Stationary High Altitude Relay Platform
Encyclopedia
SHARP, short for Stationary High Altitude Relay Platform, was an experimental aircraft using beam-powered propulsion
designed by the Communications Research Centre Canada (CRC) and built by the University of Toronto Institute for Aerospace Studies
(UTIAS) during the 1980s. SHARP used microwaves to provide energy from a ground station that powered electric motors spinning propellers to keep the aircraft aloft. The power was also used for the onboard electronics. SHARP could remain aloft indefinitely, and was intended to be used as a sort of low-altitude communications satellite
for smaller geographical areas.
. After joining Raytheon
in the 1940s, Brown started work on improving their magnetron products. This led to the development of the crossed-field amplifier
, a simple, reliable and highly efficient microwave
amplifier
. He later worked with colleagues to develop the rectenna
with, which receives microwaves (the (an)"tenna") and converts them directly to DC
power (the "rect"ifier).
Brown now had a system that converted input power to microwaves with up to 70% efficiency, then received them back with 70% efficiency, resulting in a closed-circuit of about 50% overall efficiency. Brown looked for applications of the technology, working on both solar power satellites (SPS) and the High Altitude Powered Platform (HAPP) concept. This research went as far as flying a model helicopter
using beamed power in 1965.
NASA
also invested in the rectenna concept as part of their SPS work. This was tested in a ground-to-ground experiment in 1975, and as part of this they developed lightweight versions of the rectenna. In 1982, Brown and James Trimer (of NASA) announced a new version of the rectenna using printed circuit
techniques that reduced the weight by ten times. This made aircraft applications much more attractive.
Since a satellite was too high, and a terrestrial antenna too low, what was needed was a platform between the two, covering an area of a few hundred kilometers in radius – about the size of a Canadian province. To do this the platform would have to fly at about 70,000 feet (21 km) altitude. Aircraft and helicopters could do this, but only with short endurances. Super-high-altitude aerostat
s were another possibility. Of the available technologies, helicopters appeared to be too heavy, and aerostats, joking referred to as the "Gossamer Hindenberg", were not well understood. An electrically powered ultralight aircraft appeared to be the best solution. At the time, a system using solar cell
s and batteries was considered too heavy.
The economics of the system were attractive as a replacement for conventional satellites even in some large-area deployments. The CRC estimated the aircraft would cost about $100,000 each, and operate for $2 to $3 million a year. In contrast, just launching a satellite cost about $15 million. Additionally, whereas a satellite of the era might have a lifetime of about 10 years, the aircraft could be periodically returned to the ground for servicing and upgrades, allowing it to operate indefinitely. They felt this would be attractive to third world
markets.
In 1981 SED Systems
was awarded a contract to study the power requirements of a communications platform, while John Martin of Martin Communications and James DeLaurier
at UTIAS studied aircraft configurations. In September 1982 the Department of Communications gave the go-ahead to form a formal study group within the CRC, which studied rectenna design, leading to several patents on thin-film versions.
In 1982 UTIAS built a prototype of the aircraft with a 1.3 meter high aspect-ratio wing mounted just above the fuselage, and a conventional t-tail
at the rear. This model was powered by a small gasoline engine and did not support a rectenna. The prototype demonstrated several aerodynamic problems, leading to an improved design that moved the horizontal stabilizer to the front of the aircraft into a canard
configuration. This underwent wind tunnel
testing at UTIAS during 1985 and 86.
All of these studies culminated in the go-ahead to build a eighth-scale model of the proposed production SHARP vehicle that would be powered by two small electric motors. Power for takeoff would be provided by batteries, but the platform would acquire the microwave beam after launch and self-power from that point on. The model, with a 4.5 meter wingspan, was built during 1987.
Its maiden flight at the CRC took place on 17 September 1987. The system worked as expected, allowing launch by the batteries and capture by the 1 kW broadcaster shortly after takeoff. The initial 20-minute flight time was extended to over an hour by 5 October, and on the 6th a public demonstration was made for the Minister of Communications, Flora MacDonald. Their work won the "Diplôme d'Honneur" from the Fédération Aéronautique Internationale
in 1988.
The work was picked up in Japan at the Radio Atmospheric Science Centre at Kyoto University. Starting immediately after the SHARP successes, Professor Hiroshi Matsumoto developed a similar vehicle, which flew on 29 August 1992.
Compared to SHARP, their MILAX (Microwave Lifted Airplane Experiment) vehicle had two new design features. The rectenna on the aircraft was embedded in the wings and tail surfaces, eliminating the need for the separate antenna body. The broadcast antenna was based on an active phased array
, allowing it to steer without physical movement. The system was tested by mounting the broadcast antenna on the back of a light truck, and driving it around while MILAX followed.
Another beamed-power experiment in Japan was the ETHER project, which beamed 5.8 kW of power to a helium-inflated airship.
In the years since the system was first proposed, advances in solar cells and battery technology have upset the initial calculations. The NASA Pathfinder demonstrated long-duration solar powered flight in a role essentially identical to SHARP.
Beam-powered propulsion
Beam-powered propulsion is a class of aircraft or spacecraft propulsion mechanisms that use energy beamed to the spacecraft from a remote power plant to provide energy...
designed by the Communications Research Centre Canada (CRC) and built by the University of Toronto Institute for Aerospace Studies
University of Toronto Institute for Aerospace Studies
The University of Toronto Institute for Aerospace Studies is an advanced research facility for aeronautics and aerospace engineering, located in the Downsview district of Toronto, Ontario, Canada...
(UTIAS) during the 1980s. SHARP used microwaves to provide energy from a ground station that powered electric motors spinning propellers to keep the aircraft aloft. The power was also used for the onboard electronics. SHARP could remain aloft indefinitely, and was intended to be used as a sort of low-altitude communications satellite
Communications satellite
A communications satellite is an artificial satellite stationed in space for the purpose of telecommunications...
for smaller geographical areas.
Background
The concept of using beamed power for aircraft propulsion was invented almost single handedly by William C. BrownWilliam C. Brown
William C. Brown was an American electrical engineer who helped to invent the crossed-field amplifier in the 1950s and also pioneered microwave power transmission in the 1960s....
. After joining Raytheon
Raytheon
Raytheon Company is a major American defense contractor and industrial corporation with core manufacturing concentrations in weapons and military and commercial electronics. It was previously involved in corporate and special-mission aircraft until early 2007...
in the 1940s, Brown started work on improving their magnetron products. This led to the development of the crossed-field amplifier
Crossed-field amplifier
A crossed-field amplifier is a specialized vacuum tube, first introduced in the mid-1950s and frequently used as a microwave amplifier in very-high-power transmitters....
, a simple, reliable and highly efficient microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
amplifier
Amplifier
Generally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
. He later worked with colleagues to develop the rectenna
Rectenna
A rectenna is a rectifying antenna, a special type of antenna that is used to directly convert microwave energy into DC electricity. Its elements are usually arranged in a multi element phased array with a mesh pattern reflector element to make it directional...
with, which receives microwaves (the (an)"tenna") and converts them directly to DC
Direct current
Direct current is the unidirectional flow of electric charge. Direct current is produced by such sources as batteries, thermocouples, solar cells, and commutator-type electric machines of the dynamo type. Direct current may flow in a conductor such as a wire, but can also flow through...
power (the "rect"ifier).
Brown now had a system that converted input power to microwaves with up to 70% efficiency, then received them back with 70% efficiency, resulting in a closed-circuit of about 50% overall efficiency. Brown looked for applications of the technology, working on both solar power satellites (SPS) and the High Altitude Powered Platform (HAPP) concept. This research went as far as flying a model helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...
using beamed power in 1965.
NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
also invested in the rectenna concept as part of their SPS work. This was tested in a ground-to-ground experiment in 1975, and as part of this they developed lightweight versions of the rectenna. In 1982, Brown and James Trimer (of NASA) announced a new version of the rectenna using printed circuit
Printed circuit
Printed circuit may refer to:* Printed circuit board* Printed Circuit Corporation, an electronics manufacturer...
techniques that reduced the weight by ten times. This made aircraft applications much more attractive.
Relay platform
In the era before narrow-angle broadcasting from communications satellites was possible, television broadcasters faced the problem of having technology that was suitable for greater metropolitan areas on the order of 100 km using conventional ground-mounted antennas, or large portions of the continent using satellites. Addressing the range between these two extremes normally required a network of repeater antennas, which were expensive given the smaller populations they normally served.Since a satellite was too high, and a terrestrial antenna too low, what was needed was a platform between the two, covering an area of a few hundred kilometers in radius – about the size of a Canadian province. To do this the platform would have to fly at about 70,000 feet (21 km) altitude. Aircraft and helicopters could do this, but only with short endurances. Super-high-altitude aerostat
Aerostat
An aerostat is a craft that remains aloft primarily through the use of buoyant lighter than air gases, which impart lift to a vehicle with nearly the same overall density as air. Aerostats include free balloons, airships, and moored balloons...
s were another possibility. Of the available technologies, helicopters appeared to be too heavy, and aerostats, joking referred to as the "Gossamer Hindenberg", were not well understood. An electrically powered ultralight aircraft appeared to be the best solution. At the time, a system using solar cell
Solar cell
A solar cell is a solid state electrical device that converts the energy of light directly into electricity by the photovoltaic effect....
s and batteries was considered too heavy.
The economics of the system were attractive as a replacement for conventional satellites even in some large-area deployments. The CRC estimated the aircraft would cost about $100,000 each, and operate for $2 to $3 million a year. In contrast, just launching a satellite cost about $15 million. Additionally, whereas a satellite of the era might have a lifetime of about 10 years, the aircraft could be periodically returned to the ground for servicing and upgrades, allowing it to operate indefinitely. They felt this would be attractive to third world
Third World
The term Third World arose during the Cold War to define countries that remained non-aligned with either capitalism and NATO , or communism and the Soviet Union...
markets.
SHARP
Following the work of HAPP, the CRC started work on their own version with the specific intent of making a communications platform. SHARP would use an 80 m diameter array of small parabolic dishes beaming 500 kW of power to the aircraft at 5.8 GHz frequency. At altitude, the beam was focussed down to an area just larger than the aircraft. The aircraft normally flew in a circle about 2 km across, so the beam only needed to steer a few degrees.In 1981 SED Systems
SED Systems
SED Systems is a communications company supplying both systems and services to the satellite industry. Originating in 1965, SED is located in the Innovation Place Research Park on the University of Saskatchewan campus...
was awarded a contract to study the power requirements of a communications platform, while John Martin of Martin Communications and James DeLaurier
James DeLaurier
James D. DeLaurier is an inventor and professor emeritus of the University of Toronto Institute for Aerospace Studies. He is a leader in design and analysis of lighter than air vehicles and flapping winged aircraft.-Career:...
at UTIAS studied aircraft configurations. In September 1982 the Department of Communications gave the go-ahead to form a formal study group within the CRC, which studied rectenna design, leading to several patents on thin-film versions.
In 1982 UTIAS built a prototype of the aircraft with a 1.3 meter high aspect-ratio wing mounted just above the fuselage, and a conventional t-tail
T-tail
thumb|right|Grob motor gliderA T-tail is an aircraft tail stabilizer configuration in which the horizontal surfaces are mounted to the top of the vertical stabilizer. Traditionally, the horizontal control surfaces are mounted to the fuselage at the base of the vertical stabilizer...
at the rear. This model was powered by a small gasoline engine and did not support a rectenna. The prototype demonstrated several aerodynamic problems, leading to an improved design that moved the horizontal stabilizer to the front of the aircraft into a canard
Canard
Canard may refer to:*Nicolas-François Canard , French mathematician and economist*Canard , a small wing mounted on the front of some aircraft, which can be beneficial or detrimental depending on the design of the plane and its intended use*Canard , a phenomenon in some slow-fast dynamical systems...
configuration. This underwent wind tunnel
Wind tunnel
A wind tunnel is a research tool used in aerodynamic research to study the effects of air moving past solid objects.-Theory of operation:Wind tunnels were first proposed as a means of studying vehicles in free flight...
testing at UTIAS during 1985 and 86.
All of these studies culminated in the go-ahead to build a eighth-scale model of the proposed production SHARP vehicle that would be powered by two small electric motors. Power for takeoff would be provided by batteries, but the platform would acquire the microwave beam after launch and self-power from that point on. The model, with a 4.5 meter wingspan, was built during 1987.
Its maiden flight at the CRC took place on 17 September 1987. The system worked as expected, allowing launch by the batteries and capture by the 1 kW broadcaster shortly after takeoff. The initial 20-minute flight time was extended to over an hour by 5 October, and on the 6th a public demonstration was made for the Minister of Communications, Flora MacDonald. Their work won the "Diplôme d'Honneur" from the Fédération Aéronautique Internationale
Fédération Aéronautique Internationale
The Fédération Aéronautique Internationale is the world governing body for air sports and aeronautics and astronautics world records. Its head office is in Lausanne, Switzerland. This includes man-carrying aerospace vehicles from balloons to spacecraft, and unmanned aerial vehicles...
in 1988.
After SHARP
In spite of its success, SHARP research ended as part of a larger draw-down of the Canadian research budgets. Ready for testing long-duration flights, field mice attacked the SHARP aircraft while it was in storage, and the flights never took place.The work was picked up in Japan at the Radio Atmospheric Science Centre at Kyoto University. Starting immediately after the SHARP successes, Professor Hiroshi Matsumoto developed a similar vehicle, which flew on 29 August 1992.
Compared to SHARP, their MILAX (Microwave Lifted Airplane Experiment) vehicle had two new design features. The rectenna on the aircraft was embedded in the wings and tail surfaces, eliminating the need for the separate antenna body. The broadcast antenna was based on an active phased array
Phased array
In wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
, allowing it to steer without physical movement. The system was tested by mounting the broadcast antenna on the back of a light truck, and driving it around while MILAX followed.
Another beamed-power experiment in Japan was the ETHER project, which beamed 5.8 kW of power to a helium-inflated airship.
In the years since the system was first proposed, advances in solar cells and battery technology have upset the initial calculations. The NASA Pathfinder demonstrated long-duration solar powered flight in a role essentially identical to SHARP.
Further reading
- Arthur Fisher, "Secret of Perpetual Flight? Beam-power Plane", Popular Science, January 1988, pg. 62-65, 106-107