Ground, Space Station Tests Paving Way for Robotic Satellite Servicing
KENNEDY SPACE CENTER, Fla. — NASA is abandoning plans to robotically refuel a U.S. National Oceanic and Atmospheric Administration weather satellite in orbit, but is continuing ground-based technology development and in-flight testing aboard the international space station to prepare for future exploration initiatives and for partnerships with commercial satellite operators.
A second set of Robotic Refueling Mission (RRM) tests is scheduled to begin this year following the arrival of new tools for the station’s Canadian-built Special Purpose Dexterous Manipulator robot this summer.
Last month, the Satellite Servicing Capabilities Office at NASA’s Goddard Space Flight Center in Maryland guided a robotic arm 1,300 kilometers away at the Kennedy Space Center in Florida through a series of demonstrations to transfer nitrogen tetroxide — a highly toxic, corrosive and explosive oxidizer typically used in satellite propellant — through a standard satellite fuel valve.
“On RRM, we tackled the hard things early on, like cutting of tape, cutting of little tiny lock wires, removing two different size caps and then connecting up a refueling tool and transferring simulated propellant,” project manager Benjamin Reed said.
The first set of RRM tests on the station, conducted between March 2012 and January 2013, used ethanol, which has a similar viscosity and density to nitrogen tetroxide and monomethylhydrazine fuel but is much safer to work with. The equipment was operated at a much lower pressure, roughly 50 psi rather than the 250 to 300 psi that would be needed to refuel satellites in orbit.
The Remote Robotic Oxidizer Transfer Test at Kennedy tackled both of those elements and demonstrated three different ways to move fuel — via pump, pressure and bellows.
“In particular, the pump was really difficult. No one had an oxidizer pump that we could use in our test, so we had to work with a small company to develop this new technology,” Reed said. “That added difficulty to the test but was absolutely necessary to prepare for ordinary refueling.”
The ground-based refueling test, which spanned about two weeks in February, was intended to replicate the on-orbit refueling process as closely as possible.
“We don’t want to practice transferring 7 grams [of fuel] on the ground when on orbit we’d be transferring 700 kilograms. That wouldn’t be a very realistic test. So we tried to think of all the operational details one would need on orbit and fold those in the test,” Reed said.
The next phase of RRM aboard the station will focus on other satellite repair and servicing technologies, not necessarily refueling. Equipment to be tested includes a snake-like visual inspection tool called Vipir. The device, which is about the size of a toaster, is tipped with an extendable, articulating teleoperated video camera that can be bent up and down and turned left and right for 360-degree visual imaging.
“If you needed to look around a corner or insert under a spacecraft blanket to see if maybe a micrometeoroid or orbital debris strike put a hole in structure, or if you were looking for a loose wire or a bent pin, or FOD [debris] inside a connector or a screw hole, it has the ability to do very detailed, close-up inspection work,” Reed said.
NASA had hoped to demonstrate its satellite servicing technology by refueling NOAA’s GOES-12 weather satellite, but the spacecraft was decommissioned in August 2013.
“There just wasn’t time to get everything in order,” Reed said, adding that NASA is not looking for another government satellite to refuel although it is investigating potential future joint missions with commercial satellite operators.
“The charge that the Satellite Servicing Capabilities Office has been given is to develop as a robust a suite of on-orbit capabilities as possible to give the agency — and by extension the larger domestic aerospace industry — options in orbit,” Reed said.
In addition to servicing satellites, the technologies being developed would give future astronauts traveling to and from Mars options for robotic inspection, maintenance and repair of their spacecraft. NASA also is studying if the technology could be used to snare a boulder from a rubble pile-type of asteroid and relocate it into high lunar orbit for a planned human precursor mission around 2025.
“I think there are flight missions that are tantalizingly close,” Reed said.
Whether the first robotic in-space servicing call is to a satellite in geostationary orbit, a satellite in low Earth orbit, an asteroid or somewhere else, “my job,” Reed said, “is to make sure the agency is prepared for any or all of those possible outcomes.”