GREENBELT, Md. — A simulated satellite refueling mission, one of six such robotic servicing demonstrations NASA is planning to conduct at the international space station this year, has been delayed to August from July, project officials said at the Goddard Space Flight Center here.

NASA’s Robotic Refueling Mission (RRM) uses a $22.6 million set of Goddard-built tools that attach to the end of the  space station’s robotic arm to perform simulated satellite repairs on a mockup spacecraft mounted on the station’s exterior. In August, operators at the Johnson Space Center in Houston plan to demonstrate on-orbit fluid transfer, a precursor to on-orbit satellite refueling. Some view refueling as a potential life-extender for healthy satellites that have to be pulled out of service because they run out of propellant  needed to maintain their orbits.

“We’ll demonstrate end-to-end refueling,” Jill McGuire, the RRM project manager, told an international audience of engineers, business professionals and government officials here May 30 for Goddard’s second annual International Workshop on On-Orbit Satellite Servicing. The demonstration is meant to show that a satellite fuel reservoir can be opened, refilled and resealed by a robot.

As with previous delays in the RRM program, the fueling demo was pushed back to accommodate other space station activities. Among these was the May 25 visit to the outpost by Space Exploration Technologies Corp.’s (SpaceX) Dragon capsule, which delivered cargo as part of its own  demonstration mission.

Goddard started building the RRM toolkit and mockup satellite in 2009. The hardware was carried to the station on the final space shuttle mission in July, but the project has been beset by delays ever since.

The first major RRM task, cutting safety wires, was supposed to be done in November. It was pushed into March after the loss of a Russian cargo ship last summer forced a reshuffling of space station activities. RRM activities must also be deferred to accommodate cargo deliveries; some cargo vehicles need to be grappled by the station’s robotic arm to complete their deliveries.

Such vehicles scheduled for space station visits in the second half of this year include Japan’s H-2 Transfer Vehicle in July, SpaceX’s Dragon in September and December, and Orbital Sciences Corp.’s Cygnus cargo freighter, which in the fall is slated to fly a cargo delivery demonstration mission like the one SpaceX completed May 31.

Besides the wire-cutting demonstration in March, RRM has accomplished one other task at the station: photographing the mockup satellite in periods of on-orbit day and night to see how the contrasting conditions would appear through a robot’s camera-based eyes. Programmers can use these data to build so-called machine-vision algorithms, which are needed for autonomous robotic operations, McGuire said.

RRM demonstrations tentatively scheduled for the remainder of 2012 include cutting and removing thermal insulation blankets, undoing small fasteners, and removing and stowing radio-frequency connectors, McGuire said.

Despite a string of on-orbit servicing missions during the space shuttle era — Frank Cepollina, principal investigator for RRM, counts four commercial satellites serviced by astronauts between 1984 and 1992 — no such repair mission has been carried out by robots. However, the 2007 Orbital Express mission jointly managed by NASA and the Defense Advanced Research Projects Agency (DARPA) demonstrated autonomous satellite servicing technologies — including rendezvous, capture, docking and fluid transfer and battery replacement — using two purpose-built spacecraft.

Satellite fleet operator Intelsat of Luxemburg and Washington has a long list of capabilities that will have to be checked off before robotic servicing becomes commercially appealing.

Intelsat General President Kay Sears, who runs Intelsat’s U.S. government business, wants to see “a maintenance man in space” — an orbiting spacecraft that can rendezvous with troubled satellites, inspect them and  perform any necessary repairs. The maintenance craft should also be able to replenish satellites that are running low of fuel.

Moreover, Sears said, repair craft should be able to accomplish the feats without forcing any downtime on satellite operators.

“I realize that’s a huge challenge,” Sears said. “It would take a lot of demonstrations and a lot of successful missions to do that. But ultimately, that should be our goal.”

Having a repair capability in space would have come in handy for Intelsat when the company’s New Dawn satellite failed to deploy a C-band antenna after an April launch, effectively locking out about half the transponders on the spacecraft, Sears said.

“Intelsat would have paid to have it come over and at least look at the Intelsat New Dawn satellite to see what the problem was,” she said.

Sears said Intelsat had no desire to develop a captive fleet servicing capability. “We favor a model where the fleet operator is a customer,” she said.

Intelsat had been collaborating with Canada’s MDA Corp. on a satellite in-orbit refueling service, but MDA walked away from the project in January after failing to secure government backing for a demonstration mission involving one of Intelsat’s satellites.

Meanwhile, between now and the next RRM demo in August, there will be at least one other meeting of the minds dedicated to robotic manipulation of orbiting satellites.

DARPA is hosting its Fostering Sustainable Satellite Servicing conference June 26 in Arlington, Va. The conference will focus on DARPA’s Phoenix program, in which space robots will attempt to salvage usable components from dead geostationary satellites.

In the solicitation for the Phoenix program, an award for which is expected during the summer, DARPA made overtures to international companies. Among those responding was MDA Corp.

Dan Leone is a SpaceNews staff writer, covering NASA, NOAA and a growing number of entrepreneurial space companies. He earned a bachelor’s degree in public communications from the American University in Washington.