[IceFyre13th]

I want in.....I love engineering gobbly gook

Subject: Bussard ramjet speed limit
Since I haven't seen anybody else demolish the myth about the 0.17c speed limit on Bussard ramjets, here goes. The article in Asimov's was not the first recognition of the problem; contrary to what was said in the article, this problem has been known for years, but has not been trumpeted out loud because there is a straightforward fix.
It is reasonably obvious to anyone who does a real analysis of the Bussard ramjet instead of relying on analogy from "ordinary" jets. (In the following, all velocities etc. are with respect to the ship.) The purported speed limit works as follows: thrust from the expulsion of fusion-engine exhaust is counterbalanced by intake drag from fast-moving incoming fuel hitting the ramscoop field, so net momentum transfer to the gas stream works out to be zero.
With some simplifying assumptions, the speed limit equals the engine exhaust velocity; it is easy to set an upper bound on this based on the reactions involved. The mistake is to assume that the kinetic energy of the incoming fuel is necessarily converted to heat or some other useless form. WRONG!
Suppose instead we decelerate the incoming protons against an electric field. The momentum IS transferred, but the energy is stored as potential energy. We use that stored energy to further accelerate the outgoing exhaust by letting the protons fall down the other side of the same electric-field potential hill. Other variations are possible, but the principle remains the same: use the kinetic energy rather than wasting it.
There is still some momentum transfer, because the same amount of kinetic energy does not mean the same amount of momentum at different velocities. The exhaust acceleration is less effective at producing momentum because it is applied to already fast-moving material. But this is a lesser effect; barring losses, there is always a nonzero net momentum transfer to the gas stream (unless relativity introduces some subtle complication at extreme velocities; not my specialty).
Of course there WILL be losses, and integrating this with a ramscoop may be a lot of fun, but those are problems of technology, not fundamental physics. In any event, the ramscoop is the EASY part of a Bussard ramjet, by current thinking: the HARD part is getting a decent reaction rate out of a fusion reaction burning ordinary hydrogen.
Building a ramscoop is a formidable engineering problem, but a fast proton-proton reactor involves nasty difficulties of fundamental physics. It may be necessary to go to an internal energy source, either ordinary fusion (the "ram-augmented rocket" scheme) or antimatter. The latter is the more interesting: antimatter-heated rockets have rather (!) high performance themselves, and adding "free" reaction mass makes it even better. To sum up: the near-c Bussard ramjet is not impossible, it's just complicated, difficult, and not quite the way it was visualized.