The nano air vehicle program expects to develop the smallest of tiny unmanned aerial platforms that may be custom-made for SOF missions. DARPA is soliciting innovative proposals for the research and development of a NAV system.
By Jeff McKaughan
The military forces of the United States and its allies have an ever-present need for improved capabilities enabling the timely collection of comprehensive intelligence information, particularly on the ground in urban terrain. Information gathered and transmitted by unattended ground sensors of various types may be critical to the successful execution of many military missions, including various special operations. For many scenarios, the effectiveness of such sensors is strongly dependent on their precise location. Achieving optimal performance with respect to both monitoring designated areas and the ability to reliably communicate useful collected information often requires that the sensors be placed in locations that are not readily accessible: on buildings, walls (exterior or interior, e.g., in tunnels), windows, bridges, caves, tunnels, towers, rocks and other vertical or steeply angled surfaces. Emplacing unobtrusive reconnaissance/surveillance sensors in remote or special high-security areas also demands sophisticated means for delivery. Nano air vehicles (NAVs)—small, recoverable aircraft no larger than 7.5 centimeters in length, height or width, and gross takeoff weight (GTOW) less than or equal to 10 grams—may provide an effective means for precision delivery and emplacement of small, multi-element sensor packages to locations of interest.
The Defense Advanced Research Projects Agency (DARPA) is soliciting innovative proposals for the research and development of a NAV system. DARPA envisions that a NAV system may be based on either conventional or nonconventional air vehicle designs, or potentially a combination of both. While systems that minimize acoustic and visual signatures, and offer some form of natural stealth (by mimicry), are highly desired, no such requirements are expected be defined as part of the solicitation. Nano air vehicles are envisioned as fully functional, militarily capable, fully integrated, very small flight vehicles.
The NAV program is an exploratory development program with an overall goal to develop and demonstrate flight and operation of affordable NAV systems with the potential to perform useful indoor and outdoor military missions, and to develop and demonstrate flight-enabling technologies for advanced NAV systems. Flight-enabling technologies will most likely include aerodynamic design tools; lightweight, efficient propulsion and power; navigation; communications and control; and advanced manufacturing and packaging.
Notional Mission Requirements
The mission performance requirements for the nano air vehicle include, but are not limited to:
Maximum GTOW of 10 grams (with a reserved payload fraction of 2 grams)
Maximum dimension in any direction of 7.5 centimeters
Fast forward speed of 5 to 10 meters per second
Slow forward speed of 0.5 meters per second
Range greater than 1,000 meters at 5 to 10 meters per second forward velocity
Ability to transition to the slow forward speed of 0.5 meters per second after completing the 1,000-meter high-speed ingress and maintain the slow speed for more than 60 seconds
Ability to hover in place for more than 60 seconds after completing a high-speed 1,000-meter ingress and the 60-second low-speed ingress
Ability to land from hover in a controlled manner
Ability to navigate within a 0.5-meter mean square residual error (MSRE) and drop/release a payload at the end of the high- and low-speed ingress and return to the operator
Fortunately, biology offers some hints: Insects and hummingbirds have evolved the ability to fly at this scale. In addition, recent advances in the understanding of low Reynolds number (a numbering and comparative system used in fluid dynamics—in this case airflow) physics may permit human-made flight at this scale. Thus, in order to accomplish the goal of developing a nano air vehicle system capability for military operations, this program will pursue radical and quantifiable innovations in four technical areas, each with distinct objectives:
Computational Aerodynamic Modeling and Wing Design/Manufacture Tools
This technical area involves the use of fundamental physics models at a low Reynolds number to design highly efficient (high lift to drag) airfoil geometries that can be used to manufacture and build monolithic 1 to 7.5 centimeter wings or rotors. The modeling tool should clearly demonstrate how it will be used to design and develop appropriately scaled, very lightweight wings that can be seamlessly integrated into a nano air vehicle design. For this capability, the ability to design, simulate and optimize the aerodynamic performance over an arbitrary articulation path of motion on this small scale would be necessary. In addition, a clear process for how these wings or rotors will be manufactured and integrated to other subsystems must be demonstrated. The design tools may include the ability to simultaneously analyze structural loads while possibly incorporating some level of multifunctionality to improve overall system performance.
Propulsion and Power
This will involve the integration of a reliable power source with sufficient energy and power density to carry out the notional mission objectives discussed above. In addition, the propulsion system must be capable of demonstrating highly efficient conversion of stored energy to mechanical work or thrust to propel the air vehicle system in both hover and forward flight modes of operation. Thus, highly efficient transduction actuators are required for nano air vehicle designs. Such actuators may include servos, integrated smart material elements, or nanoscale or micro-electrico-mechanical engineered actuators. System must be sized to deliver power to the communication and navigation subsystem over a range of 1 kilometer (km) for approximately 20 minutes.
Navigation, Guidance, Communication, and Command and Control
This objective area of a NAV system involves the development of reliable avionics, including necessary sensors (gyros, accelerometers, optics, etc.), actuators, electronics, software algorithms, communication system and ground control elements, for guiding a vehicle from point A to point B and back in the presence of 5-knot wind gusts in an urban environment. While autonomous operation is desired, line of sight (LOS) and non-line-of-sight (NLOS) tele-operation strategies that achieve minimal on-board processing but enable flight both external and internal to building structures are acceptable. The system must be capable of operating in GPS-denied environments and enable the operator to avoid obstacles of 0.5-meter diameter or larger. The communication link must be capable of providing a data link over a range of 1 kilometer. It is important to note that the avionics software and hardware are not considered as part of the payload of the NAV system. The NAV system must be able guide itself along a path within a 0.5-meter (1-sigma) MSRE.
Preliminary Integrated System Design
The design involves evaluation of the integrated nano air vehicle system that incorporates enabling technologies from the computational propulsion and navigation technical areas. The NAV system must also include all of the necessary ground control stations for LOS command and control electronics and software for communicating to air vehicle, as well as the necessary hardware and software interfaces for launching and retrieving nano air vehicles. System elements must demonstrate a sufficient level of performance and risk reduction at a preliminary design review level to ensure ability to conduct flight missions in Phase II.
The Nano Air Vehicle Program is expected to be executed using a multiphase approach. The base period, Phase I, will have a period of performance of 18 months and include a trade analysis and subsystem risk reduction demonstration, and conceptual and preliminary design reviews encompassing efforts under all four technical areas defined above. Phase I will be awarded with a base-line and negotiated option separated by a technical go/no-go to be suggested by the contractor for use as a “DARPA HARD” metric to graduate to completing Phase I.
A Phase II is expected to be at DARPA’s discretion based on performance and results from Phase I. If executed, Phase II will include an 18-month period of performance in which a completely integrated nano air vehicle system’s flight is demonstrated. Phase II proposed efforts will be based on a critical design review, an assembly plan for integrating the components of the nano air vehicle system, and a series of end-to-end flight demonstrations against the notional mission requirements to confirm the performance of the NAV system.
The earliest that DARPA anticipates any awards from their effort is March 2006.
Phase I Go/No-Go Metrics
Technical Area Figures of Merit
1. Aerodynamic Performance and Airfoil/Wing/Rotor Design and Manufacture Develop computational aerodynamic modeling tools to design a high performance airfoil at a low Reynolds number.
Demonstrate reliable wing manufacturing principles and achieve wing loading of > 0.1 kg/m2.
Demonstrate airfoil section steady lift to drag capability > 8 at low Reynolds number (Re < 15,000).
2. Propulsion and Power Demonstrate system electrical power to mechanical transduction conversion efficiency of at least 20 percent. Demonstrate an ability to meet power requirements for a notional mission of 1 kilometer with a total hover time of > one minute.
3. Navigation Algorithm Design and Development for Precision Time, Position and Attitude Determination Develop LOS navigation capability that ensures delivery of nano air vehicle within 0.5 meters of target location over a range of 1 kilometer in 5- knot wind gusts.
Develop LOS navigation capability that enables robust guidance inside of enclosed buildings without GPS.
Demonstrate simulated navigation of NAV system inside a building.
4. Integrated System Design Achieve preliminary design review level of integrated nano air vehicle system with command and control.
Integrated nano air vehicle system must be able to hover for longer than one minute, translate at forward speeds of both 0.5 and 5 to 10 meters per second, and support command and control over a 1 kilometer distance for approximately 20 minutes.
Integrated nano air vehicle systems must achieve a GTOW of less than 10 grams and a minimum payload mass of at least 2 grams with dimensions of 10 millimeters in diameter by 5 millimeters in depth with a uniform density.
Demonstrate measured thrust to weight ratio of greater than one at optimal GTOW.
All this must be capable between 0 and 5,000 feet MSL.
System must be capable of being tele-operated from a ground control station over a range of 1 kilometer.