Landsat-7 is in trouble. Some 438 miles above, the minivan-sized craft zips around Earth every 16 days. And for over 18 years, the satellite has captured pictures of our ever-changing planet. But Landsat-7 is running out of fuel.
If it were an Earth-bound craft, this wouldn’t be an issue. We refuel everything—planes, trains and automobiles. But up in space, it’s a different story. Satellites toil away hundreds or even thousands of miles from Earth, speeding along at thousands of miles per hour. This speed and distance leaves ground operators largely helpless if anything goes awry. That includes refuelling: Once satellites run out of gas, they’re given up for dead. The only exceptions are Hubble and the International Space Station, both of which are in low enough orbit to be reached via shuttle and worth sending people for servicing.
But with the average price tag of satellites topping a billion dollars, ditching the crafts once they hit empty is costly. It also contributes to the ever-growing space junk problem: These once-useful man-made objects become potentially deadly hazards in space. “We don't do it because we like throwing things away, we do it because there isn't any other option,” says Benjamin Reed, deputy project manager for NASA’s Satellite Servicing Projects Division, a group determined to change the way researchers view satellites.
Housed in a warehouse at Goddard Space Center in Greenbelt Maryland, the Satellite Servicing Projects Division is working toward revolutionary new technologies that would make it possible to repair, refuel and upgrade satellites while in orbit. Until now, computing power and robotics technology haven’t been sophisticated enough to make this tricky endeavour possible.
The walls of the cavernous “epicentre” of SSPD, as Reed calls it, are draped in black cloth to mimic the darkness of space during simulation runs. Robotic arms, each five or more feet long, are attached at various angles at every work station in the room. A life-size replica of Landsat-7 sits by the door, and two arms point in opposite directions, frozen mid-gesture in front of the craft.
These arms are part of the development stage for a project dubbed Restore-L—a craft intended to launch into space in the summer of 2020, designed to refuel satellites running on empty. Its first target: Landsat-7.
Refuelling in space, however, is far more complicated than you might think. First, the craft has to catch up with the satellite, precisely matching its speed. “One mile per hour slower and [Restore-L] will never catch it; one mile per hour faster, bad things [happen],” says Reed, knocking his fists together to demonstrate the destruction that would ensue.
Directing such an endeavour from the ground would be nearly impossible. Any slight communication delays from ground-based operators could result in catastrophe. So Restore-L needs a brain of its own to track and calculate its trajectory to attach to the satellite.
Enter Raven. Slightly smaller than a milk crate, this device has three optical instruments: visible light, infrared and what’s known as LIDAR, which sends out lasers and collects the scattered light. The device rode up to the International Space Station this past February and has since been attached to the outside of the station, tracking the movement of any incoming and outgoing spacecraft. The three sensors allow it to monitor these objects under all light conditions, explains Ross Henry, the lead investigator for the Raven project.
Raven is essentially helping the team develop an “autopilot system,” says Henry. It can spot incoming spacecraft at almost 17 miles away—they show up as a single pixel in an image. Raven then uses its sensors to tracks the craft’s movement. Based on an internal algorithm, Raven can spit out coordinates that detail the incoming body’s position in space and its orientation. Eventually sensors similar to Raven’s will be incorporated into Restore-L.
During its mission, these sensors will get Restore-L near to the satellite in need. In the case of the Landsat-7 repair, Restore-L’s robotic arms would then come into play, latching onto a metal ring on the bottom of the satellite, which was originally used to secure Landsat-7 to the top of its launch rocket.
Like your arm, the robot arms have three main points of motion—a shoulder, elbow and wrist, explains Reed. A camera located at its wrist helps it track its position relative to the satellite and respond to tiny changes as the pair speed through space together at thousands of miles per hour.
“That’s what we practice back here,” says Reed, gesturing to another replica of the bottom of a satellite sitting in the far corner of the warehouse. The satellite’s bottom ring sits exposed and another robotic arm stands motionless in front of the device. To practice the manoeuvre, a second robot makes the satellite bottom bob and weave while the robotic arm nabs it, continuing to track its movement.
“Now—and I'm not joking when I say this—comes the easy part,” says Reed. “And that's the actual refuelling.”
For this “easy” part of the mission, Restore-L will use five specially designed tools to gain access to the fuel valve. It must cut away insulation, remove a lock wire over the top cap and unscrew three different leak-proof caps. Two more specially designed tools will then be used to thread the fuelling arm onto the nozzle, pump in fuel under 250 pounds per square inch of pressure, and re-insulate the port. Once fuelling is complete the front half of the nozzle separates from the retracting arm. Left behind is a new fuelling port that only requires the use of two tools to complete the manoeuvre, simplifying all future refuelling missions.
SSPD’s goal is to work with other satellite designers to help make all future satellites capable of refuelling by incorporating the new fuelling port design.“Now that we've reached the point when fuelling can be discussed with a straight face, why not build our satellites to be cooperative,” say Reed. Such satellite tune-ups are the future of the industry, he says. “It is clear that most companies recognize this and are already interested in cooperative servicing.”
The team is also considering loading future refuelling crafts with enough fuel to service multiple satellites, like a mobile gas station in space. “If you can get up there and restore the life of one of these billion-dollar satellites another five or ten years, you've immediately recouped your money,” says Henry. “If you can do five of them, you've got yourself a game changer.”
In the future, the team hopes that other crafts like Restore-L can help upgrade or service other satellites. They are working towards what’s sometimes known as the five R’s, says Reed: remote inspection, relocation, refuelling, repair and replacement.
One day, throw-away satellites will be a thing of the past. Junking satellites was once a necessity, says Reed, but now, modern systems are up to the task. “The satellite industry isn't broken,” he says. “We are humbly suggesting to the satellite world, it could be better.”