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Engines with more realistic specific impulse


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Hi guys,

I'm trying to make an Apollo-like mission with a Saturn-like rocket in Real Solar System, using SMURFF (no realism overhaul). But even using the 5m and 7,5 SpaceY fuel tanks ang engines, I lack a bit of delta-V to get to Moon with three-staged rocket. I looked up the specs of Satur V and found out that while the first stage engines had ISP of about 260 s (pretty similar to the first stage engines in KSP), second and third stage had ISP of about 420 s, which is much more than all the chemical engines in KSP. And that is huge part of why I can't reach the Moon.

Do you know about a mod that adds engines with more realistic values, but that use the stock Liquid fuel/Oxidizer mix? Or should I ditch SMURFF and start learning the whole Realism Overhaul thing?

Thanks,

Michal.don

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Well, I would prefer some kind of a mod that is not wildly unballanced. I could increase the ISP, but I'm afraid that this might make the ongines over-powered, because of their weight or thrust. Also, I have no idea about the real engines ISP/atmosphere pressure reation. I don't want to make it too easy for me, I just want it to be possible :)

Michal.don

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Comparing the Saturn V's lower and upper stage engines isn't an apples-to-apples comparison -- the J-2 engine used a different fuel (LH2/LOX) than the F-1 (LOX/RP-1).  KSP's engines have performance characteristics typical of LOX/RP-1 engines (or hypergolic engines used around the same time), in the neighborhood of 300-350 sec, while Cryogenic Engines fills the 400-450 sec hydrolox niche (and gets buffed by SMURFF to match real TWRs more closely). Bear in mind that the mass fraction of hydrolox tanks is poorer than LOX/RP-1, because liquid hydrogen is fluffy stuff, so it's not a simple drop-in improvement.  LH2 will also boil off over time, so it will add some time pressure to the trans-lunar injection.

It is possible to get to the Moon without 5 or 7.5m parts and without cryogenic engines (and also without Kerbal Joint Reinforcement, which was probably the hardest part to work around), but it's certainly challenging:

Spoiler

NsWgG5U.png

Actually, the maiden flight of the "Uranus V" probably would have failed if I had used cryogenic engines -- I overdid the orbit insertion burn a little, leaving the upper stage in an elliptical orbit and with less fuel than planned.  There would only be enough fuel for the TLI burn if I placed it at periapsis, so I had to wait three weeks for the Moon to get in the right place.  I'm not sure that I would have had enough LH2 to complete the mission after that time.

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Thanks for you ideas guys, it seems it won't be as easy as I expected, and I'll have to look for some fuel mods. This is the rocket I'm struggling with:

GyVD1iN.png

It looks Saturn-ish enough for me, but some fuel tank clipping was necessary to secure enough fuel to reach the Moon in three stages. I'll try to look for some lightweight solution, but I guess the RO-time is slowly coming for me :)

Michal.don

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For what is worth, I'm not sure you should dread the Realism Overhaul so much. It's not as gamey as stock KSP, but it has it's own niche. If you feel the stock game became too easy, and you wish for additional challenges... well, you start adding mods: Life support; engines with limited ignitions; ullage sim; no overpowered gyros... once you feel comfortable with all that, you jump into the Solar system, and say: "We choose to go to the Moon..." and then do your thing. It's, in my experience, much slower to play through than the stock game, especially if you disable reverting, but, once you actually DO something, it hits you like a rush!

My first docking in Kerbin orbit: "Wow, I did it! Let's build a space station!" 

My first docking in Earth orbit: "Whew, I didn't mess up! Could I perhaps do this again?"

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