Tutorial Review of Bio-Inspired Approaches to Robotic Manipulation for Space Debris Salvage

biomimetics Review Tutorial Review of Bio-Inspired Approaches to Robotic Manipulation for Space Debris Salvage Alex Ellery Department of Mechanical & Aerospace Engineering, Carleton University, 1125 Colonel by Drive, Ottawa, ON K1S 5B6, Canada; Received: 9 March 2020; Accepted: 1 May 2020; Published: 12 May 2020



 Abstract: We present a comprehensive tutorial review that explores the application of bio-inspired approaches to robot control systems for grappling and manipulating a wide range of space debris targets. Current robot manipulator control systems exploit limited techniques which can be supplemented by additional bio-inspired methods to provide a robust suite of robot manipulation technologies. In doing so, we review bio-inspired control methods because this will be the key to enabling such capabilities. In particular, force feedback control may be supplemented with predictive forward models and software emulation of viscoelastic preflexive joint behaviour. This models human manipulation capabilities as implemented by the cerebellum and muscles/joints respectively. In effect, we are proposing a three-level control strategy based on biomimetic forward models for predictive estimation, traditional feedback control and biomimetic muscle-like preflexes. We place emphasis on bio-inspired forward modelling suggesting that all roads lead to this solution for robust and adaptive manipulator control. This promises robust and adaptive manipulation for complex tasks in salvaging space debris. Keywords: space debris mitigation; on-orbit servicing; space salvage; predictive forward models; cerebellum; preflex; viscoelastic muscle 1. Introduction The problem of space debris imposes a severe and present danger to current and future space operations. Furthermore, the space debris problem is becoming more acute with increasing numbers of satellites launched—in 2017, 400 satellites were launched, over four times the annual average from 2000–2010. Recently, SpaceX launched 60 Starlink satellites into 550 km altitude, the first of a megaconstellation of 7518 satellites into non-geosychronous orbits to bring broadband internet services globally to ensure full coverage for the 3.5 B people currently without. Telesat intends to launch a 512-satellite constellation while OneWeb intends to launch a 900-satellite constellation. Plans envisage expanding satellite constellations to 40,000. Multitudes of satellites at lower altitude reduce signal propagation time compared with geosynchronous orbit. Yet, thus far, only 9000 satellites have been launched in the history of spaceflight. Although 550 km altitude is sufficiently low for orbital decay due to atmospheric braking, these broadband internet constellations vastly increase the prospects for collision and the rapid accumulation of debris. The space debris problem has become critical and requires serious intervention to address it. It has been suggested that if 5–10 of the largest defunct satellites were disposed of annually in LEO (low Earth orbit) where space debris is most concentrated, this would prevent the Kessler syndrome from occurring [1]—the Kessler limit occurs when the rate of fragmentation of debris runs away and becomes uncontrollable [2]. It is believed that we may be approaching the Kessler limit in polar low-Earth orbit. There is, although most debris burn up in the atmosphere on re-entry, the finite prospect of being struck on Earth by surviving debris from space. In 1997, a woman in Oklahoma was struck without injury by a piece of launch shroud but most re-entering Biomimetics 2020, 5, 19; doi:10.3390/biomimetics5020019 www.mdpi.com/journal/biomimetics Biomimetics 2020, 5, 19 2 of 67 debris falls into the oceans. Nevertheless, the vastly expanding satellite population will increase this risk of human exposure. Unfortunately, the UN Liability Convention (1972) in conjunction with the UN Registration Convention (1976) do not appear to be effective—part of the problem lies in proving fault by establishing demonstrable causation by specific debris. The Chinese and Russian responsibility for the criticality of the space debris environment suggests that recent ISO standards recommending satellite disposal at the end of life are likely to be useless, suggesting technological solutions. Surrey Space Centre’s RemoveDEBRIS technology demonstrator mission demonstrated four techniques on two companion inflatable cubesats—weighted net capture, laser scanning to extract shape, harpooning a target plate and unfurling a drag sail to demonstrate fuel-less disposal by de-orbiting. It successfully demonstrated the two capture methods. There are several concerns about these approaches, not least being their propensity for generating secondary debris. The most favoured methods of space debris acquisition—harpooning and netting—ultimately involve disposal, introducing the problem of re-entry survivability and controllability, particularly for a large defunct spacecraft like Envisat. It is possible that a controlled re-entry can direct debris into the Pacific Ocean between Chile and New Zealand where there are few aircraft flights and only rarely used shipping lanes. This requires a steep and controlled descent which consumes considerable fuel. Most defunct spacecraft will require retro-fitting with a de-orbit device—if passive (such as a drag-sail), the re-entry is only partially controlled. The European Space Agency decided to redesign its e.Deorbit mission, originally for removing Envisat, to accommodate a robotic arm for its multiple utility for on-orbit servicing. One of the criticisms of e.Deorbit and other debris-specific solutions has been the lack of commercial prospects. This generally implies the capacity for satellite servicing to prevent and repair failures. There have been numerous examples of spacecraft failures that could have benefitted from robotic intervention through on-orbit servicing [3]: (i) OAO-A2 lost its star sensor due to debris collision; (ii) OAO-C, Olympus-1 and ExoSat lost attitude control; (iii) NOAA-6 accidently vented its hydrazine incurring an uncontrolled tumble; (iv) Hipparcos was launched into the incorrect orbit due to a failure in its apogee kick engine; (v) ATS-6 suffered a thruster failure, etc. There is little doubt that robotic arms—which can also mount specialised or general tooling—offer a versatility that cannot be paralleled. Indeed, in 2020, the Mission Extension Vehicle (MEV-1) successfully attached to the retired Intelsat 901 communications satellite. It deployed an apogee engine probe which pulled the 901 so that its launch adapter ring pressed against three stanchions on the MEV. It was maneouvred back from a graveyard orbit into a geostationary orbit to provide an additional 5 years service to its nominal 18-year lifetime through the supply of power and propellant from the MEV. 2. Space Salvage An alternative approach to space debris mitigation is to recover th (...truncated)