Jesse Greaves, University of Colorado Boulder; Daniel Scheeres, University of Colorado Boulder
Keywords: autonomous guidance navigation control optical sensor information gathering
Abstract:
Space domain awareness (SDA) is becoming increasingly difficult due to the exponential growth of resident space objects. The increasing demand for SDA warrants the investigation of autonomous observation platforms which can track objects without intervention. One such platform would be an optical space-based observer which can provide spacecraft-to-spacecraft absolute tracking (SSAT). Employing SSAT allows the observer to estimate its own state simultaneously with the target state, hence enabling a fully autonomous system, but requires non-linearity in the relative dynamics which can challenge estimation algorithms. Equipping the observer with an optical sensor enables cooperative and non-cooperative tracking alike but lacks immediate range information in an already challenging problem. To ensure accurate tracking, maneuvers can be employed to gather information. Therefore, this paper will develop an autonomous guidance algorithm which optimally improves state estimation of the system using a method which can be easily calculated onboard a flight computer.
Space Domain Awareness (SDA) is necessary to ensure universal security and performance of space born systems. Without adequate observational resources, conjunction events and navigation errors become plausible sources of mission failure. The need for an enhanced observational capacity to meet the current SDA demand is becoming increasingly evident due to the expanding deployment of space systems which are overburdening traditional ground-based assets. To guarantee the continued safe use of space, observational capabilities must be able to manage the growth in resident space objects, which warrants the investigation of novel observation platforms.
One promising approach to augment observational abilities is through the development of space-based observation platforms for SSAT. Space-based platforms are significantly more versatile compared to their ground-based counterparts and avoid limitations such as stagnant viewing geometries, atmospheric occlusion, and an inability to easily change observation locations. Removing these limitations is particularly pertinent for spacecraft wandering further from Earths sphere of influence, such as cislunar missions which are receiving considerable attention due to various international programs aimed at inhabiting lunar space. The methodology of SSAT enables simultaneous state estimation of the observer and target which facilitates fully autonomous tracking so that it does not require costly or timely operator intervention. The primary drawback to this approach is that it relies heavily on non-linearities in the dynamics of the system to obtain information on the entire state, which can prove challenging for conventional filters. Overall, SSAT has the potential to robustly bolster observational competency to handle the expected growth of resident space objects in the foreseeable future.
To maximize the benefit of a space-based observation platform, the observer should be able to measure cooperative and non-cooperative targets. Measurements of this type are an essential tool for an SDA asset since tracking space debris or other non-communicative bodies is a vital objective. One such sensor that can achieve this is an optical sensor. Optical sensors are ideal for SDA because they are cheap, readily available, have an abundance of supportive literature, and do not require cooperation. The major associated drawbacks with optics are limited range/range-rate information and lighting constraints.
The limited range information associated with optical sensors, in combination with the challenges associated with SSAT, provides motivation to increase information gain. Increasing information would reduce state uncertainty and improve filter performance. Fortunately, state information can be gained through the application of properly designed maneuvers which set up relative dynamics conducive to increasing information content. This motivates the primary objective of this work which is to design an autonomous guidance algorithm to improve observational abilities for SSAT assuming optical sensors.
This paper has two supporting sets of literature. First, the SSAT background proves that relative measurements can generate absolute state estimates for multiple spacecraft. The SSAT literature dates back to F. Markley in 1984 who proved this was possible in Earth orbit if the spacecraft do not have period matched orbits with identical eccentricity and phasing [1]. K. Hill expanded this work by showing it was also possible to do SSAT in cislunar space with simple range measurements [2]. More recent work has shown that the inclusion of perturbations and additional non-linearities only helps to enhance the state estimation [3], and that optical sensors are equivalently capable sensors for SSAT [4].
The second set of backing literature is dual control, or maneuvers to enhance state estimation. There are a variety of guidance algorithms designed to optimize range information for spacecraft which are performing proximity operations [5-7]. Many of these algorithms are environment specific or non-linear. This leaves room to derive a general guidance policy which is system agnostic and linearized such that it is suitable for online application. We will draw inspiration from previous optical only guidance policies, such as optimizing an observability angle for optical sensors, to derive a more general policy which improves the current state estimate.
[1] F. Markley, Autonomous navigation using landmark and intersatellite data, in Astrodynamics conference, 1984, p. 1987.
[2] K. A. Hill, Autonomous navigation in libration point orbits, Ph.D. dissertation, University of Colorado at Boulder, 2007.
[3] M. L. Psiaki, Autonomous orbit determination for two spacecraft from relative position measurements, Journal of Guidance, Control, and Dynamics, vol. 22, no. 2, pp. 305312, 1999.
[4] J. A. Greaves and D. J. Scheeres, Optical only co-estimation and maneuver classification in the cislunar regime.
[5] J. Grzymisch and W. Fichter, Optimal rendezvous guidance with enhanced bearings-only observability, Journal of Guidance, Control, and Dynamics, vol. 38, no. 6, pp. 11311140, 2015.
[6] D. C. Woffinden and D. K. Geller, Optimal orbital rendezvous maneuvering for angles-only navigation, Journal of guidance, control, and dynamics, vol. 32, no. 4, pp. 13821387, 2009.
[7] M. Ceresoli, G. Zanotti, and M. Lavagna, Bearing-only navigation for proximity operations on cis-lunar non-keplerian orbits, in 72nd International Astronautical Congress (IAC 2021), 2021, pp. 110.
Date of Conference: September 19-22, 2023
Track: Astrodynamics