PATHFINDER

Introducing Solar-Powered Aircraft

for

Observing the Environment

Without Disturbing Nature
Pathfinder

The NASA Pathfinder aircraft, designed and built by AeroVironment Inc., for the NASA Environmental Research Aircraft

and Sensor Technology (ERAST) Program, is a lightweight, remotely-piloted, solar-powered aircraft weighing less than

600 lb. Pathfinder is a proof-of-concept forerunner for the Centurion and its successor, the Helios Prototype aircraft.

Pathfinder is constructed of state-of-the-art composites, plastics, and foam. The upper surface of the aircraft’s 100-ft wing

is covered almost completely by thin solar-cell arrays that collect sunlight and convert it into electricity. This electricity

powers six small motors with propellers. Slowing down or speeding up these individual propellers allows Pathfinder to

make turns, since it does not have ailerons and rudders typical of most airplanes.

Pathfinder Flight History

Pathfinder was developed in the early 1980s, and was adopted into NASA’s ERAST Program in 1993. After initial flight

tests at NASA Dryden Flight Research Center, at Edwards, CA, it was modified with additional solar arrays and other

upgrades. Another series of development flights began in 1995. On September 11, 1995, Pathfinder reached an altitude of

50,500 ft, setting a new altitude record for solar-powered aircraft.

After more upgrades and one checkout flight at Dryden in late 1996, Pathfinder was deployed to the U.S. Navy’s Pacific

Missile Range Facility (PMRF) at Barking Sands, Kauai, HI, in April 1997. Kauai was chosen as an optimum location for

testing the solar-powered Pathfinder due to its 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 missions from PMRF. By this time it was clearly the world’s highest-flying solar-powered

aircraft. With a flight to 71,530 ft Pathfinder had also flown higher than any other propeller-driven aircraft.

Pathfinder Plus

Essentially a transitional vehicle, the Pathfinder Plus was a hybrid of the technology employed on Pathfinder and developed for the Centurion/Helios Prototype.

During 1998, the Pathfinder was modified into the longer-winged Pathfinder Plus configuration. On August 6, 1998, the

Pathfinder Plus was flown to an altitude of approximately 80,200 ft, again setting new standards for solar-powered and

propeller-driven aircraft. The goal of the flights was to validate new solar, aerodynamic, propulsion, and systems technologies developed for the Pathfinder’s successor, the Centurion/Helios Prototype.

The most noticeable change in the Pathfinder Plus was the installation of a center wing section that incorporated a highaltitude airfoil designed for Centurion. The new section was twice as long as the original Pathfinder center section and

increased the overall wingspan of the craft from 98.5 to 121 ft. The new center section was topped by more efficient

silicon solar cells that could convert 19 percent of the solar energy they receive into useful electrical energy to power the

craft’s motors, avionics, and communication systems. Maximum potential power was boosted from about 8,000 kW on

Imagine... 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, and is controlled remotely from a ground station.

Imagine the Pathfinder.
Pathfinder to about 12,500 kW on Pathfinder Plus. Pathfinder’s six motors were replaced by motors designed for the

Centurion, and two additional motors were mounted on the center section of the wing.

Centurion/Helios Prototype

Centurion began flying in 1998. It had a wingspan of 206 ft, was powered by 14 electric motors, and had an empty weight

of only 1,175 lb. In 1999 Centurion became the Helios Prototype after undergoing modifications increasing its wingspan

to 247 ft. The Helios Prototype is designed to reach an altitude of 100,000 ft, as well as demonstrate the ability to fly for

96 consecutive hours.

Helios

The Pathfinder/Centurion/Helios series of aircraft are designed to carry a payload of scientific sensors that may be used

for a variety of monitoring purposes while flying at extremely high altitudes. They fly much slower than most aircraft,

with cruising speeds of only about 20-27 mph. The slower a vehicle flies, the greater its ability to capture samples of the

atmosphere without altering them. NASA is especially interested in these vehicles for their ability to study the upper

atmosphere without disturbing it. Helios will use an energy storage system to power the aircraft at night. The solar cells

power the vehicle during the day and recharge the energy storage system for use at night. The duration of such flights

could be indefinite, making Helios suitable for missions that were previously impossible for an aircraft. It could:

• Spend long periods of time over the ocean monitoring storm developments

to provide more accurate predictions of hurricanes.

• Monitor coral reefs to determine damage caused by humans.

• Monitor forest life to provide early warning of crop damage or fires.

• Serve as a surrogate satellite when regular satellite coverage is not available.

206'

98.4'

121'

Helios (front)

Helios (side)

Centurion

Pathfinder Plus

Pathfinder

247'

Helios (top)
Classroom Activity–Pathfinder on a String

In this activity you will construct a model of the Pathfinder aircraft that

really flies.

Materials needed per student

• One meter of string or fishing line

• One drinking straw

• Transparent tape

• One sheet of letter-size paper, with template copy

• Scissors

Construction Procedure

1. Distribute the materials.

2. Students will follow the four steps marked on the template:

Step One. Make a pencil-size hole in copy of template

marked Step 1.

Step Two. Make a pencil-size hole in copy of template

marked Step 2.

Step Three. Fold along the line marked Step 3,

and keep folded.

Step Four. Align the 8.5” edges and tape them together.

3. Cut straw into three equal pieces, approximately 5 cm long.

4. Insert one of the straw pieces through both holes (see picture).

5. Thread the string through the straw to create the Pathfinder on

a String.

6. Use the other two pieces of the straw for handles (see picture).

Flying your Pathfinder on a String

Hold the straw handles, with your arms straight out, so the string through

the wing is parallel perpendicular to the ground. This forward motion

will cause air to flow over and under the Pathfinder creating lift and a

flying model. Flying Pathfinder on a String can be done indoors or

outdoors.

Explanation

The Pathfinder is a giant airfoil. What you have done is built an airfoil

model on a string. When you fly your Pathfinder model, the shape of

the airfoil creates lift. Lift is created when slow moving air molecules

under the wing create high pressure, and fast moving air molecules

above the wing create low pressure. There are many other factors that

affect the flight of your airfoil. As you walk forward, your motion is

creating the thrust that moves the airfoil forward. The forces of drag

and gravity are other forces that act upon the flight of your Pathfinder

on a String.

Extensions

• Attach paper clips (adding weight) to the airfoil trailing edge of

the airfoil and observe its flight characteristics.

• Fly Pathfinder on a String in front of a fan.

• Experiment with different sizes of paper for the airfoil.

Straw handle

Straw

Tape

String

Thread the string

through the straw

to make a handle.

Secure the handle

with a knot.
Step 4. Tape along this line

Step 3. Fold along this line

Step 1. Punch hole with pencil

Step 2. Punch hole with pencil
The cover of this poster

is a stylized look at a Pathfinder reseach flight and the promise

of solar-powered aircraft like Helios.

The night sky represents

flights that continue 24

hours a day.

Pathfinder, backlit by the

sun, cruises in the

stratosphere, above the

highest clouds.

Hurricanes and other

destructive weather

systems in the

troposphere are safely

observed from above.

Hawaii was one of the

first regions to be studied

by Pathfinder. Aerial

photographs of the

tropics can help farmers

monitor the health of

crops like sugar cane

(background, center).

High-altitude observation

of the ocean helps us

understand how humans

are affecting the undersea

ecosystem.
 EW-1999-04-003-DFRC

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http://spacelink.nasa.gov

NASA Education Home Page

Information about all of the NASA Education Programs.

http://education.nasa.gov/

Pathfinder Web Sites

Pathfinder Mission Updates

http://www.dfrc.nasa.gov/Projects/Erast/

pathfinder.html

Pathfinder Movies

http://www.dfrc.nasa.gov/gallery/movie/

Pathfinder/index.html

Pathfinder Remote Sensing Images

http://geo.arc.nasa.gov/ERAST/pathfinder/

index.html

http://hawkeye.arc.nasa.gov/ERAST/

Remote Sensing Map of Kauai, HI

http://hawkeye.arc.nasa.gov/cgi-bin/

pathfindermap?/kauai Wallsheet Credits

Cover design by Ted Huetter and Dennis Calaba

Cover illustration by Dennis Calaba

Back design and layout by Steve Lighthill

 and Ted Huetter

Pathfinder on a String Activity by Michelle Davis

Back illustrations by Dennis Calaba and Steve Lighthill

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