In-orbit service and manufacturing (IOSM) robots, therefore, need to be given every chance of success before they take off on their daring missions. The UK’s Satellite Applications Catapult aims to provide that with the IOSM Yard in Westcott, Buckinghamshire, where it replicates space on Earth to put commercial systems through their paces in simulated inspection, repair and assembly operations.
It does so using two robots that replicate the movements that IOSM devices will face in orbit by mimicking propulsion systems and low-gravity conditions. To track and verify those movements, it has added a motion capture system from US multinational Vicon.
When most people think of motion capture they likely think of film, and characters such as Andy Serkis’s Gollum in the Lord of the Rings. But the technology was actually adapted by the film industry from medical applications such as clinical gait analysis, said Vicon product manager Felix Tsui to Professional Engineering.
The technology used by the Catapult is practically identical to that used by the film industry, he added. “It's actually the exact same – it's the same cameras, same markers, in a lot of ways the same back end software. It's just how customers actually use it on the front end that changes.”
The Catapult has 33 Vicon Vero cameras covering its 27m-long, 7m-wide and 8m-tall lab, tracking the full working envelope of the two robots. The facility needed the technology because it uses standard industrial robots that are highly repeatable but “not what you would call accurate”, said robotics development lead Jeremy Hadall.
“If you tell them to go to a point in space [in the laboratory], they will always go back to that point in space over and over again, with a really high degree of repeatability. But if you then tell them to move let's say a metre in a certain direction, their accuracy is not as good,” he said.
“If I command a robot to move in our facility by a metre, I want to know where it's actually moved to… the Vicon system is able to tell us really accurately how far the robot has actually moved within the working envelope.”
By knowing that a robot and its ‘deliverable’ – a satellite, another robot or some other device – have moved a certain difference, Hadall can compare that to his request and analyse whether or not any inaccuracy is affecting the process.
A scenario using a robot with vision-based navigation, for example, could compare motion capture data with information from the navigation system, making sure that tolerances match up. By doing so, they can validate client sensor systems and algorithms by checking they are doing what they say they should do – and “therefore should, in an orbital environment, bring two space objects closer together”.
That is not the end of the challenge, however. Satellites have not been designed for IOSM, making close proximity movements around fragile components a very delicate operation.
“I call them ‘sticky out bits’,” said Hadall. “Essentially their antennas, their radar dishes, or communications dishes, or solar panels, or their thrusters – a whole load of different things. If you are getting close to that satellite, you really want to make sure you're not damaging that satellite in any way, because then you're just creating more debris and more problems for yourself.”
Close proximity movements are like formation flying, he said, before the two objects can finally dock together. Whether the target satellites are cooperative or uncooperative – stable and controlled, or tumbling and uncontrolled – determines the difficulty of the operation. The motion capture system can help assure that navigation systems will work in that scenario, matching the tumble of uncooperative satellites as they are approached.
Iterative process
The motion capture system and wider lab have gone through continuous improvement since installation of the cameras and supporting technology in late summer 2022. Shiny objects in the facility needed to be painted darker, for instance, to stop them from confusing the system. More cameras have been added, and the set up will be reconfigured soon to fit a new facility lay out.
“It's been quite a collaborative, very iterative process,” said Hadall. “This is not a normal application for a robot, or for Vicon, so we’re asking questions of Vicon at times and we’re all scratching our heads going ‘Oh wow, I didn’t know you could do that!’”
Through its work, the Catapult aims to prolong the lives of satellites in orbit, and to start building the next generation of space stations, including space-based solar power stations and large antennas and telescopes. Other applications could include removing debris or defunct satellites from orbit. Beyond that, the horizons are unlimited, with potential applications beyond Earth orbit, towards Mars and beyond.
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Content published by Professional Engineering does not necessarily represent the views of the Institution of Mechanical Engineers.