Máni an exploration mission for the Moon

Introduction

Efforts to quantify lunar surface properties, rover traversability, potential for in-situ resource utilization, or geological processes, all benefit from better optical resolution. The obvious preference for higher resolution is however bound by optical limitations potentially necessitating unwieldy large telescopes to meet the desired goals. To overcome this limitation, multi-angular photometry provides an innovative pathway to evaluate surface properties at subpixel scales, thereby alleviating the need for unfeasible telescope payloads while still meeting the desired exploration goals.

 

Mission concept

We propose a multi-angular photometry mapping mission that will provide an optical map and digital elevation model (DEM) of target areas of the Lunar surface at a resolution as good as 20 cm/pixel. Additionally,this mission will provide unique knowledge of the reflectivity and micro-texture of the Lunar surface down to µm scales. To meet these objectives, we will exploit the exciting developments in multi-angular photometric methods (Fernandes & Mosegaard, 2022; Fernando et al., 2013, 2016; Schmidt & Bourguignon, 2019) to quantify the key surface parameters and produce DEMs down to the scale of the optical resolution – as well as quantify the associated uncertainties.

To utilise the novel photometric mapping approach, a dedicated exploration strategy is required. Usually, the exploration strategy for a mapping mission is to maximise surface resolution and coverage. This implies that the acquisition of overlapping images is limited, and that images are preferentially acquired in nadir geometry (perpendicular to the surface). To apply the multi-angular photometric approach, we need multiple (5+) overlapping images at phase angles (angle between the incident light and reflected light) between 0° to more than 110° to be able to constrain the subpixel characteristics of the surface (Schmidt & Bourguignon, 2019) including precise Bayesian uncertainties propagation (Mosegaard, K. & Tarantola, 1995). This range of observation geometries has never been observed on the Moon and constitute the main goal of our mission.

 

Figure1: Concept of the mission. The target will be observed several times (> 5) at spatial resolution 20 cm/pixel, during one orbit, at several observations conditions (emergence direction). We plan to target ~1000 areas of interest all over the Moon. The main products are the images, the precise topography (20 cm/pixel), and the local average microtexture parameters (µm scale roughness, µm scale grain shape).

 

We envision the orbiter would be placed in a low Lunar orbit that enable mapping of areas of interest over the entire Lunar surface, with a nominal mission duration of three years. Key areas of interest, e.g., Artemis and Argonaut landing site candidates and other areas of geological and exploration interest identified in collaboration with ESA and the planetary exploration community, will be prioritised for observations and coverage then continuously expanded to maximise coverage of the Lunar surface.

The scientific payload consists of two imagers: a primary high-resolution panchromatic imager based on a 25 cm diameter telescope to acquire the high-resolution images needed for the multi-angular photometric mapping and a supporting wide-angle colour imager. The wide-angle colour imager provides colour documentation of the Lunar surface as context for the high-resolution greyscale images. The imagers will be fixed on the orbiter, and the orbiter attitude control system will be utilised to acquire images with the range of observation geometries required.

The resulting map of the Lunar surface properties (elevation, roughness, microtexture) will represent a clear improvement to the existing knowledge of the Lunar surface and augment existing scientific datasets to substantially improve geological maps and answer scientific questions, e.g., regarding space weathering, impact crater formation, lava flow thickness etc.. For future Lunar exploration missions, the mission data will provide key information to better assess rover traversability, landing-site suitability and characterize the candidate areas for in-situ resource utilization. In particular, the ability to provide predictions measurements of surface microtexture properties and their associated uncertainty presents a unique ability to de-risk mission-critical decisions. Furthermore, the knowledge of model uncertainty holds the potential to enable a reduction in how much data needs to be downlinked without losing trust in model predictions – thereby making photometric mapping feasible for missions further from Earth where downlink capability is limited. Finally, the refinements this mission will provide to our knowledge of the Lunar surface reflectivity holds great promise to also support Earth Observation missions by enabling high-quality independent estimates of terrestrial albedo.

 

Conclusion

This concept is currently in pre-phase A at ESA. Our proposed mission addresses three of the four exploration goals for this call, most prominently the priority area of “Providing improved / higher resolution mapping of potential landing sites and locations of high interest for Exploration”. The high-resolution multi-angle images with a resolution as good as 20 cm/pixel, but also the high-resolution DEM and the derived µm scale micro-texture properties (roughness, grain shape) will provide unprecedented information on the target areas. The mission is also relevant for the priority areas “Observing, predicting and mitigating changes that human activity will introduce to these environments” as this mission will enable quantification of temporal effects to the micro-texture of the surface after any outside disturbance. Finally, the mission can contribute to “Finding, characterising, and quantifying potential resources and understanding how local environments affect resource extraction processes” by providing precise topography and related micro-texture parameters of areas of interest for resource utilisation.

 

Reference

Fernandes, I. & Mosegaard, K., Planetary and Space Science, 2022, http://dx.doi.org/10.1016/j.pss.2022.105514

Fernando, J.; Schmidt, F. & Douté, S., Planetary and Space Science, 2016, http://dx.doi.org/10.1016/j.pss.2016.05.005

Fernando, J.; Schmidt, F.; Ceamanos, X.; Pinet, P.; Douté, S. & Daydou, Y., Journal of Geophysical Research (Planets), 2013, http://dx.doi.org/10.1029/2012JE004194

Mosegaard, K. & Tarantola, A., Journal of Geophysical Research, 1995, http://dx.doi.org/10.1029/94JB03097

Schmidt, F. & Bourguignon, S., Icarus, 2019, http://dx.doi.org/10.1016/j.icarus.2018.06.025