SING is a near ultraviolet (NUV) spectrograph with a size close to 6U CubeSat form-factor. The spectrograph operates in the wavelength range from 1800 Å to 3000 Å, with a spectral resolution of 2 Å at the central wavelength. The spectrograph is intended to operate in low Earth orbit (LEO), with the primary goal to generate spectral maps of the regions of the sky covered within the field of view (FOV) of the instrument, constrained by the orbital inclination of the spacecraft. The payload consists of the telescope in Cassegrain configuration focusing the light on the slit, the corrector lens, the concave grating, the detector, and other required electronics components. As the event rate in the UV is low, the spectrograph employs a photon-counting detector because of its low noise performance. The payload uses FPGA as the main system controller to handle the detector readout, data compression and storage, health monitoring, and telemetry. In this work, we present the optical design and its analysis, along with a brief description of the architecture of electronic subsystems of the payload.