Near Ultraviolet Transient Explorer (NUTEx): A CubeSat-Based NUV Imaging Payload for Transient Sky Surveys

TL;DR

NUTEx presents a CubeSat-based near-UV imaging payload designed for wide-field transient sky surveys in the $200-300~\mathrm{nm}$ band, leveraging a Ritchey–Chrétien optical train and a $40~\mathrm{mm}$ MCP photon-counting detector with a Raspberry Pi readout to enable open-access time-domain UV astronomy. The instrument achieves a $4^{\circ}$ field of view, a peak effective area of $\sim18~\mathrm{cm^2}$ at $260~\mathrm{nm}$, and $m_{AB}=21$ (SNR $=5$) for a $1200\,\mathrm{s}$ exposure, designed to monitor transients such as SN shock breakout events and M-dwarf flares while tolerating bright sky regions, including the Galactic plane. It integrates a modular cage mechanical design tested by FEA to ensure launch survivability (modal frequencies well above launcher resonances) and a compact electronics stack (STM32 OBC with Raspberry Pi detector readout) suitable for low-cost, rapid-development CubeSats. The mission concept emphasizes an all-sky, open-data survey strategy with potential rapid ToO follow-ups for events like gravitational-wave triggers, and positions NUTEx as a pragmatic precursor for future UV sky-mapping constellations in the NUV and FUV bands.

Abstract

The Near Ultraviolet Transient Explorer (NUTEx) is a CubeSat-based near-ultraviolet (NUV) imaging payload designed for transient sky surveys and is currently under development. CubeSats are compact and cost-effective satellite platforms that have emerged as versatile tools for scientific exploration and technology demonstrations in space. NUTEx is an imaging telescope operating in the 200-300 nm wavelength range, intended for deployment on a micro-satellite bus. The optical system is based on a Ritchey Chretien (RC) telescope configuration, featuring a 146 mm primary mirror. The detector is a photon-counting microchannel plate (MCP) device with a solar-blind photocathode, paired with an in-house developed readout unit. The instrument has a wide field of view (FoV) of 4 deg, a peak effective area of approximately 18 sq cm at 260 nm, and can reach a sensitivity of 21 AB magnitude (SNR = 5) in a 1200 second exposure. The primary scientific objective of NUTEx is to monitor the night sky for transient phenomena, such as supernova remnants, flaring M-dwarf stars, and other short-timescale events. The payload is currently scheduled for launch in Q2 2026. This paper presents the NUTEx instrument design, outlines its scientific goals and capabilities, and provides an overview of the electronics and mechanical subsystems, including structural analysis.

Figures (10)

• Figure 1: Optical design of NUTEx instrument.
• Figure 2: Spot diagrams at the telescope focal plane for different field angles (0° to 2°) marked with different wavelengths (blue: 2000 Å, green: 2500 Å, red: 3000 Å).
• Figure 3: Effective area of NUTEx (red curve) as a function of wavelength, overlaid with contributing factors: photocathode quantum efficiency (purple dashed), mirror reflectivity (black dotted), and optical transmission (green dotted).
• Figure 4: Photometric sensitivity of NUTEx: Minimum detectable brightness variation across AB magnitudes for a 10-second exposure at SNR = 5.
• Figure 5: Simulated NUTEx photon count response for GALEX-detected UV variable sources from the GFCAT, assuming a 1K seconds exposure and the estimated effective area of NUTEx, plotted in Galactic coordinates.