Mini-EUSO is a wide Field-of-View (44∘×44∘) telescope currently in operation from a nadir-facing Ultra-Violet (UV) transparent window in the Russian Zvezda module on the International Space Station (ISS). Mini-EUSO has been designed as a scaled-down version of the original JEM-EUSO telescope to raise its instrumentation's technological readiness level and demonstrate its observational principle, while performing multidisciplinary studies on different fields such as atmospheric science and planetology. One of Mini-EUSO main goals is the study of the UV background for future space missions employing the same concept as the original JEM-EUSO telescope, which requires an absolute calibration of the Mini-EUSO instrument. During the past years, a few observational campaigns have been completed, employing a ground-based UV flasher to perform an end-to-end calibration of the instrument. In this paper, we present the assembled UV flasher system, the operation of the field campaign and the analysis of the obtained data. The results are interpreted by the means of a parametrization of the Mini-EUSO photon counts. The end-to-end efficiency of several pixels has been obtained, taking into account different parameters such as the atmospheric attenuation, the optics efficiency and the multi-anode photomultiplier detection efficiency.

We review the concept of cooling Earth by the placement of a sunshield at the first Lagrange point in the Sun-Earth system. Sunshield design characteristics are described along with the conditions necessary for sunshield transport from Earth, orbital placement and station keeping.

Since 2010, the international JEM-EUSO (Joint Exploratory Missions for Extreme Universe Space Observatory) Collaboration has been developing an ambitious program with the support of major International and National Space Agencies and research funding institutions, to enable UltraHigh-Energy Cosmic Ray (UHECR) and High-Energy (HE) neutrino observations from space. Its main objective is to develop a large mission with dedicated instrumentation looking down on the Earth atmosphere from space, both towards nadir and/or towards the limb, to detect the Extensive Air Showers (EAS) initiated by such particles in the atmosphere. This strategy is intended to complement the observations made with ground-based observatories, by allowing a significant increase in the exposure at the highest energies, and achieving near-uniform full sky coverage, as part of the global effort to better characterize the phenomenology of UHECRs, discover their sources and understand their acceleration mechanism. In the last decade, the JEM-EUSO Collaboration successfully developed five intermediate missions: one ground based (EUSO-TA), three balloon-borne (EUSO-Balloon, EUSO-SPB1, EUSO-SPB2) and one space-based (MiniEUSO), and also benefited from the experience gained by the space mission TUS. Important studies for a full-scale mission have also been carried out, namely K-EUSO and the stereo double telescope Probe Of Extreme Multi-Messenger Astrophysics (POEMMA), to be considered for a NASA Probe Mission in the next decade. The technical and scientific achievements of this rich and manifold program are reported on, as well as the scientific objectives updated in the light of the knowledge gained from the previous missions, and additional scientific objectives accessible to such unique technology. Finally, the near-future developments of the JEM-EUSO Program are briefly presented, with the continuation of the Mini-EUSO observations and the new balloon-borne mission PBR.

The increasing urgency of climate change mitigation necessitates innovative solutions beyond terrestrial efforts. Space-based solar geoengineering – particularly a Planetary Sunshade System (PSS) positioned near the photo-gravitational equilibrium point L<inf>1</inf>^∗, which lies closer to the Sun than the classical L<inf>1</inf> due to the effect of solar radiation pressure – has been proposed as a potential method to reduce incoming solar radiation and stabilize global temperatures. This paper presents the preliminary design of a precursor mission aimed at demonstrating key technologies essential for the deployment of a full-scale PSS. The proposed mission features a 12U CubeSat equipped with a 400 [m²] solar sail, which will be used for propulsion, attitude control, and station-keeping at L<inf>1</inf>^∗. The mission objectives focus on validating the long-term performance of optical shielding materials, demonstrating solar sailing as a sustainable propulsion method, and assessing the feasibility of autonomous orbit and attitude control systems. The technical and economic feasibility of the precursor mission, with an estimated budget of 10M USD is examined. By addressing key uncertainties in spacecraft formation flying, material degradation, and long-term solar sailing operations, this mission represents a crucial step toward the realization of a scalable PSS for climate intervention.

The Extreme Universe Space Observatory on a Super Pressure Balloon 2 (EUSO-SPB2) flew on May 13th and 14th of 2023. Consisting of two novel optical telescopes, the payload utilized next-generation instrumentation for the observations of extensive air showers from near space. One instrument, the fluorescence telescope (FT) searched for Ultra-High Energy Cosmic Rays (UHECRs) by recording the atmosphere below the balloon in the near-UV with a 1μs time resolution using 108 multi-anode photomultiplier tubes with a total of 6912 channels. Validated by pre-flight measurements during a field campaign, the energy threshold was estimated around 2 EeV with an expected event rate of approximately 1 event per 10 h of observation. Based on the limited time afloat, the expected number of UHECR observations throughout the flight is between 0 and 2. Consistent with this expectation, no UHECR candidate events have been found. The majority of events appear to be detector artifacts that were not rejected properly due to a shortened commissioning phase. Despite the earlier-than-expected termination of the flight, data were recorded which provide insights into the detectors stability in the near-space environment as well as the diffuse ultraviolet emissivity of the atmosphere, both of which are impactful to future experiments.

Mini-EUSO (Multiwavelength Imaging New Instrument for the Extreme Universe Space Observatory, known as UV atmosphere in the Russian Space Program) is the first detector of the JEM-EUSO program to observe the Earth from the International Space Station (ISS) and to validate from there the observational principle of a space-based detector for UHECR measurements. Mini-EUSO is a telescope operating in the near UV range, mainly between 290 - 430 nm, with a square Focal Surface (FS) corresponding to a Field of View (FoV) of ∼ 44◦. Its spatial resolution at ground level is ∼ 6.3 km. Mini-EUSO was launched with the uncrewed Soyuz MS-14. The first observations, from the nadir-facing UV transparent window in the Russian Zvezda module, took place on October 7, 2019. The detector size (37 × 37 × 62 cm3) was mainly constrained by the window size. The detector is usually installed during onboard night-time a couple of times per month, approximately at 18:30 UTC with operations lasting about 12 hours. So far, 139 sessions of data acquisition have been performed. Data are stored locally on USB solid state disks. After each data-taking session ∼10% of stored data, usually corresponding to the beginning and the end of each session, are copied and transmitted to ground to verify the correct functioning of the instrument. Till now, the data of the first full 44 sessions returned to Earth and is being analysed. The Mini-EUSO FS, or Photon Detector Module (PDM), consists of a square matrix of 36 Multi-Anode Photomultiplier Tubes (MAPMTs). Each MAPMT consists of 8 × 8 pixels. A group of 2 × 2 MAPMTs forms an Elementary Cell (EC). In total there are 2304 channels. Each EC has an independent high voltage power supply (HVPS) and board connecting four MAPMTs. The HVPS system, based on a Cockroft-Walton circuit, has an internal safety mechanism which operates either reducing the collection efficiency or the gain of the MAPMTs when particularly bright signals occurr. The optics are based on two 25 cm diameter Fresnel lenses with a point spread function of 1.2 pixels. UV bandpass filters are glued in front of the MAPMTs. The system has a single photon-counting capability with a double pulse resolution of ∼ 6 ns. Photon counts are summed in Gate Time Units (GTUs) of 2.5 μs. The PDM Data Processor stores the 2.5 μs GTU data stream (D1) in a running buffer on which runs the trigger code. Sums of 128 frames (320 µs, D2) are continuously calculated and stored in another buffer where a trigger algorithm, at this time scale, is running. Similarly, sums on 128 D2 frames (40.96 ms, D3) are calculated in real time and continuously stored. Every 5.24 s, 128 packets of D3 data, up to 4 D2 packets and up to 4 D1 packets (if triggers were present) are sent to the storage (SSDs). Mini-EUSO measured the terrestrial UV background with unparalleled precision. The fraction of time in which the atmospheric UV light intensity allows the UHECR observation from space is ∼18%, compatible with the expectations from simulations conducted at the time of the JEM-EUSO studies. The trigger rate on spurious events remains within the requirements in nominal background conditions. It proved effective in detecting Short Light Transients (SLT), demonstrating indirectly that the JEM-EUSO technology can detect UHECRs from space as they show similarities in terms of light profile, intensity, duration and pixel pattern on the FS of Mini-EUSO, even though all these characteristics do not match at the same time for a single event and are not mistaken for real EAS-induced signals. The ability of Mini-EUSO to detect and study atmospheric phenomena like ELVES, and the ones linked to SLTs is unique and beyond the capabilities of any other atmospheric detector. That makes a space-based detector for UHECRs a unique instrument for the atmospheric science field. Mini-EUSO demonstrated to be the first experiment from space to perform a systematic study of meteor light curves and flux in a wide range of magnitudes.

This article presents an elementary change detection algorithm designed using a synchronous model of computation (MoC) aiming at efficient implementations on parallel architectures. The change detection method is based on a 2D-first-order autoregressive ([2D-AR(1)]) recursion that predicts one-lag changes over bitemporal signals, followed by a high-parallelized spatial filtering for neighborhood training, and an estimated quantile function to detect anomalies. The proposed method uses a model-based on the functional language paradigm and a well-defined MoC, potentially enabling energy and runtime optimizations with deterministic data parallelism over multicore, GPU, or FPGA architectures. Experimental results over the bitemporal CARABAS-II SAR UWB dataset are evaluated using the synchronous MoC implementation, achieving gains in detection and hardware performance compared to a closed-form and well-known complexity model over the generalized likelihood ratio test (GLRT). In addition, since the one-lag AR(1) is a Markov process, its extension for a Markov chain in multitemporal (n-lags) analysis is applicable, potentially improving the detection performance still subject to high-parallelized structures.

The objective of this paper is to present a roadmap for the technology development toward a Planetary Sunshade System, a space-based solar geoengineering project aimed at reversible solar radiation modification to mitigate global warming. Earth's climate change is mostly due to the increasing concentration of greenhouse gases in the atmosphere, which leads to a general rise of the temperatures. A space-based geoengineering infrastructure has been previously proposed to reduce the oncoming solar irradiance, by placing a 'solar light umbrella', called Planetary Sunshade System, between the Sun and the Earth. To address the full development of a Planetary Sunshade System, a technology roadmap is needed which considers a step-by-step high-level plan of technology development, mission planning, launch preparation, international cooperation, highlighting the multi-phase development strategy from initial design to final deployment. First, the roadmap phases for production and deployment are outlined in chronological order. The analysis of technology development begins with the current technology readiness level, encompassing system design and factors such as mass, dimensions, area, and the total number of solar-sail satellites. Logistic aspects, including in-space assembly of the fully deployed system, are also examined. Finally, launch preparation is discussed encompassing heavy launcher design, facilities, production and launch sites. The proposed roadmap not only provides a starting point for the design and development of the Planetary Sunshade System but also a critical tool for evaluating the feasibility of direct climate action from space. Through this paper, we aim to establish the groundwork for a future Planetary Sunshade endeavour, and to contribute to the broader discussion on space-based climate action.

Mini-EUSO is a small, near-UV telescope observing the Earth and its atmosphere from the International Space Station. The time resolution of 2.5 microseconds and the instantaneous ground coverage of about 320 × 320 km2 allows it to detect some Transient Luminous Events, including Elves. Elves, with their almost circular shape and a radius expanding in time form cone-like structures in space-time, which are usually easy to be recognised by the eye, but not simple to filter out from the myriad of other events, many of them not yet categorised. In this work, we present a fast and efficient approach for detecting Elves in the data using a 3D CNN-based one-class classifier.

Mini-EUSO is a wide Field-of-View (FoV, 44◦) telescope currently in operation from a nadia-facing UV-transparent window in the Russian Zvezda module on the International Space Station (ISS). It is the first detector of the JEM-EUSO program deployed on the ISS, launched in August 2019. The main goal of Mini-EUSO is to measure the UV emissions from the ground and atmosphere, using an orbital platform. Mini-EUSO is mainly sensitive in the 290-430 nm bandwidth. Light is focused by a system of two Fresnel lenses of 25 cm diameter each on the Photo- Detector-Module (PDM), which consists of an array of 36 Multi-Anode Photomultiplier Tubes (MAPMTs), for a total of 2304 pixels working in photon counting mode, in three different time resolutions of 2.5 μs, 320 μs, 40.96 ms operation in parallel. In the longest time scale, the data is continuously acquired to monitor the UV emission of the Earth. It is best suited for the observation of ground sources and therefore has been used for the observational campaigns of the Mini-EUSO. In this contribution, we present the assembled UV flasher, the operation of the field campaign and the analysis of the obtained data. The result is compared with the overall efficiency computed from the expectations which takes into account the atmospheric attenuation and the parameterization of different effects such as the optics efficiency, the MAPMT detection efficiency, BG3 filter transmittance and the transparency of the ISS window.