Nuclear Fusion Rockets v.s Fission

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  • #26
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Why do you need to have plasma rockets, I am only speaking o Fusion not nessacily jump starting the reactions.

Pulsating Fusion Rockets shoot a hyrdogen combination into a reaction chamber and blow it up with intesne FEL lasers (Which are rather weak at the moment) and shoot the resulting energy and mass left over out ans 5%c which is accelerated to 10%c with basic rocket techniques.
The rockets require no giant magnetic chamber except for expelling out the reactents.

When wecome to the deacceleration problem. Is a magnetic brake possible, (even if going away from a sun).

A mag sail is a giant magnetic ring that uses magnetic entites to make it stop quickly.
 
  • #27
Astronuc
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Arian said:
Why do you need to have plasma rockets, I am only speaking of Fusion not nessacily jump starting the reactions.
Fusion generally implies plasma.

Pulsating Fusion Rockets shoot a hyrdogen combination into a reaction chamber and blow it up with intesne FEL lasers (Which are rather weak at the moment) and shoot the resulting energy and mass left over out ans 5%c which is accelerated to 10%c with basic rocket techniques.
The rockets require no giant magnetic chamber except for expelling out the reactents.
One needs to rethink the physics, especially energy yields in terms of energy/nucleon available from fusion reactions.

Also, Lasers and SC Magnets are rather massive systems.

It makes no sense to use a fusion power plant to produce electrical energy which is then used in laser power systems (hugely inefficient), but rather use fusion directly.

Magnetic brake? Where? Against what magnetic field or charged particle field?

A mag sail is a giant magnetic ring that uses magnetic entites to make it stop quickly.
Maybe in science fiction - not in the real world.
 
  • #28
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Mag Sail- orginally propsosed by Mark Zubrin, who later said a Mag Orion (a magnetic sail that uses bombs).
The Mag Sail could be stopped by magnetic fields of planets. Jupiter's for heaven sakes would easily stop it. The Sun's for that matter could decrease it (but maybe not fast enough).

You are right aboyut lasers and magnetic fields being heavy, but then again, machine guns were big and we made small ones, we canm do the smae with lasers. The new moon ship is small then the old one. Things get smaller.

And fusion only implies that when wo atoms hit each other in such a hot, intense way, that they merge and realise mass in the form of energy. Plasma is only regared because the sun is plasma and is currently the only fusion producing machine in the solar system.
 
  • #29
Astronuc
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Arian said:
Mag Sail- orginally propsosed by Mark Zubrin, who later said a Mag Orion (a magnetic sail that uses bombs).
Actually, Robert (Bob) Zubrin proposed Mag Sail and later, with Dana Andrews, proposed an Orion-driven Mag Sail.
Arian said:
The Mag Sail could be stopped by magnetic fields of planets. Jupiter's for heaven sakes would easily stop it. The Sun's for that matter could decrease it (but maybe not fast enough).
I invite one to substantiate these claims.

You are right aboyut lasers and magnetic fields being heavy, but then again, machine guns were big and we made small ones, we canm do the smae with lasers. The new moon ship is small then the old one. Things get smaller.
The laser and magnets are heavy, and there is a limit on how small based on energy density, or specific energy of the system.

And fusion only implies that when wo atoms hit each other in such a hot, intense way, that they merge and realise mass in the form of energy.
For nuclei to fuse, they must effectively be in a plasma state - completely ionized (E > 13.6 eV) - and normally at energies of several keV.
Plasma is only regared because the sun is plasma and is currently the only fusion producing machine in the solar system.
We produce plasmas on the earth all the time, but they require much more energy input than they produce. Certainly a 'practical' fusion-based energy production device has yet to be perfected.
 
  • #30
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Astronuc said:
Actually, Robert (Bob) Zubrin proposed Mag Sail and later, with Dana Andrews, proposed an Orion-driven Mag Sail.
I'm sorry, wrong name, but I didn't have me book with me.
Astronuc said:
I invite one to substantiate these claims.
Jupiter has a large magentic field, which also creates a very large particle field, infact, only a few of its moon escape this particle field, allowing them,perhaps, exsistence. (of home for life crap)
And a magnetic field is going to stop something.
A flight manuver would be to have the positive end of the craft pointing towards jupiters positive end. The two repel, decreasing the speed of the moving craft.


For nuclei to fuse, they must effectively be in a plasma state - completely ionized (E > 13.6 eV) - and normally at energies of several keV.
Hence the laser:grumpy:
 
  • #31
Astronuc
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Arian said:
Jupiter has a large magentic field, which also creates a very large particle field, infact, only a few of its moon escape this particle field, allowing them,perhaps, exsistence.

And a magnetic field is going to stop something.

A flight manuver would be to have the positive end of the craft pointing towards jupiters positive end. The two repel, decreasing the speed of the moving craft.
The magnetic fields interact with ionized particles individually, as opposed to massive spacecraft.

Like Earth's, the magnetic field of Jupiter is like a bar magnet, but unlike Earth, it is oriented in the opposite direction, so a compass would point south, not north. Jupiter's magnetic field is tilted 10 degrees with respect to its axis of rotation, compared to a 12 degree tilt for Earth. Jupiter's magnetic field is 19,000 times intrinsically stronger than Earth's, but since Jupiter's diameter is 11 times that of Earth, the field strength on its equator is measured to be 4.3 gauss, compared to 0.3 gauss on the surface of the Earth. The strong field produces a huge magnetosphere which extends to 3 million km in the sun-facing side and reaches all the way to Saturn in the opposite direction.
http://www.mira.org/fts0/planets/099/text/txt003x.htm [Broken] - 4.3 gauss is not very strong. Magnetic fields for confining plasmas are on the order of 10T (100 kG), the higher the better. Practical SC's max out at 13-15 T, and maybe up to 20T, but that requires liquid He. Max fields are lower for HTSC.

Arian said:
Hence the laser
Does this imply ICF? It would be worthwhile investigating LLNL's National Ignition Facility.
http://www.llnl.gov/nif/project/
http://www.llnl.gov/nif/project/missions_energy.html
 
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  • #32
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Magnetic fields and magnetic fields will repel, and magnetic fields are also judged by this
t(c)= size of the magnetic field
i think we know that two is time and c is 186,000 mps. Yet in this eqation t is the time the field has exsited.
So right now we are feeling a very very weak, magnetic pull from jupiter.
Yet now I will end this magnetic debate by asking a different question-


When you have a nuclear fusion rockets, is there any way to stop it, other then turning it around and firing its engines?
 
  • #33
Astronuc
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Arian said:
Magnetic fields and magnetic fields will repel, and magnetic fields are also judged by this
t(c)= size of the magnetic field
i think we know that two is time and c is 186,000 mps. Yet in this eqation t is the time the field has exsited.
So right now we are feeling a very very weak, magnetic pull from jupiter.
Yes the magnetic field of Jupiter is relatively weak. However, I forgot you are assuming the craft is traveling at 0.1c, so one must consider relativistic magneto-dynamics. I'll have to think about this matter.

Just some thoughts:

1. The magnetic field generated by the spacecraft is limited, and falls of with distance from the craft.

2. Similarly, the field of a planet, even Jupiter is weak, and it also falls off with distance.

3. I would recommend developing the equations of a spacecraft (modeled as a bar magnet of a given field strength) traveling through Jupiter's magnetic field, say starting at 10 diameters of Jupiter, and calculating the deceleration starting at 0.1 c, and see what one achieves at 1 Jovian diameter.

Arian said:
Yet now I will end this magnetic debate by asking a different question-

When you have a nuclear fusion rockets, is there any way to stop it, other then turning it around and firing its engines?
The current rocket technology, whether it be chemical, fission or fusion requires a rocket to thrust in the opposite direction of travel in order to decelerate.

However, I doubt a fusion rocket will acheive 0.1c, and a fission rocket is also unlikely to achieve 0.05c.

BTW, what type of fission rocket is one envisioning - NERVA/ROVER type solid core with hydrogen propellant or gas core rocket (GCR) with H propellant? ROVER/NERVA systems have been built and tested, while GCRs exist only on paper.
 
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  • #34
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Fision- salt water rocket why?
 
  • #35
Astronuc
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Arian said:
Fision- salt water rocket why?
Pro - the fission energy is deposited directly into the solution (mostly water), which is also the propellant.

The propellant storage is not cryogenic.

Potentially high Isp.

Con - the reactor (neutron) physics is complicated. The solution (of U salt) would be single phase being fed into the reaction chamber, but with fissions producing energy, the solution would heat through a 2 phase region, then in theory, to single phase superheated steam. With the rapid change in moderation, this reactor could be difficult to control. Mostly like, the reactor would be externally driven, i.e. a couple core configuration.

A high Isp requires high temperature since the salt contains uranium, fission products and water. Possibly one could add hydrogen gas to the solution, but then one needs a cryogenic hydrogen storage system.

Then there is the potential to heat the solution before it enters the reaction chamber, so injection of the U salt into the water could be considered, but that presents the problem of injection of a salt or gas near the reaction chamber.

Frankly, I don't see the salt water nuclear rocket as viable.
 
  • #36
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you are basically saying its too complicated
 
  • #37
Astronuc
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It certainly is complicated.

I know this is one of Zubrin's ideas (http://www.npl.washington.edu/AV/altvw56.html) [Broken], but I'd have to review the details of his calculations, particularly the efficiency of the fission process.

It is very easy to consider Isp = vex/g, but is the vex based on the actual physics. If only the water is considered, then the calculation of Isp is incorrect. One must consider the presence of U and fission products in the stream. I would be interested in Zubrin's core design.

The other aspect is the materials degradation (corrosion/erosion) - which I suspect may not have been addressed.
 
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  • #38
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actually i was thinking about that while I read your response yesterday, but i was unfuitful coming up with a fission chamber that would move up the rocket at the rate that metal errored away.
 
  • #39
Astronuc
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Arian said:
actually i was thinking about that while I read your response yesterday, but i was unfuitful coming up with a fission chamber that would move up the rocket at the rate that metal errored away.
Well there is such a concept using Am-242m which undergoes spontaneous fission and has a reasonable fission cross-section. But the spontaneous fissioning is also a problem for handling and assembly. The spontaneous fission cannot be switched off and on - it is continuously on.

Erosion is a problem not only for fission systems, but any high temperature system, particularly where flow is involved.
 

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