## 1 Introduction
Several experimental works have been carried out, mostly under terrestrial gravity and for low to medium kinetic energy, to measure the collision time, defined as the interval between the initial contact and the moment the impactor comes to rest. This information has been obtained, for example, by direct measurements of the acceleration of objects impacting granular media [17] (Figure 1). Efforts have been made by researchers to model the drag force related to impacts [18; 19]. Scaling laws for penetration depth and for collision duration have been obtained by [PERSON] and [PERSON] [17]. According to the authors, collision time \(t_{c}\) is independent of collision velocity \(v_{c}\) for sufficiently high \(v_{c}\). [PERSON] at al. [20] logged in the laboratory, by means of piezoresistive sensor, the stress variation with time at the bottom of a lunar simulant bed during low kinetic energy impact due to free fall of sphere, an information indirectly related to the collision time. In addition, strain measurements can give information on the duration of an impact: [PERSON] et al. [21], looking at the micrometeoroid/orbital debris impact detection for spacecrafts, used fiber Bragg gratings to measure the in-plane strain fields of an aluminium plate, and the related time history, caused by projectile traveling at hypervelocity speeds. Deducing a collision time for meteoroid impact on the Moon is however still a challenge, also due to the difficulty of in situ recording of the impulse history during real impact events. The seismic excitation caused by meteoroid impact may indirectly provide information on the collision: [PERSON] et al. [22], based on Apollo-recorded impacts, found relationships between the momentum transfer of the impactor and the duration of the related seismic excitation process. Indirect information on the impact duration and magnitude may also derive from telescope observation, considering duration and brightness of the associated flash, although the light curve duration is not strictly a collision time. Another source of uncertainty is the set of geotechnical parameters of the employed simulant. Although similar to the real lunar soils in terms of composition, the reliability of simulants is necessarily limited. First, the range for geotechnical parameters of the real lunar regolith is not so narrow, whereas a specific simulant possesses a unique grain size distribution. Secondly, even assuming perfect correspondence between real and simulated regolith in terms of granulometry and mineralogy, a terrestrial laboratory generally does not reproduce the space environment. According to [PERSON] et al. [23], lunar submicroscopic iron (SMFe), as one of the main products of space weathering, is a good indicator of maturity. It is however difficult to reproduce the space weathering on Earth and, on the other hand, it is questionable that this weathering reflects on the mechanical properties of lunar soils in a relevant way. More easily, a laboratory assessment of simulant reliability could concern the response of the material to thermal cycles characterized by temperature variations such as those experienced by the regolith on the Moon surface. In this respect, permanent bulk mechanical changes could derive from fatigue of the single particles, if they are prone to crushing or fracturing. Even dealing with a \"thermally aged\" simulant, under different temperatures the material can exhibit different elastic moduli, the reason why assuming a stiffness value measured at 20 \({}^{\circ}\)C implies some uncertainties in the numerical prediction for real lunar soils. Moreover, for a given temperature, it is well known that an elastic modulus exhibits a decay (Figure 2) with increasing the strain interval over which the stiffness measurement is made [24; 25; 26]. From an engineering point of view, this problem is relevant because the designer needs to assume the expected service strain regime of the geotechnical structure before calculation.