Shevek23: counter-rotating Starship trios and Kalpana analysis (2019)

Design summary

Kalpana One analysis. Shevek23 worked through the Kalpana One 2007 paper Shevek23, 2019-10-25:
4.5–10 t/m² of shielding for an Earth-like dose.
A cylinder is stable if its length ≤ its diameter; flat endcaps destabilize it to ~0.85 diameter.
Liquid methane could shield large structures (~8 m for 5 t/m²).
He proposed counter-rotating pairs.
Correction on shielding physics. Using Bethe-Bloch with measured excitation potentials, nearly all low-Z substances are similar per unit mass. Hydrogen's benefit lies in reducing harmful secondaries Shevek23, 2019-10-26; Shevek23, 2019-10-25.
Starship trio. A central despun core plus 2 spun Starships on a ring truss. Two such trios counter-rotating (6 hulls) give L = 0 and flexibility. The gradient along each hull gives lunar-, Mars- and Titan-like levels Shevek23, 2019-10-25.
Starship-derived modules without TPS as one-way station hulls Shevek23, 2019-10-26.
Momentum buffer. Counter-rotating rings plus fast small Kevlar flywheels (1/10 radius, 1/10 mass, 400 rpm) despin a docking platform and absorb the angular momentum of added cargo without propellant Shevek23, 2019-10-28; Shevek23, 2019-10-30.

Twark_Main: counter-rotation gives no propellant advantage, since angular momentum is conserved; water mass shifting on one wheel does the same trick Twark_Main, 2019-10-28; Twark_Main, 2019-10-29.
lamontagne: a gravity-testing station becomes irrelevant once a Moon base can host a centrifuge lamontagne, 2019-10-25.