Tweakable fuel tanks

[Firov]

Each tank in KSP works on the same principle. They are prebuilt tanks which can't be structurally changed.

Just like the landing wheel tires can't be changed in size.

At least that is what I think Squad's reasoning is behind this.

You realize, of course, that the size and relative ratios of those tanks were determined by the mission designers and then built to those specifications, right? It's not like NASA engineers pulled some pre-made Saturn V sized tanks of shelf somewhere and said, "Alright guys, we've got these ready made fuel tanks, we don't really know how they work, or how to change them, so what mission can we accomplish with them?"

If they had, for some reason, wanted the first stage tank to carry only hydrogen, then they would have redesigned the internal geometry of the stage, removed the oxidizer tank, and increased the size of the hydrogen tank.

No one is wanting to change maximum fuel volumes in flight, just in the vehicle assembly building or spaceplane hanger, where we're ostensibly constructing these ships. Once that vessel touches the launch pad/runway though, those ratios should be locked in.

[Garek]

I think the point is more like, when the NASA launched space lab, they just used a spare Saturn they had lying around, without changing fuel tanks to optimize it for that task, because it was cheaper just to use it as-is. The problem is, you can't model this in KSP, not before you introduce currency. Without currency, either you allow a player to change tank types around without limits, or you always limit him/her to some constraint e.g. maximum of fuel per fuel type stays, as it's apparently implemented.

[Eric S]

I think the point is more like, when the NASA launched space lab, they just used a spare Saturn they had lying around, without changing fuel tanks to optimize it for that task, because it was cheaper just to use it as-is.

Fuel ratios aren't going to change in this situation though. If NASA ever got around to launching a thermal atomic rocket, I can promise you that they wouldn't be using tanks repurposed from something else, with mass taken up by empty oxidizer tanks. The devs mentioned that they didn't want to have to have separate fuel-only rocket tanks which is the reason our current atomic engine uses oxidizer. They said that tweakables was their solution, and the version of tweakables that we've got now isn't a solution to this problem, and in fact, I haven't seen anything that implies that they've changed the atomic engine to not use oxidizer.

[Garek]

Fuel ratios aren't going to change in this situation though. If NASA ever got around to launching a thermal atomic rocket, I can promise you that they wouldn't be using tanks repurposed from something else, with mass taken up by empty oxidizer tanks. The devs mentioned that they didn't want to have to have separate fuel-only rocket tanks which is the reason our current atomic engine uses oxidizer. They said that tweakables was their solution, and the version of tweakables that we've got now isn't a solution to this problem, and in fact, I haven't seen anything that implies that they've changed the atomic engine to not use oxidizer.

You're right about that, and I agree that's a strong point for the tweakables not being finished yet. My argument was more ment for the general "you can't use less oxidizer to pack more LF because the internal tanks are fixed" vs. "why should the supposed internal tanks be fixed when we're designing a new rocket?" discussion.

[Spyritdragon]

If im wrong, seriously, please correct me, but:

ttp://xkcd.com/1133/

Originally meant for humor, this picture can very well be used for my example. Its still a jice model of the rocket.

The amount of space needed for the oxidizer is dramatically less than the amount for liquidfuel - you need twice as many liquidfuel molecules as you need oxidizer molecules, using standard fuels.

You cant just take out the oxidiser and be able to take the same amount of units of liquidfuel - and in KSP, i dont think youd want to take oxidiser without liquidfuel - it literally has zero use without it.

So i think that instead of going into complex workings, they just decided the parts were premade with one oxidiser tank and one li1uidfuel tank, and that they can hold only so much. It wouldnt make sense to adjust the parts specifically for evety launch, and once you put a bit of liquidfuek in your oxidiser tank it cant hold any oxidizer due to the volatility of resulting mixture.

[_Aramchek_]

You cant just take out the oxidiser and be able to take the same amount of units of liquidfuel - and in KSP, i dont think youd want to take oxidiser without liquidfuel - it literally has zero use without it.

No, it does have uses, I have an ssto that runs out of oxidizer before running out of usable fuel. And if I could pack those tiny tiny little tanks with just oxidizer I would both save weight and almost double the range of the craft. I could simplify the craft both in size AND part count, leading to a much better performing craft.

Absolutist statements like "it has zero use" are rarely true, it would have been more correct if you had said you personally can't see a use for it, uses likely do in fact exist though. And definitely do for me.

[CalculusWarrior]

In my opinion, since tweakables are a fairly large and untested feature, the devs have held off completely integrating them yet. They are likely waiting for player feedback and playtesting (we are technically the alpha testers) before making any more radical changes. Changing the maximum amount of fuel/oxidizer per tank would require a complete rewrite of the fuel tanks, as you aren't just simply changing the levels anymore, you're changing the 'bulkheads'.

Think of the new SAS system; it wasn't perfect when first implemented, but almost every update since then has contained little tweaks to it to make the system work better. Tweakables are definitely a step in the right direction; changing the level of fuel tanks is only a small part of what this system can do (I've waited for so long to have landing gear be deployed straight from the VAB), and I'm confident that SQUAD will only make it better as time goes on.

[Brotoro]

...The amount of space needed for the oxidizer is dramatically less than the amount for liquidfuel - you need twice as many liquidfuel molecules as you need oxidizer molecules, using standard fuels...

Depends on what kinds of fuel and oxidizer you are talking about. In the upper stages of the Saturn V, yes, the liquid hydrogen fuel is much more bulky than the liquid oxygen oxidizer. But the opposite is true for the first stage, where the liquid oxygen is bulkier than the RP-1 fuel (which is a fancy version of kerosene).

The situation where I wished for tweakables in the past has been with space planes, where I assume the fuel we are using is kerosene (the jet fuel tanks actually say that on them as I recall). So the oxidizer would be bulkier (be it LOX or some storable like red fuming nitric acid or nitrogen tetroxide) and I should be able to more than double the amount of fuel I put into a tweaked tank if I build it to contain fuel only and no oxidizer.

[_Aramchek_]

Changing the maximum amount of fuel/oxidizer per tank would require a complete rewrite of the fuel tanks, as you aren't just simply changing the levels anymore, you're changing the 'bulkheads'.

I'm pretty sure the simulation aspect of the game doesn't run that deep.

It really wouldn't require much time or effort.

I do agree it's likely just to get the basic functionality implemented in game for all of us.

I just hope they change it in the way I described pages back at some point in the near future.

[lajoswinkler]

Why not? If I want to mix Hypergolic propellants together in a tank prior to take off, I should be able to blow myself up

Even the Kerbals have some safety standards.

So you can't stuff fuel into oxidizer tanks - but when building, you adjust the proportions of those tanks. Isn't it natural that you would make one of them purposefully smaller to accommodate less oxidizer and more liquid fuel for an SSTO craft? When it's done, it's done. But before that, it should allow you to select what portion of the entire thing will be devoted to which kind of propellant.

Maybe it could be done in a ''procedural'' kind of way - you would have a slider which would adjust max values for each propellant in your tank and THEN you can choose how much of these tanks you want to fill up with fuel. I see advantages that could be obtained by starting half-empty or by having balancing tanks for crafts with offset centre of mass. But while building, we should be able to select how big the Liquid Fuel part of the tank is in relation to the Oxidizer part. Just my 2cents, I'm sure it's been said before ^^

The point is that you have a fixed type of tank. It's a tank with two subunits, just like in real life.

OP's request would require new types of tanks. I'm not against it, but I do find it unrealistic to modify something so basic as stock tanks.

[Psycix]

Change the lengths of the two internal tanks. Done.

Edited December 13, 2013 by Psycix

[koshelenkovv]

This seems pretty rooted in reality - inside each fuel tank are separate, pressurized tanks for fuel and oxidizer. When you tweak the fuel tanks, you are changing to what percentage each one of those is filled - not the capacity of the tanks.

In reality nothing prevents to build custom tankage for any rocket stage.

Only price will be bigger.

On the other hand, making custom tanks in game will require programming this feature. Now all tanks is simply locked at fixed fuel/oxidizer ratio. There is no need to remember and process ratios for each tank on each vessel. Custom tanks will require some not negligible changes which are not in priority now.

Edited December 13, 2013 by koshelenkovv

[GROOV3ST3R]

The idea is simply to change the proportions of the sub-units within a stock tank to accomodate different amounts of fuel. All that needs is a procedural plugin that will allow us to modify this proportion for both tanks at once - simulating making one smaller and the other one larger at the same time. Procedural wings and stretchy tanks already allow us to make custom parts with physics and properties calculated in real time. Therefore, an ability to alter or possibly even replace the ''sub unit'' from inside of the tank should be possible.

We can choose how much fuel is IN the sub unit once we make it. But I want to be able to alter the sub unit itself in SPH/VAB.

SSTOs would really benefit from that - you could make a 1 tank spaceplane with a little bit extra liquid fuel for operation within the atmosphere while not having to add more heavy rocket fuel tanks or be stuck with too much liquid fuel and no oxidizer to burn it with.

Edited December 13, 2013 by GROOV3ST3R

[koshelenkovv]

So you can't stuff fuel into oxidizer tanks - but when building, you adjust the proportions of those tanks. Isn't it natural that you would make one of them purposefully smaller to accommodate less oxidizer and more liquid fuel for an SSTO craft?

Exactly.

And vice versa - to be able to place small amount of oxidizer into much sturdier airplane tanks.

It's a pity that we can not build spaceplane out of spaceplane parts and forced to use flimsy rocket tanks with 6 m/s impact tolerance which falling off on landing.

[carazvan]

Tweakable fuel tanks also allows you to check fully the COM vs COT for your ships and SSTOs as you burnup fuel.

No more guestimating how far forward/back the COM shifts; just set the fueltanks to empty and look ingame.

[Wheffle]

I think it's pretty silly to get up in arms about this. As others have pointed out, it's not realistic to be able to change the internal tank sizes for two separate components of fuel. Being able to dump oxidizer that you won't need on a space plane is a huge bonus in itself. Plus, being able to replace oxidizer with fuel would marginalize the fuel-only aircraft tanks.

It's fine if you disagree with the decision, but quit getting angry. Very silly.

[Tank Buddy]

There are still 4 days to make changes, I'm sure if they see this they will do so.

[csiler2]

Change the lengths of the two internal tanks. Done.

That's very complicated in real life, especially with US-designed rockets. The Saturn V stages were designed with very thin skins that depended on the tanks and their fuel load to help maintain rigidity and structure during launch. NASA engineers were aghast when they first saw the R-7 launcher at the 1967 Paris Air Show. The Russians were picking up the tank from either end with cranes to move it into position. Similar actions with any of the Saturn stages would have destroyed them. The R-7 Tanks were built with thicker materials, which made them less efficient, but easier to transport and move around.

It would be nice to swap out fuel types as we see fit, but I don't agree with being able to re-partition the tanks. Remember that all of the 'parts' originate from Jebediah's Junkyard and implicitly come 'as is'. It goes against the cobbled-together theme of the game if you're going in and changing all the parts to precisely what you want.

I look at it this way, if I want to modify the fuel capacity or ad NOS to my car, I don't drop out the fuel tank, change its dimensions/add partitions and put it back. I add additional pre-made tanks to the trunk or other open spaces to my car and work on it that way. This is the same approach, but with rocket parts instead of car parts.

[FITorion]

I think it's pretty silly to get up in arms about this. As others have pointed out, it's not realistic to be able to change the internal tank sizes for two separate components of fuel. Being able to dump oxidizer that you won't need on a space plane is a huge bonus in itself. Plus, being able to replace oxidizer with fuel would marginalize the fuel-only aircraft tanks.

It's fine if you disagree with the decision, but quit getting angry. Very silly.

This.

It's tweakables... not procedural fuel tanks... I have no problem at all with the way I have seen it thus far.

[GusTurbo]

Tweakable fuel tanks also allows you to check fully the COM vs COT for your ships and SSTOs as you burnup fuel.

No more guestimating how far forward/back the COM shifts; just set the fueltanks to empty and look ingame.

I didn't even think of that. That will be very useful.

[PDCWolf]

This will make it easier to understand why is tweakables a dissapointment or rather just another half-implemented feature added to the list. Think of the cilinder as a tank, and the rounded cubes as the internal tank structure:

Why should it be like this? Because the internal tank structure should be defined by the user, not constrained.

Something else I'm tired of saying: The freaking descriptions and "kerbals are ******** as orks at engineering" is a community's joke, not the theme of the game. The descriptions were (and supposedly still are) placeholders.

The joke went along thanks to the average skill back in those times were getting to orbit was a miracle and mostle everyone met the ground pretty soon after launching

Edited December 13, 2013 by PDCWolf

[annallia]

I think it's pretty silly to get up in arms about this. As others have pointed out, it's not realistic to be able to change the internal tank sizes for two separate components of fuel. Being able to dump oxidizer that you won't need on a space plane is a huge bonus in itself. Plus, being able to replace oxidizer with fuel would marginalize the fuel-only aircraft tanks.

It's fine if you disagree with the decision, but quit getting angry. Very silly.

I agree. My vision for what tweakables would entail was somewhat grander than this (but hey its early) but I don't see the big hoopla here.

[Firov]

That's very complicated in real life, especially with US-designed rockets. The Saturn V stages were designed with very thin skins that depended on the tanks and their fuel load to help maintain rigidity and structure during launch. NASA engineers were aghast when they first saw the R-7 launcher at the 1967 Paris Air Show. The Russians were picking up the tank from either end with cranes to move it into position. Similar actions with any of the Saturn stages would have destroyed them. The R-7 Tanks were built with thicker materials, which made them less efficient, but easier to transport and move around.

It would be nice to swap out fuel types as we see fit, but I don't agree with being able to re-partition the tanks. Remember that all of the 'parts' originate from Jebediah's Junkyard and implicitly come 'as is'. It goes against the cobbled-together theme of the game if you're going in and changing all the parts to precisely what you want.

I look at it this way, if I want to modify the fuel capacity or ad NOS to my car, I don't drop out the fuel tank, change its dimensions/add partitions and put it back. I add additional pre-made tanks to the trunk or other open spaces to my car and work on it that way. This is the same approach, but with rocket parts instead of car parts.

Irrelevant car analogy aside, you must realize that the Saturn V you're talking about was engineered to achieve a specific mission. I've pointed this out before, but the engineers didn't haphazardly grab a few tanks, duct tape them together, and call it a day. The fuel tank ratios were specifically calculated to achieve it's mission. In this case, to be able to achieve orbit with the Apollo missions. It was then constructed to those design specifications. Had they realized in the design phase that they, for whatever reason, needed 20% more oxidizer and 20% less fuel in the first stage they would have adjusted the internal tank geometry to accommodate that alteration. They would not have thrown up their arms and said "Well guys, our pre-packaged ACME brand tanks are the wrong size, somebody better tell Kennedy that we've got to scrap the moon mission." NASA didn't operate that way, the Soviets didn't operate that way, and SpaceX doesn't operate that way.

Again, no one is asking for this to be changeable in flight. That would be completely unrealistic, I agree. However, in the design phase (AKA VAB/SPH), there's no reason that the internal tank geometry couldn't, and wouldn't, be modified to suit the particular mission that tank is intended for within the volume limitations of that particular tank.

Also, consider the possibilities of using a single tank holding liquid fuel, oxidizer, AND monopropellent as a service module, as was done with the Apollo missions. That's what tweakables should ideally allow.

Edited December 13, 2013 by Firov

[FITorion]

This will make it easier to understand why is tweakables a dissapointment or rather just another half-implemented feature added to the list. Think of the cilinder as a tank, and the rounded cubes as the internal tank structure:

snip image

Why should it be like this? Because the internal tank structure should be defined by the user, not constrained.

I disagree. The internal tank structures should be defined and you can make MOD parts of tanks with different fuel tanks in them. Tweakables just allow you to tweak the levels within. Nothing more is needed.

Edited December 13, 2013 by FITorion

[Eric S]

It's fine if you disagree with the decision, but quit getting angry. Very silly.

For the record, I'm not angry (sorry if I came across as such). I'm just saying that this version of tweakables doesn't solve certain problems that the devs have claimed that tweakables would solve, so I suspect that this isn't the final version of tweakables.

As for the people insisting that changing the tank proportions would be unrealistic or whatever, you're missing the point that we're talking about issues that the devs have said that tweakables would solve, and this version of tweakables isn't solving them. If they've decided to resolve those issues some other way, that's fine, but since they haven't said anything about it, the options are:

1) this isn't the final version of tweakables.

2) they've decided to solve those issues some other way.

3) the issues in question have fallen between the cracks.