The U.S. Air Force Research Laboratory has dropped plans for the development of a prototype spacecraft to act as an

escort for other satellites, and is instead pursuing a broader space monitoring experiment, according to a lab official.

The laboratory

likely will keep the ANGELS acronym for the experiment but change its meaning,

according to Vern Baker, ANGELS program manager at the Air Force Research Laboratory’s space vehicles directorate,

Kirtland Air Force Base, N.M.

ANGELS originally stood for Autonomous Nanosatellite Guardian for Evaluating Local Space.

The laboratory awarded a $30 million contract

Nov. 7 to Orbital Sciences Corp. of Dulles, Va., to develop the ANGELS spacecraft, which is expected to launch in 2010, according to a Pentagon contract announcement. The spacecraft

initially was expected to cost $20 million and weigh 10 kilograms, but both figures were revised upward due to a more realistic understanding of the complexity of the technology involved in the project, Baker said during a Nov. 15 interview.

The ANGELS spacecraft

now is expected to weigh about 65 to 70 kilograms, Baker said. This still represents progress, as it is significantly smaller

than the XSS-11 spacecraft, a prior proximity operations experiment launched in 2005 that will help provide the basis for the ANGELS work, he said. Proximity operations experiments generally involve one spacecraft approaching another satellite or other object in orbit for purposes ranging from inspection to refueling. The XSS-11 satellite weighed about 140 kilograms.


also will feature more advanced systems for its electro-optical sensor and autonomous operations capability than XSS-11, and will operate at a geostationary orbit, unlike XSS-11, which operated in a low Earth orbit, Baker said.

In order to keep the cost of the work affordable, ANGELS will use similar avionics and ground systems to those of XSS-11, Baker said. Program officials

also are looking at lessons learned from other proximity operations experiments like the Defense Advanced Research Projects Agency’s Orbital Express satellite servicing mission, which launched in March, Baker said.

The program

also will examine lessons learned from NASA’s Demonstration of Autonomous Rendezvous Technology spacecraft

– also built by Orbital Sciences – which accidentally bumped into its target satellite during the experiment in 2005, as part of an effort to address safety with the ANGELS experiment, Baker said.

While the complexity of the ANGELS satellite affected the weight and cost, those two factors did not force the decision to change the satellite’s mission, Baker said.

Program officials did realize, however, that technology was not available to build

the type of space surveillance satellite they

initially wanted in the tiny package that was envisioned at the beginning of the experiment, Baker said.

The ANGELS experiment

initially was conceived as

a tiny satellite that would be placed in an orbit


a larger spacecraft so it could


out for potential signs of trouble. Laboratory officials decided this spring that the escort concept was too narrow a task, and opted for a more general space situational awareness mission, which led them to spend the next several months meeting with potential bidders to explain the shift, Baker said. The full details of what will take place under the re-planned mission

still are under discussion, he said.

The ANGELS experiment

is expected to run over the course of a year, though program officials are hopeful that the satellite will last an additional two years, allowing them to conduct further experimentation, Baker said.

The ANGELS technology will have applications to civilian space missions as well, according to an Orbital Sciences news release dated Nov. 14. However, Barron Beneski, a spokesman for Orbital Sciences, would not comment further about the program and said that company officials declined to be interviewed about the effort.

Because it

still will be a relatively small satellite, the

ANGELS spacecraft

likely will need to be launched

with at least one other satellite on an Atlas 5 or Delta 4 launch vehicle, and will be designed to fit on a secondary payload adapter ring for those rockets, Baker said.