can you power a spaceship off of fusion?

[cameron marical]

i know theres ideas for powering spaceships off of fusion, engine uses fusion to run, and use fusion to power spaceship electrically too, so long as they find a solution to these fusion problems, {which i think doing this in space would be way easier in space than on earth with gravity}, but how, if im right, the process of fusion connects atoms together. i dont see how you can use that to power anything, or use that as an engine an space. fission, i understand, could be used to propell spaceships, but you need radioactive materials, and is more dangerous, id rather use fusion because the fuel is abundant and its not any where near as radioactive.

[Klaynos]

I've no idea if this is the plan, and I suspect there are far more interesting methods but...

 

From fusion you can generate electricity which you can use to power a laser which if you point in a direction in space will accelerate you in the opposite direction as photons have momentum which if we take what newton tells us...

 

[math]F= \frac{dp}{dt}[/math]

 

and conservation of momentum we can see we get a force...

[Xittenn]

Can we make some Solar Windmills(not windmills with solar panels, nor solar wind windmills but photo driven windmills) while where at it to increase the rapidity of our transition towards electrifying our current transit system? You could use fusion to power Solar Sails................giant ones at that! You could use the generated power to ionize the resultant atoms and use them as propellant............the electrons too. I'm sure there's something there with matter/anti-matter reaction drives. On the truly theoretical side gravity singularity drive needs power I'm sure...................

[Klaynos]

Can we make some Solar Windmills(not windmills with solar panels, nor solar wind windmills but photo driven windmills) while where at it to increase the rapidity of our transition towards electrifying our current transit system? You could use fusion to power Solar Sails................giant ones at that! You could use the generated power to ionize the resultant atoms and use them as propellant............the electrons too. I'm sure there's something there with matter/anti-matter reaction drives. On the truly theoretical side gravity singularity drive needs power I'm sure...................

 

I don't quite understand what you mean...

[Xittenn]

What part...................acceleration 'caused by a laser discharge is a litle bit silly unless of course I'm mistaken. I tried to be funny with respect to this by adding that if we could easily couple light and motion we could have photon driven fly wheel electrical generators. I thought a more plausible use for fusion power with respect to space flight would be solar sails. Solar sails being an array of charged particles which could capture and use the momentum of solar winds. Solar winds being a discharge of ionized particles from the sun suspected to be of good use in space travel when coupled through the 'solar sail!' I also thought that, aside from a waste of good matter, another good use of the energy would be to ionize the atoms created by the fusion process. These ionized particles could then create momentum through a coulombic repulsive force in a process similar to your laser. I finally concluded(very briefly non-essay form) by touching on two other highly theoretical drive methods which will require large quantities of energy possibly created(probably not) or aided by a fusion process. I really did like the fusion/solar sail combination!

---

Merged post follows:

Consecutive posts merged

I had thought of opening a thread on the plausibility of a photo driven fly wheel electrical generator and had some thoughts on gas ionization as being an integral key! That however would be another thread....................

Edited January 25, 2009 by buttacup
Consecutive posts merged.

[Klaynos]

What part...................acceleration 'caused by a laser discharge is a litle bit silly unless of course I'm mistaken.

 

I've not read this paper, but it comes from a quick google.

 

http://www.springerlink.com/content/5kkq7rqnjuad0gex/

 

You can quite easily make disks with different coloured sides spin inside a vacuum, I can't recall the traditional experiment name though.

 

I tried to be funny with respect to this by adding that if we could easily couple light and motion we could have photon driven fly wheel electrical generators.

 

You can, just not in the atmosphere as there is too much air resistance.

 

I thought a more plausible use for fusion power with respect to space flight would be solar sails. Solar sails being an array of charged particles which could capture and use the momentum of solar winds.

 

Traditional solar sails use photons I seem to recall.

 

I'd imagine that solar winds are probably a bit too unpredictable...

 

Solar winds being a discharge of ionized particles from the sun suspected to be of good use in space travel when coupled through the 'solar sail!' I also thought that, aside from a waste of good matter, another good use of the energy would be to ionize the atoms created by the fusion process. These ionized particles could then create momentum through a coulombic repulsive force in a process similar to your laser.

 

For a given amount of energy work out what would have more a group of photons or some helium ions... I don't actually know the answer off the top of my head and would be interested to see...

 

I finally concluded by touching on two other theoretical drive methods which will require large quantities possibly created(probably not) or aided by a fusion process. I really did like the fusion/solar sail combination!

---

Merged post follows:

Consecutive posts merged

I had thought of opening a thread on the plausibility of a photo driven fly wheel electrical generator and had some thoughts on gas ionization as being an integral key! That however would be another thread....................

[Xittenn]

Points to look into........................ I have lots to think about <>

[cameron marical]

so you can use a laser to propel something in space, i understand this. i think ive heard of this idea too, but, is it realy plausable? i love this idea, as long as you have electricity you have momentum, but exactly how much electricity would this take? and how big and powerfull a laser would be required? i know that once your moving in space you keep moving because theres no friction or gravity, but you could also use smaller versions of these for turning.

[Klaynos]

so you can use a laser to propel something in space, i understand this. i think ive heard of this idea too, but, is it realy plausable? i love this idea, as long as you have electricity you have momentum, but exactly how much electricity would this take? and how big and powerfull a laser would be required? i know that once your moving in space you keep moving because theres no friction or gravity, but you could also use smaller versions of these for turning.

 

We can work it out if you want. How much quantum mechanics do you know?

[swansont]

It's not impressive — 1 GW gives you 3.33 N of thrust (F = P/c, where P is power) So for a 1000 kg spaceship, that's a whopping 3.33 mm/sec^2 of acceleration. Which points to this being not feasible, except for the problem of other forms of propulsion if you want to do interstellar travel. Solar sail effectiveness drops off with the square of the distance from the sun, and chemical or ion engines need propellant. You can make as many photons as you want, and since the thrust is not wavelength dependent, you are free to choose the most efficient EM radiation generation devices for your third of a milli-g acceleration per GigaWatt.

[Xittenn]

Solar Sails have only been proposed as a means to accelerate within a certain proximity of the sun. The naturally frictionless void allows the vessel to continue on its path at the velocity attained. There would be a need for alternative propulsion should you be traveling between solar systems or at the outskirts................assuming you would have to stop or for emergency purposes.

Edited January 25, 2009 by buttacup

[cameron marical]

posted by klaynos.

 

We can work it out if you want. How much quantum mechanics do you know?

 

 

not much to tell you the truth, but i really will give it my best shot.

[CaptainPanic]

So, this laser is not very effective. The major benefit of the concept is that you can put the laser on earth, and point it at the space ship. Then you leave the engine at home, while you still generate acceleration. The major disadvantage is perhaps that it is a bit of a problem to decelerate (to turn around and go home).

 

But perhaps fusion engines, as proposed in the opening post, can be generating thrust in the good old fashioned way. Make it hot, and blast it out of a nozzle. Now, I know that fusion generates a whole new kind of "hot" (the kind that vaporizes everything)... but it seems to me that we can also contain this heat with magnetic fields in a reactor nowadays. Wouldn't it be easy (conceptually at least) to make a fusion reactor including containment field, and include an opening to the backside to let out the helium and unconverted hydrogen?

 

Alternatively, I read in a scifi book, and suprisingly also on wikipedia (people really considered this), this funny idea of building an enormous shield, connect that to a huge shock absorber, and put the actual space ship on top of that. Then detonate nuclear bombs on the other side of the shield. Those could also be hydrogen bombs, I'm sure

[Klaynos]

posted by klaynos.

 

We can work it out if you want. How much quantum mechanics do you know?

 

 

not much to tell you the truth, but i really will give it my best shot.

 

Swansont actually did this for us. You use the energy of the photons to work out their momentum....

[cameron marical]

cool, tell him thanks for me, and, what is it?

[Xittenn]

So, this laser is not very effective. The major benefit of the concept is that you can put the laser on earth, and point it at the space ship. Then you leave the engine at home, while you still generate acceleration. The major disadvantage is perhaps that it is a bit of a problem to decelerate (to turn around and go home).

 

Could you imagine the heat generated in the earths atmosphere by the lasers pointing into space if even a dozen ships where doing a trek. 1Gigawatt 3.3mm/s^2 we need a good 10m/s^2 would be a much nicer number that's ummmmmmm 3Terrawatts/ship those are some pretty damn powerful lasers. I don't know what the genral in atmosphere diffusion on this would be but it can't be good and the efficiency of creating laser light is like horrible(just guessing 10%.)

 

I appologize should any of the above be incorrect...........

 

This is however presently being tested as a method of sending spaceships into orbit. The idea being a gas, emmited in doses from a subjective place on the but end of the ship, could be super heated by a laser based on earth to propel it through our atmosphere.

 

Lithium what.........................Deuteride.................ummmmmmmmmmmmmmm that's ummmmmmmmmmm.......... I like your avatar it's pretty.......

 

those poor seagulls!

 

Oh one more does anybody have any spare carbide inserts I'd like to make an engine............

Edited January 27, 2009 by buttacup

[petebro]

Having read your thread on using laserlight for spacecraft , i have designed a

similar engine utilising optics and focused light to generate onboard power

and propulsion it does propell the craft in zero gravity and is in its infancy,

[padren]

It's not impressive — 1 GW gives you 3.33 N of thrust (F = P/c, where P is power) So for a 1000 kg spaceship, that's a whopping 3.33 mm/sec^2 of acceleration. Which points to this being not feasible, except for the problem of other forms of propulsion if you want to do interstellar travel. Solar sail effectiveness drops off with the square of the distance from the sun, and chemical or ion engines need propellant. You can make as many photons as you want, and since the thrust is not wavelength dependent, you are free to choose the most efficient EM radiation generation devices for your third of a milli-g acceleration per GigaWatt.

 

The idea of using a pure photon engine is appealing because it would be pretty cool to have a "propellant-less engine" but it does seem to take a lot of energy to get any thrust.

 

Out of curiosity, what sort of returns can you get by using that same energy to superheat a propellant, where you have a standard combustion of something like oxygen/hydrogen but utilize fusion to over heat it?

 

Is it conceivable to add energy via a nuclear source that could break the classic boundaries we experience with the chemical maximum potential? A moderate gain could have large implications when it comes to getting out of Earth's gravity, as the current "max thrust / mass" of chemical propellants require massive amounts of heavy fuel.

[cameron marical]

petebro, really? id like to see it if you could have some pictures or something of it. thats really cool. how much did it cost to get a vaccum to test it in?

[CaptainPanic]

Could you imagine the heat generated in the earths atmosphere by the lasers pointing into space if even a dozen ships where doing a trek. 1Gigawatt 3.3mm/s^2 we need a good 10m/s^2 would be a much nicer number that's ummmmmmm 3Terrawatts/ship those are some pretty damn powerful lasers. I don't know what the genral in atmosphere diffusion on this would be but it can't be good and the efficiency of creating laser light is like horrible(just guessing 10%.)

 

I appologize should any of the above be incorrect...........

 

Well... 10% (guessing) efficiency for earth-based lasers is pretty good. You should realize that the spacecraft that is propelled by these 10% efficient lasers is also a lot smaller: it has no engine, no reactor for energy (or solar panels if you want). It can be as simple as a tin can with a payload. I wouldn't be surprised if an engine on a spacecraft is more than 90% of the weigth (especially with conventional rockets - it's guessing for out fusion-laser-spacecraft of course).

 

You cannot dismiss one idea because one part of the idea is less efficient. You have to look at the whole picture.

 

Still, losses in the atmosphere can be a problem... I agree with that. And I think that the efficiency problem is not so much in the atmosphere as in the concept in itself. 3.33 N thrust from a Gigawatt... well... that's not much.

 

This is however presently being tested as a method of sending spaceships into orbit. The idea being a gas, emmited in doses from a subjective place on the but end of the ship, could be super heated by a laser based on earth to propel it through our atmosphere.

I've seen that. It seems quite cool, and has the potential to be very efficient... again because you have a smaller spacecraft.

 

The idea of using a pure photon engine is appealing because it would be pretty cool to have a "propellant-less engine" but it does seem to take a lot of energy to get any thrust.

 

Out of curiosity, what sort of returns can you get by using that same energy to superheat a propellant, where you have a standard combustion of something like oxygen/hydrogen but utilize fusion to over heat it?

 

Is it conceivable to add energy via a nuclear source that could break the classic boundaries we experience with the chemical maximum potential? A moderate gain could have large implications when it comes to getting out of Earth's gravity, as the current "max thrust / mass" of chemical propellants require massive amounts of heavy fuel.

 

Funfact: the Saturn V rocket produced 190 GW, which produced 34.02 MN (MegaNewton) of thrust in the 1st stage...

 

In other words, the thrust to power ratio of the old saturn V rocket was 0.18E-3 N/W, while the laser concept gets 3.3E-9 N/W. The Saturn V rocket gets 54000 times as much thrust per Watt.

 

In other words (coming back to buttacup's guessed efficiency): I wouldn't worry too much about the 90% efficiency losses of the lasers in the atmosphere (if that number you guessed is correct). There are other losses to worry about.

 

And even then, this idea can still be more efficient than a conventional rocket. It just depends how much you want to accelerate.

 

For nuclear powered rockets (one made it as far as the test-phase in the 50's and 60's) - I linked to Project Pluto earlier this month in the engineering forum. This thread is about a nuclear cruise missile (that did not have any combustion - it just superheated normal air with a nuclear engine. Good thing they never tested it in the air, only on the ground somewhere in the desert).

Edited January 27, 2009 by CaptainPanic
fixing a link

[Mr Skeptic]

i know theres ideas for powering spaceships off of fusion, engine uses fusion to run, and use fusion to power spaceship electrically too, so long as they find a solution to these fusion problems, {which i think doing this in space would be way easier in space than on earth with gravity}, but how, if im right, the process of fusion connects atoms together. i dont see how you can use that to power anything, or use that as an engine an space. fission, i understand, could be used to propell spaceships, but you need radioactive materials, and is more dangerous, id rather use fusion because the fuel is abundant and its not any where near as radioactive.

 

If I recall, most suggestions for these spaceships required that they be built in orbit, as the fusion reactor would be difficult to lift off the ground. The nice thing about fusion is that it can give you a very high thrust for the amount of fuel you use. Ideally, you want to expel ultrahot helium (or whatever the end product of your fusion is), not photons. The heat absorbed by the reactor walls could be used to generate electricity. Despite producing efficient propulsion, it would likely not generate very much propulsion, so could not lift itself off the ground. That is why building it in orbit may be necessary.

 

A suggestion for a similar space ship had a fission reactor to power the ship and possibly to power the fusion reactor (which so far run at a loss for generating electricity, but they do produce heat).

 

There has also been suggestions of nuke powered ships, which would be able to liftoff from earth (and in fact could lift a small city into space). Using hydrogen bombs would increase its capacity and efficiency, without any increase in fallout.

 

Perhaps the most real suggestion is a fission powered space ship. It uses the fission reactor to heat hydrogen hotter (and therefore more efficient) than it can be heated chemically. It could technically use anything as fuel, but hydrogen gives the most propulsion. Another advantage is that this doesn't require oxidizer. These would be able to liftoff with more capacity than the chemical shuttles, and travel farther/quicker in space. Additionally, they could do powered re-entry, and so make them cheaper to reuse since they wouldn't need a heat shield (which always seems to get damaged and costs a ton to replace).

[Xittenn]

 

You cannot dismiss one idea because one part of the idea is less efficient. You have to look at the whole picture.

 

....................

 

In other words (coming back to buttacup's guessed efficiency): I wouldn't worry too much about the 90% efficiency losses of the lasers in the atmosphere (if that number you guessed is correct). There are other losses to worry about.

 

 

I never dismissed the idea I just said doing it on Earth was a crappy one. A space laser would be much more appropriate and easily powered by the sun.

 

I also hadn't said the laser loses due to atmosphere where 90% I said I don't know what they would be. I'm sure there is some generalization but looking at even a rough equation.................what, seven atmospheric layers, top five most ubandunt gases, probability of photon absorbtion by electron across layers of x thickness, deviation probability of photon of more than .0005% from mean path, probability of heat being generated..................................That's easilly a very big book! I did say that producing a laser at the very least a YAG laser using photo discharge tubes is like 10%. A laser diode with a capability of 5 Watts per mm would have to be like a square km in size and a mach-COIL6.0 would dissipate the worlds naturally occuring Iodine in 5.....4.....3.....2.....1......how much Iodine do we have instorage?

Edited January 28, 2009 by buttacup

[cameron marical]

no, i think it would be wise to build it in space rather than on earth, instead you could use multiple trips and keep the equipment at somewhere like the iss and when you get all the supplys in space you can make it. it might be harder, but take a lot less energy and be less harmfull. ive heard of ideas for achiving propulsion through nuclear fission in space too, the Fusion Ramjet. it works by "scooping" in hydrogen from deep space and uses that and the fission process to accelerate. but is hydrogen really just in space occasionally? other than radiation and a tiny amount of elements caused by meteors and others, i thought that space is pretty much just a vaccum, and you need to mosly rely on inner sources to accelerate{unless your in a meteor shower, wich i strongly dont recomend, or near a star, wich arent really near here, other than our own.