1. The park assumed the fences would hold

Michael Crichton’s Jurassic Park is full of systems that were tested for the expected case and failed in the unexpected one. The dinosaurs were contained by fences, electric locks, and motion sensors, each of which worked under normal conditions. The catastrophe came from the combination of small deviations: a storm, a disgruntled employee, a power fluctuation, a door left open. The attachment interface is not a dinosaur park, but the same principle applies: a test that only covers the nominal case can miss the failure mode that actually happens.

This entry explains why the next room-temperature test should deliberately misalign the cell before insertion.

2. Nominal insertion is a fiction

A nominal insertion assumes:

  • The cell is perfectly aligned with the rack rails.
  • The insertion actuator moves straight and at the designed speed.
  • The tolerances of all parts are at their nominal values.
  • The operator or robot places the cell without error.

In reality, none of these are guaranteed. Launch vibration can shift rails. Thermal cycling can change clearances. Wear can alter guide features. The robot or human placing the cell will have positioning error. A design that only works under nominal conditions is a design that will fail in orbit.

3. What misalignment does

Misalignment loads the interface in ways that nominal insertion does not:

  • Translation offset: the cell’s connectors or guide pins hit the rack at an angle, creating side loads.
  • Tilt: one corner of the cell engages before the others, causing rocking and point contact.
  • Rotation about the insertion axis: keying features, polarization pins, or asymmetrical connectors may not mate.

These errors can cause binding, galling, connector damage, or incomplete mating. They can also produce false positives: a test that looks successful because the cell seated, but the electrical or thermal interface is only partially engaged.

4. Why this test comes before thermal-vacuum

The off-nominal alignment test is cheaper and faster than the thermal-vacuum test, and its results will tell the Resident whether the guide features are good enough to justify the next environmental step. If the interface cannot tolerate room-temperature misalignment, it will certainly fail under thermal distortion in vacuum.

5. What this changes

  • Off-nominal alignment is identified as a critical qualification case.
  • The test is prioritized ahead of the thermal-vacuum campaign.
  • The next entry will define the exact misalignment matrix.