White Paper: Mechanical & Fluid Systems
Renishaw Enables Extreme Precision for Space Agency’s Experiments
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Renishaw’s advanced probing technology played a crucial role in supporting major space agency’s cutting‑edge particle physics research. Recent breakthroughs in particle physics have prompted some scientists to question a long‑standing assumption in physics: that an object’s inertial mass and gravitational mass are always identical.
To explore these ideas, engineers at the National Metrology Institute of Germany (PTB) created extremely precise cylindrical test masses for MICROSCOPE, a 300 kg minisatellite operated by CNES, the French government space agency. For the test masses, they were able to achieve 2µm – 3µm accuracy for all geometric characteristics. This level of precision was only possible by combining a high‑accuracy lathe with Renishaw’s OMP400 probing system.
Learn more about this partnership and read the full case study below.
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Overview
This document discusses the development and manufacturing of ultra-precise cylindrical test masses by the National Metrology Institute of Germany (PTB) for the MICROSCOPE space mission, which aims to test the equivalence principle that inertial and gravitational masses are identical—a fundamental concept in physics since Galileo and Einstein. Recent theoretical advances suggest potential deviations at accuracies below 10^-12 µm, motivating this experiment to measure responses of paired cylinders of different materials (platinum-rhodium and titanium-aluminum-vanadium alloys) in a zero-gravity, high-vacuum space environment to unprecedented precision.
Producing these test masses required exceptional manufacturing accuracy of ±1 µm on dimensions such as diameter, roundness, cylindricity, parallelism, and angularity across all surfaces. PTB faced challenges machining the materials—particularly the Pt-Rh alloy, prone to grain breakages using conventional tools. Specially eroded diamond tools and a high-precision Benzinger TNI Preciline lathe were employed. Crucially, the entire machining and measurement process was integrated into a single uninterrupted workflow to avoid errors from reclamping or repositioning, and in-process measurement was performed repeatedly on the lathe to tightly control dimensions within 0.01 mm during machining.
Achieving the final ±1 µm accuracy was made possible using the Renishaw OMP400 probe, a wireless, strain gauge-based high-precision probe with excellent repeatability and minimal hysteresis. This probe recorded measurement points—over thirty circular points for roundness and diameter, and multiple points along cylinder length for cylindricity. For challenging small features like 1.2 mm diameter ball indentations, a custom 0.3 mm silicon-ceramic stylus was developed. The probe’s data integrated directly into the lathe’s CNC system enabled compensation for measurement deviations in real-time to refine machining.
Verification was conducted by comparing the OMP400 probe measurements on the lathe with those from a coordinate measuring machine, confirming measurement accuracy within 1 µm after calibration and compensation. This high-precision manufacturing approach and measurement integration were key to success, enabling PTB to produce test masses suitable for the extremely sensitive MICROSCOPE experiment. These results support test of fundamental physics principles at new levels of accuracy, with possible implications for our understanding of solid-state physics and the validity of the equivalence principle.
For further details, refer to www.renishaw.com.