NASA 

National Aeronautics and 

Facts

Space Administration 

Dryden Flight Research Center 

P.O. Box 273

Edwards, California 93523 

Voice 661-276-3449 

FAX 661-276-3566 

pao@dfrc.nasa.gov FS-2002-04-DFRC 

Pathfinder

Leading the way in solar flight

The Pathfinder Plus flew two commercialization demonstration missions over Hawaii in 2002. --Nick Galante / PMRF for NASA 

Just imagine... 

• An aircraft that could stay aloft all day, powered only by sunlight. 

• An aircraft that is no more than a flying wing, able to maneuver without rudders, ailerons, tails or other control 

surfaces typical of conventional aircraft. 

• An aircraft that flies without an onboard human pilot, but instead is controlled remotely from a ground station. 

At the NASA Dryden Flight Research Center at Edwards, Calif., imagination has become reality, and that reality is the 

Pathfinder solar-powered, remotely piloted aircraft. 

Aircraft Description 

The Pathfinder is a lightweight, solar-powered, remotely piloted flying wing aircraft that is demonstrating the 

technology of applying solar power for long-duration, high-altitude flight. It is literally the pathfinder for a future fleet of 

solar-powered aircraft that could stay airborne for weeks or months on scientific sampling and imaging missions.

 Solar arrays covering most of the upper wing surface provide power for the aircraft’s electric motors, avionics, 

communications and other electronic systems. Pathfinder also has a backup battery system that can provide power for 

between two and five hours to allow limited-duration flight after dark.

1
Pathfinder flies at an airspeed of only 15 to 25 mph. 

Although pitch control is maintained by the use of tiny 

elevons on the trailing edge of the wing, turns and yaw control 

are accomplished by slowing down or speeding up the motors 

on the outboard sections of the wing. 

Pathfinder was designed, built and is operated by 

AeroVironment, Inc., of Monrovia, Calif., the firm that 

developed the pioneering Gossamer Penguin and Solar 

Challenger solar-powered aircraft in the late 1970’s and early 

1980’s. 

Pathfinder Flight History 

Pathfinder was first developed for a now-cancelled 

classified government program in the early 1980’s to develop 

a high-altitude, long-endurance aircraft for surveillance 

purposes. Known as the HALSOL (for High-Altitude SOLar) 

aircraft, its eight electric motors — later reduced to six — 

were first powered by batteries. After that project was 

cancelled, the aircraft was placed in storage for 10 years 

before being resurrected for a brief program under the auspices 

of the Ballistic Missile Defense Organization (BMDO) in 

1993. With the addition of small solar arrays, five lowaltitude checkout flights were flown under the BMDO program 

at NASA Dryden in the fall of 1993 and early 1994 on a 

combination of solar and battery power. 

After that program was ended, the aircraft was adopted 

into NASA’s newly-established Environmental Research 

Aircraft and Sensor Technology (ERAST) project in late 

1994. After further flight tests at Dryden that year, additional 

solar cells were added, eventually covering most of the upper 

surface of the wing. Pathfinder was then brought back for 

another series of development flights at NASA Dryden in 

1995. On Sept. 11, 1995, Pathfinder reached an altitude of 

50,500 feet, setting a new altitude record for solar-powered 

aircraft. The National Aeronautic Association presented the 

NASA-industry team with an award for one of the “10 Most 

Memorable Record Flights” of 1995.

 After additional upgrades and one checkout flight at 

Dryden in late 1996, Pathfinder was transported to the U.S. 

Navy’s Pacific Missile Range Facility (PMRF) at Barking 

Sands, Kaua’i, Hawaii, in April, 1997. Kaua’i was chosen as 

an optimum location for testing the solar-powered Pathfinder 

due to predictable weather patterns, high levels of sunlight, 

available airspace and radio frequencies and the diversity of 

terrestrial and coastal ecosystems for validating scientific 

imaging applications. While in Hawaii, Pathfinder flew 

seven high-altitude flights from PMRF, one of which reached 

a world altitude record for propeller-driven as well as solarpowered aircraft of 71,530 feet. 

Pathfinder “Plus” Modification 

During 1998, the Pathfinder was modified into the 

Pathfinder soars aloft from NASA Dryden on the first of its record 

altitude flights on Sept. 11, 1995. 

--NASA Dryden photo by Tony Landis 

longer-winged Pathfinder-Plus configuration. On Aug. 6, 

1998, the modified aircraft was flown to a record altitude of 

80,201 feet for propeller-driven aircraft on the third of a 

series of developmental test flights from PMRF on Kaua’i. 

The goal of the flights was to validate new solar, aerodynamic, 

propulsion and systems technology developed for the 

Pathfinder’s successor, the Centurion/Helios Prototype, which 

was designed to reach and sustain altitudes in the 100,000-

foot range. 

Essentially a transitional vehicle between the Pathfinder 

and the follow-on solar wings, thePathfinder-Plus is a hybrid 

of the technology that was employed on Pathfinder and 

developed for Centurion/Helios. 

The most noticeable change is the installation of a new 

44-foot-long center wing section that incorporates a highaltitude airfoil designed for Centurion/Helios. The new section 

is twice as long as the original Pathfinder center section and 

increases the overall wingspan of the craft from 98.4 feet to 

121 feet. The new center section is topped by more-efficient 

silicon solar cells developed by SunPower Corp., Sunnyvale, 

Calif., that can convert almost 19 percent of the solar energy 

they receive to useful electrical energy to power the craft’s 

motors, avionics and communication systems.,That compares 

with about 14 percent efficiency for the older solar arrays that 

cover most of the surface of the mid- and outer wing panels 

from the original Pathfinder. Maximum potential power was 

boosted from about 7,500 watts on Pathfinder to about 

12,500 watts on Pathfinder-Plus. 

In addition, the Pathfinder-Plus is powered by eight 

electric motors, two more than powered the previous version 

of Pathfinder. Designed for the Centurion/Helios Prototype 

follow-on solar wings, the motors are slightly more efficient 

than the original Pathfinder motors. The Pathfinder-Plus also 

validated a new flight control system for the Centurion/ 

Helios Prototype, although only the Pathfinder’s own system 

actually controlled the motors and control surfaces. 

2
Environmental Monitoring & Technical 

Demonstration Missions 

Major science activities of Pathfinder missions have 

included detection of forest nutrient status, forest regrowth 

after damage caused by Hurricane Iniki in 1992, sediment/ 

algal concentrations in coastal waters and assessment of 

coral reef health. Science activities are coordinated by the 

NASA Ames Research Center, Moffett Field, Calif., and 

include researchers at the University of Hawaii and the 

University of California. 

Thus far, Pathfinder has flight tested two new scientific 

instruments, a high spectral resolution Digital Array Scanned 

Interferometer (DASI) and a high spatial resolution Airborne 

Real-Time Imaging System (ARTIS), both developed at 

Ames. These flights were conducted at altitudes between 

22,000 and 49,000 feet in 1997. 

During the summer of 2002, the Pathfinder-Plus flew 

several demonstration missions to confirm the practical 

utility of high-flying, remotely piloted, environmentally 

friendly solar aircraft for commercial purposes. A two-flight 

series in July funded by Japanese communications interests 

and AeroVironment emphasized its potential as a platform 

for telecommunications relay services, and another NASAfunded demonstration in September saw the Pathfinder-Plus 

soaring aloft on a NASA-sponsored coffee harvest 

optimization imaging mission. Both missions were flown 

from PMRF on the Hawaiian island of Kaua’i. 

Remotely piloted, solar-powered aircraft similar to 

Pathfinder, such as the follow-on Helios ultra-long-duration 

flying wing now being developed, could spend long periods 

over the ocean, monitoring storm developments to provide 

more accurate hurricane predictions. These aircraft also 

could be used to monitor major croplands, forests and other 

large, remote expanses to provide early warning of crop 

damage or fires. In addition to their commercial 

communications relay potential, they could also be 

instrumental in quickly establishing emergency 

communications links for recovery and relief workers in 

areas struck by natural disasters where existing 

communications infrastructure has been crippled. 

Pathfinder takes off for a science demonstration mission over Hawaii 

in 2002. -- Nick Galante/PMRF for NASA 

The ERAST Program 

Pathfinder is one of several remotely piloted aircraft 

being evaluated under NASA’s Environmental Research 

Aircraft and Sensor Technology (ERAST) program. The 

ERAST program is one of NASA’s initiatives designed to 

develop the new technologies needed to continue America’s 

leadership in the highly competitive aerospace industry. 

Additional technologies considered by the joint NASAindustry ERAST Alliance include lightweight materials, 

avionics, sensor technology, aerodynamics and other forms 

of propulsion suitable for extreme altitudes and duration. The 

most extreme mission envisioned for solar-powered aircraft 

such as Pathfinder’s successor, the Helios, would reach 

altitudes of up to 100,000 feet for science and commercial 

applications, as well as fly for weeks or months at a time on 

extended duration missions with the assistance of a fuel cellbased supplemental energy system for nighttime flight. 

The ERAST program is sponsored by the Office of 

Aerospace Technology at NASA Headquarters, and is 

managed by the NASA Dryden Flight Research Center. 

Aircraft Specifications 

• Wingspan: Pathfinder 98.4 feet (29.5 meters);

Pathfinder-Plus 121 feet (36.3 meters)

• Length: 12 feet (3.6 meters) 

• Wing chord: 8 feet (2.4 meters) 

• Wing Aspect Ratio: Pathfinder –12 to 1; PathfinderPlus–– 15 to 1 

• Gross weight: Pathfinder about 560 pounds (252

kg.); Pathfinder-Plus about 700 pounds (315 kg.).

• Payload: Pathfinder—up to 100 pounds (45 kg.);

Pathfinder-Plus up to 150 pounds (67.5 kg.)

• Airspeed: Approx. 17-20 mph cruise. 

• Power: Arrays of solar cells, maximum output:

Pathfinder—about 7,500 watts;

Pathfinder-Plus—about 12,500 watts.

• Motors: Pathfinder, six electric motors;

Pathfinder-Plus, eight electric motors, 1.5 kW

maximum each.

• Endurance: About 14 to 15 hours, daylight limited 

with two to five hours on backup batteries. 

• Glide ratio (power off): Pathfinder—18 to 1;

Pathfinder-Plus—21 to 1.

• Manufacturer: AeroVironment, Inc., Monrovia,

Calif.

• Primary materials: Carbon fiber, Nomex,

Kevlar, plastic sheeting and plastic foam.

- NASA -

October, 2002 

3