Are Bussard Ramjets Realistic?

[Zor]

I have been wondering about this lately, just how realistic are Bussard Ramjets and if so are they Practical? I've heard the "does not need to carry fuel via the electromagnetic Vacume Cleaner" thing, however by design these engines would take up more room. However, they don't require insane amounts of raw materials to build or twisting space/time into a knot to propellit.

So what are your thoughts on the Practicallity of Bussard Ramjets?

Zor

[Ender]

no. the drag from the collected hydrogen is greater thenthe thrust of the expelled hydrogen.

[GrandMasterTerwynn]

I have been wondering about this lately, just how realistic are Bussard Ramjets and if so are they Practical? I've heard the "does not need to carry fuel via the electromagnetic Vacume Cleaner" thing, however by design these engines would take up more room. However, they don't require insane amounts of raw materials to build or twisting space/time into a knot to propellit.

So what are your thoughts on the Practicallity of Bussard Ramjets?

Zor

They can be practical, if one carefully chooses both the kind of scoop used (electrostatic ion scoops can involve less drag than an electromagnetic scoop can), and what reactor they're feeding the protons into. Proton-proton fusion is difficult to achieve. For a starship, you'd want to use a catalyzed fusion reaction, (CNO-catalyzed) or antimatter-assisted fusion (which also requires that some heavier element, like boron, be carried aboard the starship.) Of course, this means that the ship will have to carry reactor mass, though not as much as it would need to carry, if it relied exclusively on internal stores. And even then, the maximum achievable velocity will be between 16-30% c, though with a ramjet, the scoop can double as a braking system when one nears the particle-rich environs of a starsystem.

[Lord of the Abyss]

Another problem is that we happen to be in a low-density bubble, so a ramjet is less efficient here than elsewhere in the galaxy.

[CoyoteNature]

You also might be able to use fuel ramps of deuterium tritium or deuterium helium 3. So it would acclerate in system(yes I am aware of the acceleration you'd have to use).

Also depends on how much you hybridize it with other systems, perhaps using supplementation from beamed power systems, or don't bother with it fusing it right there and instead redirect it around the ship where you use fusion bombs to heat it up as propellant.

Building it would probably be a pretty big concern, seen things like size of large asteroids or larger. So practically it'd be really expensive to build.

[GrandMasterTerwynn]

You also might be able to use fuel ramps of deuterium tritium or deuterium helium 3. So it would acclerate in system(yes I am aware of the acceleration you'd have to use).

Also depends on how much you hybridize it with other systems, perhaps using supplementation from beamed power systems, or don't bother with it fusing it right there and instead redirect it around the ship where you use fusion bombs to heat it up as propellant.

Building it would probably be a pretty big concern, seen things like size of large asteroids or larger. So practically it'd be really expensive to build.

No, you wouldn't want to carry isotopes of hydrogen or helium. If you were going to go with something so space-intensive, you'd might as well just build the bunkerage to contain an entire trip's worth of deuterium/tritium(which is radioactive and has a half-life of 12 years)/helium-3 and dispense with the ramjet altogether. Also, trying to marry a Bussard ramjet to an Orion-type starship isn't going to get you very far. You may dump a high-energy cloud of protons out the back of your ship from the ramjet, but it will all be blown apart when that next fusion bomb goes off (meaning that the protons will have zero effect on the yield of the bombs you're using to propel the ship.)

Also, what good will a beamed power system do in deep interstellar space? Building a huge beamed-power station with the accuracy and power needed to drive interstellar ships would likely be economically unfavorable, never mind the technical challenges involved. And if you were going to build a huge beam station, then you'd might as well construct a huge solar sail for the beam to push against, and only use the ramjet to brake your ship upon it's arrival at your destination.

[CoyoteNature]

I was thinking about the problems of powering the entire ship, seems like it would take a large amount of energy to push the ship up to a high enough velocity, to power the magnetic fields serving as a ramscoop, to power the ship itself, and to keep that power level throughout the trip, to power the fields serving as a acceleration break

Would seem like a bit much to ask of the ship's own reactors, unless they put out a considerable amount of power and can keep that level high enough throughout the trip, being efficient enough to only use the fuel carried with it, and or supplement it with the fuel pulled in by the ramscoop.

And if they can it means they quickly become uneconomical to build, I was just thinking of ways to keep the overall size of the ramjet and/or starship down, one way might be to supplement part of the onboard power with beamed power, and to keep the overall fuel down, a sufficiently advanced civilization might lay packets of deuterium tritium or helium 3 and/or factories to manufacture it so that the ramscoop picks it up in acceleration.

And yes it is space intensive, but then if you get to the point where you can build a Bussard Ramjet, you should have much of the infrastructure there.

Considering there is a relative paucity of isotopes of hydrogen in interstellar space.

I mean isn't the whole point of a Bussard ramjet supposed to be a fuel saver, if you have to carry it with you, you might as well do away with it as you mentioned.

As to the building of the beamed power system, one could also argue that the ramjet itself is uneconomical endeavor as well considering the amount of resources that would have to go into building it.

Actually a starship in general is uneconomical if you want to get up to high enough speeds to get there within less then a human lifetime.