Apollo EVAs - Astronaut Experiences on the Slopes

APOLLO EVAs - ASTRONAUT EXPERIENCES ON THE SLOPES. Wajiha Iqbal1, James W. Head III2, Carolyn H. van der Bogert1, Thomas Frueh1, Megan R. Henriksen3, Valentin Bickel4, David Kring5, Harald Hiesinger1, David R. Scott2,6, and Thomas Heyer1, 1Universität Münster DE, 2Brown University US, 3Intuitive Machines, US, 4University of Bern CH, 5USRA US, 6Apollo 15 Commander. ([email protected]) Introduction: The topography of a designated landing region constitutes a critical factor in the operational safety and planning of extravehicular activities (EVAs). Digital terrain models (DTMs) and derived slope maps are therefore employed to impose constraining factors on proposed EVA paths characterized by minimal slopes and elevation discrepancies. It is evident that technical constraints are associated with the use and operation of equipment and tools, including suits and instrument carts, as well as with astronaut trafficability when on foot. Notwithstanding the advances in these areas, it is crucial to consider the observational, physiological, and psychological experiences and constraints of astronauts when planning successful EVAs. This study [1] examined Apollo astronaut reports as well as audio and video recordings to ascertain the experience and performance of the astronauts in relation to the topography and slopes encountered during their EVAs. Data and Methods: We conducted an analysis of the elevations and slopes along the traverses of the Apollo landing sites. We used the Lunar Reconnaissance Orbiter (LRO) Narrow Angle Camera (NAC) derived Digital Terrain Model (DTM) with a 2 m/pixel scale and the corresponding slope map with a 6 m baseline [2,3] (Fig. 1). The topographic profiles of each Apollo landing site traverse were extracted in ArcGIS Pro and imported into Matlab for evaluation. These profiles have been simplified and vertically exaggerated by a factor of two (Fig. 1). In addition, an extensive archive of Apollo mission journals, images, and video libraries maintained by NASA was examined [5]. From this archive, we extracted discussions among the astronauts about their experiences dealing with challenging terrain. Perception of Distances: The Apollo astronauts reported challenges in accurately perceiving the distance and size of objects [5]. Furthermore, incorrect size and distance estimations have been documented among terrestrial travelers, which are attributed to the absence of objects for comparison [5]. The perceptions of astronauts are significantly influenced by lighting conditions. In conditions with low sun angles, which are predominant during lunar landings due to the time of day, shadows appear longer (Fig. 2), and the terrain appears more hilly compared to high sun angles. [7] Perception of Slopes: The Center of Lunar Science and Exploration [7] has classified slopes with inclinations of less than 25° as highly accessible.  The Apollo 15 traverse (gray line) is shown (left) on a 10m contour DTM derived from the LRO NAC and (right) on a slope map. The bottom profile shows the change in elevation along EVA 1 (from the Lunar Module to station 2 along the Hadley Rill) and EVA 2 (from the Lunar Module to station 6A). Stations (encircled) are shown on the traverse and above their location on the profiles. However, more detailed quantitative data on the performance of Apollo and Lunokhod [7] provides spe cific guidelines for use under both Earth-based and lunar conditions [8]. The perception of slope steepness can also be affected by lighting conditions, with boulders on slopes casting particularly long shadows, which can exaggerate the actual steepness of the slope. Additionally, the lunar surface is characterized by a soft regolith, which poses a challenge for walking on uphill slopes, as reported by Apollo 15 astronauts (Fig. 2). However, the Moon's gravitational force is ~ 1/6th that of Earth, which reduces the risk of astronauts sliding downhill [4]. Astronauts have noted that they relied on their center of gravity, which shiftsas they walk downhill [4]. Moreover, Apollo astronauts frequently reported the challenge of traversing slopes due to the restricted mobility that carrying their tools and samples imposed e.g. astronauts found it difficult to climb uphill with the MET (Modular Equipment Transporter). This limitation in movement resulted in a longer time needed to complete a traverse [4].The lunar roving vehicle (Fig. 2) was introduced to the Apollo 15, 16, and 17 missions to facilitate the exploration of greater distances and steeper slopes by the astronauts. Lessons Learned for the Planning of Future Missions: The Artemis landing sites were selected for their strategic location, taking into account both scientific merit and accessibility. Specifically, these sites were chosen to be located on ridges and large crater rims at the South Pole, in well-lit areas with good ground visibility. It was hypothesized that these sites would provide access to regions of potentially volatile-rich Permanent Shadow Regions (PSRs), but it should be noted that the selected landing sites are located in more complex geologic terrains that may require more time at individual stations to successfully complete assigned tasks. For comparison, the Apollo astronauts ascended to heights of up to 500 feet (150 m) during their missions, traversing slopes of < 15°. The Apollo astronauts traversed regions near the equator on relatively flat surfaces, but they perceived these regions as uneven when viewed at low angles of sunlight. This effect can be amplified near the South Pole, potentially limiting visibility and mobility during Extra Vehicular Activity (EVA) exploration. It is imperative to prioritize safety measures [7] and draw lessons from previous successful missions to ensure optimal outcomes. References: [1] Iqbal, W., et al (2024) Acta Astro. (223), 184-196 [2] Scholten F., et. al. (2012). J. Geophy. Res. Planet 117 (E12), 2156–2202. [3] Henriksen M. R., et. al. (2017). Icarus 283, 122–137. [4] Jones E. M., Glover K. (2017). Apollo lunar surface journal. NASA. [5] Darwin, C, (1835) ch. XV, p 347, ISBN-13 : 978-1787377424 [6] van der Bogert, C. H., et. al. (2022). LPSC 53., # 1347. [7] Kring, D. A., Durda, D. (2012). LPI. #1694. [8] Basilevsky, A.T., et al. (2019). Solar System Research, 53, 383398.  (a) AS15-85-11437HR was taken during the Apollo 15 EVA1. It captured Dave Scott examining the Station 2 boulder while the rover in the foreground is resting on a ~13◦ slope.(b) AS15-85-11514HR shows Dave Scott standing next to a small crater at Station 6 during Apollo 15 EVA2. The LRV is tilted on the steep slope of ~11◦ behind him.