Mechanical and thermal design of the BlackCAT CubeSat

The BlackCAT observatory makes use of a 6U CubeSat platform with an X-ray coded aperture telescope payload. BlackCAT, utilizing its wide field-of-view (0.9 steradians), will monitor deep space for a variety of X-ray transients and flares, with a primary focus on high redshift gamma-ray bursts. The payload consists of a Detector Module (DM), a dedicated electronics package, mechanical mounts, and thermal straps for passive cooling. The DM includes the DM housing, coded aperture mask, Optical Blocking Filter (OBF), and a Focal Plane Array (FPA) consisting of four X-ray hybrid CMOS detectors (HCDs). Each of these four detectors is a 550x550-pixel Speedster-EXD silicon sensor with a molybdenum package to provide a low-strain thermal and mechanical mounting structure. The primary purpose of the electronics package is reading out and processing data from the HCDs. For optimal scientific performance, the FPA must be maintained at a temperature of -40 degrees C or below. The detectors have an aluminum OBF directly deposited because the silicon detectors are sensitive to optical light. For additional optical blocking against the brightest optical background and UV light, a separate OBF will be mounted in front of the detector surface. The coded aperture mask is a wire mesh made of nickel with a thin layer of gold coating all sides. The mask allows approximately 40% of incident X-rays to strike the detector in a unique pattern that is dependent upon source position and the open cell geometry. This allows for the angular position of the source to be determined to sub-arcminute precision. To prevent deformation due to thermal strain, the mask is required to maintain a set temperature between 10 degrees C and 20 degrees C. The DM housing acts as the primary support structure for the payload and is thick enough to provide shielding from off-axis X-rays and optical/UV light. The OBF is directly connected to the DM housing, while the mask and FPA are both thermally isolated via standoffs to meet respective temperature requirements. Additionally, the DM housing is the interface between the payload components and the chassis. We present an overview of the mechanical and thermal payload requirements, as well as design constraints imposed by the 6U CubeSat form factor. We describe the designs used to meet these requirements and present analyses to demonstrate the efficacy of these designs. The mechanical requirements and information from thermal analyses will drive the overall design of the BlackCAT CubeSat to achieve the science goals throughout the mission lifetime.