NASA and industry researchers are increasingly
confident a pilot in a remote ground station can safely
detect and avoid collisions between an Unmanned Aerial
Vehicle (UAV) and other aircraft. Detect, see and avoid
technology is vital if remotely piloted or autonomous
aircraft are to be integrated into the airspace system
shared with inhabited aircraft.

The latest round of flight tests, sponsored by NASA’s Dryden
Flight Research Center, Edwards, Calif., under the
Environmental Research Aircraft and Sensor Technology
(ERAST) program, took place April 1-4 near Mojave, Calif.

“The goal of the test was to be able to make a decision
based on radar data in enough lead time to maneuver the test
aircraft to avoid a close encounter with the intruder
aircraft,” said Glenn Hamilton, UAV subsystems project
manager at Dryden.

The Proteus aircraft, built by Scaled Composites of Mojave,
with safety pilots on board, but controlled from the ground
like a true UAV, was repeatedly directed away from
conflicting flight paths, with a variety of aircraft, some
of which did not emit any signals to show their positions.

In all 20 scenarios flown, the Proteus ground operator was
able to detect the presence of other aircraft that posed the
potential for collisions, maneuvering the test aircraft to
keep the intruding aircraft from entering a 500-foot bubble
of safe airspace surrounding Proteus.

The conflicting aircraft flew at greatly different speeds,
from a NASA F/A-18 high-speed jet to several types of
general aviation aircraft including an unpowered sailplane.

“The detection ranges were a little less than we expected,
but varied greatly from about 2.5 to 6.5 nautical miles,
based on the structure and radar cross-section of the target
aircraft,” Hamilton recalled. “We picked up the F/A-18
farther out, due to its larger radar signature, but because
of its higher speed, it didn’t give us a whole lot of extra
time to make an avoidance decision. On one head-on scenario,
we had a 610-knot closure speed, not a whole lot of time to
decide,” he said.

The use of radar to detect these aircraft included one
surprise. A 1940s-vintage fabric-covered Stinson Voyager
made a larger-than-expected radar signature, possibly due to
its large aluminum-covered tail surfaces.

The recent tests follow a series last year near Las Cruces,
N.M., in which Proteus’s remote pilot, using data from
another detection device, was able to avoid conflict with
aircraft that used transponders to identify their positions.
Researchers are encouraged by the results of both test
series, but say more work is required before a refined,
operational detect, see and avoid system can be fielded.