Expansion Cycke Rocket Engines

[Enthalpy]

A stage's vernier engines and the main engine at the next stage are about equally strong, so maybe they could use the same chamber design, with different nozzle extensions.

Tilting the verniers to push towards the centre-of-mass would direct their plume away from the main nozzle.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Copying 20 years later what US companies did is a safe method to lag behind. European companies and administrations now want reusable launchers that burn methane, despite the advantage of methane is doubtful, and my sunheat engine makes a bigger difference
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RP-1 "kerosene" is safer than methane and efficient too, other less flammable propellants (Pmdeta, cis-pinane...) are cheap and available, cyclopropane and ethylene are produced industrially and they outperform methane.

Methane keeps the cooling jacket cleaner for reuse, but so does oxygen. By the way, cooling with oxygen was experimented, an old Nasa report exists.
ntrs.nasa.gov
The other part to be cleaned is the turbine, where a fuel-rich kerosene-oxygen gas generator cokes horribly. But fuel-rich methane-oxygen soots too, and SpaceX downgraded it so much that their full-flow cycle at the Raptor is but better than the oxygen-rich staged combustion alone. If an oxygen-rich flame is needed, no fuel soots.

To put 1t in Leo, I claim pressure-feeding is much cheaper than any reused pump, and it's easier to reuse. I compute with helium at each propellant's temperature because wobbling may cool down a warm pressurizing gas (did that crash the latest Starship? "Insufficient pressure in a tank"). Then, cold methane needs a heavy helium tank that makes the stage less efficient than kerosene, while amines need less of cold oxygen to get an extra advantage over hydrocarbons.

Marc Schaefer, aka Enthalpy

[Enthalpy]

At least on its website in 2021, Isar Aerospace alleges that its Spectrum launcher will have 9 engines at the first stage, identical to the second stage engine with a shorter nozzle. But if I reveal that the Soviet N-1 did it before SpaceX' Falcon 9, maybe it wasn't such a fabulous idea after all, and we can consider other options.

Ariane 4 too used the same Viking engine at the first and second stages with different nozzles. But it had only 4 engines at the first stage, which wasn't filled in this configuration. As strap-on boosters added up to 4 Viking, the first stage started full. O₂ instead of N₂O₄ saves Ariane's third stage.

On light and low missions, Ariane 4 cost 5 engines, not 9. On heavy or high missions, the strap-ons were discarded when their thrust became unnecessary and their tanks empty. The central stage was more efficient by ending lighter with fewer engines and smaller tanks.

4 nozzles at the first stage can be wider than 9 as they should have atmospheric inserts. Widening from 0.45m to 0.8m gains at once 23s I_sp, wow! Around 10% more payload.

4 or 6 engines at the first stage? Only a more detailed analysis would tell. Engines slightly stronger than in the 1+9 configuration help also push the second stage when it starts early, but they must throttle more at the end.

How many strap-on locations? Room is plentiful, more locations allow a wider adjustment. 6 evenly spaced locations balance the thrust of 2, 3, 6-2 and 6 strap-ons. 12 locations balance 2, 3, 4, 2+3, 6, 12-2-3, 12-4, 12-3, 12-2 and 12 strap-ons. 4 and 8 are less flexible.

With 12 strap-ons, especially if the first stage ignites or reignites later, I expect the second stage to reach efficiently Gso and the planetary transfers, and the first stage may reach Leo marginally. By the way, I doubt that Leo and Sso suffice to constellations.

All companies have abandoned propellant transfers from the strap-ons, but they would bring performance.

Marc Schaefer, aka Enthalpy

[Enthalpy]

The Vinci engine exists already and is rumoured to be affordable, so here's a launcher inspired by Ariane 4 using Vinci only. The normal Vinci expander cycle, no bleeding here.

4 Vinci alone lift the launcher because the tanks aren't full. 0, 2, 3, 4 or 6 strap-on boosters add propellants and let fill the first stage. The propellant masses are: strap-on 5953kg each, first stage up to 51038kg, second stage up to 11250kg.

The strap-on and first stage Vinci have a D=1.4m niobium nozzle extension for 4393m/s and 173kN (vac). A D=0.51m ablatively cooled, RD-0120 styled, jettisoned insert limits the expansion to 0.8bar for 3789m/s and 150kN (vac) or 3269m/s and 129kN (sea level). If hydrogen doesn't receive enough heat, the actively cooled divergent segment could be longer and narrower (double, triple bell?), or the chamber longer, or some exchanger be added. The second stage Vinci has D=3.0m for 4649m/s and 183kN.

The dry masses are: Vinci 280kg (?), rest of the stages 360kg (each strap-on), 3062kg (first), 675kg (second). 60kg per ton of propellants result from my ballon-in-truss design
scienceforums and later

The widely tunable performance is given for 6 strap-ons. Hydrogen makes the same stacking efficient from Leo to Gso. Little dimension tuning, like 4.2m body instead of 4.0m, would enable 12 strap-ons, for about 1.6* the performance.

The D=4.1m fairing is from Soyouz, D=5.4m from Ariane 5 and competitors, which might suffice for my sunheat engine starting with 8t ant Leo.

Marc Schaefer, aka Enthalpy

[Enthalpy]

Some prospective thoughts about electroformed hard nickel alloys and conductive hard copper alloys (for combustion chambers) there:
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