Research note / Cycle 017
Two targets around the clamp
A reviewed paired-target drawing cancels a specified common rotation in software while retaining unequal-arm, differential-rotation and shared-motion failures.
Keep both readings
The Space Elevator Initiative needs a reference that can reach the strip endpoints without confusing their motion with support rotation. The line around the clamp left the second observation path obstructed by the occupied clamp. Reed and Voss now draw two targets on opposite sides of that endpoint line, with a separate sketch of their support paths.
North Quay reviews the drawing on January 23. It requests clearance and rigidity observations after a mock-up exists. The drawing has been reviewed; neither target bracket is fabricated, installed or calibrated. The proposal retains both individual observations, not only their average.
What symmetry removes
The authored model sets true displacement to 8 um and uses nominal offsets +20 and -20 mm. A shared 300 microradian rotation gives readings 14 and 2 um; their average is 8 um. Reversing the shared rotation exchanges those values and leaves the same average.
The adverse cases matter. Using -18 mm for the second arm leaves a 0.3 um residual. Different rotations at the two targets leave 2 um. A shared 4 um target shift survives averaging in full. These are exact synthetic sensitivities, not measurements of the proposed bracket.
A reachable target is only the start
Dover Motion’s offset-probe example supplies a new external connection: the reference axis and the point of interest can report different positions under angular motion. The refreshed uncertainty guide keeps common influences and covariance explicit. Symmetric drawings alone cannot establish shared rotation, rigid supports or calibrated coverage.
NQ-17 remains returned; KIS-61/KB-2 remain at Meridian with no mounting change or new loan. Preserve the 1000 um bidirectional grid, 25 um budget and separate 6 um return allowance. Loading and acceptance remain withheld.
Results at a glance
| Authored paired-target case | Left (um) | Right (um) | Average (um) | Residual from truth (um) |
|---|---|---|---|---|
| symmetric_common_rotation | 14 | 2 | 8 | 0 |
| reverse_common_rotation | 2 | 14 | 8 | 0 |
| unequal_arms | 14 | 13/5 | 83/10 | 3/10 |
| different_rotations | 14 | 6 | 10 | 2 |
| common_target_shift | 18 | 6 | 12 | 4 |
External research and methods
- Evaluation of measurement data — Guide to the expression of uncertainty in measurement · Joint Committee for Guides in Metrology · JCGM 100:2008 (2008). Sections 5.1.3–5.1.4 and 5.2.1–5.2.5.
- Abbé Error · Dover Motion · Motion Control Handbook, Abbé Error section (Undated online handbook; retrieved 2026-10-26). Offset-arm/encoder example and angular-error discussion.