Magnetic Field

TJohn · 2003-06-03 11:49:19

This question may have been answered or asked before. Could the Mars Direct hab enroute to Mars contain a generator of sorts and produce a magnetic field somehow to combat the effects of solar flares and microparticles?

RobertDyck · 2003-06-03 13:00:27

I think so. I have said so on other threads. The issue is to get the field strong enough and far enough away from the hab to deflect solar wind away. The farther the deflection starts, the less angle of deflection you need to miss the hab.

A mini-magnetosphere will expand to a much greater size than a simple magnetic field alone. It works by using charged plasma, then running an electric current through the plasma in a loop around the hab. The electric current creates more magnetic field, which can contain plasma to a larger size, which creates a still larger magnetic field, etc. This literally inflates the magnetosphere. The limit is how much power you have to supply the current. At the poles of the magnetic field, it will pinch in toward the spacecraft; the shape will be like an apple. At the poles the plasma will be accelerated toward the spacecraft, so this will create very strong radiation. The solution is to construct the hab as a donut, with the center dedicated to the magnetic field generator. Since the center of the donut will have strong radiation, you don't want any habitable area there. The "donut hole" would be open to space, not even pressurized. Actually, the "donut hole" would collect the plasma on one end, apply the electric current, and eject accelerated plasma out the other. The other way to apply current to the magnetosphere is a very strong rotating magnetic field. Since the plasma will flow through the "donut hole" core through the hab anyway, application of direct electric current means you don't have to carry large field coils.

The problem with a mini-magnetosphere is that the plasma is very hot. The outside of the hab must be constructed of heat resistant material, and any antenna would have to be hardened. Solar panels would interfere with the plasma flow, and melt if they aren?t armoured. If you use rotation with a tether to the spent TMI stage, then the tether will connect directly though the densest part of the plasma, and the most intense radiation. Furthermore, ferrous material would affect the magnetic field shape, and conductive material would interact with the magnetosphere current. You don?t want the tether burning out while rotating in deep space. Steel in the spent stage would also affect the shape of the magnetosphere. Due to these effects, combining a mini-magnetosphere with tethered rotation would be very difficult.

A mini-magnetosphere would change another aspect of the hab design. Robert Zubrin?s design had a radiation shelter in the center of the hab, with supplies and other hab equipment packed around the shelter to add radiation shielding. A mini-magnetosphere would have the center walled off and open to space at the top and bottom, and in that center would be radiation collected by the field of the mini-magnetosphere. That radiation would be directed through the ?donut hole?; it wouldn?t radiate outward into the hab unless it hit an obstruction. That means a radiation shelter would have to be located in the outer part of the hab. Perhaps a radiation shelter is not needed if you have a mini-magnetosphere. In case of strong radiation, just increase the field strength; then the entire hab becomes the shelter.

Would anyone care to calculate the numbers? That would require researching what types of radiation are in solar wind (proton, iron nuclei, etc), and the speed of those particles. Once you have the mass and speed, you can calculate the force required to deflect it. If you include the particle charge, you can calculate the magnetic field strength required. The greater the radius of the magnetopause of the mini-magnetosphere, the less angle of deflection is necessary to miss the hab, so the lower the field strength required. Calculating the radius of the magnetopause and its field strength requires researching the physics of a magnetosphere. The Earth?s magnetosphere is not a perfect torus; solar wind squashes it on the side toward the sun, and draws out a tail away from the sun. I expect the same thing (perhaps to a lesser degree) from a mini-magnetosphere. The critical number is the field strength at the magnetopause multiplied by the radius of the magnetopause. The larger that number, the better the radiation protection. Calculating all this would mean you are literally developing a force field to protect the spacecraft. Do we have any physicists here who would like to take on this project?

TJohn · 2003-06-03 19:13:28

Thanks, RobertDyck. When you mentioned mini magnetosphere, that got me to remember about a university that was working on that. It was supposed to be faster than nuclear propulsion. Has anyone else heard anything about this?

Shaun Barrett · 2003-06-04 03:10:19

I'm not that good a physicist to be able to calculate the kind of field strength necessary to protect the Hab. (Mind you, if you'd asked me when I was eighteen and physics was my main bag ... hmmm ... but then, that's another story! )
But putting all that aside, isn't the idea of Mars Direct to get 4 people (or possibly 6) to Mars at a budget price? It sounds to me like this magnetosphere generator, which requires a complete rethink of the Hab design and the tether arrangements, is going to make a simple plan considerably more complicated and expensive. Correct me if I'm wrong but surely this is anathema to the whole Mars Direct concept(?).

In addition, the question of 'storm shelters' has been broached. The original plan relied on a small, central, protected area - cheap, cheerful and reasonably reliable! The idea of a force field providing complete protection is no doubt better, but what of reliability and cost?
Assuming we can afford the research, testing, and implementation of such technology, what happens if it fails?! And if we're going to incorporate a shelter designed to save the astronauts in the event of a magnetosphere failure, why bother with the magnetosphere at all?

It looks to me like this idea is a bit of a white elephant. A technological marvel, to be sure, but is it really applicable to the Mars Direct plan?
???

TJohn · 2003-06-04 06:20:28

I agree, Shaun. It would definitely be more expensive to be added to Mars Direct. I thought I would post some of my rambling thoughts.

How big would the storm shelter since it would have to include space for consumables, life support, bathroom, etc.. in relation to the actual had itself?

RobertDyck · 2003-06-04 08:15:46

I agree. The mini-magnetosphere would be a "nice to have" but not necessary.

The original Mars Direct plan called for a single story habitat with the lower story dedicated to propellant tanks and engine for landing, storage for the rover, inflatable greenhouse, rover "garage" tent, and other EVA equipment. The airlock would be the center of the upper story, and the airlock would double as storm shelter. The shelter would be just large enough for the astronauts to stand, packed like sardines. Bathroom facilities in the shelter would have two options: run outside to use the normal bathroom (be quick to reduce radiation exposure), or go in a bag like the Apollo astronauts did. Remember, the storm shelter is for an emergency only.

You can see an image of the original Mars Direct floor plan here, from the "Images and Charts" link of the Mars Society main web page. Compare the efficiency of this design with the analogue habitats. My criticism of the analogue habitat designs is a lack of storage space and landing propellant tanks. They have fully utilized the lower floor for living space, leaving nothing for storage. One member stated that the space could be used after the rover, inflatable greenhouse, garage tent, etc. was removed. However, the analogue habitat has no garage door do get the rover out, or ramp to drive it down to the surface. The interior layout completely covers all outer walls of the lower floor, so there is nowhere to put such a door. There is one test I would like to see at all habitats: At the beginning of each season pack all equipment into the habitat as if it just landed. The first task of the first crew of the season is to unpack and deploy all surface equipment. That would prove the equipment can be deployed, and prove the habitat has storage room to hold it all.

TJohn · 2003-06-04 10:59:58

Right, I've seen a picture of the storm shelter. I guess that is good for emergency, but can't solar flares last for a few to several days? I posted a link here before that show very detailed pictures. You can move around and look at how the Hab is actually set up. It is very impressive. It even has pictures of rovers and ground cars.

http://www.exploremarsnow.org/

mcshlong · 2003-06-11 18:40:35

Who really cares about making a force field? Nobody else is using them in space. I think the effort is better spent on comfort for the astronauts on the way or something more practical.

TJohn · 2003-06-12 06:39:55

I understand not having a "force field" but using something like the M2P2 could get to Mars faster and a side effect is that it can provide some protection from solar flares. Nothing extra would have to be built.

RobertDyck · 2003-06-12 10:03:31

Who really cares about making a force field? Nobody else is using them in space. I think the effort is better spent on comfort for the astronauts on the way or something more practical.

Whether "nobody else is using" a technology is no criteria to select or not select that technology. You have to get the astronauts to Mars alive. The question is what radiation protection is necessary.

Free Spirit · 2003-06-12 20:00:32

I was just reading today that it might be possible to create very lightweight space craft structures from carbon nanotube composites that would not only shave off a lot of mass, but could also be impregnated with hydrogen to block cosmic rays. Apparently carbon nanotubes and hydrogen go together like peas and carrots. The article Super Spaceships Not Far Out has a lot of interesting ideas on features we might find on ships in the not so distant future.

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#1 2003-06-03 11:49:19

Re: Magnetic Field

#2 2003-06-03 13:00:27

Re: Magnetic Field

#3 2003-06-03 19:13:28

Re: Magnetic Field

#4 2003-06-04 03:10:19

Re: Magnetic Field

#5 2003-06-04 06:20:28

Re: Magnetic Field

#6 2003-06-04 08:15:46

Re: Magnetic Field

#7 2003-06-04 10:59:58

Re: Magnetic Field

#8 2003-06-11 18:40:35

Re: Magnetic Field

#9 2003-06-12 06:39:55

Re: Magnetic Field

#10 2003-06-12 10:03:31

Re: Magnetic Field

#11 2003-06-12 20:00:32

Re: Magnetic Field

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