If you want to make a trek into space you better bring a fuel cell along with you. For the past 45 years onboard fuel cells have powered every manned spacecraft launched by NASA. This technology, known to scientists for over 150 years, has become a fixture in our space program and may soon play an increasing role in our everyday lives.
Fuel cells are ideal for space missions for many reasons. Fuel cells can run for long durations without interruption as long as fuel is supplied. They produce electricity very efficiently and reliably. In addition, the light weight of fuel cells reduces total launch pad weight. Batteries, on the other hand, are heavier and must be recharged between uses. Fuel cells also provide the unique advantage of making drinking water for astronauts. Pure, clean water is the only byproduct of fuel cell operation.
So how do fuel cells work? Fuel cells do not burn their fuel or use turbines and generators to make electricity like many traditional power plants. Instead, fuel cells produce electricity by combining hydrogen and oxygen in a very controlled manner. There are many different types of fuel cells, but they all operate by the same general principle: hydrogen is fed into one side of the fuel cell while oxygen is fed into the other. They react chemically, with the help of a catalyst to speed things up, and produce electricity, heat, and water. However, the voltage generated by this reaction is relatively small. To obtain the desired voltage fuel cells must be combined into a stack. The ability to build and combine fuel cell stacks of different sizes makes fuel cells extremely modular. They can be used for a variety of applications large and small from cars, trains, and buildings to portable electronics.
NASA first used fuel cells aboard the Gemini V mission in August 1965. The Gemini spacecraft used a GE proton exchange membrane (PEM) fuel cell stack capable of providing 1 kW of power. The average power draw was 620 W. For comparison, the average U.S. home demands roughly 1.3 kW. These PEM style fuel cells powered the remaining seven Project Gemini missions before the end of the program in November 1966.
The Apollo program spacecraft also used fuel cells for power and water supply. Apollo’s manned flights occurred from 1968-1972 and first reached the Moon in 1969. Instead of using PEM fuel cells like on Gemini, the Apollo missions utilized a Pratt and Whitney alkali fuel cell plant providing peak power capability of 2.3 kW. NASA was young, but fuel cells in spacecraft were already becoming more powerful. These fuel cells were very reliable as well. The Apollo’s fuel cells were rated to run for 400 hours, but they ran for 690 hours without failing.
The improvement in fuel cell power from Gemini to Apollo merely hinted at coming advances in the technology. In 1973 United Technologies Corporation began work on fuel cells for use in the Space Shuttle Orbiter. In 1981, the first Space Shuttle was launched with three fuel cell power plants each supplying 12 kW at peak power and 6 kW in average use. These fuel cells weighed 50 lbs. less than those aboard the Apollo spacecraft and produced eight times more power. The Space Shuttle Orbiter’s fuel cells can operate for 2000 hours.
The last Space Shuttle launch will take place in early 2011. The Orbiter’s power on this mission will come from the same type of fuel cells as in the first Shuttle launch 29 years ago. With the Shuttle program nearing retirement, NASA has invested in fuel cell research for future missions. NASA’s Glenn Research Center is looking into newer PEM fuel cells, high efficiency solid oxide fuel cells, and renewable fuel cell systems capable of producing and storing energy on Mars and the Moon.
Everyone stands to benefit from NASA’s continued dedication to fuel cell technology. NASA’s tough engineering constraints have inspired remarkable technological advancements. Fuel cells progressed from producing just 5 W/lb on Apollo to 50 W/lb on the Space Shuttle Orbiter. That’s much more power for the same payload. As power becomes an increasingly valuable commodity here on Earth, this clean space-age technology starts to look more and more relevant. Fuel cells like those on spacecraft can power our homes, cars, and electronics without the production of greenhouse gases. Even for us non-astronauts, fuel cells have plenty to offer. We should thank NASA for pushing the envelope with this technology.
Posted by Boli Zhou on 08/18/10, 05:53 PM
By itself, fuel cell will not solve the world's energy problem or be a significant player. However, combined with solar cells (or wind mills), and electrolyzers powered by the renewable energy to split water into hydrogen and oxygen, hydrogen fuel cell can be an important part of an alternative energy sytem to support the escalating global energy demand.