The eXTP (enhanced X-ray Timing and Polarization) satellite is a prominent X-ray astronomy satellite designed primarily for conducting deep space X-ray astronomical observations. The satellite’s scientific payload consists of X-ray focusing mirrors. In order to fulfill the requirements of weight reduction and enhanced effective area, the thickness of mirrors is reduced to the sub-millimeter range and a multi-layer nested structure is employed. Manufacturing mirrors poses a significant challenge to both their quality and efficiency. The present research investigates the optimal replication process for mandrel ultraprecision machining, polishing, coating, electroforming nickel, and demolding. It analyzes the factors contributing to the challenging separation and the inability to release the mirror shells. Additionally, an automatic demolding device is developed, and the X-ray performance of the replication mirrors is verified. The fabrication process flow of the mirrors was initially introduced. To ensure the easy release of the mirror shells from the mandrels, a layer of diamond-like carbon (DLC) was applied as a release layer between the Au and NiP alloy. The adhesion strength of Au-C was found to be significantly lower than that of Au-NiP, as demonstrated by both molecular dynamic simulation and tensile testing. The development of an automatic demolding device with force feedback has been successfully completed. The reduction in the half-power diameter (HPD) of the mirror from 48 inches to 25 inches is an improvement that surpasses the production target.

The X-ray satellite “Einstein Probe” of the Chinese Academy of Sciences (CAS) was successfully launched on 9 January 2024 at 15:03 Beijing Time from the Xichang Satellite Launch Center in China with a “Long March-2C” rocket. The Einstein Probe is equipped with two scientific X-ray telescopes. One is the Wide-field X-ray Telescope (WXT), which uses lobster-eye optics. The other is the Follow-up X-ray Telescope (FXT), a Wolter-I type telescope. These telescopes are designed to study the universe for high-energy X-rays associated with transient high-energy phenomena. The FXT consists of two modules based on 54 thin X-ray Wolter-I grazing incidence Ni-replicated mirrors produced by the Italian Media Lario company, as contributions from the European Space Agency and the Max Planck Institute for Extraterrestrial Physics (MPE), which also provided the focal-plane detectors. Meanwhile, the Institute of High Energy Physics (IHEP), together with the Harbin Institute of Technology and Xi’an Institute of Optics and Precision Mechanics, has also completed the development and production of the structural and thermal model (STM), qualification model (QM) and flight model (FM) of FXT mirrors for the Einstein Probe (EP) satellites for demonstration purposes. This paper introduces the precision manufacturing adopted in China of Wolter-I X-ray mirror mandrels similar to those used for the EP-FXT payload. Moreover, the adopted electroformed nickel replication process, based on a chemical nickel–phosphorus alloy, is reported. The final results show that the surface of the produced mandrels after demolding and the internal surface of the mirrors have been super polished to the roughness level better than 0.3 nm RMS and the surface accuracy is better than 0.2 μm, and the mirror angular resolution for single mirror shells may be as good as 17.3 arcsec HPD (Half Power Diameter), 198 arcsec W90 (90% Energy Width) @1.49 keV (Al-K line). These results demonstrate the reliability and advancement of the process. As the first efficient X-ray-focusing optics manufacturing chain established in China, we successfully developed the first focusing mirror prototype that could be used for future X-ray satellite payloads.