From: Robert Lynn
A Bussard Ramjet is a Rocket that scoops up hydrogen from the interstellar medium using a vast magnetic and/or electrostatic field, then fuses it and fires it out the back. The concept has always had a major flaw in that hydrogen is nearly fusion-proof in conventional hot fusion except as part of Carbon-Nitrogen fuel cycle. "fusion proof" is not accurate, IMO. In fact, the situation is almost the opposite. The problem can be better stated as one in which the initial stage of hydrogen fusion is of extremely low gain. In fact, it is looking very much as if the reversible fusion reaction: P+P -> 2He ->P+P Which accounts for almost all of the nuclear reactions in any star . and which is the prerequisite reaction for eventual solar conversion into 4He - is not only EASY in a confined cavity (instead of a gravity well) but is slightly gainful in its own right. It has been assumed in most astrophysics models that proton fusion to 2He is no gain (e.g. on our sun), but it looks to me like the gain from QCD can amount to about 10^-16 eV per reaction on average. This explains part of the solar neutrino deficit. And therefore this basic proton fusion reaction itself, cannot lead to a Bussard Ramjet, at least not as initially described. Since the much more robust beta-decay, which is necessary to transmute two protons into deuterium (from 2He) is so rare, there can be no 3He or 4He in any such design due to time constraints. It requires approximately 10^20 P+P fusion reactions (sequentially) before a single beta decay is seen, and even then the deuterium does not survive long . as the neutron is stripped off most of the time before further reaction to helium. If it were not so, stars like our sun would burn up long before their normal lifetime of ten+ billion years. This only means that - in a revised Ramjet design - some portion of the interstellar hydrogen which collected, needs to be routed to LENR reactors, turned into heat and then into electricity in a completely separate system, so that the rest of the collected hydrogen (in the Ramjet funnel) can be magnetically compressed and accelerated as if in a beam line - using the electrical energy generated (from the portion of hydrogen which is fed to the LENR reactors). The end result is almost the same.
