NASA Pathfinder
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NASA's Pathfinder and Helios were a series of solar- and fuel cell system-powered unmanned aircraft. AeroVironment, Inc. developed the vehicle under NASA's Environmental Research Aircraft and Sensor Technology (ERAST) program.
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[edit] Design
Sunnyvale, California-based Sunpower Corporation supplied solar cells for Helios. The cells featured a rear-contact cell design that placed wires on the underside of the cells, so as not to obstruct the cells' exposure to solar radiation.
The fuel cell systems designed for the Helios Prototype included both regenerative and non-regenerative designs.
Ultra-lightweight hydrogen fuel storage system was designed by Quantum Technologies.
[edit] Helios operations
On 14 August, 2001, it set a world record for sustained altitude by a UAV.[1] It sustained flight at above 96,000 feet (29,250 m) for forty minutes, and at one time it flew as high as 96,863 feet (29,524 m). Later, in June 2003, the prototype broke up and fell into the Pacific Ocean about ten miles (16 km) west of the Hawaiian Island Kauai.
[edit] Significance and goals
NASA claimed that if the concept the prototype embodied proved itself, then multi-month flight would become feasible. Accordingly, Helios was a forerunner of what some call artificial "atmospheric satellites". NASA claimed such atmospheric satellites might someday replace conventional artificial satellites.[2]
NASA established two major goals for the Pathfinder:
- Reach an altitude at or near 100,000 feet (30 km) with a small payload on a single-day flight. NASA could apply the knowledge gained therein firstly to carry scientific instruments to high altitudes, and secondly when designing aircraft for, or completing missions on, Mars. NASA claimed that a vehicle so capable could also carry larger payloads to lower altitudes. This versatility would enhance the Prototype's worth.
- Achieve extreme duration. Initially, plans called for the aircraft to maintain, by the year 2003, flight for ninety-six uninterrupted hours, most of which would have occurred at an altitude greater than 50,000 feet (15,000 meters). Later, NASA delayed those plans by three years. Meanwhile, it sought to maintain, by September 2003, flight for forty hours, with at least fourteen of those hours above 50,000 feet (15,000 m).
- Background: Unlike most conventional aircraft, Pathfinder flies without an onboard human pilot. Instead, it is controlled remotely from a ground station. The upper surface of the aircraft's 100- foot wing is covered almost completely by thin solar powered panels, which collect sunlight. These solar arrays can provide as much as 7,200 watts of power. Pathfinder converts energy from the sun into electricity, which turns six small motors with propellers. Slowing down or speeding up these individual propellers allows Pathfinder to make turns, since it does not have the control surfaces of typical aircraft. Because Pathfinder is solar-powered, it can stay aloft for a week or more.
Despite being solar powered, Pathfinder is also battery powered. Pathfinder needs to have a back-up battery for those incidences where the aircraft does not receive any solar-powering. Recall that because Pathfinder can fly continually for a week or more that the aircraft will encounter periods of no sunlight.
On a mission in August of 1997, Pathfinder collected data concerning its battery state of charge. During the first ten hours of flight, the battery state of charge was recorded to be 100%. Over the course of the next three hours, the charge decreased at a steady rate of 7.5% per hour.
The aircraft most likely never saw more than 13 hours of consecutive darkness
[edit] References
- ^ Fédération Aéronautique Internationale. "List of records established by the 'Helios'"
- ^ NASA Helios factsheet
- Current Projects - Helios Prototype
- NASA Dryden Fact Sheets - Helios Prototype
- "Photovoltaic Finesse: Better Solar Cells—with Wires Where the Sun Don't Shine", an article by Daniel Cho on page thirty-three of the September, 2003 issue of Scientific American
[edit] External links
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