ROBOTIC CABLE-BASED DE-TUMBLING OF SPACE DEBRIS
The threat posed by orbital debris has grown in recent years. Any collision with space debris may add up to thousands of additional debris that increase collision probability. Recent launches of new satellite constellations to Low Earth Orbit (LEO) has further cluttered LEO and increases the chance of collision with debris.
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The most dangerous debris in orbit consists of large bodies, such as spent rocket stages. To successfully reduce the risk of collisions, and to clean up the space environment, large bodies need to be removed through the use of active debris removal (ADR) missions. One promising technology for ADR are space tethers, which can include tethered robotic manipulators, nets, and harpoons.
CURRENT RESEARCH
The objective of this research is to develop the necessary knowledge for autonomous cable-based de-tumbling of space debris.
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To de-tumble non-cooperative debris, controls need to be applied to the chaser to maintain a safe relative distance from the debris and to de-tumble the debris. Currently:
- A sliding mode controller (SMC) is employed for chaser attitude stabilization.
- To maintain a relative distance between the chaser and target debris, a feedback proportional-integral-derivative (PID) thrust controller is applied.
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The debris inertial parameters must be known in order to both properly and optimally control the debris motion after capture. However, as the debris is non-responsive, these parameters are often unknown. In this work:
- An extended Kalman filter (EKF), and an unscented Kalman filter (UKF) are applied to estimate the debris orientation, rotation vector, and principal mass moment of inertia parameters.
- It is assumed that the chaser attitude and velocity states, and the debris relative position and velocity states are known to the estimator.
- Combinations of sensors are utilized for measurement generation at both synchronous and non-synchronous update rates, such as a tension sensor, camera sensor, and gyroscopes.
KEY FINDINGS
The application of Kalman filters to this estimation problem revealed that:
- A known non-zero tension in the tether is required to estimate the principal mass moments of inertia of the debris.
- The UKF performs significantly better than the EKF for this estimation problem, and should be applied instead of an EKF.
- Best estimation results are obtained from low amplitude, high-frequency tension oscillation profiles in the tether.
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Through application of control algorithms to the tethered space debris system, we have found that:
- A PID controller is sufficient for maintaining a desired relative distance between the chaser spacecraft and debris.
- Tension in the tether is maintained and is capable of counteracting the rotation of debris in some cases.​
- Control performance is maintained when using estimated states.
Online estimation and control pseudo-code
FUTURE RESEARCH
In the future we plan to:
- Apply more robust control to dissipate the residual angular momentum of the debris.
- Release numerous assumptions in the current work.
- Investigate the performance of other estimation methods.
PUBLICATIONS
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L. Field, D. Bourabah, E. M. Botta. Online Control and Moment of Inertia Estimation of Tethered Debris. 2024 AIAA SciTech Forum, Orlando, FL, January 2024. DOI: 10.2514/6.2024-1286
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D. Bourabah, C. Gnam, E. M. Botta. Inertia Tensor Estimation of Tethered Debris through Tether Tracking. Acta Astronautica. Vol. 212 (2023), pp. 643-653. DOI: 10.1016/j.actaastro.2023.08.021
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D. Bourabah, L. Field, E. M. Botta. Estimation of Uncooperative Space Debris Inertial Parameters after Tether Capture. Acta Astronautica. Vol. 202 (2023), pp. 909-926. DOI: 10.1016/j.actaastro.2022.07.041​