Two organizations developing spacecraft capable of servicing satellites in orbit say a recent collision of two satellites that were only supposed to rendezvous will have no impact on their plans because they intend to keep humans in the loop rather than rely on spacecraft autonomy.

NASA’s Demonstration of Autonomous Rendezvous Technology (DART) spacecraft accidentally bumped into a retired Defense Department satellite last month at the end of a flight experiment that was designed — as its name suggests — to demonstrate autonomous rendezvous technology.

Engineers in Europe and the United States are designing new spacecraft, sometimes called space tugs, that would extend the lives of satellites already in orbit by docking with them to provide new propulsion capabilities or, in some cases, refuel them or even replace some hardware.

Officials at London-based Orbital Recovery Ltd. and the U.S. Defense Advanced Research Projects Agency (DARPA) reacted to DART’s failure by noting that their approaches to servicing will include human control.

“The big difference there is they attempted to do a rendezvous that is autonomous. We always have a man in the loop,” said Alex Polman, chief financial officer of Orbital Recovery.

Orbital Recovery is developing the proposed ConeXpress Orbital Life Extension Vehicle (CX-OLEV) for operators of geosynchronous commercial telecommunications satellites who presumably will pay millions of dollars to return their spacecraft to their proper orbits instead of replacing them.

Expendable CX-OLEVs would attach themselves to the existing motor fixtures of these satellites and boost them back to their proper orbits, extending their lives by up to eight years, according to Polman.

Controllers would operate CX-OLEVs manually from a ground station called the Modular Architecture for Robot Control (MARCO). MARCO was developed by the German Space Agency DLR and was tested successfully by controlling robotic hardware aboard the international space station, said Dennis Wingo, Orbital Recovery’s chief technology officer.

Polman said he expects Orbital Recovery to sign its first customer this month or in June, which would open the door to start construction of the first CX-OLEV for a launch in 2008.

Unlike CX-OLEV, DARPA’s Orbital Express mission in 2006 will test docking hardware that designers might some day incorporate into new reconnaissance or military satellites to make them serviceable.

When asked about the DART failure, Air Force Lt. Col. Jim Shoemaker, the Orbital Express program manager, noted that his mission will rely on a blend of human and autonomous control.

“We’re using degrees of autonomy where we start out very closely supervised, and after that we shift to higher degrees of autonomy,” Shoemaker said.

Before the DART launch, program manager Jim Snoddy at Marshall Space Flight Center in Huntsville, Ala., noted that some of the engineers assigned to DART also would work on Orbital Express. In addition, Snoddy described DART’s eye — the Advanced Video Guidance Sensor — as a candidate for the guidance sensor on Orbital Express.

In another indication of the links between the two programs, Camillo Arcilesi, the chief engineer for Orbital Express at DARPA, will serve on the 75-day DART mishap investigation board. His name appears on the list of members released by NASA April 22.

In the Orbital Express mission, a prototype servicing satellite known as the Autonomous Space Transport Robotic Operations (ASTRO) will attempt to dock with a spacecraft called NEXTSat, which will play the role of a satellite ready for servicing.

Boeing’s Phantom Works research and development unit in Huntington Beach, Calif., leads the $113-million, 42-month design and fabrication phase that began in March 2002. Ball Aerospace in Boulder, Colo., is building NEXTSat. Shoemaker declined to answer questions about the status of Orbital Express , except to say, “We’re in the middle of bending metal.”

Autonomy was the primary goal of the DART mission that failed April 15. After launch, DART was supposed to find and approach a 47-kilogram retired military satellite called the Multi-path Beyond Line-of-sight Communications (MUBLCOM), without any assistance.

DART successfully approached within 300 feet, according to NASA. It was supposed to conduct a series of maneuvers to imitate a spacecraft inspecting a satellite and preparing to dock with it. Instead, DART reported that it was out of fuel and had shut itself off. Tracking data later showed that MUBLCOM had moved from its original orbit, leading NASA officials to conclude that DART bumped it.

“It appears that the guidance navigation error that caused [DART] to use its fuel early caused the contact,” spokeswoman Kim Newton said May 6. She said the investigation board would study the mishap for 75 days.