[1.8+] Real Fuels

[ninjaweasel]

Wow, thanks!

Erhm... damn. Search brain for "How to build rocket" folder... there it is. Delete. Empty recycle bin.

Now what were we talking about?

[aristurtle]

They just got included in the update I made last night. And thanks for the fuel tanks, saves me from doing those myself too!

Cool, I'm glad I could help. Right now I'm trying to work on a patchset to make NearFuture work properly with RealFuels.

Speaking of which -- Nathan, did you realize when you changed the density of the XenonGas resource that it would increase the ion engine's ElectricCharge consumption dramatically? Just wondering if it was on purpose. If it wasn't, I think this should fix it:

@PART
[*]:HAS[@MODULE[ModuleEngines]:HAS[@PROPELLANT[XenonGas],@PROPELLANT[ElectricCharge]]]:NEEDS[RealFuels]
{
    @MODULE[ModuleEngines]
    {
        @PROPELLANT[ElectricCharge]
        {
            @ratio *= 0.05894
        }
    }
}


@PART
[*]:HAS[@MODULE[ModuleEnginesFX]:HAS[@PROPELLANT[XenonGas],@PROPELLANT[ElectricCharge]]]:NEEDS[RealFuels]:AFTER[NearFuturePropulsion]
{
    @MODULE[ModuleEnginesFX]
    {
        @PROPELLANT[ElectricCharge]
        {
            @ratio *= 0.05894
        }
    }
}

[Raptor831]

Cool, I'm glad I could help. Right now I'm trying to work on a patchset to make NearFuture work properly with RealFuels.

I've got the truss set tanks set up on my install, if you'd like those. I can post that up when I get back to my computer.

[aristurtle]

I've got the truss set tanks set up on my install, if you'd like those. I can post that up when I get back to my computer.

The LFO tanks are the easy part; I'm stuck on how to switch its LiquidHydrogen resource for RF's LiquidH2 without screwing up the balance they were going for.

[Raptor831]

The LFO tanks are the easy part; I'm stuck on how to switch its LiquidHydrogen resource for RF's LiquidH2 without screwing up the balance they were going for.

Ah, I see. I don't use the engines/resources/nuclear elements of NearFuture, I just grab the batteries, solar, and structural pieces. If NF is using liters, it should be easy enough. I think the limiting factor for NF is more powering the engines than fuel use.

If you don't mind my asking, how do the NF engines play next to the stockalike RF engines?

[Ralathon]

Ah, I see. I don't use the engines/resources/nuclear elements of NearFuture, I just grab the batteries, solar, and structural pieces. If NF is using liters, it should be easy enough. I think the limiting factor for NF is more powering the engines than fuel use.

If you don't mind my asking, how do the NF engines play next to the stockalike RF engines?

NF engines work great for orbital tugs, or even moon landers (with a VASMR). But in my experience they're underpowered compared to the stockalike RF engines. Its pretty hard to build something that has more dV per mass unit than a simple lqdMethane tank with a NTR. It usually means you get some monstrosity with dozens of hydrogen tanks docked to a single thruster + nuclear reactor combo.

[aristurtle]

Ah, I see. I don't use the engines/resources/nuclear elements of NearFuture, I just grab the batteries, solar, and structural pieces. If NF is using liters, it should be easy enough. I think the limiting factor for NF is more powering the engines than fuel use.

If you don't mind my asking, how do the NF engines play next to the stockalike RF engines?

They don't use one-unit-per-liter, which makes things irritating, and there's a separate LiquidHydrogen resource, and having LiquidHydrogen and LiquidH2 both in my game bugs me endlessly. I just spent the past few hours cooking up a fix that I'll post after I finish testing it.

NF only adds one chemical engine, which is basically a thinner version of the Poodle. The big draw is the electrical engines, which I like using. They generally have enormous ISP, low thrust, and high electrical requirements -- it basically fleshes out the Ion Propulsion part of the tech tree that Squad only put one part into. And they're all fairly believable, too; they're based on things that are in at least the "working prototype" stage in the real world, as opposed to KSPI's antimatter engines and Alcuberre drives and whatnot. NASA really was going to send out a nuclear-reactor-powered, ion propelled probe out to Jupiter's moons a couple years back before the project's funding got cancelled, for example.

[aristurtle]

Okay, I spent the last couple of days writing up a ModuleManager patch to fully integrate RealFuels and NearFuture, and I think it's good to go:

Download link

What this does:

- Tweaks the dry mass for the RealFuels modular xenon tanks to more closely match stock. Basically, when "useRealisticMass = false", it should have the same mass fraction as the stock tank or thereabouts, and the same amount of xenon by mass.

- Changes the NearFuture xenon tanks to use the modular tanks.

- Changes the density for the ArgonGas resource to one-unit-equals-one-liter

- Added a modular tank type for Argon and changed the NearFuture argon tanks to this type

- Added a procedural tank that can hold either Argon or Xenon.

- Changed the NearFuture LiquidHydrogen tanks to RealFuels BalloonCryogenic tanks, holding the same mass of LiquidH2 that they previously held of LiquidHydrogen. (The BalloonCryo tank type matched the old dry mass value so closely that I didn't need to change it)

- Changed the NearFuture engines that used LiquidHydrogen to use LiquidH2 instead

- Rebalanced all ElectricCharge consumption rates to match the new fuel densities -- should have the same EC per second that they had before.

- Added RealFuels engine configuration for the chemical engine in the NearFuture Spacecraft pack -- it uses MMH and N2O4, like the real-life Space Shuttle OMS thrusters. (One would hope that in the "near future" we'll find hypergolic propellants that aren't ridiculously toxic, but there's no sign of them yet, so...)

- Changed the couple of chemical fuel tanks to RealFuels modular tanks

I think that about covers it. At some point I'd like to unify the RealFuels "NuclearFuel" resource with the NearFuture "EnrichedUranium" resource, so that you can reprocess spent NTR nuclear fuel in the NearFuture nuclear reprocessing plant, but this is good enough for now.

I think I might do KSOS next, but I need to take a break from messing with config files for now.

[DracovaXIV]

I have a very bizarre issue, which has left me thoroughly confused. Basically, the better the Isp/efficiency are supposed to be, the worse the delta-V turns out. I'll give you an example: I take a stock pod, attach a fuel tank to it, and attach an engine to that. I configure the engine for N2O4 and whatnot, the delta-V comes out as X. Then I switch the engine to liquid hydrogen/liquid oxygen, and fill the tank with that. The delta-V comes out as LESS THAN X. This is vacuum delta-V as shown by VOID; I even did a test, and it worked out to be accurate both times. So then I deleted RealFuels and went to the stock Squad config for the different resources. I reduced the density of LiquidFuel and Oxidizer by half, and went into the game. Loaded a test vehicle. The delta-V was LOWER, even though the vehicle weighed less now! Then I quit out of the game, went back to the config, and set the values to double what they were originally. Went back to the same craft. The delta-V is now HIGHER, and the total mass of the craft is also higher! What's going on? Is this a known issue with some other mod, or what..?

[Ralathon]

I have a very bizarre issue, which has left me thoroughly confused. Basically, the better the Isp/efficiency are supposed to be, the worse the delta-V turns out. I'll give you an example: I take a stock pod, attach a fuel tank to it, and attach an engine to that. I configure the engine for N2O4 and whatnot, the delta-V comes out as X. Then I switch the engine to liquid hydrogen/liquid oxygen, and fill the tank with that. The delta-V comes out as LESS THAN X. This is vacuum delta-V as shown by VOID; I even did a test, and it worked out to be accurate both times. So then I deleted RealFuels and went to the stock Squad config for the different resources. I reduced the density of LiquidFuel and Oxidizer by half, and went into the game. Loaded a test vehicle. The delta-V was LOWER, even though the vehicle weighed less now! Then I quit out of the game, went back to the config, and set the values to double what they were originally. Went back to the same craft. The delta-V is now HIGHER, and the total mass of the craft is also higher! What's going on? Is this a known issue with some other mod, or what..?

Yea, you misunderstand how delta V works.

You can calculate delta V via the tsiolkovsky rocket equation:

dV = g*Isp*ln(m_full/m_empty)

If you use N2O4-MMH as fuel your Isp will be lower, but your m_full will be higher while m_empty stays the same. The added reaction mass by the higher fuel density adds more delta V than the lower Isp takes away.

This does not mean N2O4 is always superior as a fuel source however. The total mass of your spacecraft will be much higher than an equivalent craft with hydrolox, so it will be much harder to lift with your lower stages. Hydrolox just means you need a lot of tanks, but they'll be very light. So per kg of spacecraft you'll have more dV.

A good rule of thumb is to use high density fuels (kerosene, MMH etc) for your first stage, followed by a second stage using hydrolox to complete the orbital (escape) burn. Lastly you use MMH/N2O4 for orbital maneuvers since they don't slowly leak.

Although there are obviously exceptions to this rule. The Ariane 5 uses a central core with a lower than 1 TWR running on hydrolox, using SRB's to lift the rocket during the first part of ascent.

Edited July 29, 2014 by Ralathon

[Hattivat]

I have a very bizarre issue,

Ralathon already gave you a very good, but complicated, explanation, so let me give you a simple one in case you had problem understanding what Ralathon means:

The size of the tank is irrelevant. You should compare tanks of the same mass, not the same size. Since LiquidHydrogen is less dense than other fuels, you need a bigger tank to have the same mass of it. It's like with water and lead - you need a bigger bucket to carry 10 kilograms of water than you need to carry 10 kg of lead, but they weigh the same.

[DracovaXIV]

In other words, the game actually uses fuel mass expelled to calculate thrust? That's actually rather impressive. I wanted to be certain that there isn't something wrong with my game. If it's working accordingly, I'll instead focus on understanding this phenomenon.

Just to be absolutely clear... I tested this without RealFuels, like I said before. I removed the mod and I tweaked the stock Squad config, trying lower and higher fuel density with vanilla resources. One fuel tank, one engine, one payload - one stage. It seemed weird to me, because ostensibly, there would be no reason whatsoever to use higher Isp/lower density fuels.

[Ralathon]

In other words, the game actually uses fuel mass expelled to calculate thrust? That's actually rather impressive. I wanted to be certain that there isn't something wrong with my game. If it's working accordingly, I'll instead focus on understanding this phenomenon.

Just to be absolutely clear... I tested this without RealFuels, like I said before. I removed the mod and I tweaked the stock Squad config, trying lower and higher fuel density with vanilla resources. One fuel tank, one engine, one payload - one stage. It seemed weird to me, because ostensibly, there would be no reason whatsoever to use higher Isp/lower density fuels.

Your game is working absolutely fine. It actually works the other way around: The engine has a defined amount of thrust and Isp and based on that KSP calculates how much fuel mass the craft should lose per second. You can override this by using "rate" instead of "ratio" in your engine config IIRC, but yea the effect is the same.

Hydrolox gives more delta V for the same weight. So if you can fit it inside your fairing its better to use hydrolox for high dV operations:

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[DracovaXIV]

I've done a bit more testing using multistage vehicles, armed with a bit more understanding. I used a huge Procedural Parts solid main stage, a hydrolox stage for circularization, and a very small aerozine flight pack for the pod. During initial atmospheric ascent, I actually saw the dV remaining go up! That would explain my conundrum; VOID might not be designed to compute the cumulative dV of different-density fuel stages correctly!

[Hattivat]

During initial atmospheric ascent, I actually saw the dV remaining go up!

That's probably because it shows you the delta-v at the altitude you are at the time. Hydrolox stages usually have low sea-level Isp and high vacuum Isp, so the effective "at the moment" delta-v could very well rise as you climb up. It's best to have something that can show you the vacuum delta-v and sea-level delta-v separately. Mechjeb does that, don't know about other mods. Generally in RSS you need about 9500 m/s of vacuum delta-v to make it to the low earth orbit.

[aristurtle]

I'm about halfway through making a Real Fuels config for KSOS. I needed to set the external tank volume much higher than indicated by the usual ratio, but it basically matches the volume of the model.

[NathanKell]

aristurtle: yep, this is *Real* Fuels. Actual tank dimensions are the best. I've only been using the multipliers because finding the real dimensions of tanks is...hard. Because, note: you can't just use the total volume enclosed by the tank; a "tank" in KSP is actually a structural element with multiple pressure vessels.

Example, the Titan II:

So you need to figure out the volume utilization of the "tank" part (0.86 or so is a good guess if the stage is sufficiently tall; if the stage is so short that you can only fit spheres in, like the N-1's stages, then you might only have a utilization of ~.65-.75).

Also: Yes, I know about the Xenon thing.

Consider that real life ion thrusters make, say, 20 newtons of thrust. And require a lot of power. Now scale up the power draw by 100x to accord with 2kN of thrust...

[sidfu]

on aje and the stock alike pack dont they have some overlapping stuff?

[aristurtle]

Well, in real life Dawn could thrust during it's entire trip to the asteroid belt, but in KSP you're limited to a x4 time warp while the engines are on...

[rakutenshi]

Well, in real life Dawn could thrust during it's entire trip to the asteroid belt, but in KSP you're limited to a x4 time warp while the engines are on...

yeah, because RL allows 10x time acceleration when you're burning your engines. The ability to add time compression is a major factor in the reason the devs decided to increase the thrust on Ion engines so much past the real life equivalents. a 4 day burn may be realistic... but for a game it's far too boring.

[NathanKell]

in KSP you're limited to a x4 time warp while the engines are on...

Nope.

sidfu: I'm not aware of any. Also, what does that have to do with Real Fuels?

[Starwaster]

Nathan, launch clamps are replenishing SRB solid fuel on the launch pad. Ordinarily I'd never have noticed or cared, but Career Day has me testing sepratrons on the launch pad so I improvised a test stand with probe core, sepratron and and clamp. I could not shut them off.

[aristurtle]

yeah, because RL allows 10x time acceleration when you're burning your engines. The ability to add time compression is a major factor in the reason the devs decided to increase the thrust on Ion engines so much past the real life equivalents. a 4 day burn may be realistic... but for a game it's far too boring.

Dawn didn't burn for 4 days, it burned for 270. It would be neat if you could do that in KSP with time compression and some kind of autopilot system, but until they add that in, raising the thrust of the ion engines is the best we've got

[NathanKell]

Starwaster: for now you can right-click on the clamp to turn the pump on or off. Is that not working?

aristurtle: look at my above link directly responding to your post. We can.

[aristurtle]

I was in the middle of typing when you posted! I'll give that mod a shot the next time I get a day off.

I have my KSO realfuels config just about done, I'll post it soon.