Rocket engines employ the principle of jet propulsion. SpaceX Starlink use krypton as propellant for their electric propulsion system. The ducted fan produced less noise than conventional propeller propulsion. It is also used as a fuel for spacecraft propulsion. US aircraft carriers are notable for having nuclear reactors powering their systems and propulsion. A number of experimental methods of spacecraft propulsion are based on magnetohydrodynamics. Siphonophores use a method of locomotion similar to jet propulsion. Marine engineering is the discipline concerned with the engineering design process of marine propulsion systems. The squid uses the funnel for locomotion via precise jet propulsion. A variety of electric propulsion systems provide examples. A pair of propellers at the rear provided propulsion. Marine engineering is the discipline concerned with the design of marine propulsion systems. American Robert Goddard was one of the first scientists to experiment with rocket propulsion systems. They have also been suggested for use in spacecraft propulsion. Production of components for propulsion systems began.