In upcoming years aviation technology could begin to change dramatically to achieve the benefits of reduced pollutants emission and decreased dependence on hydrocarbon fuels. To accommodate a switch to hydrogen power, for example, future aircraft designs, propulsion, and power systems will look much different from the systems of today. Hydrogen fuel will enable a number of new aircraft capabilities, from high-altitude long-endurance remotely operated aircraft (HALE ROA) that will fly weeks to months without refueling, to clean, zero-emissions transport aircraft. However, the transition will require decades of research and new technology breakthroughs to fulfill the vision. Additionally, there are a number of design and development challenges that must be overcome before such systems can become operational.