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Caption: Figure 4.
Targeting accuracy for DESI fiber robots over a 3 month period of survey operations in fall 2021, during which the Focal Plane System acquired more than 7.8 million targets. The shallower red histogram shows “blind” move accuracy, i.e., the first open-loop move made toward each target. The sharper blue histogram shows positioning error after a single correction move, based on feedback from the FVC (Section 2.5). Blind move rms error is 54 μm, with 0.35% of attempted targets having error >200 μm. After the correction move, the rms error is 9 μm, with 0.03% outliers >200 μm. Errors here are with respect to the commanded target positions, and include significant contributions of measurement noise (Section 6.6) due to centroiding precision limits (∼3 μm) and air turbulence in the dome (∼3–8 μm). Turbulence subtraction code introduced in late 2021 further reduced the error to 6 μm rms. Figure 5
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© 2022. The Author(s). Published by the American Astronomical Society.
