Sweet spot for Stock SSTO rockets

[Ittiz]

I found many rocket engines seem to have an SSTO sweet spot in the engine to fuel ratio. That is how many tanks you need per rocket to get your ship into orbit. I'm not talking about space planes here, just pure rockets. I checked it out for each engine and made a list:

Main Sail: 4 & 64s per engine

Skipper: 1 & 2/3rds 64s per engine

LVT-30: 1 & 1/11ths 32s per engine

LVT-45: 1 32 per engine

Aerospike: 1 & 3/4ths 16s per engine

LV-909: 1 800 per engine

48-72: 1 & 1/2 200s per engine

The Poodle, 24-77, LV-1, LV-1R, 55-R and LV-N are all no good due to their poor ISP at ground level. That doesn't mean they're no good at all, just not good to be used alone for SSTO from Kerbin. For instance I have found ways using a combination of jet engines and LV-Ns to do SSTO. Also the LV-N is one of the best engines in low gravity fields. It needs the least fuel for a given delta V of any rocket engine in a vacuum. None of the solid boosters cut the mustard for SSTO. All of them have too much thrust to fuel.

[UmbralRaptor]

Those numbers are... high. They would tend to result in 0 payload (aside from unspent fuel) rockets that would have annoying large gravity losses.

As such, I would suggest:

[table=width: 500, class: grid]

[tr]

[td]Engine[/td]

[td]Propellant (Fuel+Oxidizer)[/td]

[td]Payload[/td]

[/tr]

[tr]

[td]LV-T30[/td]

[td]2,400 L (3x T800 or x16 + x8)[/td]

[td]1.6 tonnes[/td]

[/tr]

[tr]

[td]Skipper[/td]

[td]8,000 L (1.25 orange)[/td]

[td]4.6 tonnes[/td]

[/tr]

[tr]

[td]Mainsail[/td]

[td]16,000 L (2.5 orange)[/td]

[td]9.5 tonnes[/td]

[/tr]

[/table]

Pure rocket SSTOs seem to offer the highest payloads (and highest payload fractions!) at lowish TWRs. You can get rather more at 1.4 than at 1.8, let alone 2.2. That said, the designs in the table aren't the simplest possible. (Adequate payloads are possible with Skipper + orange tank, or LV-T30 + x16)

edit: On a related note, the Poodle and LV-N are lacking more in TWR for this than Isp. >_>