KSP/real life thrust?

[ArmchairPhysicist]

Something I’ve been needing to know, are the thrust ratings in KSP the same as the thrust ratings of their inspirational real life analog? I was looking at the stats on SpaceX’s Raptor engine and saw that for a 1.3m (atmos configuration) and a 2.4m (vac config) this mf puts out 1700kn and 1900kn of thrust respectively. On top of that it clocks an isp of 330(SL) and 375(vac). I may be wrong but KSP brain is screaming “holy rockets Batman!”

These ratings are light years ahead of any KSP 2.5 LF/O rocket. 

So I need to know. Are the thrust ratings the same or proportional in KSP to IRL? I feel like we’ve been cheated with the rocket ratings we have compared to the Raptor.

[Shadowmage]

36 minutes ago, ArmchairPhysicist said:

Are the thrust ratings the same or proportional in KSP to IRL?

Yes, and no.  They are all measured in kN, so are using the same measurements as real-world rocket engines.  So they are comparable.

However, the engines in the game are not limited (or compliant with) real-world physics; their thrust-to-size and thrust-to-weight ratios are purely set for game play balance.  Whereas the thrust of a real-world rocket engine depends on chamber pressure, expansion ratios, and thermal factors; the engines in KSP are limited only by the values in the config files.  They are not 'physically modeled' or 'fully simulated' to make sure the stats are consistent with their geometry.

TL:DR; -- stock engines are not balanced for real world considerations.

----

Your best metric for this might be the new engines that came in the Making History DLC.  Squad has made F-1 and J-2 analogues.  However the stats do not match the real-world engines for thrust, TWR, or ISP.  Even if you apply some basic scaling to the stats (to account for the KSP versions of those engines being smaller than the real-world counterparts), the stats still don't line up consistently.

36 minutes ago, ArmchairPhysicist said:

I feel like we’ve been cheated with the rocket ratings we have compared to the Raptor

Yep -- the engines in stock KSP have far worse performance than would seem prudent given the differences.

Edit:  If you want 'real world' rocket engine stats -- look into RO + RSS.

Edited April 10, 2018 by Shadowmage

[ArmchairPhysicist]

4 minutes ago, Shadowmage said:

 

Edit:  If you want 'real world' rocket engine stats -- look into RO + RSS.

I’m assuming RO is realism overhaul. What is rss may I ask?

[Shadowmage]

29 minutes ago, ArmchairPhysicist said:

I’m assuming RO is realism overhaul. What is rss may I ask?

RSS = Real Solar System.  Reworks the toy KSP system to use real world planets, distances, masses, atmospheres, etc (in so much as is

Combine the two, and you get a very much 'realism' based re-imagining of KSP.

[KerikBalm]

KSP rocket engines are nerfed, because dV requirements to get anywhere are about 1/3 what they are in real life...

That said, KSP jet engines actually are pretty powerful compared to real life. Also while the lift/1st stage engines may be rather weak, the vacuum upper stage engines are pretty good. The Apollo Command+Service module's propulsion system only had 91kN of thrust, which is quite a bit less than what the poodle gives.

The LEM descent stage only had 45 kN of thrust, so less than a terrier. Its ascent stage was a meager 16kN... so like a spark.

The new wolfhound's stats are frankly too good and too close to a real lH2 fueled engine to be balanced for KSP.

Anyway, you don't need a first stage in KSP to have 31,500 kN of thrust, because rockets don't need to be so massive to generate the required dV.

If you wanted realistic TWRs for KSP rocket engines, then their real Isp should be divided by something like sqrt(10.5) because thats the reduction in dV requirements as a result of the toy size solar system of KSP.

Enjoy your LV-N that gets ~250 Isp

[OhioBob]

The ISP of liquid fueled engines in KSP are reasonably close to real life.  Not perfect but in the ballpark.  Solid fueled boosters are well below real life ISP (about 80%).

If we compare the thrusts of the "Making History" engines to the real life engines on which they are based, the KSP engines are about 20-30% as powerful.  The exception is the Wolfhound.  Of course this make sense because everything in KSP is scaled down.  The generally excepted rule in KSP is that dimensionally rocket parts are at about a 0.625 scale compared to real life parts (1:1.6).  Since volume/mass scales by the cube, we have 0.625^3 = 0.244.  And since thrust should scale with mass, this means thrusts should be about 24.4% of real life, which agrees nicely with the MH parts.

[Gargamel]

On 4/10/2018 at 5:50 PM, ArmchairPhysicist said:

I’m assuming RO is realism overhaul. What is rss may I ask?

The forum software has this nifty feature that underlines common abbreviations used in KSP: VAB, SPH, RO, RSS, to name a few.   If you mouse over them, it will show what they mean.   The more you know :).

[Lisias]

9 minutes ago, Gargamel said:

The forum software has this nifty feature that underlines common abbreviations used in KSP: VAB, SPH, RO, RSS, to name a few.   If you mouse over them, it will show what they mean.   The more you know :).

*HOVER IT* ? All I had to do is hover the mouse pointer on it? Damn, I was trying to click (left and right) on it! =D

I'm wasting too much time on touch-screens, as it appears...