SABHASAT

This research presents Sabhasat, a pioneering 3U CubeSat designed to detect solar and gamma radiations in the LEO region, positioned over 650 km above Earth's atmosphere. Utilizing advanced sensor technologies, Sabhasat aims to enhance our understanding of space radiation and its potential impact on satellite systems. The project's objective is to develop a 3U CubeSat nanosatellite for studying solar and
gamma radiations in the Lower Earth Orbit, specifically 600 km above Earth's surface. The satellite incorporates an Active Attitude Control System (AACS), Distributed Command and Data Handling (dCDH), Communications (COMM) systems, Electronic Power System (EPS), and Peak Power Tracker (PPT). Upon successful launch, Sabhasat will be India's first indigenous CubeSat capable of detecting high-energy radiations in orbit. The basic SABHASAT philosophy is to realize innovative, distributed and modular instruments composed of tens/hundreds of simple units, cheaper and with a limited development time. The present nanosatellite (e.g. CubeSats) technologies demonstrate that off-the-shelf components for space use can offer solid readiness at a limited cost. For scientific applications, the physical dimension of a single detector should be compatible with the nanosatellite structure (e.g. 1U CubeSat of 10 × 10 × 10 cm3 ). Therefore, the single detector is of course underperforming (i.e. it has a low effective area), when compared with
conventional operative transient monitors, but the lower costs and the distributed concept of the instrument demonstrate that is feasible to build an innovative instrument with unprecedented sensitivity. A possible solution for the payload is allocated in 1U Cubesat (10 × 10 × 10 cm3 ). A mechanical support is placed on the instrument’s topside. The support is composed of two parts to accommodate an optical/thermal filter in the middle. The electronic boards for the back end and the Data Handling unit are allocated at the bottom of the payload unit. The detector core is located in the middle: this is a scintillator-based detector in which Silicon Drift Detectors are used to both detect soft X-rays (by direct absorption in silicon) and to read out the scintillation light simultaneously. The payload unit is expected to allocate a detector with

                                                                                   > 50cm^2

sensitive area in the energy range from 3–5 keV up to 2 MeV, with a total power
consumption

                                                                                        < 4W

and total weight of < 1.5kg. Given the limited resources available on-board a CubeSat spacecraft, the detection strategy must be carefully designed by taking into account mission weight and size budgets, power limitations, orbital characteristics (radioactivity and temperature variation), and the gamma-ray energy range of interest. The gamma ray enters the payload and deposits energy in the target. The energy is in turn transformed into a flash of light that is collected from the photosensor. The front-end electronics and a charge signal generated read out the signal output. The processing electronics assigns a time stamp and a Attitude Determination and Control (ADC) channel to the event. The processed event is in turn sent to the On-Board Computer (OBC), a priority is assigned based on a look-up table for event categorization, and eventually made available for the transmission to ground.The core of the gamma-ray detector consists of a detection array
of four optically independent scintillating crystals, each one of 23×23×45 mm^3 dimensions, encapsulated in an aluminium casing with overall dimensions of 56×56×46 mm^3 and equipped with a 2 mm thick quartz window for the photosensor coupling. To tag charged particle-induced events, a rejection layer (VETO) made out of 5 mm thick plastic scintillator tiles. SDDs play the double role of read-out device for the optical signal from the scintillator and of an independent X-ray solid state detector. The SDD directly absorbs low energy X-rays, while higher energy X-rays and gamma -rays are absorbed in the crystal and the same detector collects the optical scintillation photons. Only very low noise readout sensors and front-end electronics allow to reach a low energy scintillator threshold below 20–30 keV. Above these energies the increasing sensitivity of the scintillator can compensate the lack of efficiency of thin silicon sensors (450 m), so a quite flat efficiency in a wide energy band for the whole integrated system is reached.