Jupiter Turbojets

[bombo1]

I had the Idea of a jet engine that could work in Jupiters atmosphere by taking hydrogen(i think it is hydrogen in Jupiters atmosphere) from the atmosphere and replace the liquid fuel in the tanks with oxidizer. so I wonder if it is possible to use this idea to make a jet powered planeprobe to Jupiter?

by the way, this is how i feel when i write this

[SunJumper]

A while ago, I asked about this. Turns out that the oxidiser is significantly heavier than the hydrogen/hydrocarbons. Adding to this the mass of the intakes, and you'd get little benefits.

Burning the hydrogen via nuclear fusion on the other hand...

[Tex_NL]

A while ago, I asked about this. Turns out that the oxidiser is significantly heavier than the hydrogen/hydrocarbons. Adding to this the mass of the intakes, and you'd get little benefits.

Burning the hydrogen via nuclear fusion on the other hand...

First you'll need a way to capture the hydrogen. Secondly purify it and extract the deuterium. (Regular hydrogen isn't very useful in fusion, the isotope deuterium is.) And thirdly you'll need a fusion reactor. I see a lot of extra weight in this.

[Seret]

Not sure a jet engine would be the way to go really. You could run a lighter-than-atmosphere vehicle like an airship with much lower propulsion energy requirements. The Jovian atmosphere does sound pretty frisky though, could be a fun environment to try and fly around in.

[Warhorse]

First you'll need a way to capture the hydrogen. Secondly purify it and extract the deuterium. (Regular hydrogen isn't very useful in fusion, the isotope deuterium is.) And thirdly you'll need a fusion reactor. I see a lot of extra weight in this.

Actually, regular hydrogen fuses just fine; it is, after all, what most stars run on. You just need a bit more energy to get it started.

[Fractal_UK]

Actually, regular hydrogen fuses just fine; it is, after all, what most stars run on. You just need a bit more energy to get it started.

Not really, the coulomb barrier is far higher meaning you have to put in orders of magnitude more energy to get it started (deuterium-deuterium is bad enough and p+p is much much worse), plus, most of the time the (He-2) product of the reaction generally just decays back into 2 protons meaning most of the orders of magnitude more energy you've put in are spent doing absolutely nothing. You're waiting for the very specific circumstance in which a He-2 decays into a Deuterium and you get a stable product.

In other words, if you aren't a star with huge gravity to maintain high temperatures and pressures for billions of years, forget about obtaining energy via this method.

[K^2]

You're waiting for the very specific circumstance in which a He-2 decays into a Deuterium and you get a stable product.

There aren't any special circumstances. It's totally random. One in more than 10,000 ²He will undergo a β⁺ decay, the rest decaying back into a pair of protons. And not a thing you can do about changing these odds.

[Tarrow]

I had the Idea of a jet engine that could work in Jupiters atmosphere by taking hydrogen(i think it is hydrogen in Jupiters atmosphere) from the atmosphere and replace the liquid fuel in the tanks with oxidizer. so I wonder if it is possible to use this idea to make a jet powered planeprobe to Jupiter?

by the way, this is how i feel when i write this

It's not a crazy idea at all, so no need to get all bashful.

As others have said the whole capturing / separation of hydrogen "on the wing" could be problematic (i.e. heavy and / or complex). Maybe a non-combustion engine?

There's some pre-existing tech that might be able to be adapted to purpose if someone were so inclined to tweak it a bit for different atmospheric composition. It's from the pre-ICBM days and was conceived to power long-range strategic bombers.

https://en.wikipedia.org/wiki/Aircraft_Reactor_Experiment

https://en.wikipedia.org/wiki/General_Electric_X-39#The_nuclear-powered_X39

https://en.wikipedia.org/wiki/General_Electric_J87

The last link is interesting, suggesting they were near running a pair of 34k lb thrust turbojets without using combustion.

(it sometimes surprises me how much awesome tech was developed then abandoned)

[SunJumper]

Also, this is a big planet with 24.8m/s^2 'surface' gravity. Crafts will have to fly faster just to stay up.

[Seret]

Not necessarily, they'll just have to have more lift. You can have high lift without high speed, in fact more lift tends to mean more drag and therefore lower speed.

[WhiteWeasel]

Not sure a jet engine would be the way to go really. You could run a lighter-than-atmosphere vehicle like an airship with much lower propulsion energy requirements. The Jovian atmosphere does sound pretty frisky though, could be a fun environment to try and fly around in.

Hydrogen is the lightest element, how can you make an lighter than atmosphere vehicle there?

[Brotoro]

Hydrogen is the lightest element, how can you make an lighter than atmosphere vehicle there?

You use HOT hydrogen.

[Fractal_UK]

There aren't any special circumstances. It's totally random. One in more than 10,000 ²He will undergo a β⁺ decay, the rest decaying back into a pair of protons. And not a thing you can do about changing these odds.

Circumstance: a fact or condition connected with or relevant to an event or action.

I'm pretty sure that the result of a random event that occurs in 1 in ~10,000 times qualifies as a specific circumstance.

Hydrogen is the lightest element, how can you make an lighter than atmosphere vehicle there?

Jupiter's atmosphere is not solely Hydrogen, it contains quite a bit of Helium as well as various other things in low quantities. By using purely Hydrogen as a lifting gas you could lift a small proportion of that same mass, it's just a matter of making sure you have enough hydrogen to offset the mass of whatever you're trying to lift.

Edited December 7, 2013 by Fractal_UK

[Tarrow]

Jupiter's atmosphere is not solely Hydrogen, it contains quite a bit of Helium as well as various other things in low quantities. By using purely Hydrogen as a lifting gas you could lift a small proportion of that same mass, it's just a matter of making sure you have enough hydrogen to offset the mass of whatever you're trying to lift.

Depending how good the materials technology gets another option may be to have a rigid lift envelope filled with a vacuum.

[K^2]

Circumstance: a fact or condition connected with or relevant to an event or action.

I'm pretty sure that the result of a random event that occurs in 1 in ~10,000 times qualifies as a specific circumstance.

It does not. There is not an event that leads to a decay. Decay is the event. It's quantum physics. There are processes within the nucleus that contribute to both decay modes. Like, a lowest order process leading to β⁺ starting with a valence up quark undergoing flavor change and emitting a W⁺ boson. But you can't say that emission of W⁺ is the circumstance, because it's not something that happens or not happens. All of the processes are taking place, and all of them are contributing to the final outcome. Typically, a gamma burst from a β⁺ annihilating an electron is your first indication that what took place is a β⁺ decay. And it's not a limitation of measuring equipment. It's literally when the outcome is decided.

[Tommygun]

https://en.wikipedia.org/wiki/Aircraft_Reactor_Experiment

Direct Air Cycle nuclear jet engines, oh the 1950's where such a fun time for nuclear physics.

The whole future seemed bright and glowy.

[magnemoe]

It's not a crazy idea at all, so no need to get all bashful.

As others have said the whole capturing / separation of hydrogen "on the wing" could be problematic (i.e. heavy and / or complex). Maybe a non-combustion engine?

There's some pre-existing tech that might be able to be adapted to purpose if someone were so inclined to tweak it a bit for different atmospheric composition. It's from the pre-ICBM days and was conceived to power long-range strategic bombers.

https://en.wikipedia.org/wiki/Aircraft_Reactor_Experiment

https://en.wikipedia.org/wiki/General_Electric_X-39#The_nuclear-powered_X39

https://en.wikipedia.org/wiki/General_Electric_J87

The last link is interesting, suggesting they were near running a pair of 34k lb thrust turbojets without using combustion.

(it sometimes surprises me how much awesome tech was developed then abandoned)

An nuclear powered aircraft has some obvious problems, add that aircraft safety back at 1950 was horrible compared to today.

Then mid air refueling was perfected it solved the range problem.

And yes an nuclear turbojet would make a lot of sense on an body with atmosphere, imagine having it flying around on Titan.

[Fractal_UK]

It does not. There is not an event that leads to a decay. Decay is the event. It's quantum physics. There are processes within the nucleus that contribute to both decay modes. Like, a lowest order process leading to β⁺ starting with a valence up quark undergoing flavor change and emitting a W⁺ boson. But you can't say that emission of W⁺ is the circumstance, because it's not something that happens or not happens. All of the processes are taking place, and all of them are contributing to the final outcome. Typically, a gamma burst from a β⁺ annihilating an electron is your first indication that what took place is a β⁺ decay. And it's not a limitation of measuring equipment. It's literally when the outcome is decided.

Apparently you have misread the definition I provided for the word circumstance as "a fact or definition that follows from event" rather than "a fact or definition relating to or connected with an event." I have no dispute with your understanding of the physics of the situation, yet you have apparently started a discussion based upon your misunderstanding of an English definition and I'm struggling to see the value in debating it, so I'm not going to participate further in this rather pointless derailment of the original topic of the thread.

---

Getting back on topic, yes, nuclear jets would be an excellent option for travelling on atmospheric bodies using generic atmospheric propellant. It is somewhat difficult to achieve the necessary thrust with a nuclear reactor small enough to be jet mounted, the aircraft nuclear reactor experiment produced some of the early research into molten salt reactors because something compact, high power and relatively high temperature is required.

If you are interested in having a fly in KSP, I have attempted to model the thermal turbojet with reasonable respect to reality in my Interstellar mod where you'll find fission powered aircraft slow, heavy and generally low on power but extremely long lived and capable of flying in any atmosphere.

I would assume that Titan, with its low surface gravity and thick atmosphere would be almost the optimal environment for such a craft.

Edited December 8, 2013 by Fractal_UK

[Dispatcher]

I would assume that Titan, with its low surface gravity and thick atmosphere would be almost the optimal environment for such a craft.

You mentioned a "generic atmospheric propellant" and suggest Titan as a possibility for using nuclear jets. However, its lower atmosphere consists of over 95% nitrogen and less than 5% methane. That's a small fuel fraction for a jet to handle. Even our own oxidizer fraction on Earth is nearly 21% oxygen. I'm suggesting that such a "methane" jet would be impractical.

Edit: unless you are suggesting that the lower fuel fraction is offset by the low gravity and denser atmosphere. I'm not sure if that's enough to do the trick.

However, it would be relatively easy to process rocket fuel from the air and fuel a rocket plane with 100% methane. Oxidizer may be obtained by melting native water ice and splitting it into hydrogen and O2. So an even more potent fuel could be had; hydrogen, or using methane and hydrogen in combination.

Too bad the methane percentage isn't higher, as I'm writing a novel in which I'd love to have Titan jets.

As for Jupiter jets, that's an intriguing idea. Then there are also the remaining gas giants as well (with much less radiation to deal with also).

Edited December 8, 2013 by Dispatcher

[Fractal_UK]

You mentioned a "generic atmospheric propellant" and suggest Titan as a possibility for using nuclear jets. However, its lower atmosphere consists of over 95% nitrogen and less than 5% methane. That's a small fuel fraction for a jet to handle. Even our own oxidizer fraction on Earth is nearly 21% oxygen. I'm suggesting that such a "methane" jet would be impractical.

Edit: unless you are suggesting that the lower fuel fraction is offset by the low gravity and denser atmosphere. I'm not sure if that's enough to do the trick.

However, it would be relatively easy to process rocket fuel from the air and fuel a rocket plane with 100% methane. Oxidizer may be obtained by melting native water ice and splitting it into hydrogen and O2. So an even more potent fuel could be had; hydrogen, or using methane and hydrogen in combination.

Too bad the methane percentage isn't higher, as I'm writing a novel in which I'd love to have Titan jets.

As for Jupiter jets, that's an intriguing idea. Then there are also the remaining gas giants as well (with much less radiation to deal with also).

It wouldn't matter if you had 0 methane in Titan's atmosphere, you don't need any reactive chemicals to heat your propellant if you have a nuclear reactor to provide heating, in fact, fewer reactive chemicals are actually a positive because you don't need to worry about said hot reactive chemicals reacting with engine components. You can just take in atmospheric nitrogen, heat it up with your reactor and expel it to produce thrust.

Going back to your point about chemical propulsion though, keep in mind that titan actually has higher atmospheric pressure than Earth so the 5% methane is a larger absolute quantity than a 5% proportion on Earth would be. Additionally, you use more oxidiser than fuel by mass, methane burning uses 2.67x more oxygen by mass than methane, which means that with both of these factors accounted for, you can burn methane with oxygen almost as quickly on Titan as you can on Earth. Yes, you have to carry oxygen rather than methane, so you're carrying the chemical that is both heavier and needed in greater quantity but that part is accounted for by the reduced gravity on Titan.

Edit: when you take both Titan's atmospheric pressure into account and the methane/oxygen combustion mass ratio into account, burning methane in stored oxygen there would be like burning stored methane in a 20% oxygen environment.

Edited December 8, 2013 by Fractal_UK

[Dispatcher]

Thanks for the response, Fractal_UK. I'd somehow lost the context of a nuclear jet merely heating the native air (mostly nitrogen in this case) as opposed to combustion to generate thrust. This would work very well at Titan, with its relatively cold environment. In fact, preheating the air might be a necessity anyway, in order to keep engine components from freezing up.

Yes, of course the O2 would be carried, rather than fuel; which is why a combustion jet could be an acceptable method of getting around. I'm pleased that you feel that the density of the air offsets the methane fraction as such. Yet the idea of using the entire volume of inrushing air (and mostly nitrogen at that) using an atomic engine is most desirable, since efficiency is only limited by the craft design rather than by chemistry.

[K^2]

Apparently you have misread the definition I provided [...] so I'm not going to participate further in this rather pointless derailment of the original topic of the thread.

I still don't see how that definition applies, but so long as our disagreement is on semantics, I agree, it's not important.

[Nuke]

for a moon like titan you could probibly get away with a rtg powered fan.

Edited December 9, 2013 by Nuke