Docking, rendezvous and Newton’s third law – the challenge of servicing satellites in space

If you want to establish or correct a little something in house, you could assume

If you want to establish or correct a little something in house, you could assume you’d will need a human to do it. But what if you didn’t? What if robotic spacecraft could be employed to refuel satellites in orbit, include new instruments to outdated equipment and even establish entire buildings whilst in house?

Satellite-fixing robots could revive the more than three,000 lifeless satellites in orbit currently. Image credit history: Pxhere (CC0)

This thought of in-house servicing has extensive been dreamt of, but it is now turning out to be a truth. Just final thirty day period a satellite from the US defence organization Northrop Grumman docked with a further satellite in orbit, prolonging its lifestyle for several more many years and heralding an enjoyable new era for robotic missions in orbit.

With more than three,000 lifeless satellites in orbit currently, getting ways to correct aged satellites with robots could enable us cut down the sum of house junk surrounding Earth. And if we can also use robotic spacecraft to establish buildings in orbit, it could open new doors to enjoyable house missions in the long term.

Rendezvous and docking

One particular of the significant difficulties of executing in-house servicing is acquiring two spacecraft to rendezvous and dock in orbit. To make house robotics effective, organizations will need to make guaranteed they can approach a target spacecraft slowly but surely and securely, and then connect to it without having triggering any destruction.

The Northrop Grumman mission was noteworthy in that the target spacecraft was not designed to be serviced. But, notes Sabrina Andiappane from satellite experts Thales Alenia House in France, who coordinates a task called EROSS, if we can launch satellites with servicing in mind then the approach can be simplified.

‘The aim of the (Northrop Grumman mission) was to assistance a satellite that was not prepared to be serviced,’ she said. ‘We purpose to do it for satellites that will be well prepared and thus it will be more successful if you want to lengthen their life span.’

Later this year, the EROSS workforce ideas to apply docking a ‘chaser’ spacecraft with a consumer spacecraft. In a laboratory, two mock spacecraft will be held by robotic arms to simulate becoming in house, and the chaser will then approach the other spacecraft and dock autonomously – a fascinating top quality to restrict prospects of human error.

Once docked, the chaser could then install new instruments and refuel the consumer satellite. If the approach can be manufactured as uncomplicated as probable then lots of of these missions could be done in orbit with relative simplicity.

‘The aim of EROSS is to (prepare) for authentic missions,’ said Andiappane. ‘We have several making blocks like sensors, grippers and algorithms desired to perform rendezvous. And we are heading to show this ability.’

The house natural environment alone poses fairly a number of difficulties to robotic servicing missions. One particular is Newton’s third law – every single motion has an equal and opposite reaction. This signifies that in house, if you try to use a robotic arm to go a little something, you are also heading to go your spacecraft.

‘In micro-gravity each individual movement generates a reaction on the total framework,’ said Dr Thierry Germa from French geoinformation organization Magellium.


Dr Germa coordinates a task called PULSAR, which is investigating how to establish substantial buildings in orbit with robots, these kinds of as substantial mirrors for long term house telescopes. In 2021, NASA ideas to launch the James Webb House Telescope (JWST), a car with a substantial six.5-metre mirror to analyze the universe. Even so, JWST’s mirror is reaching the restrict of what we can in good shape in a rocket. So, PULSAR is looking at a further way to get a substantial mirror into orbit, by launching it in pieces and making it in house.

To triumph over the issue of Newton’s third law, the robotic spacecraft will will need to adjust its orientation to compensate for this movement whilst developing the mirror, keeping the spacecraft awesome and steady. Simply because of the complexity of this approach, it will not be probable to have a human remotely run the robotic spacecraft, acknowledged as teleoperation. As a substitute, automation will be essential.

‘The assembly approach has to be completely validated and secured because it is not probable to have a human in the loop,’ said Dr Germa.

PULSAR will apply assembling the various segments of a mock telescope’s most important mirror in a pool afterwards this year. In the long run, the workforce ideas to produce a reasonable simulation of how a mirror ten metres throughout, manufactured of 36 various segments, could be constructed in orbit. And this very same approach could be employed to establish other buildings in orbit, these kinds of as substantial antennas for telecommunications satellites, or probably even solar panels for spacecraft.


Scientists are also functioning on in-house satellite updates to lengthen the lifespan of the devices orbiting Earth and diminish the will need to carry on launching more recent satellites to exchange the aged kinds.

One particular resolution is to style satellites with various modules, or segments, that can be conveniently swapped out by a robotic servicing spacecraft.

Professor Xiu Yan from the University of Strathclyde, United kingdom and his colleagues are functioning on it. ‘We are attempting to develop a resolution to make certain the sustainability of the long term use of house,’ he said.

He coordinates the MOSAR task, which is aiming to develop an open source satellite that can be conveniently repurposed in house. ‘In certain, we are aiming to have orbital servicing, servicing and lifestyle extension abilities (for satellites).’

Each module would be about forty centimetres throughout, with a robotic arm able to autonomously detach them from a satellite or include new kinds. By working with a standardised style, any satellite could conveniently be upgraded by means of a robotic servicing satellite, without having the will need to launch a replacement.

Later this year, the task will perform a demonstration of this modular know-how in a laboratory, working with a robotic arm to apply attaching various modules to a mock satellite. And ultimately, alternatively than a satellite functioning for a constrained time in orbit, their missions could in essence turn into infinite.

‘They can continue to be there as extensive as you wish,’ said Prof. Yan. ‘It’s a paradigm shift. With this new era of satellites in house, it will turn into probable to upgrade them. So as an alternative of sending a total new satellite, you can deliver a little upgrade to an current satellite framework to make certain extensive-term and affordable use and obtain of house.’