RSS - RO Fuel Types and Some questions

[Hancer]

Dear All, I have a question:

I am using RSS and RO incl all the required mods. I am quite sufficient with the info and know-how and able to realise GEO orbits and such with these mods. But I am very poor at chemistry and fuel types and get sometimes confused. Could you please answer me these questions:

1-Procedural fuel tanks: There is a tank type selection such as fuselage, default, baloon..etc. Could you please tell me which tanks are for which fuel? Because when comparing delta v, default tank seems to get 200-300 m/s more with a default tank than cyro..etc and I see no difference in operating. However, sometimes by J2 engines wont ignite in space, so I am sure its about selecting a proper tank for the fuels. So please guide me which tanks I should be using for vacuum, fuel type and surface.

2-I am using Engine Ignitors: I still couldnt figure out how to take extra electrical ignitions with the tool box. It doesnt add additional electrical ignitons no matter where I place it.

3- "Need settling down": I am using ullage to get some g before ignitions but sometimes they work sometimes they dont. I think related with question 1.

4-Which type of fuels should I be using for most efficient 1st and 2nd stage with TWR around 1.25-13.0 at take off (to get around 4000-5000 delta v). Generally kerosene and LOX at main stage and lox and lh2 at second stage?

5-No matter what I try, I cannot get pass 16k delta v at RSS and RO with a payload of 12tonnes. So I think its impossible to have a manned flight to mars in rss/ro with saturn v type rockets.

Sorry for all these noobish questions about fuels.

[Streetwind]

This thread would be better suited to addon affairs, really, as it's extremely specific to the mods installed...

[Hodo]

Dear All, I have a question:

I am using RSS and RO incl all the required mods. I am quite sufficient with the info and know-how and able to realise GEO orbits and such with these mods. But I am very poor at chemistry and fuel types and get sometimes confused. Could you please answer me these questions:

1-Procedural fuel tanks: There is a tank type selection such as fuselage, default, baloon..etc. Could you please tell me which tanks are for which fuel? Because when comparing delta v, default tank seems to get 200-300 m/s more with a default tank than cyro..etc and I see no difference in operating. However, sometimes by J2 engines wont ignite in space, so I am sure its about selecting a proper tank for the fuels. So please guide me which tanks I should be using for vacuum, fuel type and surface.

2-I am using Engine Ignitors: I still couldnt figure out how to take extra electrical ignitions with the tool box. It doesnt add additional electrical ignitons no matter where I place it.

3- "Need settling down": I am using ullage to get some g before ignitions but sometimes they work sometimes they dont. I think related with question 1.

4-Which type of fuels should I be using for most efficient 1st and 2nd stage with TWR around 1.25-13.0 at take off (to get around 4000-5000 delta v). Generally kerosene and LOX at main stage and lox and lh2 at second stage?

5-No matter what I try, I cannot get pass 16k delta v at RSS and RO with a payload of 12tonnes. So I think its impossible to have a manned flight to mars in rss/ro with saturn v type rockets.

Sorry for all these noobish questions about fuels.

1- Cryo tanks are great for fuels that require a low temp before they begin to boil off. LH2 is one that comes to mind. If it isn't kept below a certain temp it will begin to boil off. In RF this means that you will begin to lose fuel out of that tank if it goes above that temp.

For non-cryogenic fuels you can use any other fuel tank.

2-You have to EVA to install them into the engine after you have used the ignition on that engine.

3-Some engines require a pressurized system in order to work. If you have a fuel tank that is not pressurized and an engine that requires a pressurized system you will not be able to start that engine no matter the g forces.

4-LH2+LOx is a good basic first stage fuel, so is Kerosene and LOx. It depends on what you are trying to launch.

5- Not impossible, just exteremly difficult to do. You most likely will not be able to do it in one launch. The real mission to Mars was planned to be launched in stages and docked together in orbit, refueled then launched to Mars. With a refueling tank already in orbit around Mars and a resupply module there sent remotely months prior to the manned mission.

All reasonable questions by the way.

[Starman4308]

4-LH2+LOx is a good basic first stage fuel, so is Kerosene and LOx. It depends on what you are trying to launch.

I'm not so certain on LH2/LOX first stages. The low density of LH2 leads to physically enormous fuel tanks, which poses structural/aerodynamic difficulties. LH2/LOX sea-level Isp and TWR also tends to be very poor to mediocre; it might partly be a function of the engines I'm looking at for reference (Rocketdyne J-2, Space Shuttle Main Engines), but LH2/LOX mostly shines once you get into mid-upper atmosphere.

Plus, for first stages, efficiency does not really matter. If two designs will get an identical payload to the same place, and one costs 5% less, it doesn't matter if it weighs 10x more; you haven't staged yet, so the mass isn't propagating down. Now, that would make a terrible second stage, because your first stage would have to launch 10x the payload, but for first stages, the primary considerations are TWR, cost, aerodynamics, recoverability, and stability.

Edited November 14, 2014 by Starman4308

[Hodo]

I'm not so certain on LH2/LOX first stages. The low density of LH2 leads to physically enormous fuel tanks, which poses structural/aerodynamic difficulties. LH2/LOX sea-level Isp and TWR also tends to be very poor to mediocre; it might partly be a function of the engines I'm looking at for reference (Rocketdyne J-2, Space Shuttle Main Engines), but LH2/LOX mostly shines once you get into mid-upper atmosphere.

Plus, for first stages, efficiency does not really matter. If two designs will get an identical payload to the same place, and one costs 5% less, it doesn't matter if it weighs 10x more; you haven't staged yet, so the mass isn't propagating down. Now, that would make a terrible second stage, because your first stage would have to launch 10x the payload, but for first stages, the primary considerations are TWR, cost, aerodynamics, recoverability, and stability.

This is why I said, it depends on what you are trying to launch. If it is something smallish and light you can get away with LH2+LOx.

[NathanKell]

Any kerolox engine designer would kill for a sea level specific impulse of 363 seconds (SSME). That's higher than the vacuum Isp of kerolox upper stage engines! By contrast the J-2 is an upper stage engine, so of course it's going to be optimized for vacuum and the upper atmosphere.

The real problem is that since no lower stage uses the first stage as payload, the returns on making it lighter are next to nonexistent (especially if by doing so you make it cost more). By contrast, if you make an upper stage twice as heavy it requires the equivalent of two of the old rockets under it. The N1, despite having a far, far more efficient engine in its first stage, and massing about what Saturn V did, had a LEO payload capacity of only 3/4 Saturn V. But the real kicker is it had a TLI (i.e. puts it on course for the moon) payload of half what Saturn V did. That's due to the efficiency difference between kerolox and hydrolox for a third stage.

BTW Hancer I answered your questions in the RF thread if you didn't see it yet.