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OGRE: the next-gen X-ray grating spectrometer enabled by cosine’s Silicon Pore Optics technology

The Off-plane Grating Rocket Experiment (OGRE) is an upcoming soft X-ray grating spectroscopy payload developed by The Pennsylvania State University (Penn State) designed to obtain the highest-resolution soft X-ray spectrum of Capella to date. It will employ high-energy optics technologies including reflection gratings assembled using flat direct silicon bonding at cosine.

Currently scheduled for launch in 2024 via a suborbital rocket, the instrument will serve as a “pathfinder” mission, bridging the gap between the current state-of-the-art soft X-ray spectrometers onboard the Chandra X-ray Observatory and XMM-Newton and future high-performance soft X-ray spectrometers.

To achieve the order-of-magnitude increases in performance required by future missions, newly developed X-ray optics and grating technologies will be utilized. As a pathfinder mission, OGRE will demonstrate the performance of two technologies being considered for these future high-performance soft X-ray spectroscopy missions including X-ray reflection gratings developed by Penn State and cosine.

Additionally, the OGRE spectrometer will achieve the highest resolution soft X-ray spectrum of an astronomical source to date when launched.

Randall McEntaffer, professor at Penn State University, says: “We are very happy to collaborate with cosine. Thanks to their expertise in silicon bonding, they will bring us precious help in this ambitious project.”

Next-gen X-ray grating spectrometers

In a soft X-ray spectrometer, many X-ray reflection gratings must be aligned together such that their individual spectra overlap at the focal plane. In the past, X-ray reflection gratings developed at Penn State utilized a fully active alignment methodology, where the orientation of individual gratings was monitored via various optical metrology tools, manipulated into place using precision staging, and then affixed within a grating module by hand using epoxy. These techniques were incredibly time-consuming and tedious, and were not well suited for the several hundred reflection gratings that must be aligned for the OGRE spectrometer (not to mention the several thousand required for future large-scale missions).

Therefore, a new alignment methodology has been devised that builds upon our Silicon Pore Optics (SPO) technology. Now, instead of actively manipulating the orientation of all six degrees of freedom, three are constrained through the precision manufacturing of the grating substrates. Then, by utilizing the precision staging during the stacking process at cosine, alignment in the remaining three degrees of freedom can be achieved. Additionally, instead of using epoxy, gratings are affixed into a grating stack via direct bonding. These grating plates will be turned into well-aligned flat stacks; a four-plate prototype has already been assembled at cosine.

This bonding technique forms bonds between the grating substrates themselves without relying on intermediate materials resulting in a lightweight, structurally robust, and precision aligned grating stack that can be aligned in a fraction of the time of the previous alignment methodology. Additionally, this newly developed alignment methodology is easily scalable to the several hundred reflection gratings required for the OGRE spectrometer or the many thousand required for future large-scale soft X-ray spectroscopy missions.

About cosine

cosine is a leading worldwide company in the development of space instrumentation, such as Silicon Pore Optics or remote sensing solutions with onboard processing. We combine physics and technology to bring out-of-the-box solutions to our clients. We have been developing and delivering innovative measurement systems for space and industrial applications since 1998. Our company operates 1,000 m2 of cleanrooms and high-tech assembly facilities to build and test the systems, we produce for customers at our headquarters in Sassenheim, The Netherlands.

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