Eternal Flight as the Solution for 'x'

The Centrifugally Sti ened Rotor (CSR) concept is a unique con guration approach that has never previously been attempted, which could fundamentally lead to a new approach for High Altitude Long Endurance (HALE) or ATmospheric Satellite (ATSat) missions. AT-Sats map into many missions that existing GEO and LEO satellites simply can not perform, and in particular AT-Sats align with missions were communication transmission time needs to be minimized for such capabilities as omni-present wireless broadband. The CSR signi cantly improved structural and aerodynamic e ciency open up the design space to become more feasible, with initial analysis indicating that feasibility may be possible through this concept approach in combination with energy storage of about 400 Whr/kg and thin- lm solar cells around 35%. Feasibility relates to accomplishing year round missions at high U.S. latitudes. The Phase I research focused on developing analysis tools capable of capturing the unique attributes of this multibody approach, including aerodynamic, structural, force balance, and power required. Performance comparisons were made with other HALE tool sets used in the analysis of DARPA Vulture concepts, as well as calibrations of the new tools to the most similar concepts. The initial performance analysis indicates a reduction in power required on the order of 35% compared to the prior QinetiQ Zephyr 7 HALE endurance record holder, with the Zephyr carrying less than a 5% payload fraction compared to the CSR concept with a 10% payload. A number of compelling missions have been identifed that map directly into the unique capabilities of this advanced concept. Missions include: Multi-Functional Airborne Wind and Surveillance Commercial Platforms at Lower Altitudes: Aerial platforms that operate at altitudes up to 2000 ft altitude (without FAA impediment of operational feasibility) that can both capture wind energy more e ectively than ground-based wind turbines, and provide close proximity surveillance/communications with a coverage diameter of 50 miles. The CSR concept has the potential to achieve a higher Lift/Drag ratio compared to other airborne wind concepts, which results in higher tether angles and less land area underneath the vehicle radius of operation that depends on incoming wind direction. O -shore application is particularly appealing since a CSR aerial vehicle would eliminate the need for a large/expensive mooring platform, which is required for ground-based wind turbines. The ability of this concept to have a non-moving tether from the ground to the center hub permits the inertial connection to be less complex than current airborne wind turbines. Potentially this mission concept could be applied all the way down to the level of distributed residential power production, with a sUAS sized version likely capable of providing 2 to 5 kW of power at altitudes of 500 feet with average wind speeds of less than 20 mph. Distributed Aperture AT-Sat Observatory: The CSR concept provides a large rotating structure, as well as large volume at the center hub, with the capability of operation above the majority of the atmosphere. Integrating high resolution, compact, linked optic sensors (such as the Low Mass Planar Photonic Imaging Sensor currently being developed as Phase II NIAC research) at the tip and root of each rotorwing will permit a rotating imaging array across a full 600 diameter azimuth. Combining this with a lower resolution conventional imaging system in the center hub for image lling could provide a resolution never before possible. Such an observatory could be designed as a dual-purpose system that provides imaging both upwards for space investigations, as well as for Earth imaging. Extra-Planetary Compact VTOL Exploration Platforms: A version of the CSR concept has been identified that enables full retraction of the rotorwing to achieve a highly compact VTOL vehicle that can operate at extremely low discloading (<0.03 lb/ft2) on atmospheres such as Mars that have atmospheric densities similar to Earth at 100,000 feet altitude. Because it was highly uncertain whether the centrifugal stiffening loads would be suffcient to maintain a rigid rotor-wing for this highly faceted spanwise design, a sub-scale version of the rotor-wing was fabricated and tested with success. The rotorwing experiences an increase in weight and complexity with a decrement in performance to achieve compact packaging, however was shown to be a feasible approach that could facilitate very low discloading renewable VTOL aerial vehicles which could be packaged effectively in an aeroshell. Since the performance analysis indicates a compelling advantage for this concept, the Phase I research focused on addressing the key risk area for this concept, establishing that vehicle control is feasible for this multibody dynamics problem. A complete derivation was presented which outlined how the CSR is modeled, the dynamics that dictate the equations of motion of the system, and a means of trimming and linearizing the system. This transitioned into the theory needed to control this particular vehicle, and simulations demonstrated the controller response implemented on the nonlinear system. The key hurdle to overcome from the controls point of view, is maintaining control when the exact relative position of the satellite is unknown. Estimation and reduced order estimators were shown to be able to overcome this, because the CSR vehicle was determined to be both fully controllable and fully observable. Furthermore, the system dynamics can be arbitrarily selected to meet any desired response within the limits of the actuators. Finally, parameter estimation and adaptive control techniques can be applied to this type of vehicle. A sub-scale flight demonstrator at the 30 lbf gross weight size has been initiated to validate the ability of the control system to accommodate real world disturbances as well as winds and maintain stable flight. Additionally, the sub-scale prototype permits other study assumptions to be addressed, such as the mechanical complexity of the tether reelin/out system which has not been analyzed. This demonstrator e ort will continue as part of the PhD dissertation for the lead control researcher, and be completed prior to a follow-on proposal for Phase II research.