Identification of sunlit area's, using Clementine images superimposed on a lunar south pole radar image (Arecibo Observatory)
Clementine ground tracks (green) and echo strength (white) of the Radar Reflection Experiment, showing the evidence of water-ice in permanently dark area's (red)(S.Nozette, Clementine)
EuroMoon 2000 foresees a landing on the western rim of the South Pole crater, within the scientifically relevant Aitken Basin and close to potential reservoirs of frozen volatiles and therefore a potential site for a future manned outpost.
Major advantages of this site are its essentially permanent sunlight, and the ease of recognising the terrain features for the approach and landing. In addition, a landing site close to a Pole can be observed repeatedly from orbit and the landing can be effected during every orbital pass, at the expense of a modest additional delta-V.
The target landing site is within a several kilometre square portion of the western rim of the - as yet unnamed - South Pole crater (diameter 20 km). Information about the exact nature of the terrain there is sketchy. Data from Clementine's camera, with a resolution of a few hundred metres, are available for parts of the South Pole area, and radar imaging from the Arecibo Observatory yields data with approximately 150 m resolution with fewer obscured areas. 70 m-resolution images are expected from Arecibo within the next two years.
The area around the South Pole looks rather old and is of the general highlands type, i.e. smooth, rounded-edged old craters and a thick blanket of regolith. The almost undisturbed circular shape of the South Pole crater seems to suggest a somewhat younger age. Younger craters tend to have boulders nearer to their rims, as well as external slopes of up to 20-25° (steeper than for older craters). Erosion tends to make lunar terrains smoother, even if they appear rough at lower resolution; conditions are different from those encountered in mountainous regions on Earth, because of the different geological phenomena prevailing.
The rim of the South Pole crater is expected to be reasonably free of boulders. Although boulders as large as 70 m across may be expected among the ejecta of a 20 km crater, these will be further away from the rim. However, boulders in the order of 1 m across may be as close as 1 2 km from the rim. The proposed landing scenario is therefore based on the assumptions that there are unlikely to be large boulders on the rim itself, and that the Lander can be redirected (hovering phase) if an obstacle is observed.
The landing should occur on the top of the rim, or on the less-steep outer side of the crater, to ensure good lighting conditions. To reduce the risk during landing, imaging of the landing site from orbit with a resolution of better than 10 m is to be conducted, the total area available for landing being limited by the sunlight constraints to a few square kilometres.
The landing calls for the overflight of a region with mountains several thousand metres high, whilst the South Pole crater's rim rises only about one thousand metres above the surrounding surface. The local topography and the local gravity model therefore need to be researched in advance with sufficient accuracy.
At this near-polar landing site (not more than 10 km from the South Pole), the Sun will exhibit a seasonal variation in elevation of ±1.5° (summer solstice being in April 2001). The Earth will be seen from the landing site with a variation in azimuth of about ±5.5° over a lunar day (i.e. elevation >0 for 50% of the time), rising to a maximum of 7° above the horizon around mid-summer.