Nuclear Fusion Rockets v.s Fission

[Astronuc]

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 - 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.

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

 

[Arian]

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 equation 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?

 

[Astronuc]

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 equation 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.

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 achieve 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.

 

[Arian]

Fision- salt water rocket why?

 

[Astronuc]

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.

 

[Arian]

you are basically saying its too complicated

 

[Astronuc]

It certainly is complicated.

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

It is very easy to consider I_sp = v_ex/g, but is the vex based on the actual physics. If only the water is considered, then the calculation of I_sp 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.

 

[Arian]

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.

 

[Astronuc]

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.