Most importantly, SpaceX will attempt to briefly reignite one of Starship's six Raptor engines in space. SpaceX tried this on Starship's third launch in March but aborted the engine restart after the rocket lost roll control during the flight's coast phase.

SpaceX is expected to launch its sixth test of its massive Starship from South Texas on Tuesday evening. The two-stage Starship, the largest and most powerful rocket ever built, is expected to launch about 5 p.