Piece by piece, NASA is building new technologies to refuel and repair existent satellites in orbit - and they're using the International Space Station to test them. After concluding a successful ground-based test of robotic satellite refueling technology, NASA is preparing for a new round of related demonstrations on the space station. The orbital testing focuses on real-time relative navigation, spacecraft inspection and the replenishment of cryogens in satellites not originally designed for in-flight service.
Collectively, these efforts are part of an ongoing and aggressive technology development campaign to equip robots and humans with the tools and capabilities needed for spacecraft maintenance and repair, the assembly of large space telescopes and extended human exploration.
Building Satellite-Servicing Capabilities
Since 2009, the Satellite Servicing Capabilities Office (SSCO) at NASA's Goddard Space Flight Center in Greenbelt, Md., has been investigating human and robotic satellite servicing while developing the technologies necessary to bring in-orbit spacecraft inspection, repair, refueling, component replacement and assembly capabilities to space. Following the mantra of "test, test and retest," SSCO is conducting a number of tests and demonstrations in orbit, in the air and on the ground, to prove the readiness of this technology portfolio.
Many SSCO demonstrations and tests have focused on the technologies needed to robotically transfer propellant to existent satellites in space today - and even satellites in the future that might be designed for servicing. Since its launch to space station in 2011 on the last space shuttle mission, the Robotic Refueling Mission (RRM) has been demonstrating the tools, technologies and techniques a robot would need to refuel and repair satellites in orbit.
"With more than 400 satellites in space that could benefit from robotic servicing, we thought a refueling test was the best place to start," says Frank Cepollina, veteran leader of the five servicing missions to the Hubble Space Telescope, and associate director of SSCO. "We wanted to demonstrate technologies that build life-extension capabilities - and jumpstart a discussion about new ways to manage assets in space. We never planned to stop there, however. It was only the first step."
SSCO's RRM and follow-up tests have earned great success. In January 2013, RRM demonstrated that remotely controlled robots -- using current-day technology -- could work through the caps and wires on a satellite fuel valve and transfer fluid into existent, orbiting spacecraft that were not designed to be serviced. To meet the safety requirements of space station, ethanol was used as a stand-in for satellite propellant.
A follow-up demonstration conducted on the ground, the Remote Robotic Oxidizer Transfer Test (RROxiTT), took the RRM demonstration one step further. In February 2014, a robot remotely controlled from Goddard successfully transferred corrosive satellite oxidizer, at flight-like pressures, into a mock satellite tank located at Kennedy Space Center in Florida, more than 800 miles away. This was a NASA first.
Since wrapping up RROxiTT, SSCO is broadening its portfolio to include xenon transfer technology -- propellant used by satellites with electric propulsion systems.
"The lessons we learned from the Robotic Refueling Mission contributed to RROxiTT's success and gave us confidence for future demonstrations," says Benjamin Reed, deputy project manager of SSCO. "We continue to draw from what we learned on orbit."
New Satellite Servicing Demonstration on Space Station
With RROxiTT off its checklist, SSCO is ready to flex its muscles in yet another technology arena. "Developing servicing capabilities requires looking at scenarios from every angle," explains Reed.
"A core part of our work centers on filling up satellites and their instruments with fluids that could prolong their life. But that is just one small part of the puzzle we're unraveling. We're also thinking about how those fluids will be delivered in the first place. What technologies would it take for a robotic servicer carrying fuel 22,000 miles above the Earth to rendezvous with another satellite that's waiting for service, perhaps even tumbling in multiple axes simultaneously?"
Answering that question is the objective of Raven, a demonstration of a real-time navigation system that would empower spacecraft to autonomously rendezvous with both prepared vehicles and those not designed for servicing.
"After five years of ground-based testing, we're excited to test this system in space," says Reed. "It'll help us examine how Raven's sensors, avionics and algorithms work together as an integrated system."
Delivery to the space station is slated for early 2016 as part of the Department of Defense Space Test Program-Houston 5 (STP-H5) payload.
After the Canadian Space Agency's Dextre robot mounts the STP-H5 payload to an exterior platform on the space station, Raven will track visiting vehicles in real-time, both during approach and departure. Mission operators will subsequently use collected data to improve Raven's performance in preparation for space flight on an independent spacecraft.
"Raven is maturing the technologies that would give a robotic servicer 'eyes in the sky' as it works its way through each step of safe rendezvous with a client satellite," says Matt Strube, Raven project manager. "Best of all, it helps us to mature technologies essential to NASA's long-term technology roadmap."
The Robotic Refueling Mission Takes on a New Charter
Moving from corrosive fluids to super-cool ones, SSCO is also gearing up for the second phase of their Robotic Refueling Mission (RRM). Having completed its initial roster of refueling activities, the RRM team is poised to begin a subsequent set of tasks honed on the robotic steps needed to replenish the cryogen reserves of satellites on orbit today.
Such capabilities could allow spacecraft instruments to last past their expiration date and ultimately permit satellites to perform longer.
The next Automated Transfer Vehicle, scheduled for launch to the space station in June, will deliver a new RRM task board and the Visual Inspection Poseable Invertebrate Robot (VIPIR) to accomplish RRM objectives. Built by SSCO, VIPIR is an inspection tool that provides a set of eyes for internal satellite repair jobs. The hardware will join another RRM task board delivered to the space station last summer.
With the help of the twin-armed Dextre robot, the RRM team will work their way through intermediate steps leading up to cryogen replenishment, but will stop short of actual cryogen transfer for this round of tasks because there is not sufficient available volume within the RRM module for a flask of cryogen; that will have to wait for a future demonstration, presently in the planning stage. Experiments on RRM will also include evaluation of advanced solar cell technology.
Installation of the new RRM tool and task boards on the RRM module is currently scheduled to begin this summer.
Looking Forward to New Tests and Capabilities
"It's an extremely active time for SSCO," says Reed. "But we thrive on these challenges. We're eager to see how these servicing technologies, and the capabilities that they enable, could benefit satellite owners and operators through life extension and assembly options. To replace or repair a car 5, 10 or 15 years into its life is a decision individuals routinely make. We want to give that option to satellite owners, whom previously have had only one option - decommission at end of life."
By developing robotic capabilities to repair and refuel GEO satellites, NASA hopes to add precious years of functional life to satellites and expand options for operators who face unexpected emergencies, tougher economic demands and aging fleets. NASA also hopes that these new technologies will help boost the commercial satellite-servicing industry that is rapidly gaining momentum.
"It foretells a new era of what humans will accomplish in space," says Reed.
Dewayne Washington/Adrienne Alessandro
NASA's Goddard Space Flight Center
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