Stratospheric Capsule Pressurised CFRP Shell

Beyond the pressurised shell itself, the near-space capsule programme covered three further engineering strands: a parametric CAD and FEM structural validation of the capsule's toroidal shell architecture, a physics-based splashdown impact study comparing capsule geometries for safe water recovery, and an ergonomic layout defining how four passengers are seated within the pressurised volume.

Each strand fed directly into vehicle-level design decisions — from which shell geometry tolerates a given landing speed, to where structural elements can safely pass through the passenger compartment without compromising seating and reach envelopes.

The four-passenger cabin layout arranges seats radially around the capsule's central structural cylinder, with occupants reclined and their limbs positioned within reach of the surrounding structural elements. This radial grouping keeps all four passengers close to the vehicle's central axis, making efficient use of the pressurised cross-section while preserving clear load paths for the structure passing through the middle of the cabin.

The capsule's structural shell was rebuilt as a fully parametric CAD model — 38 parts in total, including 26 shell panels and 22 joggle tabs — driven entirely from eight master boundary points and six meridional profile curves rather than fixed geometry, with a chiral joggle overlap system (50 mm overlap, self-energising under internal pressure) tying panel seams together. FEM validation under 1 atmosphere internal pressure confirmed that every structural shell panel — outer, roof, floor, transition, and cylinder junction — met a safety factor of 3.0 or better against the shell material's yield strength, with several zones (outer panels, roof, floor) clearing safety factors above 5. The one exception, a window boss reinforcement, returned a lower FEM safety factor than its hand-calculation had predicted; the review traced this to a non-conservative stress-concentration assumption in the original hand-calc and flagged the boss for redesign before the next iteration — one of five document inconsistencies identified and resolved or escalated during the structural review.

Splashdown safety was assessed through a physics-based water-impact model combining Wagner theory for wetted-width evolution, Von Karman slamming-force theory, added-mass effects from potential flow, and buoyancy and drag, integrated numerically to capture the full deceleration profile during water entry. The analysis showed that peak deceleration scales close to the square of impact velocity and inversely with capsule mass, consistent with theoretical slamming-force behaviour. Comparing capsule geometries, a toroidal shell needed to keep splashdown velocity below roughly 3 m/s to stay within safe crew deceleration limits, against roughly 7 m/s for an equivalent spherical capsule — a direct input to parachute system sizing and recovery planning.