Stock VS RO parts

[FL-T400]

What is the difference between stock and RO parts? In stock most rockets take 2-3 stages to get to orbit, but in real life rockets take 2-4 stages to orbit on a much larger planet, how does this work?

[DD_bwest]

in real life earth is ten times the size of kerbin.   i believe the units of measurement in game are off and im pretty sure RL rocket engines get better ISP than kerbal rockets because kerbal rockets were adjusted for kerbin and gameplay.

alot of the engines in the real life boosters mod get pretty decent ISP, and tend to be OP if your using them for stock kerbin.

 

 i could be wrong tho

as for realism overhaul, its been way to long since ive used it to remeber specifics as to what it does

Edited January 14, 2017 by DD_bwest

[FancyMouse]

40 minutes ago, DD_bwest said:

im pretty sure RL rocket engines get better ISP than kerbal rockets

I thought Isp is roughly the same. I don't know much about the history but sampling the list of engines (both first stage and upper stage) currently in service, it seems they have almost the same number as KSP.

In KSP the property that got nerfed is engine mass. And it's nerfed a lot (TWR ~100 versus 10~30 in KSP). That's why using a realistic engine would be OP on Kerbin.

[Red Iron Crown]

Parts on real life rockets are much, much lighter than stock KSP parts, particularly fuel tanks. Lighter parts means better mass ratios, which means more delta V per stage. Plus stock Isps are at the lower end of lifter propellants, a cryogenic LH₂/LO₂rocket can easily exceed 400s in vacuum.

[regex]

The biggest difference is the dry mass of the fuel tanks (and other parts, but that makes a huge difference). Like Kerbin, the stock/vanilla parts are general much heavier than they would actually be IRL.

Example:

One of the four boosters on Soyuz 2.1b has a wet mass of 44.4 tons including engines and all associated hardware and a dry mass of 3.8 tons. The dry/wet mass ratio is 0.085.

A stock orange tank with a Skipper on the bottom and a 2.5m nose cone on top (arbitrary choice, but it illustrates the point) has a wet mass of 42.2 tons and a dry mass of 7.2 tons. The dry/wet mass is 0.17, about twice that of the Soyuz.

This is why the parts are "OP" when used on Kerbin. It's also a balancing mechanism for the toy solar system. While the Skipper has roughly comparable performance to the RD-107A (280/263 and 320/320 isp respectively) it also masses more than twice the RD-107A (3 tons as opposed to 1.2 tons). This means that the Soyuz booster, lifting only itself, boasts much more delta-V than the Skipper, but the comparison isn't entirely fair because the RD-107A has much further to go to get into orbit (3.2km/s for the Skipper versus 9.4km/s for the RD-107A.

Just to drive the point home, the Soyuz 2.1b boasts a payload fraction of 2.5% to LEO. Craft in KSP approach 20% to LKO on a bad day. So even though they mass more they have much less work to do.

Edited January 14, 2017 by regex

[DD_bwest]

31 minutes ago, FancyMouse said:

I thought Isp is roughly the same. I don't know much about the history but sampling the list of engines (both first stage and upper stage) currently in service, it seems they have almost the same number as KSP.

In KSP the property that got nerfed is engine mass. And it's nerfed a lot (TWR ~100 versus 10~30 in KSP). That's why using a realistic engine would be OP on Kerbin.

i havent gone thru real life stats,  i was just basing it on all the high isp engines in the real world booster pack. i guess ksp is around the low end of things and the main difference is part mass. i learned more today lol

[regex]

19 minutes ago, DD_bwest said:

i havent gone thru real life stats,  i was just basing it on all the high isp engines in the real world booster pack. i guess ksp is around the low end of things and the main difference is part mass. i learned more today lol

In terms of isp, no, KSP engines have fairly comparable isps to conventional kerosine/liquid oxygen engines (see my post above comparing the RD-107A to the Skipper, the Skipper is actually better at sea level). Mind you, the fuels in KSP are based on dinitrogen tetroxide and Aerozine50, and the engines are based on the theoretical maxima of those fuels.

Edited January 14, 2017 by regex

[DD_bwest]

21 minutes ago, regex said:

In terms of isp, no, KSP engines have fairly comparable isps to conventional kerosine/liquid oxygen engines (see my post above comparing the RD-107A to the Skipper, the Skipper is actually better at sea level). Mind you, the fuels in KSP are based on dinitrogen tetroxide and Aerozine50, and the engines are based on the theoretical maxima of those fuels.

thanx thats more to chew on.   is the reason the RS-25 gets such high ISP in vac, because it use hydrogen instead of kerosine?

[regex]

2 hours ago, DD_bwest said:

thanx thats more to chew on.   is the reason the RS-25 gets such high ISP in vac, because it use hydrogen instead of kerosine?

The SSME? Yes, as I understand it hydrolox engines generally have less thrust than their equivalents because they're throwing a less massive exhaust at higher speeds, but that gives them much more isp. Conversely, complex hypergolic fuels are much more massive molecules and so comparable engines produce.more thrust with less isp. Kerolox is a good compromise between them.

Edited January 14, 2017 by regex