[1.8+] Real Fuels

[Konnor]

So... Let's suppose I want to make a hybrid engine running on HTPB and Nitrous Oxide. Something similar to what is used in SpaceShipOne, SpaceShipTwo earlier designs and Dreamchaser. First, I add a resource definition (density of 960kg/m^3 is taken from this pdf, unit cost... well, just a bit higher than stock solid fuel, if I didn't mess that up):

RESOURCE_DEFINITION
{
  name = HTPB
  density = 0.000960
  unitCost = 0.065
  flowMode = STACK_PRIORITY_SEARCH
  transfer = PUMP
  isTweakable = True
  ksparpicon = TriggerTech/KSPAlternateResourcePanel/Icons/SolidFuel.jpg
}

Then the tank (these figures are mostly made up / copypasted):

TANK
{
  name = HTPB
  mass = 0.000016
  utilization = 1
  fillable = True
  amount = 0.0
  maxAmount = 0.0
}

(this goes to RealTankTypes.cfg under Default section, i guess)

Now to the engine: I've picked the Aerojet Kerbodyne Lv-900 since it looks somewhat similar, and added a config entry for HTPB+NitrousOxide (this should probably go to stockalike engine configs thread, but as it is more of a testbed, I'll just list it here):

    CONFIG
    {
      name = HTPB+NitrousOxide
      maxThrust = 50
      heatProduction = 91
      PROPELLANT
      {
        name = HTPB
        ratio = 13.37
        DrawGauge = True
      }
      PROPELLANT
      {
        name = NitrousOxide
        ratio = 86.63
      }
      IspSL = 2.0
      IspV = 0.75
      MODULE
      {
        name = ModuleEngineIgnitor
        ignitionsAvailable = 24
        autoIgnitionTemperature = 800
        ignitorType = Electric
        useUllageSimulation = true
        IGNITOR_RESOURCE
        {
          name = ElectricCharge
          amount = 0.4
        }
      }
    }

(In retrospect, 48-7S could be another candidate, or maybe it would be better to roll an entirely new engine)

Now, the thing I don't yet understand here is the O/F ratio. Is it mass ratio or volume ratio? Anyway, I've set it to about 6.5, as listed here.

As for Isp, the sources I found show values around 250 s for both sea level and vacuum (but with theoretical maximum of 323), so I've picked the multipliers to yield 240 (SL) - 256 (vac) at base tech level.

Well... What did I do wrong with these definitions, if any? Anyone interested in using these configs?

Sources (these are what I've found, anyway; I'm not an expert in rocket propellants, mind you):

http://blog.selparis.com/spaceshipone-2003-04

http://www.thespacerace.com/forum/index.php?topic=2583.0

http://webserver.dmt.upm.es/~isidoro/bk3/c17/Space%20propulsion.pdf

http://web.it.nctu.edu.tw/~chingyao/AASRC-9.pdf

http://rwstelling.com/mediawiki/images/1/14/AIAA_HybridDesign.pdf

Edited March 2, 2015 by Konnor

[Raptor831]

@Konnor: I can't see anything wrong with the CONFIG, it looks good to me.

The ratio in the CONFIG nodes are in volume units (in RF's case, liters). Which requires a bit of math to get from the mass ratios you find in most documentation (i.e. the 6.5 oxidizer:fuel you found), but you have all you need within the resource definition (i.e. density).

Though, you might want to make an entirely new part config for your repurposed engine, since that kind of engine will have wildly different Isp from the Orbital-type that the LV909 is. That way you won't have to use really odd Isp multipliers (which just feel like an oddity waiting to happen for me).

If you want to mess around with it (or just to have a place to verify some math), you can punch in some configs here: http://bit.ly/rfstockalike It's for the Stockalike pack, but it's based on realistic numbers so any RF config should come out alright.

[Konnor]

The ratio in the CONFIG nodes are in volume units (in RF's case, liters).

All right, but it raises some more questions. As far as I know, hybrid rockets usually (but not always) use liquid oxidizers, but apparently Real Fuels defines the density of Nitrous Oxide in a gaseous state. This results in a somewhat ridiculous O/F ratio of 3146.

But this density is actually sea level density; using it as oxidizer would probably involve some compression, I guess...

For liquid state, density is 1230.458 kg/m^3, and volume ratio would be approximately 5, but it seems cryogenic with -88.47 °C boiling point.

Yet storable fuels is almost always mentioned as one of the advantages of hybrid engines.

Is there a point in adding LqdNitrousOxide resource type? For now NitrousOxide seems to be used only as monopropellant (though I can be wrong in that), and it is meant to be in gaseous state for that (I can be wrong with that too). But for the role of oxidizer, liquid form makes more sense.

[Raptor831]

N2O can be pressurized to 48 atm, according to the article here: http://www.astronautix.com/props/n2osolid.htm Which means, you can set a utilization of 48 (I believe) in the tank definition and you'll get accurate stored volume. Not sure off the top of my head if this is already set in any RF tank definitions, so you might check that.

As for the ratios, you'll just have to work with it. There's nothing wrong with having those kinds of ratios, unless there's some weird floating-point errors that I'm unaware of for the smaller side. But as far as the idea goes, it doesn't matter what numbers you put in the ratio, it just uses what you tell it.

[frisch]

I've found the "loss rate" in the tank config file. What are the units? How is loss calculated?

Apologies if this was already discussed, this is a long thread and I couldn't find it with a google search.

thank you

[Starwaster]

I've found the "loss rate" in the tank config file. What are the units? How is loss calculated?

Apologies if this was already discussed, this is a long thread and I couldn't find it with a google search.

thank you

The amount of tank content lost per second is equal to the tank's volume times the loss rate times (tank part's temperature - the tank config's listed temperature)

The temperature in the tank config is a threshold value and is typically that resource's boiling point. Heavily insulated tanks will typically be given a lower loss rate than non-insulated tanks for a given resource.

[frisch]

Thank you for the explanation.

A liquefaction system that would have mass and use electric power, but could prevent Hydrogen loss would be interesting. It would make nuclear thermal much more practical for interplanetary use.

[Starwaster]

Thank you for the explanation.

A liquefaction system that would have mass and use electric power, but could prevent Hydrogen loss would be interesting. It would make nuclear thermal much more practical for interplanetary use.

There's two radiators you can use. (one is a crappy looking white one that's been with us since the beginning and the other is a nice animated one by zzz)

[Kitspace]

Hello!

I have recently encountered with using procedural parts with real fuels on a design with radial simmetry.

Very unfortunately this mixture is extremely buggy.

The parts with simmetry refuse to change settings either independantly or uniformly and behave in an unpredictable manner reacting almost randomly to their own liking and spoiling things or even causing the game errors from having to restart the editor up to a crash. The strange behaviour includes parts changing parameters that were actually set up on a single part before applying the simmetry or inability to change settings just because everything randomly changes again with the next click or something resulting in situations of complete inability to use this design.

I believe it is a known bug for quite some time already that different people experience with different levels of severity?

I do not know for sure which thread this belongs to because the bugs happen with things associated with either mod so I will write a similar post in the other thread. Looks like using both at the same time effectively squares the randomness of the bugs experienced.

Is it fixable and what to do with it?

Help please!

Thank you!

[Kitspace]

Also I have been advised to post this issue here.

Originally it was supposed to go to Realism overhaul.

I think it is also closely related to this mod.

And another thing that makes me think something is wrong.

The masses and volumes of the procedural tanks. I have always had an annoying problem in the current state of the mod with quite insane ranges of thrust to weight ratios between ignition and burnout with small payloads. Also in its current state for me it nearly always looks like the payload mass fractions are too big for the empty stages.

Then I decided to compare the data to real world launchers data as taken from the wikipedia and the other websites they use as sources by replicating the launchers with procedural tanks and the applicable engines.

What came out from all these comparsions is that the procedural tanks are just way too light for their usable volume.

It looks like a fueled launcher weighs more than it is supposed to but the empty one weighs a lot less than it should.

Like really a lot less. Up to three times less than real ones sometimes.

What is even more weird but could be bugs of some sort is that sometimes adding up the mass of the fuels and resources in the tanks comes out more than the full launcher weight as shown by the engineer redux and the stock tool.

Meaning that such a result is physically impossible.

I will test the different combinations more but it seems that something is really wrong.

It should also be noted that the launchers compared in the tests are mostly the early historical ones.

But I think it should not make such an extreme difference despite the tank technology evolution.

Am I doing something wrong or what is going on?

Thank you!

Edited March 10, 2015 by Kitspace

[NathanKell]

Kitspace: I've been offline for over a week, apologies for delay. I believe that is a bug that taniwha's rewrite fixes; I hope to soon switch to his rewrite as the base for RF and thus fix it.

EDIT: As to the second case, can you show some examples, or at least more details? Recall that a PP and engine alone won't make up the full dry mass of a stage, real rocket stages have interstages, retros, avionics, possibly RCS and guidance, etc.

[regex]

I've been out of the loop for awhile, but I'm taking the "point man" position for the CRP integration considering I'm responsible for a lot of the weirder stuff being added, and I should really make sure they're correct. The latest post is here. I'll also be double-checking my earlier work on adding resources and making some changes as necessary.

Does anyone have any other concerns about the base densities of these resources? Do you feel like you'd be a better point person?

Please bring up your concerns. I'll be watching this thread from now on, or feel free to PM me if you'd prefer. Thank you.

I'll be assuming STP unless the resource is cryogenic, in which case I will use a value at or slightly below the boiling point. Some of the "Cold War Nightmare" resources were never adjusted in this manner.

[SymbolicFrank]

After fixing all the high-tech engines I use to use their realistic fuels (hydrogen, for most of them), I found out that that makes most of them useless, as within a 100 days or so all your tanks are empty. So, I tried making all of those tanks cryogenic, but it seems the ones I used already were. Next, I tried finding some way to configure it, but I couldn't find any. I assume it's hard-coded in the dll?

Is there a way I could change that?

NB, assuming we would actually make the kind of space trips as we do in Kerbal, I would expect us to use use cryogenic Hydrogen storage with zero boil-off, as developed by the Nasa for exactly this purpose: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110004377.pdf

[SymbolicFrank]

Ok, found it: loss_rate. It would be nice if I could specify that the tank uses a bit of electricity for the active cooling, though.

[Raptor831]

Ok, found it: loss_rate. It would be nice if I could specify that the tank uses a bit of electricity for the active cooling, though.

The cooling fin and radiator are exactly for this purpose. Try adding some to the tanks you want to keep from boiling off. They'll need electricity as well.

[SymbolicFrank]

The cooling fin and radiator are exactly for this purpose. Try adding some to the tanks you want to keep from boiling off. They'll need electricity as well.

Thanks, I'll try that. I did add some from Interstellar, but perhaps they are the wrong ones or I didn't add enough of them.

[Starwaster]

Thanks, I'll try that. I did add some from Interstellar, but perhaps they are the wrong ones or I didn't add enough of them.

The ones from Interstellar won't work with RF unless they are lowering the actual part temperature and keeping near or below the boiling point of whatever it propellant you're trying to keep from boiling off.

[Kitspace]

Nathan:

So that random tweaks thing is to be fixed soon?

That would be just extremely nice!

If one builds lots of rockets with liquid boosters or symmetric stages that can spoil lots of launches because it is hard to control it and to get used to keep a close eye on something you assume to be set up already.

Regarding the tank masses I just replicated a few rockets with shapes and sizes as close as possible to the original using the real engines and some dummies for the payload and avionics.

For example here are the stats for the Sputnik R-7.

I am writing by memory so the figures are approximate.

I hope everything is correct here but will check it when I get back to my computer.

The weight of the vessel on the pad is roughly two hundred and seventy tonnes while the dry weight of the rocket stack without payload is slightly above twenty five tonnes. The weight of the payload with the mount adapter and the fairing is roughly two hundred kilograms on top of that.

In game I take some cryogenic tanks and put them together with the size and shape of each particular part set as closely as possible to the real thing. At this point the thing weighs somewhere about five tonnes if I actually recall it correctly. Twenty more tonnes to go. Then go the engines all the first stage blocks separation things and the battery with avionics dummy which is a couple of tonnes. At this point the stack weighs about twelve tonnes meaning it should be twice as heavy at this point. Then goes the interesting part. After adding the payload and stuff and finally the fuel the weight is well over three hundred tonnes so it is carrying way more fuel than the real life thing. The summary is that the dry weight is underestimated and the amount of fuel such a stage would be carrying is quite seriously overestimated for its volume and dry weight combination.

I pick that particular case as an example here because it is the most noticeable difference so far.

My interest in this thing started when I realized that I can not pick a good engine for a generic orbit insertion upper stage with a small payload that I was making. They were all either way too weak at the beginning or giving an acceleration of over twenty gees near burnout. When I started to try everything regardless of the timeline the country and even the fuel mixture and still could not get a good engine that started to look like something is wrong. I tried to make an approximation of some known real world design with known parametres but still got the same absolutely crazy values I supposed that something in the construction is lighter than it should be and to check that I can replicate something this time by the numbers.

Thank you!

[Raptor831]

Thanks, I'll try that. I did add some from Interstellar, but perhaps they are the wrong ones or I didn't add enough of them.

To add to Starwaster's comment, there are two parts included in RF which cool down tanks: a cooling fin (white, simple fin) and a radiator (which looks like KSPIs because zzz made both parts). If you add a few of those, you should notice an improvement.

[fallout2077]

I've been trying to find a way to calculate the change in thrust and mass as the Tech Level in increased, but I am stumped. I was hoping if anybody more familiar with the mod can help me with this problem, as it would help in designing craft away from KSP. Thank you, and good night!

[regex]

I've been trying to find a way to calculate the change in thrust and mass as the Tech Level in increased, but I am stumped. I was hoping if anybody more familiar with the mod can help me with this problem, as it would help in designing craft away from KSP. Thank you, and good night!

The second post has a link to a spreadsheet where you will find all of the numbers used in the creation of the engines, fuels, and tanks for this mod.

[fallout2077]

The second post has a link to a spreadsheet where you will find all of the numbers used in the creation of the engines, fuels, and tanks for this mod.

Holy cow, how did I miss that? Thank you very, very much!

[fallout2077]

Well, I've been going through that spreadsheet trying to find the multipliers that seemed applicable, though to no avail. If you or somebody else could point me in the direction within that spreadsheet, it would be great! I'm assuming that it has something to do with the "Wgt Mult" entry in the "Isps" page. Am I wrong in this assumption? I would love to hear all the gory details! Thank you, and good day!

[regex]

Well, I've been going through that spreadsheet trying to find the multipliers that seemed applicable, though to no avail. If you or somebody else could point me in the direction within that spreadsheet, it would be great! I'm assuming that it has something to do with the "Wgt Mult" entry in the "Isps" page. Am I wrong in this assumption? I would love to hear all the gory details! Thank you, and good day!

The "isps" sheet is the one to look at. Engines will have a "type", that being one of L, L+, U, U+, O, A, S, S+, and N, which determines their isp by tech level. You need to know what role the engine was designed for, which the "Engines" sheet should provide along with the tech levels appropriate for that engine.

[fallout2077]

So I was on the right track. What I don't understand is when I try to calculate the mass of, say, the "LV-T30" engine, which is of type "L", I obtain the product .399. In-game, the actual mass at Tech Level 2 is equal to .392. Apparently I am not reading the spreadsheet correctly, or something else is amiss. I am using the values for the "L"-type engines at Tech Level 1 (seeing as how the LV-T30 starts at Tech Level 1), which is a weight multiple of .95. Please elaborate on my errors, as I must discover how to calculate the proper numbers correctly! Once again, thank you very much for your time.