A stowed solar sail is folded origami-tight around a central hub. Four telescoping booms — thin composite tubes coiled inside canisters — pay out radially and drag the membrane's corners open as they extend. Because the four corners are joined by one continuous sheet of film, the tension in that film only stays even if all four booms extend at very nearly the same rate at every instant.
If one boom runs ahead or lags behind, the fabric between it and its slower neighbors has nowhere to go — it bows, twists and wrinkles instead of lying flat. Push that mismatch far enough and the film exceeds its tear strength at a fold line: the sail snags or rips, and the mission's propulsion area is permanently compromised before any trajectory work can even begin.
- Boom synchronization — how tightly the four boom-extension motors are matched. Real hardware failures (including early NASA sail-deployment attempts) trace back to exactly this: a jammed reel or a motor running off-spec relative to its neighbors.
- Membrane tension symmetry — derived from the spread between the four boom extensions; 100% means every boom is at the same length, so tension pulls evenly in all directions.
- Wrinkle severity — visualized directly on the sail mesh as an out-of-plane ripple whose amplitude grows with the tension mismatch.
- Cross a desync threshold while under load and the sail transitions straight to a snag/tear failure — deployment does not gracefully degrade past a point, it fails.