Instrument Alignment for the tREXS Spectrograph

The Rocket for Extended-source X-ray Spectroscopy (tREXS) is a suborbital rocket that launched on September 25th of 2022. This rocket contains a diffuse soft x-ray grating spectrometer, with two channels consisting of mechanical beam shapers and reflection gratings. The mechanical beam shapers, made up of 45 plates with slits of varying size and position, allow for only x-rays to pass through and naturally form a focus at the instrument’s camera. Once through the mechanical beam shapers, the light reflects off of 2 stacks of 38 x-ray reflection gratings. In tandem the mechanical beam shapers and gratings were designed to produce a large effective area and moderate spectral resolution. We need the 38 co-aligned reflection gratings on each channel of the instrument to achieve this effective area. They need to be coaligned to ensure the spectra from each grating overlaps correctly, which results in a good spectral resolution. The bulkhead containing the gratings and mechanical beam shapers needs to be aligned to the focal plane to ensure the spectra would fall on the detectors. Any mis-alignments in this setup could worsen the spectral resolution or the effective area, so accurate alignment was an essential step to building a rocket with this targeted performance. A coordinate measuring machine (CMM) was used to accomplish alignment of the gratings and mechanical beam shapers to the payload. Using optically flat squares of silicon that are strategically placed on the grating stacks and mechanical beam shapers, we were able to measure the planes of each instrument component and their relations, which allowed us to meet our alignment tolerances for flight. In this poster we will describe the process through which we aligned the mechanical beam shapers to the grating modules, and this combined the optical system to the focal plane.