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Satellite refueling testbed completes demo in orbit

Posted: January 25, 2013

Using a robotic system mounted outside the International Space Station, NASA and Canadian engineers this week completed a first-of-its-kind refueling demonstration that could change the way operators manage fleets of orbiting satellites.

Dextre uses a nozzle tool affixed to the Robotic Refueling Mission fuel valve to transfer liquid ethanol in a first-of-its-kind satellite refueling demonstration. Credit: NASA
During six days of activity from Jan. 14 until Friday, the Dextre robot grappled tools to open a fuel valve on a mock satellite and transfer liquid ethanol into a fuel tank. Dextre, the space station's Canadian-built two-armed robotic handyman, used a wire cutter and other tools to remove locks and caps from a nozzle leading to a fuel tank inside a box designed as a testbed for satellite servicing procedures.

"We've had an incredibly successful week," said Benjamin Reed, deputy program manager of the Satellite Servicing Capabilities Office at NASA's Goddard Space Flight Center in Greenbelt, Md.

The Robotic Refueling Mission was launched on the last space shuttle flight in 2011 and placed on a platform outside the space station. The experiment includes a fuel valve, nozzle and seals similar to those used on many satellites and four tools that can be affixed to Dextre's arms.

The tools are prototypes of devices that could be used by future satellite servicing missions to refuel spacecraft in orbit.

RRM is the first in-space refueling demonstration using a platform and fuel valve representative of most existing satellites, which were never designed for refueling. Other satellite servicing demos, such as the U.S. military's Orbital Express mission in 2007, transferred propellant between satellites with specially-built pumps and connections.

"I don't want to sound overly dramatic, but it is, or it might be, the start of what could be a revolution or a new era in how satellites are built and flown in space," Reed said.

"Present-day technologies with the Dextre robot up on the space station are able undo these triple seals that are on more than 900 satellites presently operating in space," Reed said in an interview aired on NASA TV. "What that means is that fleet owners and operators, people who run these satellites, perhaps could have options in the future. The present paradigm is to operate the satellite, and when it has an anomaly or runs out of fuel, you decommission it and build a replacement, assuming you have the funds to do so."

No satellite operators are signed up for a robotic servicing mission. MDA Corp., which serves as industrial contractor for the space station's robotics systems, proposed a satellite servicing vehicle in 2011 and reached an agreement for its first customer to be Intelsat, the world's largest communications satellite operator. Canada-based MDA last year said the Intelsat agreement was no longer in effect.

ViviSat, a joint venture between ATK and U.S. Space, plans to develop a series of "mission extension vehicles" that would attach themselves to aging satellites and take over attitude control functions without transferring any propellant.

"What satellite servicing brings to the table is the possibility that one could go up with a robotic spacecraft and give it more fuel, fix a solar array, perform some sort of a servicing function, a repair, refueling or a relocation to allow that satellite to continue its operations longer," Reed said.

The Robotic Refueling Mission consists of a box-like module about the size of a washing machine. Besides the tools and fuel valve, it also includes task boards allowing the Dextre robot and its ground-based operators to practice delicate servicing procedures.

Liquid ethanol stands in for traditional satellite propellant.

Beginning Jan. 14, engineers programmed Dextre, which was perched at the end of the station's robotic arm, to complete a series of fine tasks, first cutting a locking wire, then removing two caps covering RRM's mock-up satellite fuel nozzle.

"Last night was the final act," Reed said Friday. "That's when we picked up the nozzle tool, we threaded onto the exposed fill-and-drain valve threads ... [and] we pumped 1.3 liters of liquid ethanol across this robotically-mated interface with no leakage."

More tests await RRM, including slicing off of thermal blanket insulation, unscrewing bolts, and the removal of caps that would typically cover a satellite's electrical receptacle, according to a NASA website.

Several satellites, including NASA's Hubble Space Telescope and commercial spacecraft, were repaired by space shuttle astronauts.

Reed said RRM's demonstrations show satellite servicing is possible without human presence, making refueling and repairs feasible in geosynchronous orbit 22,300 miles above the equator, an orbit out of the reach of astronauts and home to hundreds of operational commercial communications satellites.