PROJECTED CMMC LEVEL REQUIREMENT
Level 2 (Self)
TECHNOLOGY AREAS
None
MODERNIZATION PRIORITIES
Advanced Materials
KEYWORDS
Hydrogen; Liquid Hydrogen; Cryogenics; Storage; Fuel Cell; Unmanned Aerial System; UAS
OBJECTIVE
Develop a cryogenic liquid hydrogen storage and delivery solution that can achieve high hydrogen mass fraction and a low boil off rate. Demonstrate that the cryogenic liquid hydrogen storage system improves endurance, range, and continuous payload power in an unmanned aerial system (UAS).
DESCRIPTION
Hydrogen fuel-cell-powered air systems are becoming more prevalent in aviation [Refs 1-4]. Although compressed gaseous hydrogen has traditionally been employed to power these systems, cryogenic liquid hydrogen has recently started gaining traction [Refs 5-8]. Overall, liquid hydrogen storage provides added benefits such as reduced weight and volume compared to gaseous hydrogen storage, but there are still challenges to air vehicle integration and long-term use due to the extreme low temperature and other properties of liquefied hydrogen [Refs 9-10].
This STTR topic is seeking a liquid hydrogen storage and delivery solution that achieves high performance metrics while also maintaining longevity, safety, and usability for US Navy and US Marine Corps UASs. The performance metrics of interest for the delivered solution include a gravimetric hydrogen storage efficiency = 40% and volumetric hydrogen storage density of > 40 g/L. The integrated solution must also maintain a hydrogen boil-off rate of < 10% mass per day, as well as a gaseous hydrogen delivery system that can meet the flow and temperature requirements of the fuel cell. A liquid hydrogen filling method and procedure shall be defined with an emphasis on minimizing loss of hydrogen. Additionally, the storage vessel shall be reusable and able to achieve > 100 fill cycles. The storage solution and filling procedure must also meet standard safety requirements such as those called out in DOC 06/02/E on the H2 Tools website [Ref 11].
Additionally, consideration should be made for integration into a range of UAS sizes from a Group 2 to Group 5. This shall include considerations for fuel level monitoring and sloshing effects during flights, as well as meeting necessary environmental (basic hot and basic cold), shock, and vibration requirements called out in MIL-STD-810-H [Ref 12]. Ability to demonstrate that the new cryogenic liquid hydrogen delivery system can manage and mitigate thermal loads of UAS mission systems is of particular interest. Finally, cryo-compressed hydrogen solutions will also be considered if it meets the key performance parameters outlined here.
PHASE I
Develop a design for a holistic liquid hydrogen storage and delivery solution that is validated through material analysis and/or modeling and simulation. The design should include a trade study that demonstrates how metrics such as size, weight, and volume affect the overall boil-off rate as well as gravimetric and volumetric storage efficiency. The analysis should assume normal hydrogen and include expected liquid hydrogen fill rate, precooling requirements, and storage vessel cycle life. UAS load profile and fuel cell requirements will be provided by the Government and/or UAS supplier and should be incorporated into the heat leak rate and hydrogen flow requirements to optimize design. Incorporation of a battery to meet peak loads can also be considered in the optimization trade study. Investigation should emphasize UAS integration, be performed over a range of liquid hydrogen storage amounts from 0.5 kg up to 100 kg and consider thermal management opportunities such as cooling UAS systems like payload and avionics. Overall, incorporation of test data to validate analysis is encouraged.
The Phase I effort will include prototype plans to be developed under Phase II.
PHASE II
Build a prototype liquid hydrogen storage vessel and gaseous hydrogen delivery system and demonstrate a filling procedure. Complete an end-to-end bench test of the overall system to demonstrate operational performance in a relevant environment. Collaborate with a UAS manufacturer chosen by the Government to integrate the storage and delivery system.
PHASE III DUAL USE APPLICATIONS
Demonstrate the manufacturing maturity of the integrated storage, delivery, and filling system. Develop the operation, maintenance, storage, and safety procedures for using the system in an unmanned aerial vehicle. Demonstrate that the system meets all UAS requirements while also improving its operational capabilities such as endurance, range, and continuous payload power.
This technology is highly relevant to the commercial urban air mobility market. A high-performance hydrogen system would have improved range and flight time compared to current platforms that rely on batteries.
REFERENCES
Pasquini, Nicholas E. M. "NRL's Hybrid Tiger UAV Soars at Demonstration." U.S. Naval Research Laboratory, April 14, 2021. https://www.nrl.navy.mil/Media/News/Article/2498102/nrls-hybrid-tiger-uav-soars-at-demonstration/
"Hydrogen-electric and electric propulsion technology for clean, efficient and affordable flight." Zeroavia, Everett, WA USA. https://zeroavia.com/
"Zeroe: our hydrogen-powered aircraft." Airbus. https://www.airbus.com/en/innovation/energy-transition/hydrogen/zeroe
"Hydrogen fuel cells for unmanned aerial vehicles. Improve flight time, operational efficiency and total cost of ownership." Intelligent Energy. https://www.intelligent-energy.com/our-industries/uav/
Wellock, Bill, Crews Keller, Tisha "FAMU-FSU Researchers Pioneer New Hydrogen Storage System for Zero-Emission Aviation" FAMU-FSU College of Engineering, May 29, 2025. https://eng.famu.fsu.edu/news/famu-fsu-researchers-pioneer-new-hydrogen-storage-system-zero-emission-aviation
Host, Pat. "Alaka'i Technologies seeks to solve the riddle of liquid hydrogen fuel in aviation." Vetical, April 2, 2024 https://verticalmag.com/news/alakai-technologies-seeks-to-solve-the-riddle-of-liquid-hydrogen-fuel-in-aviation/
"H2FLY Passes First Filling Tests with Integrated Liquid Hydrogen Tank." H2FLY. https://www.h2fly.de/2023/04/05/h2fly-accelerates-progress-towards-zero-emission-commercial-flight-3/
"Joby demonstrates potential for emissions-free regional journeys with landmark 523-mile hydrogen-electric flight." Joby Aviation, July 11, 2024. https://www.jobyaviation.com/news/joby-demonstrates-potential-regional-journeys-landmark-hydrogen-electric-flight/
Aziz, Muhammad. "Liquid Hydrogen: A Review on Liquefaction, Storage, Transportation, and Safety." Institute of Industrial Science, The University of Tokyo, Tokyo 153-8505, Japan Energies 2021, 14(18), 5917. https://www.mdpi.com/1996-1073/14/18/5917
Lecca, Tommaso. "Hydrogen-Powered Airplanes Face 5 Big Challenges." E&E News, May 4, 2024. Scientific American. https://www.scientificamerican.com/article/hydrogen-powered-airplanes-face-5-big-challenges/
Hydrogen Tools Website. https://h2tools.org/
"MIL-STD-810H, DEPARTMENT OF DEFENSE TEST METHOD STANDARD: ENVIRONMENTAL ENGINEERING CONSIDERATIONS AND LABORATORY TESTS (31-JAN-2019)." http://everyspec.com/MIL-STD/MIL-STD-0800-0899/MIL-STD-810H_55998/
