Magnetic Cold Gas Rocketry... What If?

[Spacescifi]

So magnetizing gases with lasers has been done experimentally.

But for the scifi scenario we are going to scale everything further along.

 

Scenario: A gas has been designed that has density on par with xenon, and when cooled can be magnetized to the same level as neodynium magnets.

Question: Could this scifi technology be used for rocketry and even 100 ton SSTOs?

My thoughts: i presume it could be used for rocketry, as magnetic forces can used instead of combustion to shoot the propellant out.

Even the nozzles can be designed to give the magnetic gas one final repulsive push as it exits the nozzle.... in contrast with normal chemical rocket exhaust where the nozzle does nothing more than extract and direct thrust.

The main issue: Not sure if neodynium strength gases would provide enough force to lift off a heavy SSTO. It depends on how fast the gas is shot out since we want higher mass efficiency than chemical rocketry.

And that depends on power... which scifi ships have no lack of usually. Since the power to propel the neodynium strength magnetic gas to high velocities would come from a separate power generator.

I guess the main advantage among other things may be a bit less waste heat... even though there is bound to be times in space where the ship has to cruise and unfurl radiators simply becausd it is not getting rid of waste heat by dumping it into the exhaust since the exhaust is cold.

 

How it would probably look: No flamey exhaust... you can hear the rocket take off but see no plume... or would you?

 

I mean it is cold gas exhaust... so I would not expect to see much unless moisture in the air made it look like a plume of steam?

 

 

EDIT:

I assume the exhaust would be invisible given this video.

 

 

Edited February 2, 2023 by Spacescifi

[kerbiloid]

1 hour ago, Spacescifi said:

magnetized to the same level as neodynium magnets

Magnets are crystals. Ions are not.

[Shpaget]

What makes you think that gas wouldn't stick to the nozzle?

[insert_name]

what is this magnetic gas you speak of, and why would it perform better than hot non-magnetic gas or ion engines?

Edited February 2, 2023 by insert_name

[JadeOfMaar]

You're better off just rationalizing and copying from the ion engine tech from Star Wars. They basically run on whatever decent alkali metal like Lithium (possibly immersed in a liquid solution like Helium) for the propellant and the driver technology is either a derivative of the classic Hall Effect Thruster or a MagnetoPlasmaDynamic Thruster but able to consume a city's worth of energy to provide the levels of thrust and Isp seen and required in sci-fi movies. Cold gas isn't going to work because according to basic physics: If it's hotter it has (more) energy in it; More energy means more thrust or impulse. Additionally, if the propellant is lighter it grants even more impulse but less thrust (which is why we crave Hydrogen for rockets and Lithium for batteries. Each is the lightest element that does its job.)

Inventing a new element is pointless and a huge waste for a case like this. Also, as far as anyone who knows the Periodic Table knows, any new element that can be invented (see the hypotheticals section, by whatever name(s) it has) they're virtually all going to be highly radioactive and short-lived.

[Terwin]

If you have arbitrary amounts of power available, then this should be indistinguishable from an ion thruster(assuming that your magnetic thruster works at all).

I do not think that an ion thruster requires a particularly large exhaust area per unit of thrust, just large amounts of power(a sizeable chunk of which is used for stripping electrons off of the reaction mass to turn it into ions which you can push with electromagnetism)

As current ion engines have ISPs in the 2000-5000s range, that should be adequate for SSTO if you have arbitrary amounts of energy available without needing arbitrary amounts of weight to generate it.

With 5K isp and >1g thrust, you should be able to get to earth orbit with only a ~20% fuel fraction(I think)

So even if ~30% of your vessel is dry-weight(power/structure/engines), you could get 100t of cargo to orbit with a ~200t launch weight using a 5000s isp engine with sufficient thrust.

The current problem with high-isp engines are the thrust-to-power ratio where you need at minimum of ~50kw per newton of thrust for a 100% efficient 10,000s isp engine, or ~25kw per newton of thrust for a 5000s isp engine.

This means ~50w per gram at 10,000s or ~25w per gram at 5,000s to accelerate at 1m/s/s, so you would need at least 10 times that for launch.

This means 500kw/s or 250 kw/s for each kg of launch weight. 

The SSTO above would require >50gw/s from a mass of less than 600kg(which also includes the engines and structure) for long enough to get to orbit(for more than 8 minutes), requiring an energy density of more than 40 giga-joules/kg. 

This is roughly 300 times the fuel density of hydrogen(not counting the weight of oxygen, I think) or only about 1/2000th  the energy density of uranium.  Clearly this would need a nuclear reaction to produce the power, but would require a 50gw nuclear plant at a mass of perhaps half a ton.(not something we can manage today, and would need massive heat-ejection capability)

[Spacescifi]

1 hour ago, Terwin said:

If you have arbitrary amounts of power available, then this should be indistinguishable from an ion thruster(assuming that your magnetic thruster works at all).

I do not think that an ion thruster requires a particularly large exhaust area per unit of thrust, just large amounts of power(a sizeable chunk of which is used for stripping electrons off of the reaction mass to turn it into ions which you can push with electromagnetism)

As current ion engines have ISPs in the 2000-5000s range, that should be adequate for SSTO if you have arbitrary amounts of energy available without needing arbitrary amounts of weight to generate it.

With 5K isp and >1g thrust, you should be able to get to earth orbit with only a ~20% fuel fraction(I think)

So even if ~30% of your vessel is dry-weight(power/structure/engines), you could get 100t of cargo to orbit with a ~200t launch weight using a 5000s isp engine with sufficient thrust.

The current problem with high-isp engines are the thrust-to-power ratio where you need at minimum of ~50kw per newton of thrust for a 100% efficient 10,000s isp engine, or ~25kw per newton of thrust for a 5000s isp engine.

This means ~50w per gram at 10,000s or ~25w per gram at 5,000s to accelerate at 1m/s/s, so you would need at least 10 times that for launch.

This means 500kw/s or 250 kw/s for each kg of launch weight. 

The SSTO above would require >50gw/s from a mass of less than 600kg(which also includes the engines and structure) for long enough to get to orbit(for more than 8 minutes), requiring an energy density of more than 40 giga-joules/kg. 

This is roughly 300 times the fuel density of hydrogen(not counting the weight of oxygen, I think) or only about 1/2000th  the energy density of uranium.  Clearly this would need a nuclear reaction to produce the power, but would require a 50gw nuclear plant at a mass of perhaps half a ton.(not something we can manage today, and would need massive heat-ejection capability)

 

Won't exhaust that energetic mean you would land in lava if you did SSTO with it?

 

 

The more I learn the more it sounds that the only reasonable launch of a heavy SSTO from Earth is from the sea, and the only reasonable landing by a heavy SSTO would likewise be upon the sea.

 

It also sounds like a heavy SSTO from Earth would not want to land anywhere so as to conserve propellant and resources.

 

Instead it would rely on shuttles with chemical or solid propellants to land on airless moons.

 

But for all Earth like worlds, landing upon the sea would be best.

 

As it is, given extreme heat and radiation from exhaust, that is precisely why you would not land it on ANY land... whether the moon or Earth, since it would radiate the dust all around the landing site crew are going be walking around.

[NFUN]

17 hours ago, kerbiloid said:

Magnets are crystals. Ions are not.

I crystalize ions in my lab every day!

[kerbiloid]

1 hour ago, NFUN said:

I crystalize ions in my lab every day!

Gaseous? Oriented?

Chaotically oriented magnets with infinite axes are a thing.

[NFUN]

8 hours ago, kerbiloid said:

Gaseous? Oriented?

Chaotically oriented magnets with infinite axes are a thing.

well they're ions so they're a plasma...

[K^2]

On 2/2/2023 at 12:34 AM, Spacescifi said:

Scenario: A gas has been designed that has density on par with xenon, and when cooled can be magnetized to the same level as neodynium magnets.

The key requirement for this is that each molecule of said gas has to have a strong magnetic moment. Such molecules like to stick to each other. To prevent that, you'll have to give them a lot of kinetic energy, at which point, it's not a cold gas anymore.

Iron is actually a perfect candidate for this. Has great magnetic moment, which is why it's good for magnets, and is nice and dense. You just have to vaporize it, and then you can drive it with a magnetic field. Problem is, that takes a ton of energy, at which point, it's by far more efficient to just strip an electron, turn your gas into a plasma, and now you can have electric fields doing the work, which can be done with much more reasonable field strengths. And, of course, we're back to just building an ion drive.