Bussard ramjets?

[MC.STEEL]

So a Bussard ramjet is a theoretical method of spacecraft propulsion proposed in 1960 by the physicist Robert W. Bussard.

it works on a principle of a fusion rocket but instead of carying its own fuel it uses a giant magnetic scoop that gathers hydrogen from the surounding cosmos,then the same magnetic forces crush the hydrogen together causing a fusion reaction,proppeling the craft forward.

Its an interesting concept but i see some problems with this desing.

1 If we use the same interstellar lanes then as more gas is scooped up less and less fuel will be left making them useless at some point in the future.

2 For a field that strong you will have to make a ship very robust to not crumple in on itself,and not to talk about your keys and other such sticking to the wall furing burns.

3 Like all proposed interstellar propulshion (excluding the Orion N.P.E.) where is it going to get all that power?

BTW i have an idea, wouldnt it be neat if ships have an emergency hydrogen scoop in the times they run out of fuel

[kahlzun]

Many science fiction ideas revolve around it.

Part of the problem is that we live in an area of extremely low hydrogen density, so it would not work terribly well around here.

What was the mechanism suggested to harvest the particles in your source?

[K^2]

1) Interstellar gas generally moves at a pretty brisk pace, and there are currents. I wouldn't worry about it.

2) There are ways to shield interior of the ship from magnetic fields. As for the structure, just don't use ferromagnetic materials.

3) The original ram jet idea worked off nuclear fusion of the incoming hydrogen. The idea is that at a sufficiently high speed, the gathered hydrogen would heat up as it compresses and reaches sufficient temperature for fusion. The rest works like a conventional ram jet. (Well, a scram jet, actually.) The problem is that this turned out to generate too much drag and not enough thrust. So it would need additional power to keep it running. There have been a number of suggestions on that, but I'm not sufficiently familiar with them to say which are feasible.

[Themohawkninja]

There is one main huge problem with the Bussard Ramjet that I am aware of: It generates more drag than thrust.

[Ralathon]

You have to note that the giant scoop is going to act as a huge drag factor, this severely limits your top speed.

Gathering hydrogen from interstellar space costs you 0.5*(dm/dt)*v^2 = dE_kin​/dt where dm/dt is your hydrogen mass flow and v is the relative velocity of your ship. The mass defect of helium 4 is about 0.75% of its total mass. So fusing the collected hydrogen gives you (dm/dt)*0.0075*c^2=dE_fusion/dt of energy to play with. I'm going to be generous and assume you can use all this energy directly to counter the kinetic energy lost.

0.5*(dm/dt)*v^2 = (dm/dt)*0.0075*c^2

v^2 = 0.00375*c^2

v =~ 0.061*c

So a bussard ramjet can only ever reach a maximum of 6% of the speed of light relative to the hydrogen atoms it moves through. Any faster and the scoop just starts to act as a massive parachute. And that 6% is with very generous assumptions about the efficiency of your fusion drive. 100% efficiency is simply impossible, you need to maintain the scoop's magnetic field and thermodynamics always steals a generous portion of your available energy. So I'd be impressed if a bussard Ramjet manages 3% of c.

This may be fast enough for a generation ship, but if you want to get anywhere within a human life span it is simply too slow. A trip to the closest star would take 150 years. Not to mention that building something that can run for centuries is no simple feat either.

[MC.STEEL]

drag? i am talking about a magnetic scoop.

who would want to make a ship with a giant scoop on the front,its just silly(i bet the kerbals will try atleast)

[Ralathon]

drag? i am talking about a magnetic scoop.

who would want to make a ship with a giant scoop on the front,its just silly(i bet the kerbals will try atleast)

Doesn't matter what you make the scoop of. A sail can be made of plastic or cloth but it'll catch wind just as well. A magnetic scoop would cause just as much drag as an actual plastic/metal scoop.

[MC.STEEL]

Aha, so what about the emergency hydrogen collector i proposed?

Edited January 5, 2014 by MC.STEEL

[Ralathon]

Aha, so what about the emergency hydrogen collector i proposed?

Well, the main problem is that you need a pretty big electromagnet to gather that emergency hydrogen. Not to mention some sort of power source. Those 2 combined will probably weigh a lot more than a small canister of hydrogen behind a "Break glass in case of emergency" panel. A ship running out of fuel is rather unlikely anyway. A space mission isn't like a car ride that you take on a whim. Mission control and the engineers designing the ship calculate in excruciating detail how much fuel they need.

[crazyewok]

Mankind needs to learn to walk before we can run and at the moment we are barely crawling on our rear ends and this is like running a marathon.

All our effort should be on makeing a safe and affordable way into orbit first.

[MC.STEEL]

Mankind needs to learn to walk before we can run and at the moment we are barely crawling on our rear ends and this is like running a marathon.

All our effort should be on makeing a safe and affordable way into orbit first.

While i totaly agree with you its just fun to speculate about the future and its not like I am writing this instead of reasearching something important.

[K^2]

drag? i am talking about a magnetic scoop.

It's very difficult to re-direct flow without any drag. But here, you aren't just trying to re-direct it. You are trying to heat it up to use it for fusion. That energy has to come from, and the only place it can come from is from work of the ship on the gas. That means there is going to be a corresponding work done against the ship. Ergo, drag.

If you have an alternative energy source, you can have a low-drag scoop, and use linear accelerators to push off of the flow. It's not very efficient, but at "low" speeds, such as 10% of speed of light, it can still be more efficient than a photon drive, so it might be worth it in interstellar missions. Problem is getting all that energy. Unfortunately, even a nuclear reactor is going to be too much mass to drag if you want to actually get to 10% of c. Hence the idea of using hydrogen as fuel, and hence the drag.

[Skyler4856]

mining jupiter anyone?

[crazyewok]

While i totaly agree with you its just fun to speculate about the future and its not like I am writing this instead of reasearching something important.

No I agree it is a intresting concept.

I doubt we will crack FTL at least not in a way to transport people. But Im pretty sure we could get 90%+ to speed of light (ONEDAY) which would put 100 light years worth of stars in our range (takeing into acount time dillation). Even now we could possibly get a probe to our nearest stars in a 40/60 years time frame if we really really tried with the nuclear option.

Edited January 5, 2014 by crazyewok

[K^2]

Right now, warp drive seems a more plausible way to approach the speed of light, and potentially FTL speeds, than any kind of reaction drive we can imagine taking us to 90% of speed of light. 10% we can do without tapping into Gen-Rel for sure, but significantly beyond that, we really have to go with warp. Even with matter-antimatter photon drive, .9c is likely beyond reach, not to mention practical use, and a good photon drive at these sort of efficiencies is already beyond physics as we know it.

So if we can't do warp, I don't think we are ever going to do human interstellar flight. No telling what trans-humanity will bring, of course. We might simply get to the point where distinction between manned and an unmanned mission is non-existent and then take the slow and steady approach to space colonization. But I haven't lost hope in warp drives yet.

[crazyewok]

Right now, warp drive seems a more plausible way to approach the speed of light, and potentially FTL speeds, than any kind of reaction drive we can imagine taking us to 90% of speed of light. 10% we can do without tapping into Gen-Rel for sure, but significantly beyond that, we really have to go with warp. Even with matter-antimatter photon drive, .9c is likely beyond reach, not to mention practical use, and a good photon drive at these sort of efficiencies is already beyond physics as we know it.

So if we can't do warp, I don't think we are ever going to do human interstellar flight. No telling what trans-humanity will bring, of course. We might simply get to the point where distinction between manned and an unmanned mission is non-existent and then take the slow and steady approach to space colonization. But I haven't lost hope in warp drives yet.

Even 10% is doable.

Yes a 100/200 year journey would be hell and basically suicide in a weightless tiny tin can capsule.

If you built huge nuclear powered generation ships of millions of tons in orbit then it quite doable. As long as you have some kind of "artifiical gravity ".

[K^2]

For the coasting part, you'd definitely have to go with rotation. Any other form of artificial gravity makes warp drives look like toys. For acceleration and deceleration, it'd be nice to maintain 1G simply through that, but it might be tricky to do with NPP, which is our best bet right now.

One thing for which a Bussard Ramjet might be ideal is deceleration. You can definitely design one with reverse thrust, in which case drag is actually helping you slow down. That way you can do a 1G deceleration "for free" all the way to the target system. Depending on the design, this might also work as a re-fueling stage, in case you have to send the ship on to the next system. It's hard to come up with any single-stage system capable of significant fraction of speed of light, though. But even if it just works as a brake, you can effectively double your cruise speed for the same size ship, since all of your delta-V would go into speeding up.

So if I had to do a proposal fro an interstellar mission based on current tech, I'd go with Orion-type drive for speeding up, and Bussard Ramjet for slowing back down. This is still only conceivable, with technology and world resources as they are, as an un-manned mission. Manned mission would have to be a generation ship, as you've said, making it much, much larger, and requiring a whole lot of other provisions. Gravity, as you've mentioned, but also shielding, life support for an entire colony, way to renew or regenerate resources from water, to air, to food, and ways to patch up or even rebuild anything that goes broke during the decades or centuries that the ship would be in voyage. Even if we sort out technology, all of Earth's governments and corporations combined don't have resources to make a dent in a project like this.

[crazyewok]

Manned mission would have to be a generation ship, as you've said, making it much, much larger, and requiring a whole lot of other provisions. Gravity, as you've mentioned, but also shielding, life support for an entire colony, way to renew or regenerate resources from water, to air, to food, and ways to patch up or even rebuild anything that goes broke during the decades or centuries that the ship would be in voyage. Even if we sort out technology, all of Earth's governments and corporations combined don't have resources to make a dent in a project like this.

Hense why it would have to 1) Be Built in orbit and 2) We would need to be minning resources in space.

Which comes with my walk before we run metaphor ealier.

We need to get out in our solar system first and start exploitings it resources before we consider moveing out to nearby stars. Once we have the orbit constrution facilitys and solar system minning oneday, mega constructions like that wont be as daunting

[sp1989]

I think in terms a KSP, an extremely popular and useful MOD could be made around that concept. If I had any modding skills this would be something I would work on. Maybe Majiir of the Kethane mod and Fractal_UK of the KSP Interstellar mod could work together on something like this.

[Rakaydos]

What about a Bussard-Antimatter drive?

Have low-drag scoops bring intersteller hydrogen through the craft, and inject antihydrogen into the fuel flow, instead of relying on fusion pinch. You still need to bring antimatter along, but only as a catalyst- the compressed hydrogen forms reactant and reaction mass.

And the idea of a pure Bussard deceleration mode is a good one, that fits nicely with this design.

[meve12]

What about a Bussard-Antimatter drive?

Have low-drag scoops bring intersteller hydrogen through the craft, and inject antihydrogen into the fuel flow, instead of relying on fusion pinch. You still need to bring antimatter along, but only as a catalyst- the compressed hydrogen forms reactant and reaction mass.

And the idea of a pure Bussard deceleration mode is a good one, that fits nicely with this design.

That's a Ram Augmented Interstellar Rocket. Not that it's a bad idea; it nicely sidesteps the difficulties of proton-proton fusion.

[shynung]

Have low-drag scoops bring interstellar hydrogen through the craft, and inject antihydrogen into the fuel flow, instead of relying on fusion pinch. You still need to bring antimatter along, but only as a catalyst; the compressed hydrogen forms reactant and reaction mass.

It's not a catalyst in the traditional sense; catalysts are recovered after the reaction is done, rather than burned along with the reactants. It's just fuel here.

In my opinion, this design resembles an atmospheric jet engine; swap the turbomachinery with the magnetic scoop, ambient air with interstellar hydrogen, and jet fuel with antimatter.

[Wahgineer]

Hense why it would have to 1) Be Built in orbit and 2) We would need to be minning resources in space.

Which comes with my walk before we run metaphor ealier.

We need to get out in our solar system first and start exploitings it resources before we consider moveing out to nearby stars. Once we have the orbit constrution facilitys and solar system minning oneday, mega constructions like that wont be as daunting

But wouldn't it be nice to know "hay, its possible to build a working warp drive?" long before that?

Also, who's to say we HAVE to be able to do orbital mining before we go interstellar? If we crack the FTL egg within a couple of decades (optimistic, yet possible), no one would wait for us to start mining the asteroid belt. The public, once informed of the possibility to get to the nearest star and back within a month, would most likely get behind a project to build such a ship. Rockets would carry materials into space, the ship would be constructed, and then depart. You could say that we need to crawl before we can run, but we aren't cavemen any more: we know how to walk (albeit unsteadily). To say that interplanetary travel is unbelievably far into the future is like saying it was impossible to go to the moon in 1969: we'd sent men around it, even practiced near it. To land on wouldn't take much more effort. We're at the same place with mars today: we've sent robots there; to send men there isn't that much harder: you'll just need a bigger, better rocket.

[shynung]

Also, who's to say we HAVE to be able to do orbital mining before we go interstellar? If we crack the FTL egg within a couple of decades (optimistic, yet possible), no one would wait for us to start mining the asteroid belt. The public, once informed of the possibility to get to the nearest star and back within a month, would most likely get behind a project to build such a ship. Rockets would carry materials into space, the ship would be constructed, and then depart. You could say that we need to crawl before we can run, but we aren't cavemen any more: we know how to walk (albeit unsteadily). To say that interplanetary travel is unbelievably far into the future is like saying it was impossible to go to the moon in 1969: we'd sent men around it, even practiced near it. To land on wouldn't take much more effort. We're at the same place with mars today: we've sent robots there; to send men there isn't that much harder: you'll just need a bigger, better rocket.

It makes perfect sense to improve our orbital/extraterrestrial mining capability before going interstellar. Otherwise, even if we can go to other stars, all we'll be able to do is an Apollo-style mission: land, do some science, and return. Given the fact that interstellar distances need decades to cross, even in a fast ship, a simple land-science-return mission is a silly waste of resources. With all that investment into interstellar travel, we might as well be building a generation ship to colonize the destination star system in the meantime.

Also, an interstellar mission using technologies available in the near future is not comparable to a Moon landing mission using 1960s technology; they are differing in difficulty by several orders of magnitude. It might have taken about 3 days going from LEO to Lunar orbit, but it will take years to go to Alpha-Centauri, which is about 4 light-years away.

[Wahgineer]

It makes perfect sense to improve our orbital/extraterrestrial mining capability before going interstellar. Otherwise, even if we can go to other stars, all we'll be able to do is an Apollo-style mission: land, do some science, and return. Given the fact that interstellar distances need decades to cross, even in a fast ship, a simple land-science-return mission is a silly waste of resources. With all that investment into interstellar travel, we might as well be building a generation ship to colonize the destination star system in the meantime.

Also, an interstellar mission using technologies available in the near future is not comparable to a Moon landing mission using 1960s technology; they are differing in difficulty by several orders of magnitude. It might have taken about 3 days going from LEO to Lunar orbit, but it will take years to go to Alpha-Centauri, which is about 4 light-years away.

You miss read what I said: a warpdrive would cut the travel time to the nearest star down to 2 WEEKS, which is a round trip of about a MONTH. That's a third of the time it would take a VASMIR propelled Mars mission to just get to Mars. Even if it was just a simple land and return, that's all we would need to ignite the public interest. "first man to walk on another planet around another star" "(insert astronauts name), faster than the fastest man alive!""Star Trek: it's no longer fiction" All of those headlines have quite a ring to them. If we can build an FTL ship, no matter how expensive, it would still be more economical/feasible/practical then a Bussard Ramjet. Hence why i support NASA's development and testing of a warpdrive.