Roboticists developing satellite-servicing technology at ’s have completed a ground-based teleoperations demonstration that transferred corrosive nitrogen tetroxide (NTO) through a standard satellite-fueling valve at (KSC), using a robot controlled from Goddard.
The ground test, and the upcoming second phase of the Robotic Refueling Mission (RRM) on the International Space Station, continue pushing technologies that may allowto stretch the service lives of expensive science satellites in Earth orbit robotically, as has been done with astronauts over five space shuttle servicing missions to the Hubble Space Telescope.
In the Remote Robotic Oxidizer Transfer Test (RROxiTT) completed in February, Goddard engineers set up an industrial robot equipped with custom software in the satellite-fueling facility at KSC and used it to transfer NTO, controlling the operation from a robotics workstation 800 mi. away at their Greenbelt, Md., NASA field center.
The Goddard group also designed a tool to interface with the standard satellite servicing valve on the KSC testbed, while Kennedy engineers developed the hose management system and propellant transfer assembly attached to the back end of the robot.
For space station crew safety, the on-orbit refueling tests have used ethanol as a simulated propellant rather than NTO or toxic hydrazine used in satellite propulsion systems. At Kennedy, technicians wore the Self-Contained Atmospheric Protection Ensemble (Scape) suits required for spacecraft fueling, while at Goddard Alex Janas, the lead RROxiTT roboticist, worked in shirtsleeves as he teleoperated the refueling test rig.
“The biggest takeaway here was the forced integration points in this test,” Janas said. “We’ve always been developing the software and the mechanisms and the propellant transfer all separate from each other. The fact that this test forced us to integrate with all the other teams, I think, was one of the biggest lessons. We gained a lot of information about each other’s systems and how we interact.”
Meanwhile, additional task boards and other hardware for the Goddard-developed RRM testbed on the ISS are scheduled to arrive as early as this summer in the next European Automated Transfer vehicle. Some of the tools that the station’s Canadian-built Special Purpose Dexterous Manipulator (Dextre) robot will employ in the next phase of the RRM work already have been delivered to the space station.
Designed to be passed through the airlock in the Japanese Experiment Module Kibo, the new demonstration hardware includes a “visual inspection poseable invertebrate robot tool”—dubbed Vipir—that will allow extremely close visual examination of in-space hardware to aid diagnosis of problems.
“One of the key functions of a robotic servicing vehicle is to be able to see what’s wrong,” says Frank Cepollina, a longtime space-servicing expert at Goddard who is associate director of the Satellite Servicing Capabilities Office there. “. . . We have what’s called a Vipir, which is an extensible, articulated arm. It allows you to sit there on the ground and move this inspection camera 360 degrees around, lift the elbow, look up, look down, all these kinds of things.”
Overall, the second phase of RRM has enough work to fill about 12 months that could be stretched over a three-year service life, depending on ISS operational priorities. Other tasks include reassembly of cryogenic valves that were disconnected earlier, robotic work with electrical connectors linked to a solar-powered LED indicator to show when connections are made, and an experiment to test plugging techniques with an open aluminum tube. The hardware also includes four-junction gallium arsenide solar cells supplied by Glenn Research Center that will be tested in space on the RRM real estate.