Aug. 19, 1998 NASA's remotely piloted, solar-powered Pathfinder-Plus flying wing reached a record altitude of more than 80,000 feet during a developmental test flight Aug. 6 in Hawaii. The altitude is the highest ever achieved by a propeller-driven craft and surpasses the official record altitude of 71,530 feet for a solar-powered aircraft set by an earlier version of the Pathfinder last summer. The Pathfinder-Plus is an upgraded version of the Pathfinder solar-powered aircraft developed under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program, led by the Dryden Flight Research Center, Edwards, Calif.
The Pathfinder-Plus was aloft for almost 15 hours during the record flight. It lifted off from the U.S. Navy's Pacific Missile Range Facility (PMRF) on the island of Kaua'i shortly before 8 a.m. Hawaii time Thursday, and reached its peak altitude of 80,285 feet as recorded by radar tracking at about 3:30 p.m. after a long ascent. Pathfinder-Plus spent near three hours above its previous record altitude, with much of the flight ocurring over the Pacific Ocean west of Kaua'i. After an equally long descent, controllers on the ground brought the lightweight flying wing to a safe landing on the PMRF runway at 10:40 p.m. Hawaii time.
Jeff Bauer, ERAST deputy program manager at Dryden, said the record flight was "just picture perfect. We had an absolutely excellent flight. We are looking forward to future successes as we move towards developing new technologies for improving the quality of life in the new millenium."
Bauer credited the teamwork between NASA, PMRF and AeroVironment, Inc., the firm that designed, built and operates Pathfinder-Plus, for achieving this milestone in solar-powered flight.
W. Ray Morgan, vice president and director of AeroVironment's development center in Simi Valley, Calif., echoed Bauer's comments.
"I believe we will be operating solar-powered aircraft as stratospheric satellites routinely in the next century," he said. "The success of this type of aircraft, however, depends on doing everything as best as can be done--not only in the technology, but in the operation of the program as well. I'm grateful to NASA for the vision and support in letting us pursue this dream. It is a tremendous thrill to be a part of this team."
Pathfinder Plus is one of several high-altitude, long-duration aircraft being developed and evaluated under the ERAST program, part of NASA's response to growing scientific requirements for measurements at higher altitudes and durations than the current fleet of airborne scientific platforms permits. The program is working to develop the technology base for a future fleet of remotely piloted aircraft that could serve as high-altitude science and telecommunications platforms. Concurrent efforts in developing, miniaturizing and integrating sensors for science missions is also under way. Pathfinder-Plus had flown twice previously this summer at PMRF. The goal of all flights was to validate new solar, aerodynamic, propulsion and systems technology being developed for the Pathfinder's successor, the Centurion. The Centurion is now under construction by AeroVironment.
A testbed for much of the Centurion technology, the "Plus" version is actually a hybrid of Pathfinder and Centurion. The Centurion is slated to begin low-altitude battery-powered development flights at Dryden in October, with high-altitude solar-powered flight tests planned for the summer of 1999. With a wingspan of 206 feet, Centurion has been designed to reach and sustain an altitude of 100,000 feet for up to two hours. Pathfinder-Plus's wingspan has been extended from just under 99 feet to 121 feet by the replacement of the 22-foot Pathfinder center section with a new 44-foot-long section that incorporates a high-altitude airfoil designed for Centurion. The new center section is topped by more efficient silicon solar cells developed by SunPower Corp., Sunnyvale, Calif., that can convert 19 percent of the solar energy they receive to useful electrical energy. That compares with 14.5 percent efficiency for the older solar arrays that cover most of the surface of the middle and outer wing panels from the original Pathfinder. In addition, the Pathfinder-Plus was powered on its record flight by eight more-efficient electric motors for the Centurion, two more than had powered the previous version of Pathfinder.
Pathfinder-Plus flight operations are being conducted at PMRF to take advantage of a combination of Kauai's low latitude and prevailing winds, which allow a good sun radiation angle for the solar arrays for longer periods than do more northerly locations. The ERAST program is managed for NASA by NASA Dryden. The NASA Ames Research Center, Moffett Field, Calif., heads the sensor technology development. The NASA Lewis Research Center, Cleveland, Ohio, and NASA Langley Research Center, Hampton, Va., are contributing expertise in the areas of propulsion, structures and systems analysis.
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