Orbiting robots could help repair and power satellites in space
In a few years, NASA’s OSAM-1 mission will launch into space and use a robotic arm to refuel the Landsat 7 Earth observation satellite. Image: NASA
- Currently, there are approximately 4,852 active satellites in orbit, playing crucial roles in communications, remote sensing and other tasks.
- Almost all were started knowing that if something broke, there was no way to fix it. Most satellites also need fuel to occasionally adjust their orbits.
- Once that’s gone, they could become so much space junk, adding to the already large stream of debris circling the globe.
- Over the past few decades, researchers have made progress toward the goal of having a robotic mechanic in space who can fix satellites when they break.
For more than 20 years, the Landsat 7 satellite circled the Earth roughly every 99 minutes, capturing images of nearly the entire surface of the planet every 16 days. One of many devices that have observed the evolution of the globe, it has revealed the melting of glaciers in Greenland, the growth of shrimp farms in Mexico and the extent of deforestation in Papua New Guinea. But after Landsat 7 ran out of fuel, its useful life effectively ended. In space, regular maintenance has not been an option.
Now, however, NASA has a potential fix for these weakened satellites. In a few years, the agency plans to launch a robot into orbit and maneuver it to a Landsat 7 grab distance. The robot will use a mechanical arm to grab it and refuel it in flight.
If successful, the mission would mark a milestone – the first time a satellite has been refueled in space. And this mission is just one of many planned public and private endeavors to use robots to repair and improve the billions of dollars worth of satellites in orbit.
Ultimately, efforts like these could lead to better and cheaper satellites that reduce the cost of internet and cell phone networks, provide better weather forecasts, and give unprecedented views of planetary change and the universe. . They could even enable a new wave of construction in orbit, with armies of robots building satellites, space stations and even starships bound for Mars.
Give satellites a longer life
Currently, there are approximately 4,852 active satellites in orbit, playing crucial roles in communications, remote sensing and other tasks. Almost all were started knowing that if something broke, there was no way to fix it. Most satellites also need fuel to occasionally adjust their orbits. Once that’s gone, they could become so much space junk, adding to the already large stream of debris circling the globe.
“Imagine you’re going to buy a car tomorrow,” says Brian Weeden, head of an industry group called the Consortium for Execution of Rendezvous and Servicing Operations (CONFERS). “And you have to keep in mind that you can never put more gas into it. You can never change the oil. You can never maintain or repair anything. And you have to use it for the next 10 years. Now, how expensive and complicated do you think this car is going to be? This is exactly what we have done with the satellites.
To keep satellites running for as long as possible, engineers build redundant systems and pack as much fuel as possible. All this excessive engineering increases the costs of building and launching satellites – a modern communications satellite can cost around $500 million.
Almost all construction and repairs that have taken place in space thus far have relied at least in part on astronauts, including fixes on the Hubble Space Telescope and construction of the International Space Station. But sending humans into space is extremely expensive, so the effort to develop robots to do the job has increased in recent years.
“What we would really like to do is have a way to have a robotic mechanic in space who can fix satellites when they break,” says Carl Glen Henshaw, head of robotics and machine learning at the US Naval Research Laboratory.
Robots to the rescue
Over the past few decades, researchers have made progress toward this goal. In a 2007 NASA demonstration project, a pair of specially built craft docked in orbit and transferred fuel. More recently, in 2020, aerospace company Northrop Grumman successfully launched two “mission expansion vehiclesequipped with their own engines and fuel, which attached to two commercial satellites and propelled them into new orbits.
Two new missions that should be launched this decade will make it possible to go even further in the service. Demonstration projects will use semi-autonomous robots equipped with mechanical arms to add fuel to satellites in orbit, and even to perform simple repairs.
For his part, Henshaw is working on Robotic maintenance of Geosynchronous Satellites, a mission funded by the US Defense Advanced Research Projects Agency (DARPA). If it succeeds in a demonstration planned for 2024, it would be the first time that a robotic craft has managed to grab a satellite that was not specifically designed to dock with it. Henshaw and his colleagues recently explored some of the challenges faced in satellite maintenance with space robots in Annual review of control, robotics and autonomous systems.
There are many such challenges. Because existing satellites were never intended to be serviced, they lack the markings, called landmarks, that would make it easier for a robot to visually orient itself with the moving satellite. There are no fasteners designed for the robot to hold on to. And the parts of a satellite that protrude, like antennas and solar panels, tend to be too fragile to grab.
Another problem is the time lag between the robot and the Earth. For a robot operating in geosynchronous orbit, at around 35,000 kilometers, distance and signal processing create a communication delay of several seconds between the robot and its controllers on Earth. The robot will therefore have to manage the most crucial tasks on its own.
On the plus side, the work can build on existing robotic arms in space, including two currently in use on the International Space Station.
For a demonstration mission, Henshaw and his fellow engineers plan to choose one of thousands of old, inactive satellites “parked” in distant orbits. A robot would match orbits with the satellite and maneuver about two meters away, using cameras and a laser rangefinder. When close enough, the robot uses one of its two arms to grab an aluminum ring that previously anchored the satellite to the launcher.
The other robotic arm would be able to nudge and prod solar cells or antennae that failed to deploy properly — a problem that happens every two or three years, Henshaw says. And it would be able to attach new instruments outside the satellites, such as more powerful transmitters, cameras or antennas.
Sometime after 2025, NASA plans to launch an even more ambitious robot. On-orbit maintenance, assembly and manufacturing 1 (OSAM-1) would first handle a complex refueling operation of an existing satellite. Then he would demonstrate that he can build completely new structures in space.
Landsat 7 will be first on OSAM-1’s to-do list. Launched in 1999 by the US Geological Survey in low Earth orbit, at an altitude of around 700 kilometers, the work of the satellite has been taken over by more advanced satellites. But it offers scientists the opportunity to test robotic refueling.
“Twenty years ago, technicians powered up the satellite in preparation for launch, and they never thought anyone would touch that interface again,” said Brent Robertson, NASA’s OSAM-1 project manager. .
OSAM-1 will use its robotic arm to cut through a layer of insulation, cut two wires and unscrew a bolt before connecting a hose and pumping out 115 kilograms of hydrazine fuel, Robertson says. (To see video here.)
Although repair and maintenance of existing satellites is the most immediate objective, in-orbit assembly and manufacturing is potentially more important in the long term.
OSAM-1, for example, has an additional mission that will carry a separate robot called Space Infrastructure Dexterous Robot (SPIDER), designed to demonstrate that it can put things together in space. SPIDER’s first task will be to assemble a seven-piece three-meter antenna that it has carried into orbit.
Using a process similar to 3D printing, OSAM-1 will also aim to show that it can build structural components from scratch, creating strong yet lightweight composite beams from carbon fiber spools and other textiles. Beams like these could be connected to form structural components of a satellite or other structures in orbit.
If the missions being planned are successful, robotics could usher in a new era of space construction that is unaffordable today – fuel depots, space mining operations, larger space stations for space tourism, and even spacecraft bound for Mars built in orbit.
“We want to demonstrate that we can build these things. No one has done this before,” Robertson says. “If you have the ability to assemble things in space, you can bring your own hardware or have hardware sent to you. And you can build much bigger things.
Kurt Kleiner is a Toronto-based freelance science journalist.
This article originally appeared in Knowable magazinean independent journalistic enterprise of Annual Reviews.