SHARP

(Stationary High Altitude Relay Platform)

The idea for SHARP was first conceived in 1980. In September 1982, a research and development program was approved by the Department of Communications. A 4.5 metre wing span model (eighth scale) of SHARP took its maiden flight on September 17, 1987 at Communications Research Centre. On October 7, 1987 the first public demonstration occurred in the presence of the Minister of Communications and the press. This flight was recognized as being the first of its kind by the Fédération Aéronautique Internationale.

SHARP in flight.
Photo courtesy of John Martin and George Jull

Gerry Bower and Tom Ohno with SHARP prototype.
Photo courtesy of John Martin and George Jull

Joe Schlesak, 1981

CRC Photo 81-3391

The concept of power transmission using radio waves has a long history, going back almost one hundred years to Heinrich Hertz and the very beginning of radio in 1888. However, only since the 1970s have the major technical barriers been reduced to a level such that power transmission by radio could be seriously considered as a practical proposition. William C. Brown, working with his colleagues at Raytheon Corporation, was a pioneer in microwave power transmission. Brown helped develop the rectenna that converts microwaves to direct (DC) current. Probably the most important element of the project was that Brown and his fellow engineers solved the critical problem of how to convert the microwave beam power into the desired DC power out of the receiving antenna. Brown's solution was the "rectenna" - an assemblage of little dipole antennas connected to a network of semi-conductor diodes that rectifies, or converts AC to DC power. Later, studies concerned with assessing the feasibility of the Solar Power Satellite (SPS) and the High Altitude Powered Platform (HAPP) found that magnetron power sources and various types of rectennas, operating at 2.45 GHz, could meet the requirements of microwave power transmission.

An important SPS spin-off was research done at NASA to develop the most efficient possible DC to DC power transmission system. In 1982, Brown (Raytheon) and James F. Trimer (NASA) announced the development of a thin-film plastic rectenna using printed-circuit technology that weighed only one-tenth as much as any previous rectenna. The discovery coincided with the beginnings of the Canadian program at CRC. SHARP used a CRC-developed version of the thin-film rectenna.

The SHARP concept envisages the use of pilotless airplanes as platforms for relaying telecommunication signals, providing surveillance and monitoring services. The airplanes would circle slowly for many months at an operating altitude of 21 kilometres and relay signals within a diameter of 600 kilometres (which is about the width of a Canadian prairie province). Microwave power would be transmitted from a large ground antenna system to a circling airplane. The power beam would be accurately focused onto the airplane. A rectenna (rectifying antenna), mounted on the lower surfaces of the aircraft would receive and convert microwave power to DC power. The DC power would be used to drive electric motors on the airplane for propulsion, to power the payload and control systems and to charge standby energy storage units. A schematic diagram is shown below.

Potential commercial communications services include mobile and personal communications, broadband fixed radio, and direct-to-home multichannel television and sound broadcasting. Non-communications services include surveillance (eg. terrestrial waters), environmental monitoring (without contributing to pollution) and remote sensing. Because of SHARP's considerable payload weight and power capacity, these services can be offered on an integrated basis. Because of its proximity to earth, the two-way time delay for traffic to-and-from a SHARP platform will be negligible, compared to those for satellite links.

Since the form and power requirements of such an airplane were unclear, a study was conducted under contract by SED Systems of Saskatoon in 1981. Craft configurations were investigated by John Martin and Professor James DeLaurier of the University of Toronto Institute for Aerospace Studies (UTIAS). These researchers identified particular aircraft configurations which were most favourable in terms of aerodynamic characteristics and rectenna catchment area. The SHARP research program was commenced at CRC in 1982 in the Radio Communications Branch, headed up by R.E. Barrington. From 1982 to 1986, the project was headed by Dr. George W. Jull. When Dr. Jull retired, the position of project manager was handed over to Joe Schlesak. Prior to 1986, J. Schlesak was responsible for research on microwave power transmission. During 1982 and 1983, intensive development of lightweight thin-film rectennas was pursued by Dr. Adrian Alden and Tom Ohno. This led to the development and patenting of particular configurations of power rectifying antennas systems, which were well suited to the particular powering requirements presented by the circling SHARP A/C. Concurrently, ground-based power generation/transmission was investigated by Dr. George Jull, Arne Lillemark and Joe Schlesak and, under contract, by Miller Communication Systems. During the same period, Professor DeLaurier and students at UTIAS conducted studies relating to flight vehicle requirements.

As SED recommended, a lightweight model biplane with a wingspan of 1.3 metres was designed and constructed at UTIAS in 1982. It was then fitted with experimental rectennas at CRC. To provide the necessary microwave power, a low-power ground station was designed and constructed at CRC under the direction of Joe Schlesak. From 1982 to 1986 Arne Lillemark carried out analytical studies to determine cost-effectiveness of delivering a wide variety of telecommunications and broadcasting services to regions across Canada. In February 1984, a comprehensive and systematic feasibility study was undertaken by CRC staff and consultant contractors. The feasibility study, directed by Dr. Edward Hayes, was completed in March 1985. John Palmer contributed to the study by researching payload, Howard Reynaud investigated A/C, Rob Milne examined power and Richard Bonnycastle studied rectenna feasibility. During the study, a radically new aircraft configuration was identified which promised an optimum compromise between minimization of microwave beam power flux density and high aerodynamic efficiency. After the study, the decision was made to develop a flight demonstrator model of 1/8 scale. Professor J. DeLaurier and his students at UTIAS conducted analytical and wind tunnel studies at UTIAS during 1985-86.

A fundamental design problem which required solution arose because of a potential conflict between a desired aerodynamic configuration of an aircraft, which would dictate high aerodynamic efficiency, as well as a configuration which would lead to interception of a high fraction of an incident microwave powering beam. An aircraft with high aerodynamic efficiency would have long and slender wings. However, an aircraft with high power collection efficiency would not have long and slender wings, since such a configuration would demand a high level of usable power.

As a result of research studies, a unique configuration of platform was invented and patented. An essential feature of the aircraft was the positioning and shape of a large disc, appropriately located just behind the wings. The underside of the disc was covered with printed circuit antennas, which receive and convert microwave energy to direct-current energy, to power the payload and the electric motors which drive two large diameter propellers.

On September 17, 1987, everything was ready for SHARP's first flight. At 7:20 a.m., the aircraft was launched by Tom Ohno on battery power, was acquired by the beam, and flew for over twenty minutes solely on microwave power. This was a first for Canada and the world. Gerry Bower controlled the flight path by radio.

On October 5, a microwave-powered flight of one hour was achieved. On October 6, a public demonstration took place, attended by the Minister of Communications, Flora MacDonald. William Brown, the father of modern microwave power transmission also attended, as well as the Canadian and foreign media. Work on SHARP has continued at CRC, as researchers have studied certain technicalities in the system's design. The SHARP project maintains an active status in the Technology Transfer Office and is described elsewhere on the CRC website

Ron Barrington (originator of the SHARP project), Stu McCormick (Director of project), Joe Schlesak (SHARP project manager), George Jull (retired SHARP project manager), Adrian Alden (rectenna development), John Martin (conceived and developed aircraft), Jim DeLaurier (developed and tested aircraft), Marc Gregoire (tracking system), Bill Mather (microwave power systems), Tom Ohno (rectenna development), Grant Phillips (tracking system), Gerry Bower (SHARP remote control pilot) and the staff and students of the University of Toronto's Institute for Aerospace Studies all participated in the SHARP project.

Objectives

To take advantage of microwave power transmission developments associated with the Solar Power Satellite and High Altitude Powered Platform concepts and adapt these to Canadian needs.
To investigate the feasibility of using unmanned aircraft powered by microwave to relay telecommunications signals.

The research into SHARP led to the issuance of the following patents:

United States Patent	4,943,811
United States Patent	5,045,862
United States Patent	5,321,414
United States Patent	5,563,614
Canada Patent	1,307,842
Canada Patent	1,309,769
Canada Patent	2,006,481
Canada Patent	2,011,298

Although the SHARP project is not being actively pursued in Canada, Japanese scientists have expressed interest in SHARP and its related technology from the beginning. A Japanese team flew a successful test model in August 1992. The model was developed over three years by a research group led by Professor Hiroshi Matsumoto of the Radio Atmospheric Science Centre at Kyoto University in Japan. This technology was closely related to CRC's work on SHARP. The Japanese are still interested in this area of research.

By mid 1987, the vehicle and the ground power station had been developed enough so that sustained microwave-powered flight was imminent. At this point fate - in the form of a nesting fieldmouse - intervened. The mouse consumed portions of the airplane's structure, eating through the plane's balsa wood and badly damaging the plane. Repairs delayed flight attempts for six weeks.

The following is a list of Canadian published work related to SHARP:

DeLaurier, J., Gagnon, B., Wong, J., Williams, R., and Hayball, C. "Research on the technology of an airplane concept for a Stationary High Altitude Relay Platform (SHARP)." Presentation at the 32nd Annual General Meeting of the Canadian Aeronautics and Space Institute, Montreal, May 27, 1985.

Jull, G.W., Lillemark, A., and Turner, R.M. "SHARP (Stationary High Altitude Relay Platform) Telecommunications Missions and Systems." Presentation at the IEEE Global Telecommunications Conference, New Orleans, December 2-5, 1985.

Martin, J.F. "Aircraft configuration studies for a Stationary High Altitude Relay Platform (SHARP)." Paper presented at the Association for the Unmanned Vehicle Systems Symposium (Silicon Valley Chapter), October-November 1985, Menlo Park (also published in Unmanned Systems Journal, 1986).

Renaud, A.H. and Martin, J.F. "Airplane Concept for Stationary High Altitude Relay Platform (SHARP)." Presentation at the 32nd Annual General Meeting of the Canadian Aeronautics and Space Institute, Montreal, May 27, 1985.

Schlesak, J., Alden, A., Ohno, T. "SHARP rectenna and low altitude flight trials." Presentation at the IEEE Global Telecommunications Conference, New Orleans, December 2-5, 1985.

Sources

Fisher, Arthur. "Secret of Perpetual Flight? Beam-power Plane." Popular Science. January 1988. 62-65, 106-107.
Jull, George. "An Overview of SHARP." Prepared for Internet. Ottawa; July 1997.

Prepared By

George Jull