We have been working with methane and talking about methane for 40 years. There has never been an engine produced that runs on methane.

The tests we did back then indicated that it would not be a big hurdle for the [space shuttle main engine] to achieve. But its a matter of getting started and having time to run the verification test program to satisfy everybody that it can meet the mission requirements.

When the shuttle is retired I can immediately take the engine assets out of the shuttle program and fly them on these vehicles.