The residential level sits under 30 m of rock; the main shafts continue to the
−3000 m deep levels, where the dark-matter experiment lives. Four analytic accounts shaped
the elevator — and the most interesting limit is not the motor.
Rope, 1/g. Hoist rope self-weight scales with gravity, so a 3000 m Martian
shaft loads its rope like an 1140 m terrestrial one. On Earth this depth means staged hoists
and transfer stations; on Mars a single friction-drive belt runs pit-to-portal, margin 2.4×.
Ears, 52 Pa/s. The shaft is pressurized, and 3000 m of gas column adds
~13 kPa of self-weight between portal and pit bottom. At the rated 12 m/s the pressure ramp
is 52 Pa/s — comfortably inside the ~300 Pa/s ear-comfort envelope. The cab could go faster;
your ears could not.
Power, 47 kW. Counterweighted, the drive only fights the 900 kg payload
imbalance: 47 kW peak at low gravity, and each descent regenerates ~7 kWh back into the
storage yard. Leakage, 7×10⁻⁷ sr. A straight shaft is a skylight for cosmic
rays — but depth is its own collimator: the pit subtends a solid angle that makes the direct
beam negligible, and a borated cab-roof plug seals the docking gap.
Below, the foyer is the interchange: a 20 × 12 m vaulted vehicle airlock hall (6 m³ personnel
cycle: 0.2 kWh, 3 minutes, 90% gas recovery) with the elevator doors on its right wall — and,
on its left, a viewport. Behind that window a 2500-triangle diorama fakes the whole cavern city:
tower silhouettes, lit-window grids, street lamps, a skylight band. The cheapest square meters
in the district buy its most important sentence: there is a city down here.
Two more doors open off that same left wall. At z = −13 is
hab-rec-01, the recreation hall — the one room where low gravity is the
entertainment rather than the constraint. The half court carries two rims: the regulation
3.05 m in yellow, and a Mars-rules 4.66 m in red, because
jump height and hang time both scale ×2.63 and on the yellow rim everyone
dunks and nobody learns anything. Beside it an 8 × 6 m wall is climbed ropeless:
at 0.38 g the effective load is 38% of body weight and a fall arrives with 38% of the energy.
There is billiards, where the cushions behave exactly as on Earth — collisions are governed
by mass, not weight — while the roll runs 2.6× further, so every player
relearns position play; a 15-seat cinema whose quiet is structural, the surrounding basalt
attenuating >60 dB above 100 Hz; a bar where the head on a poured beer
outlives the conversation; and four arcade cabinets, one of them running this city's own MB-1
bigram chip.
Five meters further along, at z = −18, sci-lab-01: six
instruments — GC-MS, ICP-OES, XRD, Raman, SEM and a water line — sharing one platform,
one queue board and one standards cabinet. Each is a small argument about which planet you are
on. The GC-MS carries no helium, because there is none to import: its carrier is electrolytic
hydrogen, 3.9 g/sol, 0.014% of the ISRU line. The ICP is the one instrument
that is cheaper here — it burns 6.4 kg of argon a sol, and Martian air is
2.1× richer in argon than Earth's, so the gas comes off a cold box that
already exists. The XRD runs a cobalt anode for the same reason MSL's CheMin did: cobalt's
Kα sits below the iron absorption edge, where a copper tube would set an iron-rich planet
fluorescing. And every vacuum system in the room skips its backing pump — 600 Pa of
ambient Mars is what a two-stage rotary vane delivers on Earth — a stage the planet
provides for free, saving 19.7 kWh a sol.
The two rooms are neighbours, and that is a problem with a number attached. An 80 kg player
landing from a 1.32 m jump puts 4.2 kN into the floor; the SEM next door wants
a VC-D floor, 6.25 µm/s. Twenty-five meters of basalt between them turns that landing into
0.054 µm/s — one hundred and sixteenth of the spec. A hand envelope
had put a continuous slab at ~7 µm/s, uncomfortably marginal, and the FEM overturned it at
1.6. The basketball is not the problem it sounds like.
