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Renishaw’s new pioneering encoder boldly goes into space

November 2014

TESAT laser terminal encoder

Renishaw, the global metrology specialist, has reached another milestone in the application of its technology by deploying products in space for the first time. The European Space Agency's Sentinel-1A satellite was launched from the European spaceport in Kourou, French Guiana, on April 3rd 2014, with Renishaw's new space-encoder technology installed on the advanced Optical Communications Payload (OCP) of the satellite; part of a revolutionary inter-satellite laser communication system. The OCP provides an optical Low Earth Orbit (LEO) to Geostationary Earth Orbit (GEO) communications link via a pair of Laser Communication Terminals (LCT) by space telecommunications company Tesat-Spacecom (Tesat) of Backnang, Germany. The GEO LCT is currently accommodated on Europe's AlphaSat.

Space is an exceptionally harsh environment that demands encoder performance far in excess of normal operational limits. Space-qualified components also need to be inordinately reliable as repair while in orbit is economically unfeasible and so the selection of qualified technology is an arduous process. As a world leader in precision engineering technologies, Renishaw succeeded in adapting to the ultimate challenges of space-borne applications by drawing on this significant expertise.

Tesat encoder

Tesat required a new rotary (angle) encoder for the coarse pointing assembly (CPA) of its 2nd generation LCT, which is essentially a telescope with coherent receiver and transmitter hardware. The space-qualified encoder was developed in collaboration with Tesat and shares much of its core technology with Renishaw's proven TONiC™ encoder range. It is designed to withstand operating temperatures from ‑40 °C to +80 °C, bombardment by solar / cosmic radiation and high mechanical loads consistent with rocket launch. Radiation hardening, combined with Renishaw's extremely robust optical detection principle, has resulted in the encoder achieving qualification for an impressive 15 years service in a Geostationary Earth Orbit (GEO) environment.

Renishaw and Tesat's advanced space-encoder is installed on both rotary axes of the CPA and will be integrated into the LCTs of a number of future space platforms including the Sentinels, the European Data Relay Satellites EDRS-A and EDRS-C. The encoder system consists of a stainless steel ring with ablated graduations on the periphery and a specially adapted readhead. IN‑TRAC™ reference marks are directly embedded into the incremental channel and arranged so that the distance between any two marks is unique. This means that only a small rotation is required before the absolute position is known. Another advantage is that there is no contact between the rotary ring and static readhead, which eliminates friction and, hence, hysteresis error as well as potential wear or any need for lubrication. The system achieves a resolution of less than 0.5 µrad, with a short-range error of <0.5 µrad and long-range error of <5 µrad.

This development was funded on behalf of the German Aerospace Center (DLR) by the Federal Ministry of Economics and Technology based on legislation by the German Parliament in the framework of project 50YH0932 of TESAT with Renishaw as subcontractor.

Refer to link: Laser link offers high-speed delivery