N251-056 TITLE: Compact Prime Power Source for Unmanned Aerial Systems

OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Advanced Materials;Sustainment

The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.

OBJECTIVE: Develop a compact, highly efficient prime power source that provides a power density exceeding currently available technologies for future Department of Defense (DoD) unmanned aerial systems (UASs) while maintaining an acceptable form factor, exhibiting reliability for extended endurance operation, providing compatibility with multiple payloads, and demonstrating suitability for potential re-use.

DESCRIPTION: Many industries and DoD systems utilize turbine-generator (turbo-generator) powertrains due to their unmatched energy density and power to weight ratios. In airborne applications, these powertrains can distribute electric power to both propulsion systems and tactical payloads. In theory, this permits ideal dynamic allocation of power to both aircraft performance (e.g., dash / climb speed) and payload functions. Platforms that support Modular Open Systems Approach (MOSA) payloads naturally benefit from increased available payload prime power. Increased platform prime power permits larger or more capable MOSA payloads and increases the platform operational flight envelope.

Turbo-generators are the identified (incumbent) solution of choice due to their high specific power, ability to use approved high energy density liquid fuel sources such as Jet Propulsion-10 (JP-10), low vibration, reduced maintenance, and overall safety when compared to other potential solutions such as lithium batteries. However, turbo-generators (or other prime power sources) meeting the stringent size, weight, performance, reliability, operational lifecycle, and environmental requirements for existing DoD UASs are already at the limits of available technology. Small turbines and generators suffer from scale effects that drive their ideal operating point to higher turbine inlet temperatures and shaft speeds greater than conventional materials and designs allow. Operating at off-ideal conditions reduces the overall thermal efficiency, mass-specific performance, and operational life of miniature turbine generator systems. Solutions that mitigate these challenges and meet overall performance objectives may require innovation in multiple technical areas including:

• Cycle design – such as recuperation or supercritical carbon dioxide
• Advanced high-performance materials (ceramics or superalloys)
• Novel manufacturing or machining techniques
• Advanced miniature high-speed bearing, lubrication, and seal systems
• 3D optimized magnetics (rotor / stator)
• Highly integrated power conversion and engine / generator control electronics
• Thermal management

While turbo-generators using JP-10 are currently the solution of choice, alternate solutions will be considered. However, the potential safety impact of alternative designs (relative to a baseline of JP-10 fueled system) will be weighed during selection. Proposers should therefore identify any required mitigation elements (e.g., storage, handling, disposal, etc.) necessary to provide a credible path to qualification and approval for shipboard use.

The main objective of this SBIR effort is to maximize power density and efficiency where power density is defined as the ratio of generated electrical power to weight. However, the source must also be operationally useful so the solution must also be capable of meeting a number of performance objectives. Principally, the proposed solution should:

1. deliver a full rated net DC power (averaged over 1.0 sec into an ideal load), at 270VDC nominal (in accordance with MIL-STD-704F), of 20 kW (threshold) to 25 kW (objective),

2. be capable of rapid start without operator intervention and be capable of ramping up output power from idle to 75% of the full rated output power within approximately 200 msec of receiving the command to do so (idle is defined as the minimum state of operation required for the power source to maintain its own function),

2b. time from cold-start to idle will also be factored in during the selection process

3. be capable of storage, start, and operation in horizontal and vertical orientation, and

4. be capable of rapidly increasing (surging) power output when commanded. For this requirement, a nominal surge rate of 2.5 kW per 50 msec, starting at 50% rated power, is desired. Note that, in meeting this requirement, the source controller may assume feedforward information regarding load surge demand. However, absent this information, the source shall maintain safe operation.

Note that acceptable solutions must also anticipate the intended application of UAS deployment. Therefore, solutions that can be realized in an axially symmetric form factor with the center of gravity located on the center axis are desired. For demonstration purposes, a cylindrical form factor of 90 mm radius should be assumed. Mating interfaces (e.g., fasteners, connectors, fittings, etc.) should not break the 90 mm radius cylindrical boundary. Within these constraints, the most power-dense solution is desired to have a mass less than 11.5 kG for fuel based systems (this weight does not include the fuel). As weight is a critical design factor, all solutions (fuel and non-fuel) will be compared by Wh/kg (fuel will be considered in this calculation). Any ballast required to meet the center of gravity requirement is included in the mass. Within the cylindrical form factor, a target volume of 0.0125 m3 is desired. However, for highly efficient solutions, this may be relaxed provided the increase in efficiency results in a comparable decrease in the volume required for energy storage/fuel. For fueled systems, the exhaust should not interfere with the intake and preferably be directed along the axis. Solutions should accommodate communications with the UAS using a standardized digital, differential (balanced), and galvanically isolated interface, preferably CAN, Ethernet, or RS-422, to provide command and control signals and receive status, diagnostic, and built-in-test information from the power source.

To simplify the design trade-space, the baseline for comparing the Specific Fuel Consumption (SFC) of each proposer will be conducted at sea level and at 50°C. As such, each proposer shall present SFC (kg/kWh) and fuel flow (ml/min) data with respect to the power setting at a voltage of 270 VDC at sea level and at 50°C. The proposer shall describe how their SFC changes with respect to temperature and altitude. The proposer shall also define their "specific power" (kW/kg), defined as their threshold power level of 20kW, at sea level at 50°C divided by the weight of their engine system, to include the weight of everything except fuel. If a proposer presents a solution which does not include fuel, their specific power solution will be compared to the fueled solutions by adding the weight of the fuel required to match the endurance of the non-fueled solution. Acceptable solutions should anticipate and address the operational environment through design, as supported with analysis, modelling and simulation, limited testing, and proven practice. The application is intended for a maritime environment with operation anticipated over a temperature range of -32° to +55° C and non-operation (storage) over a range of -40° to + 70° C. A launch acceleration of 50 G, aligned with the center axis, is expected. In addition, the solution should be designed to withstand normal shipboard shock and vibration requirements (defined in the applicable Military Standards).

The solution should be designed for reliable service over at least three mission cycles (10 objective) with a mission cycle defined as start and operation, followed by six hours of non-operation during which time, refueling, recharging, and minimal maintenance (e.g., lubrication) are acceptable. For fueled solutions, mission operational time is fuel dependent and should not be fundamentally constrained to less than four hours other than by the fuel supply. However, for demonstration purposes, the operational time is 60 minutes. In comparing fueled versus non-fueled solutions, the baseline (weight, volume, form factor) is a JP-10 fueled turbo-generator with fuel sufficient for 60 minutes of continuous operation at full rated power. Within the constraints detailed herein, power density and efficiency are the primary measures of success for this SBIR effort. Therefore, in assessing both fueled and non-fueled solutions for power density and efficiency, the total weight (power converter plus energy storage) shall be considered. Therefore, fueled solutions shall use the total weight of the turbo-generator plus fuel storage required to provide full rated power for 60 minutes as the metric for comparison. Non-fueled solutions shall use the total weight of the converter plus the energy storage system required to provide full rated power for 60 minutes as the metric for comparison.

Finally, logistical and operational realities have shown that the system might sit idle for extended periods of time in a fueled (charged) and ready state. The solution should therefore anticipate long periods of system standby and provide for a service life of at least 10 years. During periods of system standby, low-level electrical power will be provided to the prime power source to maintain system diagnostics and provide fault monitoring. However, during the service life (unless deployed for a mission), maintenance will not be performed nor will the energy storage be changed. Therefore, lubricants, seals, filters, etc., and the energy source must be chosen for long-term stability meeting the service life. For fueled solutions, the fuel must remain stable and not degrade other system components.

PHASE I: Propose a concept for a compact prime power source suitable for UAS deployment that meets the objectives stated in the Description above. Define an architecture, develop initial designs for key components, and identify critical areas requiring innovation. Demonstrate the feasibility of the concept in meeting the Navy need through analysis, modeling and simulation, and limited testing of key components or subsystems, where possible. Produce a development plan with specific tasking and milestones to support the Phase II effort. Manufacturing is anticipated to be a critical issue in realizing the power source. Identify areas of the proposed design that are likely to present manufacturing challenges. In the Phase I Option if exercised, identify and propose manufacturing processes to address key manufacturing challenges, develop test procedures, specifications, interface requirements, and a capabilities description necessary to build and demonstrate a prototype in Phase II.

PHASE II: Develop, demonstrate, and deliver a prototype prime power source based on the concept, architecture, specifications, plans, and processes resulting from Phase I. Demonstrate performance through stationary (fixtured) testing at the proposer’s facility or at a facility of their choosing (flight testing is not required). Collect, organize, and summarize test results and deliver to the Naval Research Laboratory. For demonstration purposes, the prime power source shall be oriented so that the longest axis is vertical. For fueled solutions, the fuel tank may be located separately from the power source, provided performance is not affected. Develop an initial technical data package including key drawings, schematics, assembly drawings, and process documents for key components and especially those components identified as requiring innovative manufacturing techniques. Develop a cost estimate for the power source in production quantities (use 100 and 400 units as a baseline). Upon completion of the effort deliver the prototype to the Naval Research Laboratory.

PHASE III DUAL USE APPLICATIONS: Support the Navy in transitioning the technology for Government use. Assist in integrating the power source into specific Navy systems and support environmental testing and qualification. Modify electrical, control, and mechanical interfaces to meet individual system configurations and produce application-specific source control drawings. Create production-ready technical data packages. Assist the Navy in development of operation and maintenance documentation, safety procedures, performance predictions, and training materials. Identify and propose manufacturing cost reduction initiatives and long-term product improvement programs.

The prime power source developed under this effort is expected to have multiple future applications in the area of military UASs. It potentially has land-based applications including serving as the power source for remotely deployed repeater stations and weather monitoring stations. As commercial use of medium size drones expands, innovative elements of the power source (especially components benefiting from affordable manufacturing technologies) will find their way into the commercial market.

REFERENCES:

1. Vick, Michael. "High efficiency recuperated ceramic gas turbine engines for small unmanned air vehicle propulsion." PhD Thesis, February 2013. https://www.researchgate.net/publication/269400720_High_efficiency_recuperated_ceramic_gas_turbine_engines_for_small_unmanned_air_vehicle_propulsion

2. Vick, Michael; Young, Trent; Kelly, Matthew; Tuttle, Steven and Hinnant, Katherine. "A Simple Recuperated Ceramic Microturbine: Design Concept, Cycle Analysis, and Recuperator Component Prototype Tests." ASME Turbo Expo 2016: Turbomachinery Technical Conference and Exposition, Seoul, South Korea, June 13-17, 2016. https://asmedigitalcollection.asme.org/GT/proceedings-abstract/GT2016/V008T23A030/241118

3. Li, Jingqi and Li, Yulong. "Micro gas turbine: Developments, applications, and key technologies on components." Propulsion and Power Research, Volume 12, Issue 1, March 2023, pp. 1-43. https://www.sciencedirect.com/science/article/pii/S2212540X23000123

KEYWORDS: Turbine-Generator; Turbo-Generator; Power Source; Power Conversion; Unmanned Aerial Systems; Novel Manufacturing

TPOC 1: Will Crespo-Miranda
Email: [email protected]

TPOC 2: Eric Silberg
Email: [email protected]

TPOC 3: Matthew Hazard
Email: [email protected]

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