From photographic record to virtual worlds: the case of Apollo and rover missions

Thanks to the computational power of current graphic cards, photographic archives can be turned into three dimensions virtual worlds. The Structure from Motion photogrammetry technique simply requires a set of overlapping images, acquired from different viewing points, to reconstruct in 3D the observed landscape elements. This technique can also be applied on rock samples characterized in the laboratory. We have applied this technique to scanned photographs of the Moon acquired during the Apollo 17 mission [1, 2, 3]. In the case of the “Station 6” geological waypoint investigated by the astronauts at Taurus Littrow during their third EVA, we found that 154 images can be automatically aligned into a single photogrammetric project [4]. This allows to generate a textured polygonal mesh of the nearly complete Station 6 area and to retrieve the respective size and orientation of the large main boulders that bounced down the North Massif, coming to rest at a change in slope.

     We have also shown in [4] that 3D reconstruction process also works for lunar rock samples that have been photographed during the 70s before being sawed for analysis. This allows for example to setup a Virtual Reality (VR) immersive simulation where the user can replace the samples at their exact location and orientation directly on their parent boulder. Satellite images such as Kaguya/TC or LRO/LROC can be used to provide the general context in the VR simulation. They can eventually be completed by other cartographic products, as would be done in a GIS system, to include for example false color composites from Clementine to give some compositional context to the in situ sites. 

    Following the work on Station 6, we have undergone new 3D reconstructions on the next geological waypoint, the Station 7. In this case, we were able to reconstruct three rock samples in 3D using 96 LPI laboratory archived photographs. Their parent boulder and the local lunar ground was reconstructed using 85 Apollo images. These new 3D elements have been added in the previous VR simulation (Figure 1).

    The 3D analysis can be used for outreach, education or scientific investigation. For outreach, the use of an application designed for a standalone VR headset provides the most versatile and cost effective solution. More ambitious projects (with a wider high-resolution cartographic coverage and several highly detailed digital outcrop models) would benefit from a VR headset connected by a cable to a gaming computer. In addition to students, this kind of 3D reconstructions could also be used in astronaut training simulations to provide realistic cases. On the science side, it allows to investigate problematics linked for example to the effect of space weathering on lunar surface rocks. We could also envisage deriving the absolute position and orientation of specific lunar rock samples, which could give new insight and constrains to paleo-magnetic studies [5, 6]. Forthcoming robotic (and possibly manned) missions could take advantage of these new photogrammetric capabilities to optimize the image acquisition strategy during the in situ exploration phase.

Figure 1: Perspective view of a Virtual Reality scene of Station 7 reconstructed using photogrammetry on a set of Apollo photographs. The ground is mainly retrieved from the 360° panorama taken by G. Cernan. An LRO image provides the context. Astronaut’s footprints and rover tracks appear readily in the textured photogrammetric ground. The LRV is a 3D model added to give a better sense of scales. Sample 77115 has been also reconstructed in 3D from archived photographs and replaced at its original location on the parent boulder. Station 6, located at 475m and also included in the VR simulation, is seen in the upper left

References

[1] Wolfe, E.W. et al., Geologic investigation of the Taurus-Littrow Valley: Apollo 17 landing site. U.S. Geol. Surv. Prof. Pap. 1981, 1080, 225–280

[2] Schmitt, H.H. et al., Revisiting the field geology of Taurus-Littrow. Icarus, 298, 2–33, doi:10.1016/j.icarus.2016.11.042, 2017

[3] Le Mouélic, S. et al., Investigating Lunar Boulders at the Apollo 17 Landing Site Using Photogrammetry and Virtual Reality, Remote Sensing, vol 12, 11, DOI10.3390/rs12111900, 2020.

[4] Le Mouélic, S. et al., Photogrammetric 3D reconstruction of Apollo 17 Station 6: From boulders to lunar rock samples integrated into virtual reality, Planet. Space Sci., 240, doi:10.1016/j.pss.2023.105813, 2024.

[5] Weiss, B. P. & S. M. Tikoo, The lunar dynamo, Science 346 (6214), 1246753, 2014.

[6] Nichols, C.I. O. et al., The paleoinclination of the ancient lunar magnetic field from an Apollo 17 basalt. Nature Astonomy, 5, 1216-1223, 2021.