Atomizer/projects/gigabit-m1-frame-stiffness

GigaBIT M1 — Reference Frame Stiffness Characterization

Client: StarSpec Project: P04-GigaBIT-M1 Created: 2026-03-04 Status: Active — Model Setup

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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/