Servicing satellites poses a tricky challenge

Uncrewed satellites orbiting Earth and other planets in the solar system travel at thousands of kilometres per hour, their missions spanning years or even decades. They were built to last on their own, but how might space agencies service them if parts break down, or if they run low on fuel?

That’s where space robots come in, reports Live Science. According to panelists speaking at Future Con, a convention held in Washington, DC, where talks and exhibits explored the intersection of cutting-edge science with science fiction and popular culture, robots will be very useful.

At a panel “Robots in Space,” NASA scientists explained how engineers are designing robots to perform a seemingly impossible precision task in space –  refuelling satellites that are travelling at thousands of kilometres per hour.

Space robots are not new to science fiction, and plenty of machines today perform complex scientific tasks on Earth and in space –  from surgically correcting eye defects to helping astronauts on the International Space Station (ISS) during spacewalks. Several robots even dwell on the surface of other worlds, such as the Mars rovers: the now-defunct Spirit and the still-active Opportunity and Curiosity.  Experts from NASA’s Satellite Servicing Projects Division (SSPD) appeared at Future Con accompanied by a scale model of a space robot called Raven, part of a mission that will be capable of tracking, locating and refuelling autonomous spacecraft – including satellites that were not designed to be serviced in space, according to a description on the NASA mission website. The mission, Restore-L, is expected to launch in 2020, NASA reported.

The Raven module recalls the three-eyed raven from the HBO series “Game of Thrones”. It also has a trio of “eyes,” or sensors, which gather data in visible and infrared wavelengths, and through lidar (radar detection of laser-generated light pulses).

Recently, Raven was sent to the ISS to gather data, Future Con panelist Ross Henry, project manager for the Raven module at SSPD, told the audience. By “watching” vehicles with its three sensors as they approached, docked and departed, Raven gathered valuable information about how spacecraft move, which will help NASA engineers prepare it to locate and track fast-moving satellites, Henry said. Since the beginning of the US space program, about 5000 satellites have been engineered, of which around 1400 are in orbit now. Of those, only one is designed to be refuelled –  the ISS, according to Benjamin Reed, a deputy project manager for NASA’s Satellite Servicing Capabilities Office. Present and future satellite designs will be better suited for servicing in space, but Restore-L will address special trials posed by earlier generations of satellites, thereby significantly extending their useful life spans, Reed said.

Spotting most satellites in the blackness of space is enormously difficult, because they’re not “retror-eflective,” meaning they don’t reflect light back to the light source, Reed said. Picture a roadside stop sign — its surface is treated to scatter light so you can see it at night, even when the pole holding it up is effectively invisible. Of all the satellites in orbit, only the ISS and the Hubble Space Telescope are retrore-flective, Reed said.

And finding the satellite is just the beginning. A refuelling mission will also need to get close to the fast-moving spacecraft — no small feat when both are travelling around 16,400 mp/h (26,393 km/h), Reed said. After Restore-L is in position, the tricky work of refuelling begins. Robotic arms controlled by operators in Maryland will cut through a protective shield on the satellite, remove the thermal cover, unscrew several protective caps and pump in highly explosive fuel, Reed told the panel audience. And then Restore-L needs to replace all those caps and covers, in the reverse order. Once the servicing mission is ready to go, NASA probably won’t deploy a squadron of refuelling robots — more likely, it will design an individual spacecraft capable of refuelling a dozen or more satellites, according to Reed.   The project’s challenges are considerable, but the progress made by NASA scientists in recent decades is no less incredible, Reed told the audience. The first in-space servicing mission — a spacewalk to repair a damaged solar shield on Skylab — took place in 1973, and the 40 years that followed saw the design, launch and subsequent servicing of Hubble and the ISS — servicing conducted by both humans and robots, he said.


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