"Bussard ramjet" for collecting fuels from the atmospheres from suns and planets.

[Strawberry]

A semi common sci fi trope Ive encountered is civilizations harvesting gases from atmospheres for there spacecrafts, I think this absolutely rocks and is super cool. In order to not only save code work, but also for cleanliness purposes, assuming air serves similar to ksp1 where intake air itself is a resource, really all that needs to be added is some additional air intakes, air tanks (in order for you not to be able to create bootleg RAPIER engines with air tanks just have intake air be converted into compressed air and have jet engines not be able to run on this), and an isru part that refines air (and maybe additional heat shielding to where you can design something like this), with different fuels granted for different atmospheres.

This would 1. Encourage high risk high reward aeromanuvering by having increasing rewards for risking your vehicle burning up. 2. Add a way for spaceships to refuel up on fuel without landing on a planet by sending probes down there to collect these gases, 3. Encourage space plane designs even when not planning on exploring planets with atmospheres due to this capability (and spaceplanes are cool) and most importantly 4. Encourage and enable radically different and highly complex vehicle design. Instead of playing it safe why not fly that interstellar vehicle directly into the sun with enough heat shields to make the rage a middle aged women gets when her order is wrong feel like a winters breeze. 

Edited July 16, 2022 by Strawberry

[Ember12]

I don't think this is really feasible.  If a planet had an atmosphere you could make fuel out of, it would probably have combusted already.  You could synthesize H2 and O2 from water vapor, but atmospheres aren't that substantial.  If you could somehow condense all of the water in a 1 meter square of Earth's atmosphere, going up to space, it would fill two 24-packs of water bottles.  Of course some planets might have a much higher concentration, but it would still be hard to get enough, even just to counter the speed lost from aero drag.

For stars, as soon as you get anywhere near the atmosphere you'll get vaporized.  KSP2, while having futuristic technologies,  is mostly confined to stuff where we know how it might work.  Nobody knows how to survive that close to a star.

There is, though, one place I can see this being useful.  A very good fusion fuel is Helium-3, which is found in the atmospheres of many gas giants.  So special spaceplanes that harvest it from Jool-like planets and ferry it to an orbiting starship would be a useful application of this idea.  But flying starships directly through an atmosphere is never really going to work, because you have to add a huge amount of (very heavy) heat shielding and structural support, which would severely compromise their range.

Edit:  I hadn't considered the possible collection of hydrogen for a nuclear engine.  Given nuclear engine exhaust velocities of around 10 km/s, this could feasibly be used to produce enough thrust to counter the speed lost to drag with some left over.

Edited July 16, 2022 by Ember12
Clarity and grammar

[Strawberry]

You dont really need to get "that" close to stars , skimming the corona at very fast speeds will lead to more then enough lightweight gases to do fusion (hydrogen and helium seem to be the two in game) (yes it would still be far more practical to have a specialized vehicle for this, and most players will probably do just this, but that is not nearly as cool). You can always go outwards to get less of the heat of a star. Gas giants though I do see as by far the main application for this, collecting hydrogen and helium. The reason for why this would work on other smaller planets even though it wouldnt be nearly as useful (unless people need to do special trips to collect a fuel as mundane as oxidizer) is because why wouldnt it, once you got the system hard adding this capability to other planets should be trivial, and also I think you could add a lot of nice little details like being able to collect monopropellant from eves atmosphere.

Edited July 16, 2022 by Strawberry

[Ember12]

I don't understand the "why wouldn't it".  You can't use any gas as a fuel.  There are three main types of engine to consider: 

Combustion, where you burn something like hydrogen with oxygen, or use more exotic fuel mixtures.  Possible fuels: Oxygen, hydrogen, hydrocarbons, or more complex molecules.

Nuclear propulsion, where you heat up a light gas and fire it out the back.  Possible fuels:  Mostly just hydrogen and water

Fusion engines, where you fuse atoms to create energy and thrust.  Possible fuels: isotopes of hydrogen and helium.

If a planet has one of these in its atmosphere, you're in luck, if you can collect enough to offset drag.  But many planets in our own solar system don't have any of these.  Mercury, Venus, Mars, nearly all the moons of Jupiter and Saturn don't have any of these in their air.  Actually refueling a combustion/nuclear rocket would not be something you could rely on. 

 

Refueling from a star?  Just... no.  You can't do it.  The sun's corona clocks in at two million degrees Kelvin.  There is literally no material known that can stand up to even a fraction of that.

[Strawberry]

Im not saying, "why wouldnt it" as in, "why wouldnt it be practical to use" Im saying "why wouldnt it" as in "why wouldnt this be an interaction the game has" it doesnt need to be a useful interaction, but it does need to be an interaction because it works like how players would consider it to work (it consumes air spits out resources, so why would some planets with oxygen or other resources that are collectible just refuse to work), and also its a neat little detail that would probably be a one or two line change per planet. The thing about the corona is due to coronal heating, its way hotter then the surface, but also way less dense. There are actually plenty of materials that can exist in the corona of the sun, in fact the parker space probe has already been in the corona of the sun! Of course, that was the outer corona, however 2 million degrees sounds like a lot, but when you realize that its basically a vacuum, its not as hard as one would assume.

 

The confusing thing about the sun is that the wattage output per area is less then that of a reptile. Assuming the sun is actually realistic unlike ksp 1, the main thing is, the big quirk about the sun is the lower you get, the colder it is, however the more dense the gas gets as well. Despite this however, while the sun is very hot, its also very big and very undense. Even when you get to the surface of the sun it's 5778 K (for comparision graphene has a melting point of ~4500k and iirc that was confirmed to be a heat shield option and is also very thermally conductive which actually helps here as it spreads out the heat), however the surface density is only 10^{-9} g/cm^3, by terrestrial standards a vacuum. Of course, when you're travelling at thousands of kilometers a second, this gets dense fast, however again you can just go to higher altitudes if its too much. This is assuming we dont get rid of this heat, which we are very capable of doing, say through using the heat to heat up propellant, however even without this, flying through the sun is surprisingly practical with future tech (which considering that the majority of fuel you'll be collecting is for fusion fuel, this is definitely a late game strategy), especially considering our sun is ~75% hydrogen in mass and ~25% for helium (keep in mind too that lighter elements tend to be closer to the surface). 

Edited July 16, 2022 by Strawberry

[Ember12]

Right, but if you're flying through an extremely thin part of the sun's atmosphere, you can't get that much material from it.  

[t_v]

3 minutes ago, Ember12 said:

Right, but if you're flying through an extremely thin part of the sun's atmosphere, you can't get that much material from it.  

Just like with regular atmospheres, even if it is not dense, if you fly through a couple hundred (or million) kilometers of the stuff, you are bound to collect at least some material. Flying at 30,000m/s, if you just used a standard 1.25m intake, you would be taking in 36,000 cubic meters of the not very dense gas every second, and if you went lower and faster, you could genuinely use a star as a way to (very slowly) refuel an efficient ship, at least enough to get it to a local gas giant. 

[Ember12]

 

6 minutes ago, t_v said:

Flying at 30,000m/s, if you just used a standard 1.25m intake, you would be taking in 36,000 cubic meters of the not very dense gas every second

The sun's corona is 10^13 (ten trillion) times less dense than Earth's atmosphere at sea level.  To put that in perspective, a one-square-meter intake could get as much gas from traveling one meter on Earth as it would get from traveling the distance to Neptune and back through the sun's corona.  That means circling the sun more than two thousand times.

Edited July 16, 2022 by Ember12

[t_v]

11 minutes ago, Ember12 said:

 

The sun's corona is 10^13 (ten trillion) times less dense than Earth's atmosphere at sea level.  To put that in perspective, a one-square-meter intake could get as much gas from traveling one meter on Earth as it would get from traveling the distance to Neptune and back through the sun's corona.  That means circling the sun more than two thousand times.

You’re right sorry, I was looking at the photosphere, which was only 100,00 times less dense. That does put things nearly outside of the realm of possibility. If, in general, atmospheric resource collection is in the game, I would still like to see stars have resources around them, if only to show how dense (or more accurately, not dense) their Coronas are. 

[Strawberry]

That's why you fly through a less thin part, there's a careful tightrope that has to be walked here, however considering you're likely going very fast and very far you'll inevitably encounter a lot of gas. You'll probably need to fly below the surface of the sun if you want a fair bit of gas, which while difficult is definitely possible. Due to hydrogens high specific heat (in fact the highest unless you get into some truly exotic stuff like storing the heat in fundamental particles like neutrinos or electrons (the more degrees of freedom per mass the better, you do not want to do this, this will mess up your materials if they touch them.)), storing the specific heat in the form of heat sinks probably wouldn't be viable all the way (while you do get a high amount of energy from fusion, you'll have to carry a lot of heat sink mass per hydrogen). Your best bet of dealing with the heat (assuming you don't result to truly exotic stuff like using the heat to store the energy in nuclear/chemical bonds) is expelling it, and ironically enough due to the previous mentioned stuff, hydrogen would be your best fuel here. Transferring this heat to hydrogen and sweating it out (ideally through a thruster) should be more then capable of allowing you to deal with enough heat to where once you get to space you can radiate out the excess in space and turn a profit. 

Edited July 16, 2022 by Strawberry

[Ember12]

There's not really a "tightrope".  If there's enough gas to collect, there's enough to melt your spaceship, and there is not a good way to get rid of this much.  As you suggested, you would have to concentrate the heat in some hydrogen and then spit it out.  But this would require a ludicrously powerful heat pump, with a mass comparable to the rest of your ship, and even that might not be enough to keep the rocket's skin from melting off.  

[Strawberry]

You dont really need to have a heat pump to do this, graphene is a really good thermal conductor and has a very high melting point. If you have graphene with a good thermal insulator underneath, you can easily get the heat to where you want it to go due to graphene transferring the heat where you want it to. Your best bet would be a special graphene coated chamber to where the gas enters, gets heated up here instead of the large tank, and then expelled. You don't need to transfer all of the heat, just enough. 

Edited July 16, 2022 by Strawberry

[Bej Kerman]

A Bussard ramjet is possible. In addition, they're meant to scoop up material from Interstellar space, and not planetary atmospheres. I know because this Wikipedia article actually cites papers, and the writers of this article know the physics of what they're talking about. I did my research. Just saying "a Bussard ramjet is meant to collect stuff from atmospheres, the Bussard ramjet wouldn't work, there's a tightrope etc."  without any citations is conjecture, which in scientific terms means bologna. Please, research the topic to ensure your conclusions are accurate. This is proper physics and KSP 2 will be getting involved in actual physics, even if simplified somewhat. It's no use saying the ramjet won't work because your intuition says so, even if professional papers disagree.

[Strawberry]

I used the term bussard ramjet in quotation initially due to there not really being a word to describe this (just ramjet we tend to think of for producing thrust instead of collecting gas and scoop is a bit vague). I am very much not saying that Bussard ramjets are a term used for scoops for gases from asterial bodies, I am using bussard ramjets as an analog to explain what this thing is, I am not using the term to explain what bussard ramjets are, if you think in any way we were describing bussard ramjets you should reread what we said. 

Edited July 16, 2022 by Strawberry

[Bej Kerman]

13 minutes ago, Strawberry said:

I used the term bussard ramjet in quotation initially due to there not really being a word to describe this (just ramjet we tend to think of for producing thrust instead of collecting gas and scoop is a bit vague). I am very much not saying that Bussard ramjets are a term used for scoops for gases from asterial bodies, I am using bussard ramjets as an analog to explain what this thing is, I am not using the term to explain what bussard ramjets are, if you think in any way we were describing bussard ramjets you should reread what we said. 

I don't have anything to reread. You applied the word Bussard ramjet to something that is mostly unrelated without clarifying that you were doing this because you didn't know a better word. It's not my fault for not understanding something you didn't make clear.

[Strawberry]

Quotations can be used to indicate that a word or phrase isn't meant to be taken literally. I did not mean to misrepresent an already existing thing, only using that term once was a very intentional aspect on my part. I used that word to exist as a primer to explain a concept that unlike bussard ramjets a lot of people here may not be familiar with due to this concept being found mostly in niche internet sci fi. This is a simple and understandable misunderstanding that should be moved past.

Edited July 16, 2022 by Strawberry

[Ember12]

1 hour ago, Strawberry said:

If you have graphene with a good thermal insulator underneath, you can easily get the heat to where you want it to go due to graphene transferring the heat where you want it to. Your best bet would be a special graphene coated chamber to where the gas enters, gets heated up here instead of the large tank,

The problem is, it would take a lot of gas.  Your spaceship would be heated up as it approached the star, so the gas would be pretty hot to begin with, and it would be depleted quickly.  If you're using hydrogen you've gathered from the star, it's already really hot so it won't give any benefit.  

[Bej Kerman]

19 minutes ago, Ember12 said:

The problem is, it would take a lot of gas.  Your spaceship would be heated up as it approached the star, so the gas would be pretty hot to begin with, and it would be depleted quickly.  If you're using hydrogen you've gathered from the star, it's already really hot so it won't give any benefit.

Can you link a paper that supports this? I doubt with how they actually work (and the fact we will inevitably come up with ways to counter the heat) that any of this would be 100% true. Burden of evidence is on you.

[Ember12]

No, I did not get that from a paper, so it could be wrong.  But you're gathering hydrogen, it's at the temperature of whatever layer of the sun you're in, and now it's inside your ship.  Assuming that its temperature is too hot for your ship to function, you'd have to expunge at least an equal amount of hydrogen to keep the temperature down, making fuel gathering useless.  And your spaceship has already been heated up by radiation as it approaches the star.

As I said, this does not have scientific backing, so if you find anything that disproves this I will stand corrected.  But I can't see any way that you could gather more gas than you use for cooling.

[Strawberry]

There isn't really any direct scientific paper basis for this, researching how to capture gas from the sun will probably get you some odd looks from your colleagues and besides you have better things to do anyways. Fortunately for us however, we dont need a scientific paper to determine if this is possible, with "some" back of the napkin calculations, we should be able to make a pretty decent guess. You'd definitely need to carry cold hydrogen with you, you'd be using the heat transfer to perform work in the form of propelling your ship forward and to cool down the ship. The fact that mixing an equal amount of pure hydrogen will always equalize the temperatures, there's no engineering around this, this is just basic thermodynamics. Fortunately for us however, the sun isn't pure hydrogen. The sun has a specific heat of roughly 12 j/g K, compared to hydrogens 14.304 j/g K. This alone however, is only a ~20% difference however, likely not good enough with this alone.

Fortunately for us, we don't need to cool it down all the way, as long as it doesn't melt the tank its in, and the tank is strong enough to handle the extreme pressure that this tank will likely have to save space, then we are golden. While the tank will conduct heat to anything touching it, since we are in space we don't need for it to touch the rest of the ship much, after all we have no gravity and can easily get a vacuum to get rid of most conduction. The question becomes now though, what material works best for the tank. We need a material that has both a high melting point, and a high ultimate tensile stress. Fortunately for us however, we already have a material more then capable of this. Graphene has a melting point of 4500 K and an ultimate tensile strength of 130 Gigapascals¹. Lets assume that we want to cool down our gas to 4000k², doing some back of the napkin calculation^{3, 4}, we get that you need a ratio of 27.7% of cold 20K hydrogen and 72.3% star gunk to get hydrogen at 4000 K. This means that for every gram of hydrogen you use for cooling your collected gas, you get slightly over 2 grams of collected gas back⁵. You'll have excess gas to still use for cooling and manage to gain more at the end of the day. Keep in mind that these numbers are for our sun, for kerbol you'd get a smaller margin due to the increased temperatures, but considering that red giants have around half the temperature of our sun, they'd be relatively very easy to collect fuel from. 

 

1. While I don't feel like bothering to calculate the maximum pressure this can hold, if someone wants to this walks you through all the equations you need to do in order to do that.

2. I don't feel like doing the math here for whatever the ideal temperature would be

3.  This is assuming you're at the surface of the sun, the deeper down into the sun the more efficient cooling gets but also the more drag you'll get. Again someone else can do the math if they want specifics.

4. For the actual calculations here, assuming surface of the sun temperatures (these numbers are slightly off because they dont calculate in the heat added from a ship travelling at mach 10 slamming into it), and hydrogen at 20K, we get a Δt of 1778 for the gas that's being cooled and 3980 for the gas that's getting heated , if we have 1 be the cold gas we already have we know that q₁ = m₁*14*3980= q₂ = m₂*12*1778, doing some basic algebra we get 55720m₁ = 21336m₂, if we have m1 + m2 = 100, doing that thing I hated doing when I took algebra class, we can calculate the percentage of mass you'd need for each. 

5.  Around 1.5 grams of hydrogen and .5 grams of helium. 

Edited July 17, 2022 by Strawberry

[Ember12]

I don't quite understand the part where you said

16 minutes ago, Strawberry said:

q₁ = m₁*14*3980= q₂ = m₂*12*1778

Could you explain how you got that please?

[Strawberry]

Sorry forgot to specify, used q = mcΔt (specific heat formula), q is the energy transferred in joules, m is the mass, c is the specific heat and Δt is the difference in temperature. Since we know that the energy transferred between both substances is the same, we can set the equations equal to each other and go from there.

Edited July 17, 2022 by Strawberry

[Ember12]

Okay, thanks, I get it now.  I agree with your math on the fuel-obtained front.

But the fuel tank is not the whole ship.  The whole thing has to be cooled, which for a big starship is going to be very hard.  There will also be a LOT of drag on various parts of the ship. 

I used this drag calculator, with the following values: A velocity of 430,000 mph (the speed of the Parker Solar Probe), an atmospheric density of 1.41 g/cm^3 (the density at the surface of the Sun), a drag coefficient of 0.1 (I'm calculating the drag on a spherical fuel tank, and I believe spheres have about that drag coefficient) an area of 100 square meters (a tank with a 10-meter diameter).

The output was over 50 trillion pounds, which is far more than any strut system could hold.  It would also implode the tank.

[Strawberry]

1.41 is the average density of the entire sun, the surface's (photosphere) density is 10^-9. Id imagine you'd have the starship mostly in a fairing, with only the areas you'd need exposed exposed. Assuming this fairing is in a airfoil shape a drag coefficent of .05 should be achievable. With the same area, you get 20 thousand pounds of force, not a small amount of force mind you, but considering the first stage of a saturn V put out 7,500,000 pounds of square force, its definitely forces a rocket can handle.  For a ksp comparision, the reliant engine puts out twice the force at sea level.

Edited July 17, 2022 by Strawberry

[Ember12]

You're right, I totally misread that statistic.

On the heat front, do you have any idea how to calculate the amount that would be needed to cool an entire ship?