NASA's $15 million solar-powered Helios wing is scheduled to break a world altitude record for propeller-driven aircraft on August 8.
The date, set on Wednesday, will be revised if several technical issues are not resolved.
The engineering team has about 100 different items to take care of that were discovered during Helios' last test flight on July 14, NASA's Dryden Flight Research Center spokesman Alan Brown said.
"None of the problems are major, but there's such a volume of things that they have to deal with," Brown said.
For instance, the pitch of the propeller needs adjustment. It was decided that the propeller could provide better drag during Helios' decent, and better pitch on take off, if its position were tweaked, Brown said. Beside a few other software and hardware issues, the majority of the needed adjustments are procedural.
"After flying, it's found out certain procedures sometimes don't work as well as you'd like," Brown said.
During this interim period, the crew from AeroVironment, a California-based clean-energy engineering company that built Helios, will take a nine-day hiatus from their work at the test flight center at the U.S. Navy's Pacific Missile Range Facility on the island of Kauai.
The crew has been in Kuaui since April working six days a week, 12 hours a day.
Potential in the sky
The upcoming record-breaking flight at 100,000 feet isn't just a chance for NASA and AeroVironment to prove their engineering prowess, said Brown. The atmosphere up there is almost identical in density to the atmosphere of Mars.
NASA will need an unmanned, foldable glider or plane to fly at low altitudes at Mars in the near future, Brown said. Helios, able to fly at slow speeds and low altitudes, would provide better images of the Martian surface than either a rover or a satellite could provide.
And although the promise of Red Planet reconnaissance is exciting, NASA also hopes to use Helios as a platform for environmental surveillance here on Earth, said Brown. The Helios, unlike satellites, will be able to change its altitude and take-off and land over and over again. Also, surveillance of water and land will be much more detailed at Helios' 19-mile (31-kilometer) altitude compared to those from a satellite orbiting 150 miles up.
Helios' ability to sail at lower altitudes also provides an opportunity for the telecommunications industry. TV, radio and cellular phone signals spread out the longer they travel. Therefore, the lower positioning of the aircraft would require much less energy for data relay.
Perpetual motion machine, sort of
The next step in Helios' evolution will be equipping it with fuel cells so that it is independent of the Sun for energy. A continuous four-day test of the cells will have to be achieved by 2003, said Brown.
Right now, the solar panels on Helios' wings produce 37 kilowatts of power, but the plane only needs 10 kilowatts to fly. The rest is wasted as heat. The ability to capture as much of this extra energy as possible would enable the plane to fly for months at a time.
Fuel cells work as a proton exchange membrane, using the excess solar power to split water molecules. When clouds or darkness obscure the Sun, the cells produce power by allowing water molecules to rebind. Still, proton exchange membranes that are efficient and light enough for Helios do not exist yet.
As far as Brown is concerned though, these cells will be made eventually and will make Helios the closest anyone has come to a perpetual motion machine.
"This is exciting stuff. We're not just putting nuts on bolt or bagging groceries here," he said.
The final step in getting Helios in the skies is figuring out a cheaper process of manufacture. Currently, Helios has cost $15 million to build, $10 million of which has been spent on the solar cells alone. For it to be commercially viable, said Brown, the craft will have to cost somewhere between $3 and $5 million.
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