In an interesting first-of-its-kind experiment, Japanese engineers tested a new rocket engine powered by liquid methane sourced from cow dung, which may lead to the development of a more sustainable propellant, according to The Independent. This marks a “world-first” test of liquid biomethane (LBM) of a rocket engine fuel.In an interesting first-of-its-kind experiment, Japanese engineers tested a new rocket engine powered by liquid methane sourced from cow dung, which may lead to the development of a more sustainable propellant, according to The Independent. This marks a “world-first” test of liquid biomethane (LBM) of a rocket engine fuel.