Spacecraft Navigation around Small Bodies in Early-Characterisation Phases

Spacecraft Navigation around Small Bodies in Early-Characterisation Phases

Moreno Villa, Víctor (TU Delft Aerospace Engineering)

Mooij, E. (mentor)

Delft University of Technology

Aerospace Engineering

2018-04-06

Asteroid exploration is a new booming field for planetary sciences and space engineering. This navigation study deals with the first characterisation of the binary asteroid system, Didymos, for ESA's AIM mission. In particular, it tackles the estimation of its highly-uncertain environment and the scale-factor indetermination problem.

Previous asteroid missions, such as NEAR-Shoemaker and Hayabusa, solved the scale-factor indetermination using ranging instruments while Rosetta combined simultaneous optical navigation and radiometry to solve for it. However, the imposed low-budget character of AIM makes both of these solutions impracticable; radiometry is only gathered when SC-ground communications are established while the fixed navigation camera and the non-steerable high-gain antenna (HGA) prevent the possibility of simultaneous optical and radiometric data. New navigation strategies are studied to effectively solve the proposed problem without incurring into higher operational costs that outweigh the initial system savings.

A GNC simulator was designed to test the behaviour of orbit determination (OD) methods used at ground control centres involving high-precision filtering techniques and realistic measurements models developed on projects for ESA, including a landmark matching model for image processing. Compromise navigation strategies were found, where the OD is first carried out by the sole use of radiometric measurements. These carry information on distances, although referenced to Earth, whereas optical measurements only provide angular information. Then, landmark matching navigation techniques are incorporated to refine the orbit solution and obtain the most precise characterisation of the system, including the landmarks position knowledge.

Results show a difference in magnitude between the along and cross-track directions and the radial direction, caused by the lack of information along the line-of-sight of the optical measurements, which cannot be removed, A weak correlation was found for the relative position of the Earth and the Sun, implying a good level of independence on the simulated scenario's epoch. Manoeuvre execution errors were found to directly drive the performance of the GNC. The inclusion of either a steerable HGA or an altimeter is seen to improve equally the navigation performance.

Taking into account all these considerations, a final navigation strategy that tackles both operational constraints and mission design is proposed. These recommendations and analyses can serve as a starting point for any further asteroid-navigation assessments, in particular, for the newly proposed HERA mission.

http://resolver.tudelft.nl/uuid:e3ab8a21-9404-4ff4-ab39-07f84c96ab45

Student theses

master thesis

© 2018 Víctor Moreno Villa