The Interstellar Ramjet: Engineering Nightmare

Authors: Albert Jackson and Peter Schattschneider Ph. D

Description: Long ago it was noted that the mass ratio problem is for an interstellar spacecraft was an enormous problem. One solution was to acquire propellant along the route, such a propulsion system to get around the mass ratio problem was formulated by Robert Bussard in 1960. His solution, the interstellar ramjet, which would gather interstellar hydrogen and through hydrogen fusion provide thrust. Bussard and later Dan Whitmire noted the extreme reactor conditions needed for the proton-proton reaction. Whitmire showed for the p-p process that the reactor length would have to be about 1000 km long! Bussard noted that to scoop hydrogen for a 1g ship one need an inlet area of the collector to be of the order of 1000 km in radius. Bussard also proposed that a magnetic field might be used as the collection agent. Recently we have shown that there are sever constraints on a magnetic ram scoop. Namely that the characteristic size and mass of the source of the magnetic field can be of the order of hundreds of kilometers and a thousand kilotons respectively. This is an extreme constraint on the engineering physics of an interstellar ramjet. Fishback’s limit on final mission speed is a much smaller value now. All this before one considers system efficiencies, radiation losses, drag and radiation damage. Further the scoop constraints limit the viability of the augmented and laser powered ramjets.