Near Future Saucer

[Kryten]

1 hour ago, Dave Angel said:

I think there was a plan to add a rotating module to the ISS called the Nautilus-X, but it got canned - as most of the experiments planned relied on zero-g conditions it was seen as an expensive option.

Nautilus-X was in interplanetary transport study. The ISS module was CAM; en.wikipedia.org/wiki/Centrifuge_Accommodations_Module

[Green Baron]

 

6 minutes ago, K^2 said:

*snip*. I honestly don't see us making regular round trip flights to Mars until we learn to do something like that with our ships.

Or else the poor guys will be in a very bad shape after a few months ...

 

[shynung]

9 minutes ago, K^2 said:

If you aren't going for a ring station, I think tethers are the way to go. Once you're at a cruising trajectory, simply extend you engines/reactors/whatever on a long tether and give the system a gentle spin.

Even better, we can put the engines ahead of the crew compartment, and leave the tether extended. This not only puts some distance between the engines and the crew (which can reduce the mass for radiation shielding), but also makes the G vector during thrust and spin identical.

[Nuke]

i think id use a polywell or dpf reactor (though i have doubts about the latter, same plasma contamination issue that fusors have) powering mach effect drives. woodward was claiming reactionless drives with the same capability as an f1 class engine. they would actually be phased arrays of smaller thrusters and would give you a great deal of fault tolerance and serviceability. polywell could be a few meters across where a tokamak (which runs on money and is only capable of fusing dreams into disapointment) would be utterly massive. also i dont think there is a means of direct conversion possible for a tokamak, meaning a big thermodynamic engine and a lot of radiator area. the polywell would only need enough radiator to dump what cant be directly converted, which could be as small as about 10% of the output.

given a sufficient powerplant lifting a centrifuge to orbit would be trivial. ive done it in kerbal with an absurd number of boosters with the rocket equation biting me in the buttocks. i had an idea for a plasma/nuclear toroidal ship with the habitation being a small toroidal tube surrounded by a larger toroidal fuel tank. the ship would not spin, since most of its mass doesnt need to, the centrifuge would run on rails in the habitat tube with each car being on trunions so it could operate at high g loads and for surface operations. a nuclear reactor could be placed at the center of a hub with enough distance to greatly limit the shielding requirement (that and the propellant surrounding the crew). a small ring of shielding is used instead of a larger disk shaped shield you might expect. since the majority of possible vectors for radiation would point into empty space with only a thin band of stuff (from its perspective) that needs to be blocked from radiation.

Edited June 8, 2017 by Nuke

[magnemoe]

2 minutes ago, Nuke said:

i think id use a polywell or dpf reactor (though i have doubts about the latter, same plasma contamination issue that fusors have) powering mach effect drives. woodward was claiming reactionless drives with the same capability as an f1 class engine. they would actually be phased arrays of smaller thrusters and would give you a great deal of fault tolerance and serviceability. polywell could be a few meters across where a tokamak (which runs on money and is only capable of fusing dreams into disapointment) would be utterly massive. also i dont think there is a means of direct conversion possible for a tokamak, meaning a big thermodynamic engine and a lot of radiator area. the polywell would only need enough radiator to dump what cant be directly converted, which could be as small as about 10% of the output.

An working polywell reactor using boron would work very well as an fusion engine as it is. An tritium powered polywell would be smaller and easier but just generate heat like other reactors. 

 

[sevenperforce]

3 hours ago, shynung said:

Even better, we can put the engines ahead of the crew compartment, and leave the tether extended. This not only puts some distance between the engines and the crew (which can reduce the mass for radiation shielding), but also makes the G vector during thrust and spin identical.

With a nuclear engine you can afford a bit of cosine losses.

 

[-Velocity-]

A couple points:

The "EM drive" is essentially a hoax so you shouldn't consider that.

Also, fusion reactors should not be considered realistic to use in a nuclear thermal rocket.  You can't have your plasma to cool down and you can't have it touch anything.  You could extract thermal energy from the containment vessel, but I don't think that it will be easy to get your fuel as hot than with certain kinds of nuclear thermal rocket designs we dreamed up already, decades ago.  Nuclear fission fuel doesn't care what the ambient temperature is, it doesn't have to be held in isolation from the walls of its containment chambers, it's easy and quick to turn off and on... heck, in a dirty design you can even have your propellant flow THROUGH your fuel.

Also, since the amount of fusion fuel fusing at any one time in a reactor would be very small, I don't think you can get the power densities in a fusion reactor that you can in a fission reactor.  You'd have a major thrust-to-weight ratio problem.  Fission reactor power densities can get so high that they literally can explode by accident, the same can never happen for a fusion reactor.  Yes, thermonuclear bombs use fusion explosions, but that is by using a nuclear fission bomb as the containment and igniter for the fusion explosion.  And heck, most thermonuclear bombs actually get most of their energy from fission anyway (the fusion being mainly used as a source of high energy neutrons that ignite fission reactions than would never be achievable with lower-energy fission-generated neutrons alone).

Who knows, MAYBE with laser confinement (forgot the technical term for it) like at the NIF you could somehow make a nuclear thermal fusion rocket.  It just sounds like a stretch though when normal nuclear thermal fission rockets are so much easier and simpler.

 

Edited June 9, 2017 by -Velocity-

[magnemoe]

45 minutes ago, -Velocity- said:

A couple points:

The "EM drive" is essentially a hoax so you shouldn't consider that.

Also, fusion reactors should not be considered realistic to use in a nuclear thermal rocket.  You can't have your plasma to cool down and you can't have it touch anything.  You could extract thermal energy from the containment vessel, but I don't think that it will be easy to get your fuel as hot than with certain kinds of nuclear thermal rocket designs we dreamed up already, decades ago.  Nuclear fission fuel doesn't care what the ambient temperature is, it doesn't have to be held in isolation from the walls of its containment chambers, it's easy and quick to turn off and on... heck, in a dirty design you can even have your propellant flow THROUGH your fuel.

Also, since the amount of fusion fuel fusing at any one time in a reactor would be very small, I don't think you can get the power densities in a fusion reactor that you can in a fission reactor.  You'd have a major thrust-to-weight ratio problem.  Fission reactor power densities can get so high that they literally can explode by accident, the same can never happen for a fusion reactor.  Yes, thermonuclear bombs use fusion explosions, but that is by using a nuclear fission bomb as the containment and igniter for the fusion explosion.  And heck, most thermonuclear bombs actually get most of their energy from fission anyway (the fusion being mainly used as a source of high energy neutrons that ignite fission reactions than would never be achievable with lower-energy fission-generated neutrons alone).

Who knows, MAYBE with laser confinement (forgot the technical term for it) like at the NIF you could somehow make a nuclear thermal fusion rocket.  It just sounds like a stretch though when normal nuclear thermal fission rockets are so much easier and simpler.

 

Most fusion rocket designs uses pulsed fusion, you typical use lasers and an electrical field to generate fusion in an pellet or charge, this turn the pellet into high temperature plasma you use an magnetic field to redirect backward for trust, benefit of this is very high ISP, higher than ion engines. it has the beauty that you don't need break even fusion for it to work. you can get electrical power from solar or an reactor. 
Yes getting close to or even past break even would be an benefit as you could pulse faster and increase trust, you would also not need much external power for the engine reducing weight. 

An boron fusion reactor could run in constant trust mode as you could have an opening in the reactor for the  fusion byproduct. 
All of this is low trust high isp engines who are heavy, typical use would be an manned mission to mars or asteroids

EM-drive, i'm a bit more optimistic here as in it might work. It will however never be anything more than an good ion engine who don't need fuel. 

[-Velocity-]

6 minutes ago, magnemoe said:

Most fusion rocket designs uses pulsed fusion, you typical use lasers and an electrical field to generate fusion in an pellet or charge, this turn the pellet into high temperature plasma you use an magnetic field to redirect backward for trust, benefit of this is very high ISP, higher than ion engines. it has the beauty that you don't need break even fusion for it to work. you can get electrical power from solar or an reactor. 
Yes getting close to or even past break even would be an benefit as you could pulse faster and increase trust, you would also not need much external power for the engine reducing weight. 

An boron fusion reactor could run in constant trust mode as you could have an opening in the reactor for the  fusion byproduct. 
All of this is low trust high isp engines who are heavy, typical use would be an manned mission to mars or asteroids

EM-drive, i'm a bit more optimistic here as in it might work. It will however never be anything more than an good ion engine who don't need fuel. 

No, I was speaking to the concept of nuclear fusion thermal rocket, not a nuclear fusion rocket, and furthermore, one that could generate a TWR > 1.  The nuclear fusion thermal rocket concept doesn't seem to make a lot of sense, except maybe in the case laser-initiated inertial confinement (if that's the correct technical term for it), and even then, it doesn't make sense to use an external propellant.  Just use it as a regular fusion rocket.  I just think the OP heard about the nuclear thermal rocket concept and thought it would be cooler if it was a nuclear fusion thermal rocket, the heck with whether that makes sense or not.

Edited June 9, 2017 by -Velocity-

[magnemoe]

7 hours ago, -Velocity- said:

No, I was speaking to the concept of nuclear fusion thermal rocket, not a nuclear fusion rocket, and furthermore, one that could generate a TWR > 1.  The nuclear fusion thermal rocket concept doesn't seem to make a lot of sense, except maybe in the case laser-initiated inertial confinement (if that's the correct technical term for it), and even then, it doesn't make sense to use an external propellant.  Just use it as a regular fusion rocket.  I just think the OP heard about the nuclear thermal rocket concept and thought it would be cooler if it was a nuclear fusion thermal rocket, the heck with whether that makes sense or not.

Yes, I probably did not notice because the idea don't make much sense as you say. 
At least in the traditional thermal engine way. 
Technical an pulsed fusion reactor uses the pellet wall as reaction mass, it even make sense to have some material who absorb the x-ray and proton radiation giving you charged plasma. 
 

[K^2]

Technically, muon-catalyzed fusion thermal rocket is a theoretical possibility. And it could even have sufficient TWR to be used as an ascent vehicle. We just don't have means to produce muons efficiently enough to make it work. The magic number for muon beam production efficiency is 20%. Alternatively, a π^- beam at 27% efficiency would do just as nicely, as it has a near 100% decay to μ^-. We can probably handle efficiency on the order of a few percent with available methods, and equipment is ridiculously heavy, which is not good news for a rocket.

Edit: Looked at some recent articles, and the best we have for muon production is still smashing a proton beam into a neutron-rich target with just the right energy to knock some pions out of it, then collecting and sorting through debris to pull muons from it. As you might imagine, this is a very, very inefficient way to make particles.

Edited June 10, 2017 by K^2