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You still need power to contain the plasma so that it doesn't melt the ship to pieces.
That's what your magnets do.
Fuel cells. Once the lasers/microwaves heat the reaction, they are hardly needed anymore-the reaction is a chain exothermic reaction.
Why would you use a fission reactor to power a fusion spaceship?
Finally, you have to actually convert the energy from the fusion into electrical/mechanical energy, which may not be as easy to do as it is in fission.
Actually, you don't. You use the same concept as in a NTR. Let the hot plasma and hydrogen leak out of one end. No need for electrical energy.
You can get high thrust out of a magnetic fusion drive by using hydrogen propellant (in addition to the plasma), and high isp by using pure fusion plasma without hydrogen. With hydrogen, your isp is 10,000 seconds, without, its up to 2 million seconds.
I wonder if you could use 50/50, and get the best of both.
The Saturn V would have cost as much in itself as the entire Shuttle does now.
And the Columbia accident's cause is unknown. It probably wasn't the ETs, in fact. I've heard various ideas as to why it happened.
Isn't that kind of what I said, not only about fusion, but about pretty much everything else?
Why not liquid or gas core fission? In space, dirty thrust doesn't matter?
Sorry, not table-top Tokamak, table-top dense focus thruster:
http://www.islandone.org/APC/Nuclear/12.html
DENSE PLASMA FOCUS (DPF)
An alternative to large fusion or antimatter-catalyzed micro-fission/fusion systems is the dense plasma focus (DPF) thruster under evaluation at Lawrenceville Plasma Physics (LPP) and the University of Illinois. The DPF thruster has the potential of being a compact (table-top sized) magnetic confinement fusion (MCF) device that operates in a magnetic "pinch" mode to compress the fusioning plasma. This device could also operate on a number of fusion fuels including aneutronic fuels like p-B11. However, unlike most ICF or MCF devices, it is not designed to operate at a high "gain", where gain is defined as the fusion energy output divided by the energy input to make the fusion reaction occur. In fact, the gain of the DPF thruster is estimated to be around one, corresponding to "break-even". Thus, from a spacecraft point of view, the DPF thruster has the potential of acting like an electric propulsion engine with an efficiency of 100% and with the Isp of a fusion engine (e.g., 106 lbf-s/lbm when directly using the fusion products, down to 4000 lbf-s/lbm with hydrogen added to the fusion products).
This concept, previously supported by the Air Force Phillips Laboratory (Edwards AFB) and now by JPL, is still in its early stages of development. To date, theoretical modeling and some limited testing have shown the preliminary feasibility of the concept.
As for nuclear pulse, it is terrible inefficient and hogs alot of uranium as well as releasing enough radiation to kill the crew and damage the payload. And what do you do about those intense square wave thrust pulsations? Shock absorbers? Not good enough. Stick with NEP (vapor core is best),
Fusion pulse could alleviate the radiation and inefficiencies, including the fuel hogging. Fission pulse is brute force only, though.
A Tokamak based thrust may be able to be the size of a tabletop.
Also, fusion pulse propulsion could be very fast, and done in a small space.
But I like the truss idea. We could use it as the basis of an ever-expanding outpost. Pehraps in time, a community of outposts could grow around the original outpost.
I was thinking, you have a hangar or docking point on your large ship, which is in the belt. So, you have a bunch of smaller (maybe shuttle sized) ships that do the actual mining. They pick up their cargo, bring it to the large outpost, and go back. You can mine many asteroids at a time this way, and you have manuverable ships to do it.
Based on this principle, you could have a shipyard on your outpost churning out dozens of these mining ships.
An Orion drive may be a good idea to get it out there, lots of thrust for the mass, so it allows a bigger vehicle. This would require orbital construction (I dont want an Orion-based launch, bombs in the atomosphere doesnt suit me), or a space elevator to send the pieces of our ship up piecemeal, to be assembled in space.
Or, a hybrid NEP/NPP (the same could go for fusion) might be best. Good isp for cruising, good thrust for initial thrusting.
Sure, what I'm saying is, every type of propulsion/power/design, etc. will have its place, espeically once private industry finds its way into space.
Fusion will have its uses, plasma sails will have their uses, too.
Like I was saying, in the carrier thread, fusion can be used to power a permanent outpost in, say, the asteroid belt, that has the option of remaining parked, or mobile. And it could generate a lot of power. Fusion drives would probably be faster, too.
So, this is just an example of why each design would have its benefits.
I see what you're saying. My initial purpose of this thread was for longer-term ideas, though.
The asteroids I'm referring to are inside Earth's orbit--the "Atens." Easier to get at than the Moon's surface: Dead comets (dirty water-ice, mineral salts, etc.) in addition to the general run of regular sizes and shapes. They're almost impossible to observe and count from here, because of the glare from the Sun. But once prioritized, a quite small orbiting telescope will be able to pick them out.
Sure, I see what you're saying. My general idea was for a large carrier, or more appropriately, I guess, an outpost in the belt, where a huge fleet could be built, and research can be done, and so on. An Earth orbit base isn't really suited for this goal. It also wouldn't have the deep space capability. A belt-base telescope would have much more range. Also, you could build them in your outpost, with no launch costs.
dicktice, and why should we expect this to actually work, when no spacecraft has ever been built on this concept?
Fusion has actually been accomplished, not sustained or controlled, but accomplished. We also know more about nuclear physics from experience.
What more do you need for a fusion drive that you don't need for a plasma drive (besides the reactor and D-T/H3)? Water?
And where do you get your power from?
They are not designing anything new. They don't have the resources to do so. Sure, the Soyuz is nice, but it doesn't take into account the advances in technology. The same fundamental design can be used, but it can be improved. A Model-T had four wheels, and the same basic design as, say, a BMW, but I defy you to tell me that a BMW is no more advanced than a Model-T.
The Shuttle was a very successful vehicle, and without it, the ISS wouldn't exist. In fact, the Russians tried to copy it, with Buran, and succeeded, but it just shows you who had taken the lead, by the '80s.
Now they're blowing it again, frittering away funds on a ridiculous space weapon system instead of utilizing up-and-coming engineering graduates on manned space. That's what happened to me and my betters, by the way, during the 1950s...if it hadn't been for that stubborn bunch in the inspired von Braun team...well you figure it out.
Funds that wouldn't go to the space program anyway. The graduates could choose what work to do, we have a free society. If they wanted to work on, say, NEP drives, they could. Our government doesn't choose people's jobs entirely for them, people do.
China lacks innovation. As I said, they take bits and pieces from everyone else. The only agencies which continue to develop new technologies on a sustained basis are NASA and the ESA, and there's no competition there.
Just because a launch vehicle is still used doesn't mean the agency is in its heyday. NASA is not in its glory days, either, but it is still, at this point, the most successful agency out there.
How much did we have to cover for the Russians in building the ISS? They are a huge factor in the cost overruns we sustained on the program, because they defaulted on contracts.
The asteroid belt is a much better target from Mars, which would greatly help Martian infrastructure (which should be developing by the time missions like those I'm talking about happen). Also, the belt has many, many more asteroids, and you can sit in one spot and have an endless supply.
You really don't have to manuver much to get to the asteroids, and you also have a docking port for deep solar system missions.
It could even have a hangar to build new facilities and ships on site. Which means, once again, better launch conditions to Mars and the deep solar system. You also have a self-sufficient material base (except for food and other supplies, which could be acquired through a ships/material->supplies trade), which could be used to continue a chain of building ships, acquiring resources, and so on.
Heheh, I don't understand most chemical or nuclear reactions, I just know that you can't reverse entropy, and any process which is entropic (ie, all energy processes, like turning mass into energy) cannot be reversed.
What is heat? Think about it, Josh. You still have matter, the form is the difference. You may not be able to take x and bring it back to y, but you still have the same amount of matter. Otherwise, our universe would be dead by now.
http://www.101science.com/lawofcon.htm
"Matter cannot be created nor destroyed"
Proper measurement is significant.
All components of a reaction must be accounted for.
Matter is not destroyed on the Sun, it changes form.
And as I've said, fusion can get more payload around, faster, and with more flexibility than a plasma sail.
Fusion has actually been performed.
And have any tests been done to show that this works?
Fusion we know can work, look at the Sun. And we're just below breakeven. Wishful thinking.
If you want your own plasma sail thread, have fun, but you are still hijacking a thread.
I'd be willing to wager that it'd be safer than sitting upon the ?pinky finger of god.? We're talking pixy dust here. Not fusion reactions wherein matter itself is destroyed.
Do you know what fusion is? Nothing is destroyed, it is merely fused. Matter can never be destroyed, anyway, it's a law of physics.
We don't even know if fusion is possible yet. But let's say that it is, and that we'd be able to contain it and everything. I would find it hard to imagine that fusion reactors wouldn't require constant maintenance.
We know fusion is possible, because it has been accomplished. We have multiplied our energy ratio many many times over the past decade, as preston said.
And a functional fusion reactor wouldn't need much maintenance, in fact, the only maintenance it would need would be a new wall every few decades, if at all. To stop and start the reaction, you turn on/off microwaves and supply/cut off fuel. It's much safer than fission-no moderation needed. You control the reaction by insertion of fuel (easily controlled by computers weighing in many different performance variables.)
Didn't I say if they destroyed them I would support another 6 weeks of inspections? Gee, that's right, I did.
Changing circumstances can change opinions.
Didn't read it.
Abstain doesn't mean "no" Josh. What I said is entirely accurate. The majority of people who took a side said "yes." 19 people were not convinced either way, but the anti-Bus, i mean anti-war side, or the pro-war side.
14 votes is significantly more, Josh, considering that another 19 didn't deicde, and only 4 would have tipped the scale.
What they said was, "We don't know," which, for all purposes, might as well have been no.
That's fantastic. We could even design the ship as a hab in itself. For example, it just parks itself, "unfolds," and sits there, with a docking port for expansion/resupply. Maybe even a new reactor can be brought out to replace the first one, and new equipment, etc.
I actually saw an article that suggested that this may be better for terraformers.
In any event-this news is not all that terrible as it's been made out to be. Most of the CO2 was always expected to come from the regolith, not from the caps. We know there is a large fraction of Earth pressure's worth of CO2 in the regolith, but we can't say just how much.
I just thought that at least there'd be an alternative if Mars wasn't viable, and considering "when it's steam boat time, you steam", I don't see why you couldn't do both scenarios, at least to some extent?
Wouldn't a transport system of scale economics from Earth to the rest of the Solar System or indeed from Mars to the asteroid field and beyond, require shipyards, starbases, intergravity transit infrastructure, i.o.w habitats principally built from space material and thus moonbases etc?
The power and energy requirements for acceleration to fractions of light speed for interstellar travel, is greater than what the entire world currently consume in a whole year. Don't the magnitudes suggest things like tapping the inexhaustible power of the Sun, that is building what is basically solar power satellites, just like the high frontier crowd say?
I guess you could build shipyards at LaGrange points, but I don't see why you would want habitats, besides for the workers. You could use materials from the asteroid belt to build your ships and facilities. And yes, for power, you could use solar power, and probably by that time, it will be converted to electricity far more efficiently.
The world needs the accumulated American research and scientific discoveries as a stepping stone to Mars, I don't see why it needs the United States per se (sorry!).
Because the U.S. remains the primary source of engineering, university education, and progress in the world. Russia's space heyday has passed, and Europe is many steps behind, for the most part. China is coming into their own, but they really can't do much without replicating other programs (not just in the space industry, in everything from software to jet airplanes).
So America remains the driving force in space, at least until the private industry takes over.
Interestingly, and this is quite a blow to the Bush admin, but Turky voted no on allowing US troops within their territory. This is pretty freaking huge, especially since Turkey was to be given billions if they allowed this to happen. I mean, man, wow, I can't think of a bigger statement.
Actually, they didn't say no. It was voted "yes" by significantly more people than voted "no." It was the 19 people who couldn't decide that determined the election. A majority of those who took a side approved the measure.
This means we save $30 billion. Fantastic.
At this rate, I'd like to see inspections continue. I am thoroughly convinced Saddam has more. If we find it, I am also sure he will play the same wag-the-dog game as he has done this time.
But until then, let's show the world who the real "evil" ones are here.
I think you exaggerate the dangers involved with plasma sails, soph. The good ones will be hundreds if not thousands of kilometers across, you'd be so far from the belts that they wouldn't be an issue. They'd just be pretty lightshows for travellers.
Yeah, and where are you going to build and deploy sails as large as countries? Actually, you'd be right in the middle of the Van Allen belt, if a flux occurred. It's not quite safe, Josh.
And I don't see what you mean by degrading materials and subject to space debris, we've been over this before. A plama sail would be much more robust than a foil sail, by far more robust than any other sail out there.
The sturdiest titanium is subject to collisions, Josh. It's simple engineering, a collision with a hot, fast object will tear apart your sail.
As the sail is pounded with more rays, the material may lose its superconductivity. This is what I meant by degrading materials.
I'd be willing to wager that a plasma sail engine would last much longer than a fusion engine, since it's so simple.
We've had fission reactors last for 50 years. With new advances in materials and the fusion process, fusion reactors can probably last much longer.
A question: if you have these immense plasma sails, how do you slow down and stop at a planet? Land? Manuever?
Josh, if you can find an actual source that contradicts what I'm saying, fine. I'm basing what I say on published material.
It doesn't matter how robust it is-if a cometoid or meteroid hits a sail, it'll crack.
Twenty years would take me out of the picture, Soph.
I imagine the plasma sailing spacecraft essentially as a lump of water-ice, surrounded (when sailing) by the plasma cloud of hydrogen ions (from melt-water) which would provide incidental protection from radiation (aurora-wise) in addition to the absorption protection provided by the ice thickness.
Great, and where does you payload fit into the equation?
Also, plasma sails might create Van-Allen belts, which your water can't do much to help with.
On a long mission, your plasma sails would lose some conducting power, which slows you down, and decreases the payload you can bring along.