WASHINGTON — Later this year, in the next major milestone for NASA’s robotic refueling demonstration program, an operator in Maryland will take control of a robot 1,400 kilometers away in Florida and attempt to fill a mockup satellite with a corrosive fuel oxidizer.
It would be the first so-called Robotic Refueling Mission (RRM) demonstration in which a remotely operated robot handles nitrogen tetroxide, one of the dangerous chemicals used aboard real satellites, said Frank Cepollina, associate director for the Satellite Servicing Capabilities Office at the Goddard Space Flight Center in Greenbelt, Md., and principal investigator for RRM.
The nitrogen tetroxide test is tentatively scheduled for “the fall or winter timeframe this year,” Cepollina said in a Feb. 19 interview. The robot and model satellite will be located at the Kennedy Space Center, which is equipped to safely store, handle and — if necessary — clean up the hazardous fluid.
The experiment will be a follow-on to a January demonstration at the international space station (ISS), in which an operator at the Johnson Space Center in Houston used the station’s robotic arm to transfer an ethanol-based fluid between two reservoirs built into a dummy satellite. Ethanol has about the same density as hydrazine, a common satellite propellant considered too dangerous to experiment with near the crewed ISS.
In the ground-based test NASA is planning, “we’re going to attempt to demonstrate nitrogen tetroxide transfer in the very same way,” Cepollina said. “But instead of the robot in space being operated from Houston, the master will be at Goddard, and the robotic slave will be at Kennedy.”
As with previous RRM tests, the nitrogen tetroxide transfer will rely on existing robotic hardware, but require some custom software. The software “is being written,” Cepollina told SpaceNews. The test also will need some nitrogen tetroxide pumps that have not been built yet, Cepollina added.
“That will be one of the drivers,” Cepollina said. “We’re waiting for the pumps to be finished and be delivered to Kennedy.”
The goal of the RRM project, which is funded by NASA’s Human Exploration and Operations Mission Directorate, is to mature technology needed for robotic satellite servicing, particularly of geostationary communications satellites that were not designed to be refueled, or even touched, after launch.
From 2009 to 2011, NASA spent about $22.6 million to build and launch the RRM hardware, which includes the mock satellite now hosted at ISS and a set of custom-built tools designed by Goddard engineers for use with the station’s Canadian-built robotic arm. NASA spent $9.2 million on RRM in 2012 and is on track to spend another $10 million this year, NASA spokesman Dewayne Washington wrote in a Feb. 20 email.
These figures include RRM operations at the space station, but also design and development work on new satellite servicing tools and hardware that could be flown to space for a second set of RRM demonstration missions Cepollina’s team plans to conduct through 2015.
The first shipment of new hardware is tentatively scheduled to arrive at ISS aboard one of Japan’s H-2 Transfer Vehicles, Cepollina said. The next launch of the Japanese cargo hauler is scheduled for August. A second cache of new RRM hardware would be sent to the station in 2014 aboard a yet-to-be-identified launch vehicle, Cepollina said.
The RRM demo satellite, which includes valves, caps, heat blankets and other features commonly found on real communications birds, has been installed on the station’s Express Logistics Carrier-4 platform, which faces Earth. It was sent to ISS in July 2011 aboard the Space Shuttle Atlantis during STS-135, the final shuttle mission.
When the space station’s schedule allows, an operator at Johnson Space Center uses the station’s Canadian-built robotic arm and the Goddard-designed satellite servicing tools to practice remote servicing tasks.
As with every demonstration task the RRM team has performed, the fluid transfer demonstration — what Cepollina called the Robotic Refueling Mission’s “main event” — was completed a little later than expected. Ground teams started performing sample servicing tasks in March 2012, almost five months later than envisioned when the RRM hardware launched. Earlier satellite servicing demonstrations included cutting away thermal insulation and wires so the robotic ISS arm could reach and remove a fuel cap.
In May 2012, Goddard briefed an international audience about the early results of the RRM project at the center’s second On-Orbit Satellite Servicing workshop. But this year, with federal travel budgets on ice, Goddard decided not to host another workshop. However, members of Cepollina’s RRM team will travel to upcoming space conferences to discuss the project.
The first such briefings will happen at the Satellite 2013 conference being held March 18 to 21 here. Benjamin Reed, Cepollina’s deputy, and Jill McGuire, RRM project manager, will present findings from the latest robotic refueling experiments at ISS, including the January fluid transfer demonstration.
Cepollina believes that between the global satellite communications industry and government-operated craft, there are enough expensive assets in geostationary orbit that repairing and refueling them makes more financial sense than replacing them before their transponders fail. Cepollina sees robotic servicing craft as a logical follow-on to four astronaut-led commercial satellite repair missions facilitated by NASA between 1984 and 1992.
