Resilient Rockets

Spacecraft and automobiles could benefit from a new NASA technology that protects the insides of scorching-hot engines.

Once humans return to the Moon and begin "living and working there for increasingly extended periods of time," as outlined in the new Vision for Space Exploration, increasingly frequent trips between the Earth and the Moon will be necessary to ferry people and supplies.

Keeping a "space ferry" parked in Earth orbit, instead of returning it to the ground and spending money and fuel to launch it off the planet's surface each time, is one scenario for making the commute to the Moon more economical. A smaller vehicle would then be used to move people between the ferry and the ground.

This idea has some advantages, but it also suffers from an engineering obstacle - namely, maintenance. How do you maintain a vehicle that never returns to Earth?

The main engines of the Space Shuttle, the current crème de la crème of liquid rocket propulsion, must be returned to the ground between each mission for extensive maintenance. Severe conditions inside the engine combustion chamber - the reactive chemicals and the temperatures in excess of 2760°C (5,000°F) - cause a roughening of the material from which the combustion chamber liner is constructed (called "blanching"). The inner surface of the liner slowly becomes powdery and flaky, and this corrosion will worsen if the surface isn't polished between each mission.

An artist's concept of an Earth-to-Moon space ferry.

Similar engines would eventually become a safety threat to a space ferry after several roundtrips to the Moon without making pit stops on Earth.

Special coatings can protect the engine combustion liners from damage, but these coatings too have their flaws. Because materials expand by varying amounts when heated, the coating will expand differently than the liner itself under the high temperatures of rocket firing. At the sharp boundary where the coating binds to the liner surface, this difference in expansion will shear the two apart, leading to separation and flaking. The coating solves one problem but creates another; regular maintenance is still mandatory.