Add GigaBIT M1 frame stiffness characterization project

- 3 studies: sensitivity (Method D), stiffness sweep (Method B), robustness
- Atomizer specs with run matrices, Zernike annular OPD extractor
- War-room validated hybrid B+D method

projects/gigabit-m1-frame-stiffness/README.md

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+# GigaBIT M1 — Reference Frame Stiffness Characterization
+
+**Client:** StarSpec
+**Project:** P04-GigaBIT-M1
+**Created:** 2026-03-04
+**Status:** Active — Model Setup
+
+---
+
+## Objective
+
+Determine minimum stiffness requirements for StarSpec's reference frame at 5 mirror support interface points. Quantify WFE sensitivity to frame compliance so StarSpec can design their frame to spec.
+
+## Approach
+
+**Hybrid B+D method** (war-room validated):
+
+1. **Method D (Sensitivity):** Prescribed unit displacements at each unique interface point, extract Zernike WFE sensitivity coefficients (nm/μm per DOF per point)
+2. **Method B (Stiffness Sweep):** CBUSH spring-to-ground at 5 interface points, sweep K to find knee points
+3. **Robustness:** One-soft-point, combined compliance, correlated displacement tests
+
+## Key Numbers
+
+| Metric | Value |
+|--------|-------|
+| Baseline WFE @ 40° | ~7.0 nm RMS (J5+ filtered) |
+| Baseline WFE @ 60° | ~13.0 nm RMS (J5+ filtered) |
+| ΔWFE budget (frame) | ≤ 1.0 nm RMS |
+| System allocation | ≤ 22 nm RMS (contract) |
+| Mechanical target | < 14 nm RMS |
+| Total runs | ~42 |
+
+## Interface Points (5 total)
+
+| Label | Type | Symmetry |
+|-------|------|----------|
+| V_top | Vertical support | Unique (on Y-Z symmetry axis) |
+| V_left | Vertical support | = V_right mirrored |
+| V_right | Vertical support | = V_left mirrored |
+| L_left | Lateral support | = L_right mirrored |
+| L_right | Lateral support | = L_left mirrored |
+
+**Unique points to test:** 3 (V_top, V_side, L_side)
+
+## Model
+
+- **Solver:** NX Nastran SOL 101 (linear static)
+- **Coordinate system:** Global (Z = optical axis)
+- **Zernike extractor:** Annular OPD, 50 modes, J5+ filtered RMS
+- **Reference subcase:** 20° elevation
+- **Test subcases:** 40° and 60° elevation
+- **Inner radius:** 135.75 mm (central hole)
+- **Outer radius:** 500.0 mm
+
+## Project Structure
+
+```
+gigabit-m1-frame-stiffness/
+├── README.md                   ← You are here
+├── models/                     # NX model files (drop .prt and .sim here)
+├── studies/
+│   ├── 01_sensitivity_method_d/  # Unit displacement sensitivity (9+3 runs)
+│   ├── 02_stiffness_sweep_method_b/  # K sweep campaigns (20 runs)
+│   └── 03_robustness/           # One-soft-point, combined, correlated (8 runs)
+├── deliverables/               # StarSpec requirement document (Rev A)
+├── kb/                         # Knowledge base notes
+└── images/                     # Plots, screenshots
+```
+
+## PKM Reference
+
+Full documentation: `obsidian-vault/2-Projects/P04-GigaBIT-M1/03-studies/Reference-Frame-Stiffness-Characterization/`