In Poul Anderson's 1970 novel Tau Zero, a starship crew seeks to travel to the star Beta Virginis in hopes of colonizing a new planet. The ship's mode of propulsion was a so-called "Bussard ramjet," an actual (though hypothetical) means of propulsion which had been proposed by physicist Robert W. Bussard just a decade earlier. Now, physicists have revisited this unusual mechanism for interstellar travel in a new paper published in the journal Acta Astronautica, and alas, they have found the ramjet wanting. It's feasible from a pure physics standpoint, but the associated engineering challenges are currently insurmountable, the authors concluded.
Even if we managed to get up to significant sub-light speeds (say, 0.1c or higher) - does the environment make interstellar travel impractical as we likely couldn't travel fast enough and not hit too much debris to destroy/damage a ship at those speeds?
Hasn't the Bussard ramjet been questionable since about 1978? See Heppenheimer, T.A. (1978).
T. A. Heppenheimer published a paper... noting the problems with the p-p chain for fusion without citing Dan Whitmire’s solution. Heppenheimer notes radiation losses but does not cite Whitmire and Fishback, who addressed the problems of bremsstrahlung and synchrotron radiation in the reactor and the scoop field.
Apparently there are only two ways to salvage (sort of) the Bussard RJ concept. One is bringing "an easier type" of fuel along to fuse and then mixing it with what the scoop collects as reaction mass. The Ram Augmented Interstellar Ramjet. (RAIR),or most feasible, laying down fuel "packets" infront of the stove pipe like vessel prior to vessel launch. Fuel and Vessel would be lauched in a way to where the vessel intercepts the fuel in a "head on" fashion vis-a-vis opposition Olberth launching. Opposite directional Olberth launching of both fuel and vessel is to increase velocity of both to ensure high velocity impacts.Fusion ignition occurs when the space "ship" impacts the fuel at high velocity. There is no scoop on the second version to create "drag" in the IP or ISM.
Maybe this is a dumb question, but how does a Bussard ramjet slow down? Surely the scoop must always face the direction of travel? So once you're at 12% C, how do you stop?
I believe the Cassenti toroidal field scoop concept was suggested to try to help mitigate the drag effects of what Bussard originally envisaged as/for his ram scoop. I image you are aware Andrews and Zubrin found the original Bussard scoop concept to create enough drag in the ISM to limit the vehicle to +/- 12% of C....
that's if P-P fusion were possible and the ISM were dense enough to collect that amount of hydrogen. Note the the drag + lack of adequate fuel collection and our inability to even consider P-P fusion make the the BRJ untenable. K Hambsch
Hasn't the Bussard ramjet been questionable since about 1978? See Heppenheimer, T.A. (1978). "On the Infeasibility of Interstellar Ramjets". Journal of the British Interplanetary Society. 31: 222Not referenced in this recent paper, so perhaps something is different.
QuoteIt's feasible from a pure physics standpoint, but the associated engineering challenges are currently insurmountable, the authors concluded.
It's feasible from a pure physics standpoint, but the associated engineering challenges are currently insurmountable, the authors concluded.
Wait...they're saying that it's theoretically possible, but we don't know how to build one yet?I'm shocked that we can't build a Bussard ramjet, in this day and age. Next they'll be telling us they can't build an interstellar spacecraft. Or a General Products hull.
Quote from: daveklingler on 08/16/2023 04:37 pmWait...they're saying that it's theoretically possible, but we don't know how to build one yet?I'm shocked that we can't build a Bussard ramjet, in this day and age. Next they'll be telling us they can't build an interstellar spacecraft. Or a General Products hull.Clearly we just need to find some Slaver stasis boxes.The lighthuggers from Revelation Space were supposed to be some sort of ramjet but they had insanely advanced technology for p-p fusion (not even the crews seemed to really understand it). It would require fiddling with the weak force somehow and maybe something else like a muon. p-p molecules are possible with muon catalysts but they fly apart almost immediately, unless one of the ps undergoes beta+ decay.Otherwise, maybe a ram augmented fusion engine, with interstellar p and stored d, giving you He3 exhaust and ~5MeV. Perhaps some kind of breeder cycle might work using the interstellar p.Who knows, maybe Fermilab is onto something with their possible fifth force discovery and that could eventually be applied.*I am not a physicist