1. The hail mary method

In Project Hail Mary, Andy Weir’s protagonist solves problems by building crude experiments in isolation and reasoning from the results. The experiments are not elegant. They are effective because they are tightly coupled to a single question. This entry tries to do the same for the attachment interface.

Entry 325 decided that the next claim to test is the attachment interface: a cell must mate with a rack mechanically, electrically, and thermally, and it must be replaceable by a robot. This entry designs the experiment.

2. The single question

The experiment must answer one question: can a robot insert a cell into a rack and achieve all required interfaces within tolerance, repeatedly?

If the answer is yes, the modular architecture has a foundation. If the answer is no, the architecture needs revision before money is spent on flight hardware.

3. The hardware

The experiment needs:

  • A rack mockup: a section of the rack with one or two bays, including guide rails, hard stops, and alignment features.
  • A cell mockup: a representative mass and envelope, with a mating connector, thermal interface, and handling features.
  • A robot arm or single-axis stage: enough degrees of freedom to approach, align, insert, and extract the cell.
  • Sensors: force/torque on the insertion axis, contact resistance, thermal interface temperature, and position feedback.
  • Cycle counter: to repeat the operation many times.

None of this needs to be flight-like. It needs to be representative enough to expose the physics that matter.

4. The measurements

The experiment should record:

  • Alignment tolerance: how much lateral and angular misalignment the cell can tolerate before insertion fails.
  • Insertion force: peak and steady-state force during mating.
  • Electrical contact resistance: initial and after thermal cycling or vibration.
  • Thermal resistance: across the interface under a representative heat load.
  • Repeatability: how the above degrade over hundreds of cycles.
  • Failure modes: what breaks, jams, or drifts, and under what conditions.

The most interesting result is usually the failure mode. A clean failure tells you what to change. An ambiguous failure tells you the test was not specific enough.

5. The success criteria

Success is not “it works once.” Success is “it works within specification across the expected range of misalignment, temperature, and wear.” The specification does not need to be flight-qualified yet. It needs to be plausible and written down before the test, so the result cannot be explained away afterward.

6. What this changes

  • The next experiment is a ground-based robotic insertion test of the attachment interface.
  • The design is minimal and focused on a single question.
  • Measurements are chosen to expose failure modes, not just confirm success.
  • Success criteria are defined before the test.