The Dual-Aircraft Platform (DAP) is a patented concept for achieving a low-cost atmospheric satellite which utilizes wind shear as the primary energy source, and has the potential to stationkeep without a substantial energy storage system. DAP consists of two glider-like Unmanned Aerial Vehicles (UAVs) connected via a thin, ultra-strong cable which literally sails without propulsion, using levels of wind shear commonly found in lower Stratosphere (e.g., near 60,000-ft). The two aircraft are positioned at different altitudes, as far as 3,000-ft apart, to encounter substantially different wind velocities. The device operates similar in principle to a kite-surfer in which the upper aircraft, referred to as the SAIL, provides lift for both aircraft and aerodynamic thrust, while the lower aircraft, known as the BOARD, provides an upwind force to keep the platform from drifting downwind. Each aircraft extracts additional energy via solar film and possibly a wind turbine to operate the avionics, flight controls, payload, and for intermittent use of propulsion.
The DAP concept is expected to provide substantially larger levels of power to onboard payloads, compared to conventional solar aircraft. Consequently, the primary objective of the proposed work is to directly compare the performance of a conventional solar aircraft with the DAP for a 3-month mission as a communications relay, remaining within 150-miles of Orlando, at an altitude of 50,000-60,000-ft, using physics-based flight dynamics simulations. A related objective is to evaluate new flight operations and controls strategies that may lead to improved DAP performance in these simulations. NASA KSC’s Doppler radar (5-min intervals), radiosonde data, and a gust model, will be used to construct realistic time-varying atmospheric profiles for use in the flight simulations.
Aircraft platforms which could stationkeep in the stratosphere for years, referred to as atmospheric satellites, represent a long-standing, grand challenge to the aeronautics community, and have enormous potential societal and economic impact. Such platforms would diversify and expand surveillance capabilities (e.g., NASA’s earth science missions) and communications bandwidth and availability (e.g., for underserved remote areas of the US), at a fraction of the cost of orbital satellite networks. Constellations of such platforms could also potentially be integrated into the NAS to facilitate inter-aircraft communications or to support aircraft navigation and surveillance.
A platform including two winged aircraft are tethered during flight by a single tether near their respective centers of gravity. The tether is windable about a reel, so that a distance between the aircraft can be changed during flight. The aircraft contain avionics configured to enable autonomous flight using natural wind gradients. One aircraft imposes aerodynamic forces on the other, through the tether, while flying at an altitude where wind speed is significantly different than wind speed at an altitude of the other aircraft. The two aircraft cruise back and forth within a maximum distance from a station on the ground. Cruise conditions are established using an iterative computer algorithm which utilizes flight measurements. The aircraft communicate information between each other, and the ground, and contain a payload which performs a useful function at high altitudes.
Background of the Invention
Known high-altitude long endurance (HALE) aircraft which carry fuel, for example the Northrop Grumman’s Global Hawk, are limited to one day of operation. NASA and DARPA have been pursuing the development of HALE aircraft which carry no fuel, and which are also know as “atmospheric satellites”, including for example Boeing’s SolarEagle. These craft are designed to collect solar power for propulsion and operations. Consequently, these aircraft must store large amounts of energy during the day to run propulsion during the night, requiring very large flexible wing covered in solar cells and heavy batteries. In the case of AeroVironment’s Helios, a structural failure has resulted.
The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “prior art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.
Summary of the Invention
In accordance with the disclosure, a stationkeeping apparatus, comprises first and second winged aircraft each containing fixed and moveable control surfaces and avionics configured to enable said respective first and second aircraft to perform autonomous flight using natural wind; a tether connectable near the center of gravity of said first and second aircraft; and a tether length adjuster operative to increase or decrease a length of said tether extending between said first and second aircraft when said tether is connected, to thereby change a distance between said first and second aircraft when said first and second aircraft are in flight.
In various embodiments thereof, said tether is at least 500 meters in length; said tether is between 500 meters and 8 kilometers in length; said first and second vehicles are configured to fly at different altitudes; at least one of said aircraft further includes a docking mechanism configured to attach and release said aircraft from a deployment vehicle; the apparatus further includes internal propulsion within at least one of said first and second aircraft; and, the apparatus further includes a wind turbine and generator configured to provide electricity during a flight of at least one of said first or second aircraft.
In a further embodiment thereof, the tether length adjuster includes a mechanism selected from the group consisting of: reel, spool, pulley, pinch rollers, moveable gripper, and gripping arm.
Further in accordance with the disclosure, a method of station-keeping, comprises connecting first and second winged aircraft together by a tether and a tether length adjustment mechanism, the first and second aircraft containing fixed and moveable control surfaces and avionics configured to enable said respective first and second aircraft to perform autonomous flight using a natural wind differential; and, changing a length of said tether, during flight of the first and second aircraft, using said tether length adjuster, to thereby change a distance between said first and second aircraft when said first and second aircraft are in flight.
In embodiments thereof, the method further includes flying the first and second aircraft, connected by the tether, at different altitudes with respect to each other, where the wind speed is substantially different at the different altitudes.
SOURCE – NASA NIAC, Patent