Eco-friendly alternatives to fossil fuels are venturing beyond Earth—and into space.

First conceived of in 1945, this is a rocket that replaces burning chemical fuel with a nuclear reactor that is used to heat up a propellant. This propellant is most likely hydrogen, though ...

Cornell said the next step is to drain the New Glenn rocket of its fuel. The company began filling the vehicle’s fuel tanks with propellant — including liquid methane, hydrogen and oxygen ...