Pathfinder is a remotely controlled, solar-powered flying wing, designed and built as a proof of concept vehicle for a much
larger aircraft capable of flying at extremely high altitudes for weeks at a time.

It was built by AeroVironment, Monrovia, California, a company that developed the human-powered Gossamer Condor and Gossamer Albatross lightweight aircraft during the 1970's, and later made the solar-electric-powered Gossamer Penguin and
Solar Challenger. The basic configuration and concepts for Pathfinder were first realized with the HALSOL (High Altitude Solar) aircraft, built in 1983 by AeroVironment and the Lawrence Livermore Laboratory.

Pathfinder is constructed of advanced composites, plastics, and foam, and despite a wingspan of nearly 100 feet, it weighs only about 600 pounds. The wing is very flexible, which enables it to distribute the load almost entirely along its span.

It is propelled by 6 electric motors, each turning a composite propeller. Electric current from solar arrays provides power during daylight, while stored energy allows flight after dark. The batteries allow an endurance of about two hours in darkness.

On September 11, 1995 the aircraft achieved a major milestone in the ERAST program when it was flown to an altitude of
50,567 feet during a nearly 12-hour mission. The previous altitude record for a solar-powered aircraft was 14,000 feet. In 1997 the craft was flown to over 71,500 feet near Hawaii, a world record at that time for propeller-driven as well as solar-powered aircraft.

It is one of several unpiloted prototypes under study by the NASA ERAST (Environmental Research Aircraft and Sensor Technology) program, a NASA-industry alliance which is helping develop advanced technologies that will enable aircraft to study the environment of the Earth during extremely long flights at altitudes in excess of 100,000 feet.

Pathfinder flies very slowly, within a narrow speed range. Takeoff is at about 17 miles per hour, cruise speed is about
21 miles per hour, and it climbs at 150 feet per minute. Pathfinder pilot Dave Ganzer says, "It's like flying underwater, because everything happens at such a slow time-scale."

Because of its slow speeds Pathfinder flights are meticulously planned around the weather. Winds during takeoff and landing
need to be less than 12 miles per hour. Mission simulations are flown before, and even during a flight to negotiate changing weather. Winds aloft often make the aircraft fly backwards or stationary (relative to the ground), but winds that can adversely affect the Pathfinder usually diminish above an altitude of 30,000 feet.

Pathfinder mostly flies by autopilot, with a pilot and flight test engineer commanding the mission from the ground. Although the pilot has a control stick, the aircraft is usually "flown" using rotary switches that change aircraft headings and turn rates by
means of the autopilot. It is described as an easy plane to land: its normal descent rate of 70 feet per minute is lowered (by throttle) to 40 feet per minute, and the plane is steered into the wind until touchdown.

Pathfinder Project Home Page
Pathfinder Fact Sheet

ERAST Program Home Page
ERAST Fact Sheet

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