The HALSOL-Pathfinder was designed to act as a technology demonstrator for the eternal aircraft, which would be a much larger and heavier aircraft. Currently called "Helios" or solar rechargeable aircraft (SRA), it would have a wingspan of 200 feet, made up of five, 40-foot-long segments.
There would be four landing gear gondolas. The solar array would produce 21.6 kilowatts, powering the eight motors — the same motors as were used on Pathfinder. The Helios-SRA would weigh about 1,100 to 1,200 pounds, and have a payload of 150 to 200 pounds. Its operational ceiling is planned to be about 60,000 to 65,000 feet; top speed would be around 100 knots.
Unlike the HALSOL-Pathfinder, the Helios-SRA would be optimized for high-altitude cruise, rather than climb.[587]
To allow around-the-clock flights, the Helios-SRA required an energy-storage system — a proton-exchange membrane fuel cell. Excess electrical current from the solar array would electrolyze water into hydrogen and […] and stored separately in the wing spar. At night, the hydrogen and oxygen would be allowed to recombine into water. The energy released would be converted back into electrical power for the motors. These fuel cells would be carried in the wing leading edge. The system has less than half the weight of rechargeable batteries.[588] Low-level research is currently under way on the fuel cells. This is a two- to three-year program. Although the technology is understood, the problem is putting it into a lightweight package. The Helios-SRA could be ready in 1997 or 1998.
In the post-Cold War political environment, attention is shifting to dual-use technology — military systems that can also have civilian applications.
Pathfinder and Helios-SRA are prime examples. The ability to reach high altitudes, then stay there for months at a time, opens numerous possibilities in the area of atmospheric research. Sporadic, one-shot measurements of atmospheric conditions cannot give the needed baseline data to detect changes. To distinguish normal atmospheric variations from changes caused by natural and man-made sources, it is necessary to take measurements throughout the day-night cycle.
The Pathfinder, for example, could be flown continuously over the Yukon Valley in Alaska during the summer. It could monitor the flow of air pollution from Russia as well as the effect of local volcanoes. The data would be provided at very low cost, compared to satellites. Another advantage is that the Pathfinder's electric motors give off no exhaust emissions.
It could carry sensitive chemical detectors without their measurements being contaminated by the plane itself.
Other research projects would utilize the Helios and its ability to fly continuously through the night. One possibility would be storm tracking.
Major storms develop in the subtropical areas of the Atlantic and Pacific, then move toward North America over several weeks. A Helios could be "parked" over the storm, monitoring its development. Continuous data on atmospheric conditions and water temperatures would result in better predictions of storm strength and movements.[589]
Another application is high-altitude astronomical observations. The Helios can fly above most of the atmosphere, which would allow instruments to observe in ultraviolet and infrared wavelengths. These observations cannot be made from ground-based telescopes because the atmosphere and water vapor absorb these wavelengths.
A Helios could also serve as a "pseudosatellite" for communications. If communications links are disrupted by a natural disaster, such as an earthquake or severe storm, cellular phone equipment could be carried by a Helios, which would act as a long-distance relay station. As MacCready observed, "mouths water when they hear about this."[590]
The final, indirect result of a Helios would be improved electronic and solar technology. The payload limitations would encourage development of ultralightweight electronics and sensors, much as satellites did in the 1950s and 1960s.[591] Just as the solar-powered car efforts made Pathfinder practical, a Helios development effort could improve solar technology.[592]
It has been estimated that a Helios-SRA would cost between $2 and $3 million, assuming a minimum production run of twenty aircraft.[593] Although the possible uses of such an eternal aircraft are many, it still faces many technological problems. In particular, the development of flyable fuel cells are the key to day-night flights. As a White project, Pathfinder-Helios now faces a political environment that views new and innovative ideas with dis-interest or hostility.
The HALSOL was not the only Black UAV program. In the early 1980s, DARPA began a Black study of long-endurance UAVs under the code name "Teal Rain." This looked at both short- and long-term possibilities.[594]
In December of 1984, DARPA issued a $40 million development contract to Leading Systems of Irvine, California, to build a medium-range, low-cost tactical UAV. Leading Systems, in the best tradition of high-tech companies, had started in a garage in 1980. The control system for the UAV was built in the living room of one of the founders.[595] The navy, army, and Marine Corps soon became involved with the project. The navy was given control.
As with earlier Black airplanes, the goal was the rapid building of the prototypes. The program office had few government personnel, while the number of support contractors was kept small. This kept the amount of program reviews and paperwork to a minimum.[596]
Called "Amber," it could carry either a warhead or reconnaissance or ELINT equipment. The inverted "V-tail" stabilizers hung down from the rear fuselage. The long wing was mounted on a small pylon atop the fuselage. On the strike version, the wing would be separated from the pylon; the UAV would then fall to the target. The piston engine was located at the rear.
It used technology originally developed for Indy car engines. The Amber took off and landed on a set of long and sticklike retractable landing gear.
Although it was as large as a light airplane, the Amber was more akin to the simple battlefield support UAVs, rather than the complex strategic drones used earlier.
Once the contract was issued, Leading Systems began work on six prototypes called the Basic Amber — three A45s, with the pointed nose of the strike version, and three B45s, with the bulged nose section of the reconnaissance version. Flight tests began in November 1986 at the Leading Systems test facility at the El Mirage Airport, in the Mojave Desert, near Edwards Air Force Base. On June 16, 1987, a 20.25-hour flight was successfully made. The initial test program was completed in June, and the Basic Amber was judged to have performed "extremely well."[597]
During September and October of 1987, the Basic Ambers underwent a second series of tests at the army's Dugway Proving Grounds in Utah.
These proved out the low-drag aerodynamics, lightweight structure, control system, and engine. The third Amber prototype was lost during the tests.
When the UAV was placed in a high-angle-of-attack or high-g condition, it would start to oscillate.[598] This was corrected, and by 1988 flight durations of thirty hours at 17,000 feet, and thirty-five hours at 5,000 feet had been demonstrated. The maximum altitude reached was 27,800 feet.[599]
587
Lt. Col. Dale Tietz, "Raptor/Talon Briefing," Ballistic Missile Defense Organization, 1993; and Dornheim, "Raptor/Pathfinder to Test High-Efficiency Propulsion," 60.
588
Brown, "The Eternal Airplane," 74; and AeroVironment Inc., "Backgrounder — Pathfinder Solar-Electric Aircraft."
590
Conversations with NASA personnel at the Pathfinder display, 1993 Edwards AFB Air Show; and "Solar-Powered Spy,"
592
Ballistic Missile Defense Organization, "'Pathfinder' Solar-Electric Unmanned Air Vehicle Data Sheet," 1993.
594
Louis C. Gerken,
597
Leading Systems, Inc. "Demonstrated 35 hrs endurance; large payload; 27,800 ft" (Irvine, Calif.: Leading Systems Inc., 1988); and John D. Morrocco, "Navy Plans Operational Trials for Amber RPV in 1989,"