Design and Development of a PS4-OP Payload for Solar Spectral Irradiance Measurements and Technology Demonstration of Small-Satellite Subsystems

This article describes the design and development of INSPIRE-0, a payload on the spent stage of the ISROs PSLV. Recently, the Indian Space Research Organisation (ISRO) released an announcement of opportunity inviting proposals to develop payloads that can be tested on the PS4-Orbital Platform (PS4-OP). This platform is a novel idea formulated by ISRO to use the spent fourth/final stage of the Polar Satellite Launch Vehicle (PSLV), called the PS4, to conduct in-orbit scientific experiments and technology demonstration of small-satellite subsystems. INSPIRE-0 is a PS4-OP payload, jointly developed by the Laboratory for Atmospheric and Space Physics (LASP) at the University of Colorado Boulder, the Indian Institute of Space Science and Technology (IIST), and the Nanyang Technological University (NTU) in Singapore. This payload has two main objectives. Firstly, the scientific objective is to characterize the solar spectrum using a novel sensor, developed by NTU, that has a wide frequency range from visible to near the infra-red region. The specific objective of the INSPIRE-0 payload is to demonstrate that accurate Solar Spectral Irradiance (SSI) continuous measurements are possible using new compact and robust disruptive technologies. A successful demonstration will pave the way for a future constellation of CubeSats that will provide a very cost-effective way to monitor the Total Solar Irradiance and SSI of the sun in the various spectral bands. Secondly, the INSPIRE-0 payload aims to flight qualify the in-house developed subsystems for the INSPIRESat-1 small satellite mission, namely, the Command and Data Handling (C&DH) Subsystem and the Electrical Power Subsystem (EPS). The article first describes the systems architecture of the payload which has a size of 15cm x 10cm x 7.5 cm, a mass of 1kg, and power consumption of 1.75 W. This is followed by the details of the science instrument and an overview of the different subsystems, namely the C&DH, the EPS, and the PS4-OP interface board. The article concludes with the details of the testing, including comprehensive performance tests and environmental tests, performed to prepare the payload for a planned launch on the PS4-OP in the third quarter of 2021.