Working backwards, the Mercury orbit to Earth can be done with a kolibri, fuel, capsule, and parachutes. TWR is irrelevant here.
To get from mercury to orbit also requires only a Kolibri (assuming this requires 1,000m/s delta V) and a TWR of 0.4. Since these two stages only require a single Kolibri, I had a hunch and tried combining these two stages Mercury-LmO-Earth stage. It weighed less as one stage:
Code:
Stage Mercury-Earth Report:
Bill Of Materials
2 x parachute
1 x capsule
1 x Kolibri engines
20.0 tons tanks
total weight 25.30 tons; deltaV=3167m/s (>3103); thrust=15.0T; TWR(earth)=0.59 (>0.40); burn time=312s (>309)
Working backwards some more, we will need to travel from LEO to LmO (Trans-Mercury Injection). The deltaV for this is 644 + 17 + 59 + 436 + 1364 + 244, and theoretically could also be done with a Kolibri, but geez this is a deltaV of 6800 now and is getting absurd. The tank size required was also prohibitive, so I left the Trans-Mercury Injection as its own stage. Two stages, actually, as it was more efficient.
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Stage TmI 2 Report:
Bill Of Materials
1 x (stage Mercury-Earth 25.30T)
1 x separator-4w
1 x Valiant engines
35.0 tons tanks
total weight 62.70 tons; deltaV=1915m/s (>1844); thrust=40.0T; TWR(earth)=0.64 (>0.01); burn time=220s (>215)
Stage TmI 1 Report:
Bill Of Materials
1 x (stage TmI 2 62.70T)
1 x separator-4w
1 x Valiant engines
80.0 tons tanks
total weight 145.10 tons; deltaV=1881m/s (>1849); thrust=40.0T; TWR(earth)=0.28 (>0.01); burn time=504s (>498)
The choice of Valiant here must have been a tight fit between the lower ISP of a Kolibri and the higher weight of a Frontier. Interesting.
Next up, a standard optimized two stage to LEO with a 145T payload, assuming deltaV for earth is 3,000, TWR 1.2 on the ground, and TWR 1.0 in the air.
Code:
Stage LEO 2 Report:
Bill Of Materials
1 x (stage TmI 1 145.10T)
1 x separator-4w
3 x Frontier engines
135.0 tons tanks
total weight 298.50 tons; deltaV=1485m/s (>1467); thrust=300.0T; TWR(earth)=1.01 (>1.00); burn time=117s (>116)
Stage LEO 1 Report:
Bill Of Materials
1 x separator-4w
1 x (stage LEO 2 298.50T)
8 x Frontier engines
295.0 tons tanks
total weight 641.90 tons; deltaV=1517m/s (>1515); thrust=800.0T; TWR(earth)=1.25 (>1.20); burn time=96s (>96)
Looks like 8 frontiers on the bottom, and three more on top. Okay, let's build it:
Made it to LEO with some extra deltaV in stage 2 (8.4% in the tank). Great, always appreciate a boost to an injection. If I remember right, I used the rest of stage 2 to expand the ellipse a little (but staying in earth SOI), and on the next pass laid on the Valiant.
As luck would have it, I ran out of gas, dropped stage 3, and performed the landing on a Kolibri. Oops, not sure what went wrong there.
Supposed to have 100% in that tank but only reading 72%. Bad piloting? Incorrect deltaV for deorbiting Mercury? Beats me.
Will I make it home? Well, I can always try making a low Mercury orbit to save some gas, and hope for the best! Orbiting Mercury with a periapsis of 2544 (has to be above 2500 to time warp!).
Accelerate in that transfer window into earth's atmosphere...
Had to try that a couple times because the moon got in way the first few tries. And... home, with a little retroburning.
Woo burned all fuel except 3% in the last tank. I fly smol and TIGHT!!!
These were all Hohmann transfers. I suppose a gravity assist could have saved me some fuel. Anybody else taken astronauts Mercury and back in 1.5?