[1.8+] Real Fuels

Starwaster · January 3, 2015

Which fuels specifically are you saying should be affected and what exactly are you proposing be done to them?

StoryMusgrave · January 3, 2015

@NorthStar: Wow. I really hope you are talking about gasses only, but your mention of the Shuttle ET and Falcon, kinda points to the thought that you think the same of things like LOX/LH2/MMH/NTO. You can obviously pressurize a GAS, the latest SpaceX ISS transfer is due to move a Nitrogen/Oxygen Recharge System (NORS) which is a tank that is pressurized to 400bar, which is actually close to double normal. So 1L of tank volume yields ~395L of gas at 1atm. RealFuels can and does simulate this with the 'utilization' parameter. However, you don't, AND CANT, 'pressurize' a MMH tank and suddenly create 400% more volume. It's not happening. Physics. Want proof? Actually read documentation of Apollo, Gemini, Space Shuttle, etc. Physical tank capacity roughly equals fuel volume and weight regardless of pressurization.

When it comes to mass fractions and whatever, these are all editable within RealFuels. If you aren't happy, create your own and change fuel tank types yourself. It's not hard. Formatting can be found in the RealTankTypes.cfg file within the RealFuels/Resources directory.

NathanKell · January 4, 2015

Northstar1989: StoryMusgrave already basically answered, but just to expand a bit, the pressure in a (highly-)pressurized tank comes from the *pressurant*, not somehow magically compressing the liquid propellant to hundreds of atmospheres. ServiceModule tank type *is* for highly-pressurized tanks; you can see this by checking how many liters of tank volume is used when you add x liters-at-STP of a gas (say, Nitrogen).

Churaragi · January 4, 2015

Quick note:
The standard mass of a RealFuels (\ProceduralParts\Parts\ZOtherMods\RFTank.cfg) tank is 1.0. This is, unfortunately, the value KSP uses to calculate the mass for the Launchpad maximum tonnage. A ship that is calculated as ~14t by MechJeb is calculated as 22.1t by the launchpad preventing me from launching it (non-upgraded launchpad has max allowed of 18t). I like using rounded conical tanks to make my rockets look pretty, so each middle tank with a rounded top and bottom will weight 3.0t according to KSP.
The 1.0 does not change when the procedural part is stretched, so I understand that an average number has to be chosen until someone figures out how to make KSP calculate the launch mass properly. I'd suggest making the base mass 0.5 or so, which makes tanks of 2m and smaller more accurately weighed by the launchpad.

This was posted on the Procedural Parts thread.

I have the same issue.

However there is a detail. It works fine when you first add a procedural tank/srb to the rocket, the mass is displayed correctly on the VAB and MJ.

However when you load a rocket, the dry mass changes to the default(1 for tanks, 3,7 for SRBs).

It happens with the other tanks affected by RF as well.

Is it just a problem on my end? Can someone confirm please.

Basicaly the masses are different when you load a rocket, compared to when you first build it, and MJ is calculating the masses correctly, but the VAB isn't.

NathanKell · January 4, 2015

No, that is a problem I need to fix.

Northstar1989 · January 5, 2015

@NorthStar: Wow. I really hope you are talking about gasses only, but your mention of the Shuttle ET and Falcon, kinda points to the thought that you think the same of things like LOX/LH2/MMH/NTO. You can obviously pressurize a GAS, the latest SpaceX ISS transfer is due to move a Nitrogen/Oxygen Recharge System (NORS) which is a tank that is pressurized to 400bar, which is actually close to double normal. So 1L of tank volume yields ~395L of gas at 1atm. RealFuels can and does simulate this with the 'utilization' parameter. However, you don't, AND CANT, 'pressurize' a MMH tank and suddenly create 400% more volume. It's not happening. Physics. Want proof? Actually read documentation of Apollo, Gemini, Space Shuttle, etc. Physical tank capacity roughly equals fuel volume and weight regardless of pressurization.

How do you think the pressurization on a liquid fuel tank works, exactly? The pressurant gas itself never (or rather, isn't supposed to) enters the engines- the pressure is transmitted through the *liquids* (which, by the way, are initially pressurized in the fuel tanks of pressure-fed engines with high combustion chamber pressures- in those cases the pressurant is only used to *maintain* the initial pressure by replacing lost fuel, rather than to create it). Some liquids, such as water, are basically incompressible and will simply transmit this force, but other liquids will increase in density in response to pressure, and a few can even be compressed all the way to a solid state...

Liquid Hydrogen, one of the most important cryogenic fuels, is known to be *particularly* compressible for a liquid. Like liquid CO2, it can be substantially compressed (unlike CO2, it is difficult to compress it all the way to a solid, as the melting point of Hydrogen is so low). If you don't believe me, I suggest you do a simple Google search for "liquid hydrogen compressibility".

This means that fuel tank with LH2 under pressure *will* contain substantially more fuel mass than one at 1 atmosphere of pressure.

I don't know off the top of my head how compressible N204, LOX, or any of the Hydrazine-derivatives (UDMH, MMH, Aerozine), but at least *some* liquid fuels/oxidizers are compressible to quite a substantial degree.

Arguing about a basic fact of physics (that some liquids ARE compressible- LH2 in particular) distracts from my point. Pressurization enables masses of liquid to be stuffed into a tank greater than what could be achieved with 100% utilization at 1 atmosphere of pressure, thus *effective* utilization can greatly exceed 100% in highly-pressurized fuel tanks. (at least when the fuel tank contains a compressible liquid- such as LH2)

Regards,

Northstar

- - - Updated - - -

the pressure in a (highly-)pressurized tank comes from the *pressurant*, not somehow magically compressing the liquid propellant to hundreds of atmospheres.

I hate to contradict you NathanKell, because your modding work is so brilliant and you clearly have a strong background in physics and some fields of engineering, but some liquid propellants *are* compressible.

If you compress Liquid Hydrogen to hundreds of atmospheres when you first put it into the tank (this requires very powerful compressors), then you can easily fit *many* times more fuel mass into a tank of the same volume.

It's no free lunch though- the tank mass scales with pressure in a pressure vessel (due to the requirement for thicker/stronger walls), and you end up getting an inferior fuel fraction in the tank (as 100 Liters of LH2 at 100 atmospheres pressure will contain less than 100 times the mass of fuel due to its compressibility factor). This is why most pressurized LH2 tanks are only pressurized at a few atmospheres of pressure (anywhere from 4-5 atm to as low as 1.5 atm for the Space Shuttle External Fuel Tank) if the goal is merely to reduce the volume of the fuel tanks (while holding the same fuel mass) rather than to feed a pressure-fed rocket engine.

ServiceModule tank type *is* for highly-pressurized tanks; you can see this by checking how many liters of tank volume is used when you add x liters-at-STP of a gas (say, Nitrogen).

OK, so then this principle just needs to be extended to compressible LIQUID fuels (scaled accordingly for the fuel type- some liquids, such as LH2 or Liquid CO2 are highly compressible, while others such as Water are basically incompressible) to attain an accurate balance. Like I said before, this is one of the advantages of Service Modules- they can compress more fuel mass into a compact form. The downside is that they have an inferior mass fraction- which is already accurately accounted for in RealFuels.

Regards,

Northstar

Edited January 5, 2015 by Northstar1989

Starwaster · January 5, 2015

How do you think the pressurization on a liquid fuel tank works, exactly? The pressurant gas itself never (or rather, isn't supposed to) enters the engines- the pressure is transmitted through the *liquids* (which, by the way, are initially pressurized in the fuel tanks of pressure-fed engines with high combustion chamber pressures- in those cases the pressurant is only used to *maintain* the initial pressure by replacing lost fuel, rather than to create it). Some liquids, such as water, are basically incompressible and will simply transmit this force, but other liquids will increase in density in response to pressure, and a few can even be compressed all the way to a solid state...
Liquid Hydrogen, one of the most important cryogenic fuels, is known to be *particularly* compressible for a liquid. Like liquid CO2, it can be substantially compressed (unlike CO2, it is difficult to compress it all the way to a solid, as the melting point of Hydrogen is so low). If you don't believe me, I suggest you do a simple Google search for "liquid hydrogen compressibility".
This means that fuel tank with LH2 under pressure *will* contain substantially more fuel mass than one at 1 atmosphere of pressure.
I don't know off the top of my head how compressible N204, LOX, or any of the Hydrazine-derivatives (UDMH, MMH, Aerozine), but at least *some* liquid fuels/oxidizers are compressible to quite a substantial degree.
Arguing about a basic fact of physics (that some liquids ARE compressible- LH2 in particular) distracts from my point. Pressurization enables masses of liquid to be stuffed into a tank greater than what could be achieved with 100% utilization at 1 atmosphere of pressure, thus *effective* utilization can greatly exceed 100% in highly-pressurized fuel tanks. (at least when the fuel tank contains a compressible liquid- such as LH2)
Regards,
Northstar
- - - Updated - - -
I hate to contradict you NathanKell, because your modding work is so brilliant and you clearly have a strong background in physics and some fields of engineering, but some liquid propellants *are* compressible. If you compress Liquid Hydrogen to hundreds of atmospheres when you first put it into the tank (this requires very powerful compressors), then you can easily fit many times more fuel mass into a tank of the same volume. It's no free lunch though- the tank mass scales with pressure in a pressure vessel (due to thicket walls), and you end up getting an inferior fuel fraction in the tank (as 100 Liters of LH2 at 100 atmospheres pressure will contain less than 100 times the mass of fuel due to its compressibility factor). This is why most pressurized LH2 tanks are only pressurized at a few atmospheres of pressure (anywhere from 4-5 atm to as low as 1.5 atm for the Space Shuttle External Fuel Tank) if the goal is merely to reduce the volume of the fuel tanks (while holding the same fuel mass) rather than to feed a pressure-fed rocket engine.
OK, so then this principle just needs to be extended to compressible LIQUID fuels (scaled accordingly for the fuel type- some liquids, such as LH2 or Liquid CO2 are highly compressible, while others such as Water are basically incompressible) to attain an accurate balance. Like I said before, this is one of the advantages of Service Modules- they can compress more fuel mass into a compact form. The downside is that they have an inferior mass fraction- which is already accurately accounted for in RealFuels.
Regards,
Northstar

You are overestimating the degree of compressibility. Pressurization of the shuttle fuel tanks was not for the purpose of storage. That's what chilling it is for. The only way to substantially get more hydrogen into a tank is to chill it even further. Look up hydrogen slurry slush.

Pressurization of the hydrogen (and oxygen) tanks is only to assist in feeding it into the engines. You are not going to get 150% storage capacity out of liquid hydrogen through pressurization. It's not going to happen.

Edit:

I wonder, could THIS be the source of the confusion on this issue?

http://en.wikipedia.org/wiki/Compressed_hydrogen

Edited January 5, 2015 by Starwaster

StoryMusgrave · January 5, 2015

@Northstar: If you are SO sure of yourself. Provide one example of documented proof that liquid compressibility has been used in any space program.

FYI. The Shuttle ET (LWT) LH2 tank is 331in in diameter, 1160in long, obviously curved on both ends and has a capacity of 1515461L. Total USABLE LH2 is 1431630L (based on weight). That's over 80000L difference. Care to explain to me oh 'pressurized one' how compressibility plays a factor in INCREASING the amount of LH2 in a tank?

Northstar1989 · January 9, 2015

@Northstar: If you are SO sure of yourself. Provide one example of documented proof that liquid compressibility has been used in any space program.

What you're asking doesn't make any sense. There's already extensive proof that compressed (as a side-effect of pressurization) fuels have been used in space programs (especially with pressure-fed rocket engines). You want me to get inside the rocket designer's heads, and provide their logic for designing things the way they did?

With some notable exceptions, a lot of that reasoning isn't exactly flaunted out in the open- only a few key reasons are given for any design choice. And like I said before, LH2-compression is a design trade-off: it comes at the cost of reduced mass-fractions (a CRITICAL design factor in upper stages). It's usually not even a worthwhile benefit for the increase in tank-mass: but is very important to simulate for a stage that is going to be highly-pressurized anyways (such as one attempting to re-create a real life rocket design with a pressure-fed upper stage).

Just go and look up the compressibility factor of LH2 if you really want to see how compressible it is, by the way.

FYI. The Shuttle ET (LWT) LH2 tank is 331in in diameter, 1160in long, obviously curved on both ends and has a capacity of 1515461L. Total USABLE LH2 is 1431630L (based on weight). That's over 80000L difference. Care to explain to me oh 'pressurized one' how compressibility plays a factor in INCREASING the amount of LH2 in a tank?

First of all, sources on the #'s would be helpful.

Second, did you even bother whipping out a calculator when you cited those #'s? That may SOUND like a low utilization, but that's actually 94% utilization- quite impressive really!

EDIT: Calculations based on the Shuttle's External Fuel Tank volume and LH2 mass reveal only a 0.16% increase in fuel-density due to pressurization (based on a density of 70.85 kg/m^3 at STP. And it turns out the LH2 tank is pressurized at roughly 2 atm, rather than the average pressure of 1.5 atm for the whole EFT- as the LOX is much less pressurized...) So I guess I was wrong about the External Fuel Tank, entirely. Still doesn't mesh with the figures I've seen on LH2-compressibility, though...

Perhaps the stated volume on Wikipedia includes the pressurant as well? (which would throw of ALL attempts to calculate how compressed the LH2 is...) The source page yields a 404 Page Not Found- so there is absolutely no way to figure out from the source what the Wikipedia figures actually refer to (the stated LH2 mass seems suspiciously low just based on expected increases in density from temperature alone, for instance, as STP is a *much* higher temperature than the LH2 tank's operating temperature...)

- - - Updated - - -

You are overestimating the degree of compressibility.

Not at all. More likely, you're overestimating how drastic I think the effect is. A 400% utilization at 40 atmospheres of pressure (a # I simply made up before) is 1/10th the fuel-density of an ideal fully-compressible liquid, for instance. And has 10x more fuel tank mass relative to fuel mass (40x tank mass but only 4x fuel mass) to boot!

I never said that pressurization is some sort of magical cure-all, only that it's an important factor we need to accurately simulate (by allowing utilization to exceed 100% for highly-pressurized tanks. We're talking 2-digit atmospheres of pressurization here for very small increases in fuel-density...)

Pressurization of the shuttle fuel tanks was not for the purpose of storage. That's what chilling it is for. The only way to substantially get more hydrogen into a tank is to chill it even further. Look up hydrogen slurry slush.

Both chilling and pressurization increase utilization. Chilling increases thermal leakage into the tank (which ultimately drives boil-off) however, whereas pressurization actually reduces it (by requiring increases in the thickness of tank walls- thus improving the insulation provided by the tank walls themselves...) So they're different approaches with different consequences. That being said, chilling *IS* the much more mass-effective solution. Any real attempt to significantly increase LH2 fuel-density would almost certainly make use of both, with a *very strong* preference for chilling, however... (if you're using composite materials for the fuel tank, rather than steel or titanium, the tank material itself has reasonable insulative qualities if thick enough. So it makes some sense to pressurize so as to gain the extra insulation from the thicker tank, and reduce the burden on the turbopump if you're not using a pressure-fed engine to begin with... Honestly, chamber pressure and turbopump considerations are the only real motivations for LH2-pressurization...)

Pressurization of the hydrogen (and oxygen) tanks is only to assist in feeding it into the engines. You are not going to get 150% storage capacity out of liquid hydrogen through pressurization. It's not going to happen.
I wonder, could THIS be the source of the confusion on this issue?
http://en.wikipedia.org/wiki/Compressed_hydrogen

That link has nothing to do with it. I'm intelligent enough to know the difference between gaseous hydrogen and LH2. I *suggest* you actually question your own assumptions before jumping to the conclusion that I must be wrong. You'll find plenty of evidence out there to support the fact that LH2 *is* indeed significantly compressible. A wise solution to increasing LH2-density? Probably not (the mass-penalties in tank-mass are enormous). But an important factor to simulate for stages that are already going to be highly-pressurized anyways (such as a service module attempting to re-create a real life pressure-fed stage).

Regards,

Northstar

P.S. If you're wondering why chilling increases thermal leakage into the tank, it's because it reduces the surface temperature of the stage's outer skin (if tank temperature is reduced without a corresponding increase in insulation). This alters the balance of thermal energy leaving vs. entering the tank via thermal radiation. The temperature drop may seem small in further cooling LH2, but thermal radiation follows the Stefan-Boltzmann Law- radiation is controlled by the FOURTH power of temperature. So even a small drop in temperature means a relatively large drop in thermal radiation. The colder an object is in space, the faster in gains heat from the environment (even space can be thought of as having an ambient temperature, of sorts, due to the average levels of infrared radiation passing through it), the hotter it is the more slowly (and if heated to a sufficient temperature, any object will *lose* energy to its environment rather than gain it).

Edited January 9, 2015 by Northstar1989

Starwaster · January 9, 2015

Not at all. More likely, you're overestimating how drastic I think the effect is. A 400% utilization at 40 atmospheres of pressure (a # I simply made up before) is 1/10th the fuel-density of an ideal fully-compressible liquid, for instance. And has 10x more fuel tank mass relative to fuel mass (40x tank mass but only 4x fuel mass) to boot!

Not possible. If anything, at 400% I'm clearly underestimating you.

This is what I suggest to you (because I can safely say that your proposal is NEVER going to be adopted into Real Fuel. It is not sane or realistic)


@TANK_DEFINITION
[*]:FINAL
{
	@TANK[LqdHydrogen]
	{
		%utilization = 4
	}
}

Put that in a .cfg file anywhere in GameData that you like.

That should do what you want. Rinse and repeat with other fuel types for TANK

StoryMusgrave · January 9, 2015

What you're asking doesn't make any sense. There's already extensive proof that compressed (as a side-effect of pressurization) fuels have been used in space programs (especially with pressure-fed rocket engines). You want me to get inside the rocket designer's heads, and provide their logic for designing things the way they did?

Don't make sense? You are joking right. "Provide one example of documented proof that liquid compressibility has been used in any space program." It's pretty simple. I'm asking for hard quoted data of any spacecraft in which a liquid has been compressed to achieve MORE liquid volume than the tank has capacity for under 1atm. Ex. a 300L tank that holds MORE than 300L of fluid, under pressure. Because that is EXACTLY what you are proposing happens, and it is quite laughable, really.

With some notable exceptions, a lot of that reasoning isn't exactly flaunted out in the open- only a few key reasons are given for any design choice. And like I said before, LH2-compression is a design trade-off: it comes at the cost of reduced mass-fractions (a CRITICAL design factor in upper stages). It's usually not even a worthwhile benefit for the increase in tank-mass: but is very important to simulate for a stage that is going to be highly-pressurized anyways (such as one attempting to re-create a real life rocket design with a pressure-fed upper stage).
Just go and look up the compressibility factor of LH2 if you really want to see how compressible it is, by the way.

It sounds like you want it become part of RealFuels because IN THEORY it might work.

First of all, sources on the #'s would be helpful.
Second, did you even bother whipping out a calculator when you cited those #'s? That may SOUND like a low utilization, but that's actually 94% utilization- quite impressive really!
EDIT: Calculations based on the Shuttle's External Fuel Tank volume and LH2 mass reveal only a 0.16% increase in fuel-density due to pressurization (based on a density of 70.85 kg/m^3 at STP. And it turns out the LH2 tank is pressurized at roughly 2 atm, rather than the average pressure of 1.5 atm for the whole EFT- as the LOX is much less pressurized...) So I guess I was wrong about the External Fuel Tank, entirely. Still doesn't mesh with the figures I've seen on LH2-compressibility, though...
Perhaps the stated volume on Wikipedia includes the pressurant as well? (which would throw of ALL attempts to calculate how compressed the LH2 is...) The source page yields a 404 Page Not Found- so there is absolutely no way to figure out from the source what the Wikipedia figures actually refer to (the stated LH2 mass seems suspiciously low just based on expected increases in density from temperature alone, for instance, as STP is a *much* higher temperature than the LH2 tank's operating temperature...)

Fair enough. Weights found here "JSC - 26098". Dimensions are from the 1988 NSTS News Reference Manual. Both would be appropriate for the LWT.

Oh so...you have just admitted your 'theory' is completely wrong. Guess we are done here. My main point is and has been that utilization is going to be <= 100%. Not ever have I, OR ANYONE, ever seen a spacecraft with a liquid utilization of a tank >100% of a tanks physical capacity due to being pressurized, at any level. As Starwaster said, it's not sane or realistic. Drop it.

Wikipedia...Wikipedia...really. Much better sources out there. Glad you at least attempted to go to whatever source was quoted there. It is funny how in one section, which does specify the SLWT, says volume is 1497440L, then shortly later, it has an unspecified tank volume of 1514611L. (~800L from my source). Now I quoted USABLE LH2. When unusable LH2 is added raises the filled volume to 1451547L. Still an absolutely fantastic utilization, and one that Procedural Parts does allow one to modify.

Not at all. More likely, you're overestimating how drastic I think the effect is. A 400% utilization at 40 atmospheres of pressure (a # I simply made up before) is 1/10th the fuel-density of an ideal fully-compressible liquid, for instance. And has 10x more fuel tank mass relative to fuel mass (40x tank mass but only 4x fuel mass) to boot!
I never said that pressurization is some sort of magical cure-all, only that it's an important factor we need to accurately simulate (by allowing utilization to exceed 100% for highly-pressurized tanks. We're talking 2-digit atmospheres of pressurization here for very small increases in fuel-density...)

RealFuels CAN AND DOES accurately simulate utilization due to pressurization. OF GASSES, just like it is, and is configurable to boot.

Again, like Starwaster said, since it's not going to happen because IT'S NOT REALISTIC OR ACCURATE. Feel free to modify your utilization of tanks to whatever you THINK it can be.

Both chilling and pressurization increase utilization. Chilling increases thermal leakage into the tank (which ultimately drives boil-off) however, whereas pressurization actually reduces it (by requiring increases in the thickness of tank walls- thus improving the insulation provided by the tank walls themselves...) So they're different approaches with different consequences. That being said, chilling *IS* the much more mass-effective solution. Any real attempt to significantly increase LH2 fuel-density would almost certainly make use of both, with a *very strong* preference for chilling, however... (if you're using composite materials for the fuel tank, rather than steel or titanium, the tank material itself has reasonable insulative qualities if thick enough. So it makes some sense to pressurize so as to gain the extra insulation from the thicker tank, and reduce the burden on the turbopump if you're not using a pressure-fed engine to begin with... Honestly, chamber pressure and turbopump considerations are the only real motivations for LH2-pressurization...)

You are talking theory. You admit that chilling is more mass effective, which face it, IS the name of the game in space travel, so why should Nathan change something that otherwise for all practical purposes IS accurate and realistic on some whim of a theory that is counter-productive to space travel in the first place. Not to mention the fact that utilization IS modeled. Starwaster already gave you the MM code needed for the change. But don't expect it to become 'standard'.

That link has nothing to do with it. I'm intelligent enough to know the difference between gaseous hydrogen and LH2. I *suggest* you actually question your own assumptions before jumping to the conclusion that I must be wrong. You'll find plenty of evidence out there to support the fact that LH2 *is* indeed significantly compressible. A wise solution to increasing LH2-density? Probably not (the mass-penalties in tank-mass are enormous). But an important factor to simulate for stages that are already going to be highly-pressurized anyways (such as a service module attempting to re-create a real life pressure-fed stage).

You are wrong about the space program. That's what we are talking about. It hasn't been used. Period. As this is a space program, you won't see it here either. As such. RealFuels ALREADY HAS THE CAPABILITY OF CHANGING UTILIZATION. So your entire magic show is all for naught. Good day. Happy tanking.

Starwaster · January 9, 2015

Wikipedia...Wikipedia...really. Much better sources out there. Glad you at least attempted to go to whatever source was quoted there. It is funny how in one section, which does specify the SLWT, says volume is 1497440L, then shortly later, it has an unspecified tank volume of 1514611L. (~800L from my source). Now I quoted USABLE LH2. When unusable LH2 is added raises the filled volume to 1451547L. Still an absolutely fantastic utilization, and one that Procedural Parts does allow one to modify.

Well, to be fair: Wikipedia often has some pretty good information. It's just wise to fact check it against something reliable. NASA has a lot of good documents archived on its servers. So does faa.gov, on aeronautics and space travel. (including reentry)

Rayder · January 9, 2015

I seriously doubt you could compress any liquid to 500% its density - or more - even Liquid Hydrogen. Water only compresses 0.5% at 150 atmospheres. In liquid state there are already no gaps between the atoms so the only practical way to increase the density is to lower the temperature. Even at that, you won't get anywhere near the compression rate of 500% (more like 1-5%)

If such an example exists, I would love to see any liquid compressed down to 1/5 it's original volume.

Starwaster · January 10, 2015

I seriously doubt you could compress any liquid to 500% its density - or more - even Liquid Hydrogen. Water only compresses 0.5% at 150 atmospheres. In liquid state there are already no gaps between the atoms so the only practical way to increase the density is to lower the temperature. Even at that, you won't get anywhere near the compression rate of 500% (more like 1-5%)
If such an example exists, I would love to see any liquid compressed down to 1/5 it's original volume.

Yeah well the thing is, 'even' liquid hydrogen doesn't compress that well to begin with, no matter what Northstar thinks. If you look at what it takes to liquefy it, a hell of a lot of energy goes into it, a lot of compression and cooling and even more compression and cooling on top of that and what's the end result? ~70kg per kiloliter at -253C. And that's as good as it gets for us, at least right now with today's technology. Actually, there's also slush hydrogen which is about ~85kg per kiloliter and has to be kept even colder, basically to the point of freezing. But we don't use (nor have ever used) slush hydrogen in anything even though it's a density increase of 20% (NASA calls 10%-20% significant btw). A proposal as an alternative fuel is as far as it's ever gotten. So, liquid hydrogen, 70kg / KL. That's it. That's the best going today because NASA doesn't want to deal with the logistics of frozen hydrogen slurpies in a tank that's just going to start boiling off as soon as it's filled.

Northstar1989 · January 10, 2015

You are wrong about the space program. That's what we are talking about. It hasn't been used. Period. As this is a space program, you won't see it here either. As such. RealFuels ALREADY HAS THE CAPABILITY OF CHANGING UTILIZATION. So your entire magic show is all for naught. Good day. Happy tanking.

You're overstepping your bounds. I was *NOT* wrong about tank pressurization being commonly utilized in space programs (mainly to ease the load on turbopumps, or eliminate them altogether- as with pressure-fed rocket engines- both of which strategies have seen real use in space). Or about LH2 being compressible.

What I was wrong about was the DEGREE of compressibility- it appears very high pressurizations only yield a tiny increase in density (Raydar was close- you only get about 12-15% compression at 150 atm with a MASSIVE mass penalty of *150 times* the tank mass...) Nonetheless, real service modules are sometimes pressurized at 30-40 atmospheres if they're feeding pressure-fed rocket engines... This leads to a very small (5-6%) increase in LH2 density- not worth the extra fuel tank mass, and not worth simulating in RealFuels- where you can already out-perform real tanks by achieving utilization of 100% with Procedural Parts mod (remember, the space shuttle EFT was only 94%, and is one of the highest known utilizations...)

All being said, a pressure-fed rocket engine requires a pressurized fuel tank. There are mass-savings on turbopumps, etc., vs. a pump-fed design, but according to THIS document, the mass-costs of heavier fuel tanks only make pressure-fed engines lighter for total burn-times less than 1 minute (in practice, that means they're only lighter for an OMS designed to boost a spacecraft into a slightly higher orbit). The *real* reason to use a pressure-fed rocket is that it's simpler, cheaper, and easier to design... (which is why they see extensive use in every Big Dumb Booster proposal)

Regards,

Northstar

Edited January 10, 2015 by Northstar1989

Sideswiper22 · January 11, 2015

It appears Aerojet Kerbodyne's cfg. is not up to date so I made an updated config:

http://www./download/t3113lzzxy3viyy/AerojetKerbodyne_tanks.cfg

I also made a config for Tantares and Tantares LV because it's not yet supported:

http://www./download/vbd89s3ekjnos6k/Tantares_tanks.cfg

http://www./download/h3bv6tfiy4lli1r/TantaresLV_tanks.cfg

EDIT: Fixed TantaresLV.cfg

Edited January 11, 2015 by Sideswiper22

Geher · January 11, 2015

NOTE: You NEED an engine pack in order for engines/RCS to use the new fuels

I don't get it. I can't find any Engine Pack where the engines don't take just Liquid Fuel and Oxidizer. Does somebody have a list of Engine Packs that support Real Fuels?

Tellion · January 11, 2015

I don't get it. I can't find any Engine Pack where the engines don't take just Liquid Fuel and Oxidizer. Does somebody have a list of Engine Packs that support Real Fuels?

Second Post in this Thread.

Lexx Thai · January 11, 2015

I have a question about RealSettings.cfg: Nathan, can you explain me about MFS_TECHLEVEL structure fields (TLISP, TLTWR and TLTHROTTLE)?

Geher · January 12, 2015

Second Post in this Thread.

I can't find "Real Engines", but "Reaching for the Stars" works fine for me.

Thank you very much.

Czerky · January 15, 2015

Are there any plans to add dynamic costs to the RF Procedural Parts tank? I noticed that the cost is always zero when they're added to a vessel/resized.

NathanKell · January 15, 2015

Czerky: Make a *large* tank (like, 5m x 10m, say). Show the RF GUI, and add a LH2 tank. Now tell me again that it costs 0.

Psawhn · January 16, 2015

Czerky: Make a *large* tank (like, 5m x 10m, say). Show the RF GUI, and add a LH2 tank. Now tell me again that it costs 0.

Well, you're right, $28 is a lot more than $0.

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Actually, is Real Fuels supposed to modify the cost of tanks? Because currently the prices for tanks are completely unadjusted from stock. I'm finding that the tanks themselves are often more expensive than the engines, to the point that dense fuels like kerolox are invariably much more cost-effective than choices like hydrolox. For example, a Jumbo-64 fuel tank costs twice as much as a Mainsail, so using the lowest volume of fuel possible (and thus the fewest number of fuel tanks) becomes the key consideration.

I'm currently using the stockalike pack, but with all the prices commented out because it was making all the engines even cheaper than stock and exacerbating this problem. However, I skimmed the module manager .cfgs in the RFTS pack and it doesn't appear to modify tank or engine prices either.

I haven't touched Realism Overhaul, however I expect it probably wouldn't have this problem because it will have had a careful balance pass for all masses and costs.

NathanKell · January 16, 2015

RftS is *very* out of date. The only mod that prices everything for the Real*.* universe is RP-0, though it's nowhere near finished.

RealFuels, like all the realism mods in the RO stable, uses 1 fund = $1000 in 1965 dollars. So that tank costs $28,000 USD (probably something like $400k in today's dollars). Propellants, however, are dirt cheap: think about how cheap a gallon (rather more than a liter!) of gas was in 1965...

RP-0: http://forum.kerbalspaceprogram.com/threads/103196-0-25-Realistic-Progression-Zero

(note that ONLY the mods listed as supported are supported by RP-0, and if it's not even listed as WIP, then *none* of the prices will be correct...)

Psawhn · January 16, 2015

RftS is *very* out of date. The only mod that prices everything for the Real*.* universe is RP-0, though it's nowhere near finished.
RealFuels, like all the realism mods in the RO stable, uses 1 fund = $1000 in 1965 dollars. So that tank costs $28,000 USD (probably something like $400k in today's dollars). Propellants, however, are dirt cheap: think about how cheap a gallon (rather more than a liter!) of gas was in 1965...
RP-0: http://forum.kerbalspaceprogram.com/threads/103196-0-25-Realistic-Progression-Zero
(note that ONLY the mods listed as supported are supported by RP-0, and if it's not even listed as WIP, then *none* of the prices will be correct...)

I don't mind that propellants have very low costs. Even still, that procedural tank itself costs only 1.5 funds, so by your conversion ratio it's $26,500 USD (1965) worth of hydrogen stuffed into a $1,500 USD (1965) hydrogen tank. You just described the propellants as being dirt cheap, so I don't think it's correct that the tank is less than 6% the cost of the propellant. (And if the propellant is dirt cheap, I can only describe the tank cost as loose change.)

On the other hand, a stock Jumbo-64 tank costs $12.8 million USD in 1965 dollars (Or $95.6 million in 2014 dollars) at 12,800 funds. At least the tank:propellant cost ratio is in the correct direction that time .

I don't know what the realistic cost for tanks should be, but it must be somewhere in the middle between rounding error and new F-16. :sticktongue:

I'll look at RP-0 for prices on engines and tanks and see if there's a scaling factor I can apply to stock fuel tanks.

[1.8+] Real Fuels

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