Question Fusion reactors to power spaceships!! How do you convert the energy into propulsion?

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Jul 27, 2020
Theoretically the Earth could be ignited like the Sun, would the reaction stop when free or would more fuel be made available?

We seem to have reached an understanding of sorts.

Fusion is occurring from hydrogen in the high pressures of containment, so you will have to add a little as it fuses into helium. Basically, keep feeding it hydrogen, and bleed off the product, and it runs for a long time.

And yes, containment failure would be catastrophic, but limited in nature. The temperature would rapidly collapse since fusion would cease on containment failure. Probably not as nasty as a nuke melt down, but very nasty in the immediate area of the 15 million K plasma venting!
Jul 27, 2020
Fusion reactors only work with hydrogen -> helium at about 15 million K. You need much higher temperatures to fuse larger atoms than hydrogen. Once containment collapses, the fusion reaction will collapse as the hydrogen is blown away. It is not possible to sustain the fusion without the containment of hydrogen at enormous temperatures and pressures.
Dec 4, 2019
Space is nothing like water as water provides resistance and in Earth water you have Earth gravity to repel against. Space is a vacuum with nothing to grab onto or push against.
To put it in a slightly different way, you cannot "row" in space, there is nothing to row against as it is a vacuum you have heard about so many times.

There is nothing absolutely nothing to push against unless you provide it yourself, such as a big bag of rocks you throw off the back of your ship. You can use rocket, fusion, fission etc. to provide the throwing power. If you want to get up to a high speed you need a bigger bag of rocks which will take more energy to get the unthrown rock up to speed before they are thrown out. And you will need fewer but a large number of rocks to slow down again once you get near to where you want to be. YOU CAN'T WIN. I know the word rock is crude, although it is in the word rocket, but take it to mean some kind of mass, whatever it may be.

Ion engines might sound like you do not need rocks, but the ions thrown out are the rocks, small as they might be, This is an efficient way to gain a little thrust by electrically accelerating ions to very, very high speeds. They are very little mass but partially make up for that by the great energy in their very high velocity.

What makes the electricity though to accelerate the ions? Fusion or fission alone would not do that. On earth we use an inefficient process to convert heat to electricity, using boilers to make steam to turn turbines to then finally turn electric generators. This is very heavy, bulky stuff to be carried to space. Not going to happen that way.
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Jan 16, 2020
I've been reading science fiction for 60 years, been a scientist for over 50, and dabbled in nuclear engineering while in the Navy during the Vietnam Conflict. That being said, an ion drive that throws a fuel out faster than any other rocket-type engine is the best drive for long distances, assuming you can heat up the fuel enough to make it go faster. Some of the comments here claim that a rocket-type thrust must work against atmosphere or gravity. If that were the case, rockets could not maneuver in space, and we know they can. That is not how Newtonian physics works. If we had fusion reactors, which we do not, we could superheat and throw something out the back end of a rocket and get it moving without expending a lot of fuel. Speed can overcome mass limitations, and there are formulas that show how that works. In space, according to some, we will find one hydrogen atom every cubic centimeter. If a ship could collect those, they could be used as fuel. If the ship is moving at a substantial fraction of the speed of light, it could gather a lot of hydrogen fairly quickly. The problem we have yet to even address, though, is how to protect the people from the cosmic and other radiations. To reach the nearest habitable planet would take several generations, even at relativistic speeds, so some form of shielding would be required.
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Jul 27, 2020
That being said, an ion drive that throws a fuel out faster than any other rocket-type engine is the best drive for long distances, assuming you can heat up the fuel enough to make it go faster.

Thank you for confirming my previous posts, @Ratwrangler. It is a pleasure to finally hear from someone who knows what they are dealing with.

It would seem however that one would not need to capture more hydrogen, since a little goes a long ways, and you should be able to take all you need at launch. And if you are at relativistic speeds, you don't need more fuel for the fusion reactor since you are at cruising speed already. Braking for orbital insertion is another story.

But exhausting hydrogen for thrust, even close to c, is not going to provide much force from such a light element, but I am game. Xenon is currently used because of its high mass (ca 131, more than two orders of magnitude heavier than H.) Whatever the exhaust drive is made of, it needs to be cheap and you need to start with quite a bit of it.

Still, no one has addressed my basic question which started this inadvertently contentious thread:

How do you energize the drive exhaust from a fusion reactor which creates "static" energy at 15 million K.

You noted that "we could superheat and throw something out the back end of a rocket and get it moving without expending a lot of fuel." But HOW would that be accomplished? Ion drive, okay. How does it work? Enormous mag fields to throw out the ions, or direct ion energizing from the reactor, or some by other means? Sounds like a tough tech challenge.

It would seem that the answer to my question is slowing being reveled by an unexpectedly contorted process. Perhaps it simply is not possible.

Thanks again for a breath of fresh air!!
Mar 6, 2020
Ion propulsion does not need much thrust because there is no gravitational field in space to escape and with that the acceleration is constant. So in terms of what we have now a conventional thruster could put a ship in orbit, and the ion thruster could then take over and continue increasing speed to some as of now unknown value
That's true, but it still would be worth our while to have stronger ones.
Sep 23, 2020
That's why you study chemistry always trying to explode something how about exploding something by supercooling molecules to my understanding get smaller if coole Nod

There you go with the heat thing again chemy get some more chem books in fact study refrigeration

say you had a platform in space I am talking about weightlessness space you have a rocket sitting on this platform you push the rocket firing button what do you think happens everything is just wonderful the rocket shoots off think again
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Mar 19, 2020
Considering the notion of ion thrust as being one of the most likely saviors of fusion-powered propulsion, it seemed a good idea to review the state of that tech. The wiki site (1) gives useful data on the results of current ion-drives for light-weight spacecraft.

From the wiki site (1), we see that :

"The Deep Space 1 spacecraft, powered by an ion thruster, changed velocity by 4.3 km/s (9,600 mph) while consuming less than 74 kg (163 lb) of xenon. The Dawn spacecraft broke the record, with a velocity change of 11.5 km/s (26,000 mph), though it was only half as efficient, requiring 425 kg (937 lb) of xenon."

end quote.

The three ion thrusters for Dawn were running for over 200 days to obtain that velocity (2). They are slow but efficient. Humans are neither, and for good reason. We do not want to spend a lot of time in space getting hammered by cosmic radiation, etc.

It appears that Xenon based thrusters is the current tech (1) :

"Ion thrusters in operational use have an input power need of 1–7 kW (1.3–9.4 hp), exhaust velocity 20–50 km/s (45,000–112,000 mph), thrust 25–250 millinewtons (0.090–0.899 ozf) and efficiency 65–80%[3][4] though experimental versions have achieved 100 kilowatts (130 hp), 5 newtons (1.1 lbf)."

end quote

It reminds us that thrust is measured in Newtons (a measurement of force), and gives some interesting details and how ion thrust may apply to our fusion-based spaceship, with so much energy from so little mass. There must be a way to make it work, right?

It is clear from the above details one would have to ionize a lot mass of some element(s) and feed it into a "Thrust Plasma Stream" heated by our fusion reactor, which then exhausts it at relativistic speeds to get our spaceship moving quickly, to an acceptable velocity, and slow it quickly, such as for an orbital insertion.

Still, what is the "fuel" that is to be ionized and exhausted, and how would that be done considering the temperatures involved? We must form the ultra-super-heated "drive plasma" from fusion energy, and then vent these ionized particles at relativistic speeds. It would seem to present a substantial design effort, to say the least.

Alternatives are more then welcome!


What If we just put nine horses on the spaceship to power it?
Dec 4, 2019
Sure. The density of energy in space, by tacking on it and transferring its momentum to your vehicle.
What are you talking about? There is no density of energy in space. The momentum of nothing is almost exactly NOTHING. You are just dreaming up idiocies. Wouldn't hurt for you to take a physics course, one well beyond high school though.
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