up to 1000km. With the sequential single-arc approach adopted in this work, the beacon navigation solution does not allow improving the co-estimated dynamical parameters (such as radiation pressure and thrust scale factors), which results in a strong influence of the parameter a priori uncertainties on the propagated spacecraft state formal errors. The sensitivity analysis highlights the strong dependency of the obtainable state uncertainty on the image processing performance. In segments outside the main asteroid belt, the radiometric solution yields formal errors smaller by one to two orders of magnitude compared to the beacon navigation solution. Within the main asteroid belt, the beacon navigation performance is improved due to the proximity of the beacons, which provide a practically kinematic position determination and smaller formal errors of up to one order of magnitude compared to the radiometric solution. The combination of radiometric tracking and beacon observables suggests that the required radiometric tracking time could be significantly reduced, while maintaining the same level of formal errors, or potentially even improving it.

The presented work highlights the potential of celestial beacon navigation for deep-space orbit determination. At the example of the EMA mission to the main asteroid belt, beacon navigation yields comparable formal uncertainties to the baseline radiometric tracking setup, given the high dynamical uncertainty during the low-thrust arcs. A beacon-augmented solution could therefore potentially reduce the required ground station tracking time, while maintaining comparable formal uncertainties during the cruise phase.