SubscribeA breakthrough in telecommunications relay capability has been achieved with the successful relay of high-quality television signals, third-generation cell phone transmissions and Internet linkage through an uninhabited remotely operated aircraft flying high over Hawaii.
During two demonstration flights the last week in June and a third in mid-July, AeroVironment's Pathfinder-Plus solar-powered flying wing successfully re-transmitted a high definition television (HDTV) signal and relayed cellular audio and video calls from the stratosphere above the Hawaiian island of Kauai. Both flight demonstrations were conducted over the U.S. Navy's Pacific Missile Range Facility (PMRF) on the western coast of the Hawaiian island of Kauai while the Pathfinder-Plus lazily circled overhead at an altitude over 65,000 feet. During the second flight, researchers also established an Internet link through the aircraft as the Pathfinder-Plus descended through about 21,000 feet altitude.
Both demonstrations were sponsored and funded by a team of Japanese telecommunications researchers from the Japanese Ministry of Communications laboratories and private companies.
John Del Frate, project manager for solar powered aircraft at NASA's Dryden Flight Research Center, said the demonstration is believed to be the first stratospheric relay from a fully functional, remotely operated High Altitude Platform Station (HAPS) aircraft employing practical, commercially-available HDTV, cell phone and Internet linkage equipment. While a similar demonstration relaying a high-speed broadband payload was conducted two years ago by Raytheon Co. and Angel Technologies from the Proteus aircraft, that demonstration was flown at a much lower altitude of 45,000 feet by a piloted aircraft.
"We have been working on this project for four years and we are very pleased with the test results and the cooperation between Japan and the United States," explained Dr. Ryu Miura of the Japanese Communications Research Laboratories. "The test data, which exceeded our expectations, showed the link to be very stable and reliable. We believe this is due to the very smooth platform the Pathfinder-Plus provides. "This success implies significant potential and a broad scope for HAPS telecommunications applications," Miura added. "The test data will be very useful in the development of future commercial telecommunications systems."
Del Frate said the first demonstration, flown by the Pathfinder-Plus June 24, demonstrated how high quality TV signals may be transmitted in the future. After a lengthy climb to the planned target operational altitude of about 65,600 feet—or 12 miles high--the aircraft was placed in a "station keeping" orbit directly over the Navy facility. The Japanese telecom team then beamed up a signal to the aircraft, which then re-transmitted the signal back down to HDTV monitors on the ground for more than two hours. Using only one watt of power, the signal blanketed an area equivalent to a large metropolitan region such as Tokyo or Los Angeles with a very high quality signal-to-noise ratio typical of fiber optic systems, far superior to what traditional TV broadcast systems can achieve.
"It's absolutely amazing what the right vantage point can deliver," added Del Frate. "It was better than any HDTV system I have ever seen in the United States—virtually photographic quality—it was very impressive."
The primary goal of the second demonstration June 28 was to demonstrate that the solar-powered aircraft could be used to establish a third-generation mobile phone wireless link in the stratosphere. The Pathfinder-Plus flew a station-keeping orbit at 65,600 feet (20 km) over the payload ground control station at PMRF for more than four hours, while the Japanese telecom team worked to overcome interference from other transmission sources in Hawaii. After establishing the link, the team successfully relayed cellular phone calls and video conferencing through the aircraft until the aircraft had to begin its descent.
During the descent in late afternoon, the Pathfinder-Plus was flown back over the airfield, placed in a station-keeping mode again at 24,000 feet altitude, and the researchers were able to establish an Internet link through the aircraft.
On the third flight July 20, the Pathfinder-Plus again carried the third-generation IMT-2000 mobile telecommunications system capable of voice, data and video two-way cell phone transmission. Japanese engineers also validated a new "look down" antenna on the aircraft that was less susceptible to interference from distant side-angle signals experienced during the second flight. They were then able to relay two-way voice and video without any external antenna and high-speed Internet access with an auxiliary antenna at various altitudes up to 65,000 feet.
"AeroVironment was excited to have demonstrated that our solar-powered aircraft can act as a reliable, secure, 12-mile (20-km) -high tower for the sophisticated communication payloads built by our Japanese friends," said AeroVironment vice-president Robert Curtin, director of the firm's Design Development Center in Simi Valley, Calif. "This mission was exactly what the Pathfinder-Plus and its family of solar-powered aircraft are hoping to do on a continual routine basis."
The project was conducted in a collaborative arrangement between the U.S. and Japan. In this arrangement, the Communication Research Laboratory and the Telecommunications Advancement Organization of Japan's Ministry of Public Management, Home Affairs, Post and Telecommunications developed and operated the telecommunications payloads and funded the flights. AeroVironment, Inc., based in Monrovia, Calif., modified the Pathfinder-Plus to safely carry the payloads, and conducted the flight operations at PMRF.
NASA's Dryden Flight Research Center provided the use of the aircraft for this series of missions as well as safety oversight of aircraft preparation and flight operations. PMRF provided a home for the aircraft and the team, use of the airfield and coordinated access to the airspace where the flights were conducted. AeroVironment subsidiary Skytower, Inc., and Japan Stratosphere Communications, Inc. provided the necessary technical information exchange and communications to enable the international effort.
Later this year, AeroVironment will fly the Pathfinder-Plus on another mission designed to demonstrate other potential commercial applications of UAVs. The Coffee Harvest Optimization study will have the aircraft flying precision patterns over a major coffee plantation on Kaua'i, while special cameras capture and transmit images of the ripening coffee to field managers on the ground. That effort is led by Dr. Stan Herwitz of Clark University, AeroViroment and NASA under a grant from NASA's Earth Science Enterprise, and is expected to take place in late September and early October.
NASA and AeroVironment engineers are currently working to extend stratospheric flight time of solar-powered aircraft to durations exceeding two weeks, and eventually up to six months. When that time comes, payloads similar to the telecommunications payload flown this summer are expected to be ready for the HAPS capability. Next year, NASA is planning to demonstrate the ability to sustain high altitude overnight flight with the Helios Prototype, which set a new world altitude record for non-rocket-powered aircraft of 96,863 feet last year.
NASA Dryden Flight Research Center
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