A little closer to the ground, commercial industry and NASA have partnered to explore the benefits of hydrogen, not as a rocket fuel, but in a fuel cell system.
The Helios unmanned aircraft utilized a hydrogen fuel cell system regenerated by solar power. These experimental long-range unmanned vehicles utilize a hybrid system in which hydrogen fuel cells are replenished by electrical power from solar arrays. During the day, solar cells produce electricity which separates water into hydrogen and oxygen through electrolysis.
At night, the fuel cells generate electricity from the stored gases, and the cycle continues. This unique combination offers theoretically indefinite day and night continuous operation. Fuel cells may be suitable for long-range light duty, but where do other aircraft fit in?
Several major commercial airliners have their eyes on hydrogen as a clean alternative fuel for traditional turbojet and turbofan engines. Airbus plans to use hydrogen as a combustion fuel for three new ZEROe concepts. Image courtesy of Airbus. All three ZEROe concepts utilize liquid hydrogen fuel to power modified gas turbine engines. Finally, a bold blended-wing body design offers enhanced flexibility for hydrogen storage and distribution as well as cabin layout.
Before hydrogen can see widespread use as an alternative fuel, the aerospace industry must overcome several key obstacles to adoption. Dani Murphy brings a wealth of experience from NREL National Renewable Energy Laboratory where she was involved in research for hydrogen infrastructure , including filling station design and safety. For decades, WHA has worked with the aerospace industry to overcome the safety challenges associated with hydrogen.
For SLS to fly, combustion takes place in two primary areas: the main engines four Aerojet Rocketdyne RSs and the twin solid rocket boosters built by Orbital ATK that provide more than 75 percent of thrust at liftoff. Combustion powers both propulsion systems, but the fuels and oxidizers are different. Liquid oxygen LOX serves as the oxidizer. The boosters, on the other hand, use aluminum as fuel with ammonium perchlorate as the oxidizer, mixed with a binder that creates one homogenous solid propellant.
Hydrogen, the fuel for the main engines, is the lightest element and normally exists as a gas. Gases — especially lightweight hydrogen — are low-density, which means a little of it takes up a lot of space. To get around this problem, turn the hydrogen gas into a liquid, which is denser than a gas. Seriously cold. Once in the tanks and with the launch countdown nearing zero, the LH2 and LOX are pumped into the combustion chamber of each engine.
When the propellant is ignited, the hydrogen reacts explosively with oxygen to form: water! The hydrogen-oxygen reaction generates tremendous heat, causing the water vapor to expand and exit the engine nozzles at speeds of 10, miles per hour!
The specific requirements of a mission are the primary consideration for propellant selection. For example, NASAs new human launch system, designed to replace the space shuttle, will use solid propellants for the first stage, liquid hydrogen and oxygen for the second stage, and liquid propellants for the service module in order to reach the International Space Station.
This propellant architecture can then evolve to support future lunar and Mars missions. Sign up for our email newsletter. Already a subscriber? Sign in. Thanks for reading Scientific American. Create your free account or Sign in to continue. See Subscription Options. Discover World-Changing Science. Read more from this special report: The Science of Pro Football.
Bryan K. Glenn Research Center, provides the following explanation. Get smart. Sign Up.
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