Designing payload hardware and interfaces for the Landolt NASA Space Mission

Abstract

The NASA Landolt Space Mission aims to put an artificial star in space in geosynchronous orbit, allowing scientists to calibrate ground telescopes to accurately measure the brightness of stars and understand the accelerating expansion of the universe, fundamental properties of stars such as age and radius, and the sizes and habitability of exoplanets. To achieve this, Landolt’s payload includes a laser module, which requires a photodiode printed circuit board (PCB) unit to measure light intensity by producing an electric current. However, as the Landolt Mission takes place outside Earth’s protective atmosphere, the payload components risk exposure to ionizing radiation. As existing photodiode PCB units do not contain radiation-hardened components, we custom-made our own PCB with radiation-hardened components. To visualize the board design, we developed a 3D design of the PCB, and started with making a 3D model of a radiation-hardened LMP7704-SP ceramic flatpack, a type of integrated circuit packaging used when high thermal and electrical performance is required. We gathered its dimensions from Texas Instruments, and developed the model with the FreeCAD software. Specifically, the LMP7704-SP ceramic flatpack acts as an amplifier for the photodiode PCB, by taking in a small signal and enhancing it. Additionally, to ensure all interfaces of the Landolt Mission correspond with one another—like the payload to the spacecraft bus, for example—Interface Control Documents (ICD) must be drafted. ICDs define the functional, electrical, mechanical, and data interfaces between systems to ensure compatibility and integration. The six ICDs are as follows: Payload to Spacecraft Bus, Payload to Launch Services, Payload to Ground Systems, Payload to Ground Calibration, Tech Demos to Payload, and Science Operations Center to Observatories and Archives. We initiated drafting the six ICDs for the six mission interfaces in compliance with the Landolt mission requirements, NASA NPR 7120.8 and NPR 7120.5 guidelines, and the NASA Interface Management documents.