NASA, DARPA, and others are developing technologies to support autonomous refueling and maintenance capabilities for satellites while they’re orbiting Earth, as part of a wider ambition to advance autonomous servicing capabilities that’ll enable a new era of infrastructure building in space.
On-orbit satellite servicing will help extend the mission lives of satellites, but the technology that’s being developed to do so will help usher in a new era of space systems, according to Space System Loral’s Al Tadros, VP of Space Infrastructure and Civil Space. SSL is currently developing a spacecraft bus for NASA’s robotic payload, to be used in NASA’s Restore-L mission, slated for launch in 2020.
The technology and capabilities being developed by NASA will help create new methods for maintaining and upgrading spacecraft in ways that are unfeasible for humans to execute. The Restore-L mission has been heralded by NASA as an “unprecedented” advancement in realizing cost-effective space infrastructure.
“We believe that refueling is one element of the future architectures [in space],” Tadros said in an interview with The Downlink last month. “The capabilities that are being developed, demonstrated and evolved for Restore-L – what this means is that future science missions, future exploration missions, including human exploration, will be able to be robotically assembled, serviced, fueled, maintained, repaired. It’ll really enable a lot of missions that we can’t reasonably do right now.”
Satellites today are constructed and launched with very finite life cycles in mind — earning the moniker of “one-and-done” missions. A mission may last anywhere from a few years to multiple decades, depending on the nature of the mission, but satellite life is constrained by fuel limits. There’s only so much fuel a satellite can carry with it up into space and use during the course of its mission.
Once that fuel runs out, the satellite is left to remain in orbit, or de-commission itself by falling back down to Earth. “Most satellites will never see a refueler,” Tadros said. “As it uses up its fuel, that’ll typically be the end of the mission life.”
NASA’s Restore-L mission is a technology demonstration mission that’ll see a refueling satellite make contact with US Geological Survey’s (USGS) Landsat 7 in low Earth orbit (LEO). Landsat 7 was launched into LEO in 1999, aboard ULA’s Delta II rocket, as one of a family of Landsat satellites used for obtaining satellite imagery of Earth. Landsat 7 is scheduled for retirement in 2021, and it’s around that time that NASA’s Restore-L will make contact with and refuel the satellite in a demonstration which, if successful, will extend Landsat 7’s lifespan.
The Restore-L spacecraft is based on SSL’s 1300 series spacecraft bus. With a few modifications, which NASA and SSL teams have just agreed upon, the spacecraft will be tailored to act as a satellite refueler, equipped with two robotic arms and a tank of extra fuel.
After completing a Systems Requirements Review with NASA last month, SSL will finish building the bus, along with all its design modifications, by the end of 2018. From there, it’ll shipped off to NASA’s Goddard Space Flight Center in Maryland, where NASA engineers will integrate the robotics payload and conduct a series of environmental tests over the course of the following 18 months. “Then it’ll get shipped out to the launch base and sometime in the later part of 2020, it’ll be launched,” Tadros said.
Satellite Refueling 101
Refueling a satellite while it’s in orbit around the Earth is a bit tricky. One of the big enablers of this capability is improved robotics. For the Restore-L mission, NASA’s payload will include advanced robotics designed to do all the hard work of refueling Landsat 7 – like grasping the satellite, unscrewing the tank cap, and connecting the fuel hose. The ability to complete those types of tasks robotically will prove transformative to future space missions.
Here’s how the mission will take place: Once the refueler is launched into space, it will rendezvous with the client satellite. “We first have to dock to it. That’s quite complex, however, and we need to make it very reliable and fool-proof,” Tadros said. “How does it match the orbit and approach the Landsat satellite, and how do we get within reach of a 2-meter robotic arm? That is the first task we have to conduct.”
Once the refueler is close enough to the client satellite, it’ll reach out with its robotic arms and grab ahold of the satellite, using the same connection point that was used to connect the satellite to the launcher vehicle that it rode up into space upon. “It’s a very sturdy attachment point,” Tadros said.
The refueler will then seat the satellite on a pedestal and begin the refueling process. “The robotic arms are used to pull out a hose and connect to the fill and drain valves,” Tadros said. Once again, easier said than done. First, the refueler must cut through the thermal blankets and caps that cover those valves, then push the blankets aside and hold them back, using a set of special tools. Then, it’ll attached a hose to the fuel tank and fill ‘er up. Once refueling is complete, the spacecraft must re-seal the tank.
“For Restore-L, we’re actually going to leave an attachment on the fill and drain valve to ensure that it’s sealed once we disconnect the hose,” Tadros said. “That’s a precaution that we’re taking. It’s been up there for many years and we want to make sure that there aren’t any leaks or any chance of leaks when we disconnect from the spacecraft.”
For the Restore-L mission, NASA will perform a few maneuvering techniques, using the refueler to re-position Landsat 7. “That just requires us to use the propulsion system on Restore-L to nudge the orbit and verify it went where we wanted it to. That’s a final demonstration,” Tadros said. “Then we release it robotically.”
From there, the Restore-L mission is complete. NASA doesn’t have any other specific plans for the spacecraft, but does intend to take the technologies developed for Restore-L and transfer them to interested U.S. companies to jumpstart a commercial servicing industry; in fact, NASA recently held its first Satellite Servicing Technology Transfer Industry Day at Goddard Space Flight Center’s Robotic Operations Center, where NASA showed off some of its top technologies to commercial industry participants.
As for Restore-L, Tadros noted a few other companies have approached SSL about using the spacecraft. “There are other satellites in that area and there are definitely other opportunities,” he said.
Otherwise, the spacecraft will remain in polar orbit until it runs out of fuel. “When it’s all depleted, like many of NASA satellites, it’ll use the remaining propellant to de-orbit it,” Tadros said, and meet its final end.
Revolutionizing Space Systems
The Restore-L mission is just one of the satellite servicing projects currently in development. “This is not just a one-mission-and-it’s-all-solved kind of thing,” he said. “This is a really complex capability.”
DARPA is working on its own Robotic Servicing of Geosynchronous Satellites (RSGS) program, which will involve a spacecraft capable of performing multiple servicing missions, spanning, relocation and orbital maneuvering, inspection and repair of mechanical anomalies, and even installing upgrades or attaching new payloads to the satellites. SSL is partnering with DARPA on developing and operating this servicer.
Tadros and others see robotics-led servicing capabilities as laying foundation for a greatly expanded scope of future space operations. “The potential is much bigger than any one demonstration,” he said.
For satellite businesses, on-orbit refueling and maintenance will see huge cost savings realized as companies are better able to manage their satellites in space. “It means we no longer have to fit everything into one fairing. We no longer have to fill the satellite up with fuel for the whole life, and hope that it launches in the right orbit and that it all works right,” Tadros said.
But the technology demonstration will also help advance future rendezvous operations in space (such as asteroid exploration, where researchers will be able to study their materials more closely), as well as future uses of ever-advancing telerobotics, such as assembling spacecraft and habitats in space.
“It really changes the paradigm of what space systems are,” Tadros said “As astronauts go beyond the space station back to the moon, and asteroids and Mars, this is the kind of capability we have to have in order to stage the infrastructure: to supply it, to maintain it, and to support the astronauts as they conduct their important missions. That’s what all of this is leading to, and it’s pretty exciting.”