Thread: Space Craft Propulsion

Is it possible to use earth's magnetic field to overcome gravitational field of earth and go into outer space? And since whole universe is filled with magnetic fields from galaxies, clusters and super-clusters, can we use that to navigate our spacecraft in the outer space? We can create a powerful magnetic field around the spacecraft and control the shape of the field so as to repel from the earth's magnetic field in required direction. Once we reach outer space (away from earth's magnetic influence), we can change the craft's magnetic field so as to utilize sun's magnetic field for propulsion.

No, the earth's magnetic field is not strong enough to lift more than a trivial mass.

The Earth's magnetic field is very weak. It can turn a compass needle but that is about it. Try holding a magnet in different orientations. Can you feel the effect of the Earth's field?

So what you guys are telling us is that in any particular point on the earth's surface the earth's magnetic field is less intense than a magelev rail that lifts several tons of bullet train? Darn.
How about a giant stadium sized geodesic sphere with nanotube fabric covering from which you pump out the air to create a giant vacuum balloon? How high would that go without a propulsion system?
If you could beam electricity or energy (microwave?) from a ground station to the balloon craft, is there an electric based propulsion system that could use electricity and push the craft higher up in the thin atmosphere(other than plain propellers)?
If lasers can focus light(elecromagnetic energy), could there be a ground based Maser tower that focuses and amplified an artificial maglev magnetic feild into a beam that could lift a craft like a maglev balloon (and push it even while kilometers up in the atmosphere)?

Originally Posted by icewendigo

How about a giant stadium sized geodesic sphere with nanotube fabric covering from which you pump out the air to create a giant vacuum balloon?

What fantasy substance are you going to find for the balloon that is both lighter than the volume of air the balloon displaces, and at the same time strong and rigid enough to keep from being crushed by atmospheric pressure?

Originally Posted by Janus

Originally Posted by icewendigo

How about a giant stadium sized geodesic sphere with nanotube fabric covering from which you pump out the air to create a giant vacuum balloon?

What fantasy substance are you going to find for the balloon that is both lighter than the volume of air the balloon displaces, and at the same time strong and rigid enough to keep from being crushed by atmospheric pressure?

I dont know, maybe it's not possible, but if a guy could make 0.2 mm aluminum plates for a rigid airship in 1896 I hoped the latest materials could achieve something that is both lighter and stronger than aluminum? Maybe 0.1mm aluminum with 0.05 mm of nanotube mesh? If its strong enough to contemplate creating a space elevator maybe its strong enough to create a rigid airship?

But what about a ground based energy beam tower to feed a craft, is that as far fetched too?

Originally Posted by Janus

What fantasy substance are you going to find for the balloon that is both lighter than the volume of air the balloon displaces, and at the same time strong and rigid enough to keep from being crushed by atmospheric pressure?

I know ... unobtanium.

Maybe a better solution is a balloon with no rigidity filled with a light gas. Say, hydrogen.

You are still not likely to get enough force from the earth's magnetic field to overcome a strong wind.

Originally Posted by icewendigo

Originally Posted by Janus

Originally Posted by icewendigo

How about a giant stadium sized geodesic sphere with nanotube fabric covering from which you pump out the air to create a giant vacuum balloon?

What fantasy substance are you going to find for the balloon that is both lighter than the volume of air the balloon displaces, and at the same time strong and rigid enough to keep from being crushed by atmospheric pressure?

I dont know, maybe it's not possible, but if a guy could make 0.2 mm aluminum plates for a rigid airship in 1896 I hoped the latest materials could achieve something that is both lighter and stronger than aluminum? Maybe 0.1mm aluminum with 0.05 mm of nanotube mesh? If its strong enough to contemplate creating a space elevator maybe its strong enough to create a rigid airship?

There is a difference between tensile strength( which is very high for carbon nano-tubes), and resistance to buckling (which is what is needed to a hollow structure from collapsing under air pressure). Nanotube are fairly weak when it comes to buckling stress. Think of it this way: How much pressure cab you pump into a 1 liter plastic bottle before it bursts, compared to how little you have to decrease the inside air pressure before it starts to collapse in on itself?

How much pressure cab you pump into a 1 liter plastic bottle before it bursts, compared to how little you have to decrease the inside air pressure before it starts to collapse in on itself?

Ok that makes it easier to understand (darn its difficult to find a neat and cheap way to reach orbit).

If the earths magnetic field is weak, can't we produce strong enough magnetic field around spacecraft to repel earth? It's like a very strong magnet repelling very weak magnet. The strong magnetic field spreads over a large area of earth's surface utilizing large portion of earth's magnetic field for lift.

I'm guessing that the amount of energy required would be huge. Even if it is possible. I'm guessing you would need to build an electromagnetic several miles (or tens of miles) across. This would probably have to be superconducting. How do you make this light enough and strong enough that it is able to lift its own weight and plus that of a payload. Plus its energy source. Just doesn't sound very practical.

It's not as if magnetism is some magic form of free energy.

There are probably more efficient mechanisms. Like wings and jet engines.

Originally Posted by icewendigo

Ok that makes it easier to understand (darn its difficult to find a neat and cheap way to reach orbit).

Choose to be born on a smaller planet.

Magnetic field is freely available all over the universe right? From the planets, stars, galaxies and even clusters. So I am thinking if we can come with a technology which uses magnetic field as the propulsion, we can navigate across the universe with little fuel(if we can make permanent magnets with that strength which retains its magnetism long enough). We need a paradigm shift in space propulsion if we have to travel through inter planetary systems. (It can also happen if 4th spatial dimension is theoretically proved and if we can escape into that dimension to travel vast distances).

Originally Posted by nikhil.gona2012

Magnetic field is freely available all over the universe right?

At any significant distance from bodies such as the Earth or Sun the magnetic field will be vanishingly small. If it is too weak to be of any use on Earth, I don't see how the interstellar/intergalactic field will be any use at all.

So I am thinking if we can come with a technology which uses magnetic field as the propulsion, we can navigate across the universe with little fuel(if we can make permanent magnets with that strength which retains its magnetism long enough).

A large permanent magnet is going to have a very large mass. So it will require a lot of energy to make it move. You need to work out how much energy is stored in a magnet. Clue: not much.

Originally Posted by icewendigo

Originally Posted by Janus

Originally Posted by icewendigo

How about a giant stadium sized geodesic sphere with nanotube fabric covering from which you pump out the air to create a giant vacuum balloon?

What fantasy substance are you going to find for the balloon that is both lighter than the volume of air the balloon displaces, and at the same time strong and rigid enough to keep from being crushed by atmospheric pressure?

I dont know, maybe it's not possible, but if a guy could make 0.2 mm aluminum plates for a rigid airship in 1896 I hoped the latest materials could achieve something that is both lighter and stronger than aluminum? Maybe 0.1mm aluminum with 0.05 mm of nanotube mesh? If its strong enough to contemplate creating a space elevator maybe its strong enough to create a rigid airship?

But what about a ground based energy beam tower to feed a craft, is that as far fetched too?

What about a ridgid LTA ship filled with helium. The ballon could carry a payload to the reaches of the atmosphere and there launched into orbit. The LTA could have the envelope absorb heat from a ground based laser to increase its bouyancy and after the launch the LTA could pump the gas into tanks to lower the ship to the ground. The obiting payloads could be used to make a space platform and a space ship yard. Small robot prospector vessels could be sent out to gather raw materials to build actual manned craft. After this point the solar system would be ours to expand into.

Once you get above the air, there's no such thing as LTA.

Let's start with the combined Lorentz force.

F = Force
q = Charge
E = Electric forces from opposite/same charge (not important to this question, but I'm mentioning it to be thorough)

v cross B is the part that's important here.

v = velocity of the charge
B = magnetic field

F = q(v X B)

My point is, if B is very weak, can we not make up for it by making v very large? Consider electrons racing around at relativistic speeds inside a superconducting coil.

..... of course the problem with a coil is you've got equal numbers of electrons racing around in opposite directions, canceling each others' velocities, but also at the same time the magnetic field of planet Earth is slightly curved. So there might be a way to arrange/position a sufficiently large coil or ring so that parts of it approach the field at different angles depending on its orientation. Maybe the electrons which are headed "right" pass through that field at a slightly different angle than those electrons which are headed "left"?

Is there any theory in physics community on spacecraft propulsion based on virtual particles in the vacuum?

Originally Posted by nikhil.gona2012

Is there any theory in physics community on spacecraft propulsion based on virtual particles in the vacuum?

A virtual particle being one that does not actually exist? I have strong doubts of getting real movement out of a system involving virtual particles.

There is no free lunch. To get movement you have to either expend energy or differentially harvest an energetic medium that occures in nature. The known energetic mediums of deep space are gravity, magnetic forces and starlight. The trick is differential harvesting.
Here's an idea, make a substance that differentially blocks neutrinios coming from one direction, but is transparent to neutrinos that are going in other directions. A neutrion sail could get some thrust everywhere.