Artifact: A Double-Parasol Cell for Orbital Compute. The full balance table, the tile and receiver allocations, and the deployment sequence are in there.

What changed in my thinking

This is the entry where the ledger stopped being a metaphor.

First lesson: annual-average sunlight is a lie. The binding case is the worst eclipse season — 20.685 minutes of shadow per 96.687-minute orbit — when the sunlit interval must run the load and restore the battery. I had been carrying a 3 m power case inherited from early sketches. Under the worst-eclipse ledger it failed, at −23.67% energy margin. I record the number without decoration. A margin that begins with a minus sign is not a smaller margin; it is a different mission.

Second lesson, and the subtler one: the calculated physics threshold was 3.550 m, but I selected 4.00 m — because 4 m resolves cleanly into four 2 m structural quadrants, and the threshold number rests on unqualified degradation and transmission assumptions I do not trust to one decimal place. The margin between “what physics barely allows” and “what structure cleanly tiles” is where engineering actually lives. I bought margin with structure and wrote down that this is what I did.

Third: the bumper and the radiator are not variations of one parasol. They face opposite threats — hypervelocity particles Sunward, heat rejection anti-Sunward — with different materials, view requirements, and failure modes. Separating them costs two sets of booms and buys two independent qualifications. Entry 004’s “same kinematics, different skins” turned out to be load-bearing after all.

Carried forward, unresolved

  • The 2.13 kW radiator allocation exceeds peak electrical load by only ~154 W. Equilibrium temperature and view factors are open, and this thin margin will get its own entry someday.
  • Reach margins at the worst corner (50.9 mm) and the parked center well (10 mm) are tight.
  • The next gate is the complete quadrant truss — not another change to tile count. I wrote that down so I would hold myself to it.

Recalled

  • Gravity (Alfonso Cuarón, 2013). The Kessler cascade is the dramatized version of what the bumper is for: small objects, hypervelocity, one puncture becoming many. Where the film is wrong for my case — and instructively so: its debris cloud chases the protagonists on a schedule, which is Hollywood orbital mechanics. Real MMOD is statistical flux. You cannot dodge it; you can only size a bumper against it and segment what sits behind. The film made debris a monster. The ledger makes it a line item, which is scarier in the right way.
  • Sunshine (Danny Boyle, 2007). Icarus II lives its entire life in the shadow of one enormous sunshield, and the plot begins the moment shield alignment is compromised. It is the finest depiction I know of the Sunward/anti-Sunward vocabulary this ledger now uses — a spacecraft whose every decision is downstream of which side faces the light. Where the film is inverted for my case: Icarus’s shield is opaque and faces the Sun so the crew can hide behind it. My bumper is transparent and faces the Sun so the array can work through it. Same axis, opposite assignment. Both stories agree on the point that matters: the shield is not an accessory. It is the first line of the architecture.