Mechanical Design

The rocket's cabin is composed of three segments, each with a hexagonal cross-section. The widest hexagon is 2 m across at its widest point. The cabin is 2.3 m tall. The cabin bolts to a triangular gantry, to which are bolted three 2.3 m aluminum tube legs. These legs are bolted to concrete pier blocks buried in earth. Each segment of the cabin is made of welded 3.2 cm square steel tubing, painted to avoid rust, and skinned with aluminum riveted to the tubing. The floor of the cabin is expanded steel. One face of the bottom section is a hinged panel forming the main entry hatch. The latch is a metal handle that actuates a tab. It is reached via a “rope” ladder made from 5 mm stainless steel cable with steel tube rungs. Like the legs, the ladder is anchored to buried concrete pier blocks. A steel-framed, cloth-sling “couch” provides seating for two skinny astronauts, and folds up to stow away against the wall. One panel of the tallest segment opens as a window to provide light or cooling; it is secured with an expanded-steel grating. If we didn't protect it, someone would be tempted to try to climb out there. I would, if I were seven. The topmost segment is a hinged hatch, for great 4.6 m high views. It's accessed via a rigid interior ladder that folds and stows. Its footholds stop far enough from the top to discourage small people from climbing out the top.

Planning for assembly

The design calls for creating in-plane quadrilateral surfaces on the metal frame, so that each aluminum panel can be riveted along all of its edges. Square tube makes for easy welding, because straight cuts make ready joints. Each face of the cabin has three tubes in plane, and then borrows its fourth edge from the neighboring face; I welded on a flat strip of steel to provide a fourth planar surface to which I could rivet the skin.

Prototyping in paper

One challenge was figuring out how to cut the correct angles on the ends of the tubes. I'm pretty good at working out the side-length trigonometry for the wire frame, but those compound angles really made me dizzy. I had a bill-of-materials spreadsheet that converted coarse measurements ("bottom segment has radius 24 inches") into lengths and quantites of square tube. I extended it to also tell me what compound angles to cut on the end of each tube.

The math was hard enough that I was still unconvinced that it would work on real metal, so I then built a little python script that simulated the effect of each cut on the miter saw, and emitted a PostScript page that cuts and folds into a paper model.

One tube on each face requires two compound cuts on one end, to provide clearance for the bottom edge of the adjacent face. The math was indeed hard; the paper models showed an error on pretty much every step.