Robots could identify and remove space junk

There is a lot of space junk orbiting Earth. Norwegian researchers believe that in the future, there will be a market for its removal, and have developed an entirely new type of robot vision that will make this possible. This has stimulated the interest of the European Space Agency (ESA).

SINTEF is developing a new 3D camera that is robust and accurate enough to be the "eyes" of a planetary rover exploring the surface of Mars. However, since the ESA withdrew from its collaboration with the Russians because of the war in Ukraine, SINTEF researchers are now looking into other applications closer to Earth.

"Mars is still an interesting target for us," says Jostein Thorstensen at SINTEF. "But right now it all seems a little far away, so we're looking at other opportunities. Servicing satellites and the removal of space junk have emerged as very interesting areas," he says. Thorstensen is a Senior Research Scientist at SINTEF's Department of Smart Sensors and Microsystems.

There are thousands of satellites and many of them require servicing and repairs in order to extend their lifetimes. Some simply need refueling. Increasing amounts of space junk are also becoming a major problem. Thousands of decommissioned satellites are still in orbit around Earth.

"We're already in dialogue with major European players in the space sector and are pleased to see that our technologies are stimulating interest," says Thorstensen. "Early in 2023 we're planning to conduct initial tests of the camera in collaboration with these organizations," he says.

The ESA: The next Mars mission?

In September 2022, the ESA had plans to send a planetary rover to Mars in collaboration with the Russian state space agency Roscosmos. However, when Russia invaded Ukraine in February, the ESA withdrew from the project. But the ESA continues to keep its ExoMars program alive. The rover, named Rosalind Franklin, is currently in Italy and is ready to go, but it is as yet unclear as to how it will get to Mars and be able to land on the planet.

Roscosmos has delivered some instruments for the rover and should have also supplied the landing module that would safely guide the rover onto the Martian surface. The plan included in the ExoMars program is for the rover to collect samples and drill a borehole to a depth of two meters. The samples would then be collected as part of a later mission and transported back to Earth for analysis.

In 2016, the ESA and Roscosmos launched a space vehicle carrying a satellite that continues to orbit Mars to this day. The satellite is measuring gases that may provide indications of the existence of life on the Red Planet. At the same time the satellite was put into orbit, a test landing was carried out using an Italian-built test module called Schiaparelli EDM. However, the landing procedure was initiated too early and the vehicle crash landed at 300 km/h.

Since 1997, the U.S. has sent a total of five rovers to Mars. Two of these, Curiosity and Perseverance, are still active on the Martian surface. China is the only other country that has succeeded in landing a rover on Mars. The vehicle Zhurong arrived on the planet in May 2021.

(The rover Rosalind Franklin is named after the British chemist who discovered that the DNA molecule consists of a double helix—a discovery for which her colleagues Maurice Wilkins, Francis Crick and James Watson later received the Nobel Prize.)

Environmental protection in space?

The ESA is eager to see that legislation governing environmental protection should also apply in space. Between 3,000 and 4,000 of the satellites sent into Earth orbit since 1957 now represent space junk. The number of satellites orbiting our planet is growing explosively.

Since 2019, the Elon Musk-owned company SpaceX has launched more than 3000 satellites into low Earth orbits, and this is just the beginning. Musk's Starlink system consists of small, low-tech satellites. But others may be much larger and more complex, costing hundreds of millions of Norwegian kroner.

All about 3D photography

We humans have two eyes that provide us with stereoscopic vision. Each eye sees a little differently, giving us the opportunity to use depth vision. When an object is very close, we tend to squint to get it into focus. This principle is applied by researchers in order to create 3D videos. Two cameras, each mounted with a laser, are positioned a short distance from each other and project a pattern onto the object that requires imaging.

The cameras operate with a resolution of 500 x 500 pixels, and each pixel is capable of measuring with an accuracy of 0.2 millimeters. The pattern projected onto the object by the laser creates a unique code in the pixels of the two cameras. But the code will not be positioned in exactly the same place on the image.

The displacement between the two cameras enables detailed information to be obtained about the distance to the object. By using triangulation, combined with advanced data processing, it is possible to build a three-dimensional image.

School of hard knocks

A robot equipped with a camera and operating in orbit around the Earth has to be robust. SINTEF's camera system has succeeded in demonstrating that it is exactly that. In preparation for the extreme conditions on Mars, the equipment was subjected to testing under harsh conditions. Thorstensen's colleague Runar Dahl-Hansen says that the camera has to withstand severe shaking, high and low temperatures in a vacuum, high exposure to gamma radiation and electric fields five times stronger than a lightning strike.

"In fact, the properties of the microscopic mirror become enhanced after exposure," says Dahl-Hansen. "Stress tests have been found to induce 'beneficial' chemical defects and cause them to be distributed in such a way that they improve the performance of the piezoelectric material," he says.

Facts about electricity saving using piezoelectric materials

Piezoelectric materials are able to convert electrical energy into mechanical energy, and vice versa. Their efficiency is very high. Up to 90 percent of the energy is conserved during the conversion.

SINTEF's 3D camera is equipped with a millimeter-sized piezoelectric mirror that has been developed and constructed at SINTEF's MiNaLab. The mirror can be used to control and manipulate light with nanometer precision.

The ESA want more

"The ESA was so pleased with the camera that it awarded SINTEF funding for a follow-up project," says Thorstensen. "Even if the mission with the European Martian rover is now postponed due to the ESA's withdrawal from its collaboration with the Russians, it would never have been realistic to have a camera ready at such short notice," he says.

"We're still in a relatively early phase," says Thorstensen. "The technology will not be ready for use in space for several years. But interest from major space sector players offers hope that in the future, SINTEF technology can look forward to a role in space—either on a Martian rover or a servicing satellite. Preferably both," he says.

Why is the SINTEF-developed 3D camera better than others when it comes to repairing satellites?

"It is compact, consumes very little energy, and provides fantastically detailed close-up images," says Thorstensen.

"Weight, size and energy consumption are key factors when you put a robot into Earth orbit. Our system has less complex optics control electronics than other 3D cameras, which makes it potentially more robust and reliable," he says.

What about market potential?

"The use of and need for specialized 3D cameras is on the increase," says Thorstensen.

"For example, organizations operating in fields such as industrial robotics, logistics, medicine and inspection are all interested in highly miniaturized cameras offering high-quality 3D data," says Thorstensen.

Provided by SINTEF