One of the major achievements of planetary science in the past century has been the discovery of a population of asteroids and comets that have the potential to impact our planet. These objects are collectively known as Near-Earth Objects (NEOs), which include both asteroids and comets whose orbits bring them within 1.3 astronomical units (au) of the Sun. Among them, a subset is classified as Potentially Hazardous Asteroids (PHAs) — objects that have an Earth Minimum Orbit Intersection Distance (MOID) of 0.05 au or less and an absolute magnitude (H) of 22 or brighter, indicating a size large enough to cause significant damage in the event of an impact. Imminent Earth impactors have been shown to "come" from two principal directions in the sky, one towards local midnight and the other towards the local midday [1].While midnight impactors are well covered by existing optical survey telescopes, midday impactors present a major observational challenge. From the ground, observations in the direction of the Sun are nearly impossible due to its overwhelming brightness, which prevents the detection of faint asteroid signals. The Chelyabinsk event of 2013 highlighted this vulnerability, as the ~20-meter asteroid responsible for the airburst was completely undetected before impact, approaching from a region of the sky that was effectively unobservable by existing surveys [2]. A promising solution to this problem is to place an infrared telescope at the Sun-Earth L1 Lagrange point. From this vantage point, such an observatory would be able to scan the region of space closest to the Sun with unprecedented sensitivity, detecting asteroids that would otherwise remain hidden. This is the fundamental concept behind NEOMIR (Near-Earth Object Mission in the Infrared), a proposed ESA concept mission, designed to provide early warning for asteroids approaching from the daytime sky [3]. NASA's Near-Earth Object (NEO) Surveyor will also be at L1 Lagrange point [4], but NEOMIR will be complementary in terms of survey region. By observing in the infrared at small solar elongations, NEOMIR would complement existing ground-based surveys and significantly enhance our ability to detect and respond to imminent impact threats. By positioning NEOMIR at the Sun-Earth Lagrange point L1, ESA aims to maximize early detection capabilities for hazardous asteroids approaching from the Sun's direction. However, these asteroids are typically detected at high phase angles (angle between the Sun and the observer as seen from the asteroid) as seen from NEOMIR at L1 Lagrange point.Hence, the mission's success will depend on addressing the technical and observational challenges posed by high phase-angle detections, ultimately improving our ability to provide timely warnings for potential impactors. Unlike visible-light observations, which rely on sunlight reflected off an asteroid's surface, in the medium infrared it is possible to measure the thermal radiation emitted by the asteroid itself. This advantage becomes especially crucial at high phase angles — when the Sun, the asteroid, and the observer form a nearly straight line. At such angles, only a small fraction of the asteroid's illuminated surface is visible in reflected light, making it difficult to detect the body. However, in the thermal infrared, an asteroid's emission originates from most of its surface, which remains warm and radiates detectable heat. Despite these advantages, observing asteroids in the thermal infrared at high phase angles presents significant challenges. The extreme observing geometry complicates flux predictions, as both standard and sophisticated thermal models have not been fully validated for such conditions. Additionally, space-based detectors operating near the Sun must contend with high background noise from zodiacal dust emission and stray light, which can limit sensitivity. Overcoming these obstacles requires careful optimization of telescope location, observation strategy, and data processing techniques.To simulate NEOMIR observations of imminent Earth impactors, we employ a ThermoPhysical Model (TPM; implementation based on [5]) to compute infrared fluxes from synthetic asteroid populations. These fluxes will then be analyzed with simple thermal models, which output the estimated diameter of the synthetic asteroid. The error between these derived diameters and the original ones (used as input for the TPM) will then be discussed. In this presentation, we provide an overview of the NEOMIR mission and present a simulation framework to estimate the infrared fluxes of synthetic asteroids, using a TPM and physically plausible assumptions about their properties (e.g., thermal inertia and pole orientations).AcknowledgmentsThis work was supported by the French government through the France 2030 investment plan managed by the National Research Agency (ANR), as part of the Initiative of Excellence Université Côte d'Azur under reference number ANR-15-IDEX-01. This work was supported by JSPS KAKENHI grant Number JP23KJ0640.References:[1] Veres et al., 2009, Icarus, Vol. 203, 472.[2] Müller et al., submitted to Advances in Astronomy.[3] Conversi et al., 2024, Proceedings of the SPIE, Vol. 13092, 130922H.[4] Mainzer et al., 2023, PSJ, Vol. 4, 224.[5] Delbo' et al., 2007, Icarus, Vol. 190, 236.