1. The flight where power became the problem

Jim Lovell’s Apollo 13 returns because power is the resource that quietly enables everything else. When it is abundant, no one thinks about it. When it is scarce, every decision becomes a trade. The desktop’s cells will face the same reality every eclipse and every degraded-battery day. The power distribution system must know how to share, shed, and survive.

This entry explains why the multi-cell power bus must be tested on the ground.

2. What a multi-cell power bus does

The desktop is not a single satellite with one battery and one solar array. It is a federation of cells, each with its own generation, storage, and load. The power bus connects them so that:

  • A cell in sunlight can power a cell in shadow.
  • A cell with excess battery capacity can support a cell with a degraded battery.
  • The aggregate load can be shared across multiple power paths.
  • A faulty cell can be isolated before it drags down the bus.

3. What can go wrong

A multi-cell bus has failure modes that a single-cell bus does not:

  • Back-feeding: a failed cell draws current from the bus instead of supplying it.
  • Bus collapse: one cell shorting or overloading can pull the whole bus below minimum voltage.
  • Unbalanced charging: some batteries get overcharged while others stay undercharged.
  • Slow fault detection: if isolation is not fast enough, a fault propagates before it is contained.
  • Ground loop or control conflict: multiple cells try to regulate the same bus voltage.

4. Why this test follows vibration and shock

The vibration and shock test proved the rack and cells survive launch mechanically. The power distribution test asks whether the electrical connections and control logic survive operation. A connector that looked fine after vibration may fail under current. A software state machine that looked correct in simulation may deadlock when a real cell drops offline.

5. What this changes

  • Power distribution testing is identified as the next qualification step for the electrical system.
  • The test must cover normal operation, fault injection, and recovery.
  • The next entry will define the exact power distribution test matrix.