The ramjet was a proposed variant of the fusion engine, but rather than carrying along its own fuel, it would use enormous electromagnetic fields to ram scoop hydrogen from the interstellar medium. The high energy protons enter the ram scoop, confined by magnetic field lines and then meeting under the conditions for fusion reactions to occur, producing a high energy exhaust jet. In theory, if the interstellar ramjet can be made to work, then relativistic star travel will be possible.