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The facts: The actual Service Propulsion System of the Apollo C/SM was a small low-efficiency hypergolic engine with 91 kN thrust and a specific impulse of 319 seconds. The J-2 rocket engine on the Saturn V was a high efficiency rocket engine with 421 seconds Isp, and 486 kN of thrust. The Wolfhound is the in-game SPS analogue. It has an Isp of 412 seconds and a thrust of 375 kN. The Skiff is the in-game J-2 analogue. It has an Isp of 330 seconds and a thrust of 300 kN--barely better than the LV-T30 Reliant. The in-game description describes it as having "high vacuum efficiency" and as being "powerful." I do believe Squad have mixed up the stats for the Wolfhound and the Skiff. But there is a deeper issue which is less obvious. In KSP, the densities of the LiquidFuel we use are comparable to the densities of Kerosene or Hydrazine. These are medium-to-low efficiency fuels and the engines in-game are pretty much balanced around that sort of fuel. Fuel density plays a huge role in rocket design. Bigger tanks are needed to store Hydrogen and Oxygen than Hydrazine and N2O4 in real life. The argument for or against having swappable fuels is not one I want to have right now, but what is important is that 412 or 421 seconds of specific impulse with KSP fuel density is far outside the realm of realism and game balance. 412s Isp with a high thrust to weight ratio results in an engine which may rival the nuclear thermal rocket LV-N "Nerv." Higher thrust, twice the propellant density (LV-Ns can only use LiquidFuel--and actually unless the LV-N is secretly an open cycle gas core NTR running on hydrazine it is a bit overpowered too) At the very least a fix patch needs to swap the characteristics of the Skiff and the Wolfhound, that much is clear. But arguably even then the skiff should be buffed. EDIT: Also the "fixed" Wolfhound's TWR is far too high. The SPS is 91 kN for what should be a larger engine, versus 375 or 300 kN. TLDR: The bug is that the Skiff and the Wolfhound are very obviously swapped with their Masses, Thrusts, and Specific Impulses. The design flaw: The Wolfhound (which should be the Skiff) is super overpowered because it uses low-density high efficiency with high-density fuel--essentially packing more delta-v into a given space. From a realism and a gameplay standpoint both.