Weighing the world's heaviest telescope at eight points with corrections for lifting perturbations

This technical note presents a summary of internal reports [Parker DH, Anderson R, Egan D, Fakes T, Radcliff B, Shelton J. GBT rolling weight measurements: methods, results, estimation of uncertainty, and auxiliary measurements. GBT Memo 222, The National Radio Astronomy Observatory, 2003; Parker DH, Anderson R, Egan D, Fakes T, Radcliff B, Shelton J. GBT rolling weight measurements: methods, results, estimation of uncertainty, and auxiliary measurements. Technical Report A0335, The National Radio Astronomy Observatory, 2003. Includes Appendices (≈ 250 pp.)], on weighing The National Radio Astronomy Observatory (NRAO), Robert C. Byrd Green Bank Telescope (GBT)-the world's largest (100 m), fully steerable, radio telescope (and involving, possibly, the most accurate large-scale metrology field measurement of weight conducted to date). The measured weight was 74 405 kN (4.448222 N/lbf), with a combined standard uncertainty (level of confidence ≈ 68%) of ± 213 kN, or a relative combined standard uncertainty of 0.3%. Two measurements of a wheel pair (mounter on a common support beam), conducted 15 days apart, reproduced within 24 kN, or 0.3%. The measured weight distribution revealed a maximum wheel pair load of 9781±44 kN, or 46% greater than the original wheel and track design assumptions, and nearly 9% greater than the final symmetric load estimation. Corrections were made for perturbations in the measured forces, due to lifting approximately one-eighth of the structure at a time. The load cells were custom calibrated to more closely match the actual field conditions. Parallel measurements are also presented from the hydraulic jack pressures.