Recent interest in sending humans to the moon, Mars, or other destinations beyond low Earth orbit has created an increased need for autonomous spacecraft navigation. Because traditional navigation ...

Optical Navigation Using Planet’s Centroid and Apparent Diameter in Image

This study introduces novel algorithms and the underlying mathematics to process photographs of planetary illuminated bodies and use them for navigation purposes. The goal is to accurately estimate the observer-to-body relative position in inertial coordinates. The main motivation is to provide autonomous navigation capabilities to spacecrafts by observing a planet or a moon. This is needed, for example, in human-rated vehicles in order to provide navigation capabilities in a loss-of-communications scenario. The algorithm is derived for the general case of a triaxial ellipsoid that is observed bounded by an elliptical cone. The orientation of the elliptical cone reference frame is obtained by eigenanalysis, and the offset between the elliptical cone axis and the body center direction as well as the equation of the terminator are quantified. The main contribution of this paper is in the image-processing approach adopted to derive centroid and distance to the body. This is done by selecting a set of pixels ...

Image Processing of Illuminated Ellipsoid

Optical navigation techniques were required to successfully complete the planetary exploration phase of the NASA deep-space Voyager mission. The last of Voyager's planetary encounters, with Neptune, posed unique problems from an optical navigation standpoint. In this paper we briefly review general aspects of the optical navigation process as practiced during the Voyager mission, and discuss in detail particular features of the Neptune encounter which affected optical navigation. New approaches to the centerfinding problem were developed for both stars and extended bodies, and these are described. Results of the optical navigation data analysis are presented, as well as a description of the optical orbit determination system and results of its use during encounter. Partially as a result of the optical navigation processing, results of scientific significance were obtained. These results include the discovery and orbit determination of several new satellites of Neptune and the determination of the size of Triton, Neptune's largest moon.

Optical navigation during the Voyager Neptune encounter

Stardust is a mission to fly by Comet Wild-2 in early 2004 and return samples of the coma to Earth. During its 120-150 km flyby of the comet nucleus, a secondary science goal is to obtain images of the nucleus using the onboard navigation camera. Due to the 40 minute round-trip light time, ground processing of navigation data to update pointing information to maintain the nucleus in the camera field-of-view is impractical. Thus, a simple, reliable, and fast algorithm was developed to close the navigation loop onboard during encounter. The algorithm uses images of the nucleus during approach to update target relative state information. This involves centroiding on the image to obtain nucleus center-of-figure data and then processing the data through a Kalman filter to update the spacecraft, position and attitude. Monte Carlo simulations were then performed to test the algorithm. These simulations incorporated errors in spacecraft initial position and in attitude knowledge to provide a "truth" model which the filter must recover from. The results of the simulations proved that the algorithm was successful in maintaining the nucleus in the camera field-of-view assuming nominal values for the error sources. Even with worst case errors, the algorithm performed successfully in over 90% of the cases.

Autonomous nucleus tracking for comet/asteroid encounters: the Stardust example

Future space exploration missions require increased autonomy. This is especially true for navigation, where continued reliance on Earth-based resources is often a limiting factor in mission design and selection. In response to the need for autonomous navigation, this work introduces the StarNAV framework that may allow a spacecraft to autonomously navigate anywhere in the Solar System (or beyond) using only passive observations of naturally occurring starlight. Relativistic perturbations in the wavelength and direction of observed stars may be used to infer spacecraft velocity which, in turn, may be used for navigation. This work develops the mathematics governing such an approach and explores its efficacy for autonomous navigation. Measurement of stellar spectral shift due to the relativistic Doppler effect is found to be ineffective in practice. Instead, measurement of the change in inter-star angle due to stellar aberration appears to be the most promising technique for navigation by the relativistic perturbation of starlight.

https://www.mdpi.com/1424-8220/19/19/4064/pdf

StarNAV: Autonomous Optical Navigation of a Spacecraft by the Relativistic Perturbation of Starlight.

Optical observations were necessary during the Voyager II Uranus approach and encounter in order to meet mission navigational requirements. In this paper, the overall optical navigation system and operation at Uranus are outlined. The formulation of the optical observables are presented, as well as their subsequent integration into the overall orbit determination products. Optical data analysis and some resulting orbit determination results from Uranus are shown. Certain scientifically important results were natural outcomes of the optical data analysis, and these are also reviewed. Finally, certain optical navigation related problems are anticipated at the forthcoming Neptune encounter in 1989; these are briefly discussed as are plans to deal with them.

A. J. Donegan

Papers

Interplanetary optical navigation - Voyager Uranus encounter