The Lunar Orbiter II-070-H image (Frame 70, High resolution) has a unique feature that is relevant to the LCROSS mission. This image shows the impact site of the Ranger 8 mission. This location was identified decades ago and is discussed in the NASA SP-168 online address. This location was also photographed during the Apollo 16 mission (NASA SP-315 page 29-46) but at a lower resolution of 3-5 meters. The image was taken from an altitude of 45.81 km. The resolution is about 0.4 meters per pixel. The crater from the Ranger impact is not well defined in the existing film database, especially as it appears at the boundary between two framelets.
Figure 1 is the reproduced trajectory of the Ranger 8 mission from NASA SP-168:
Figure 2 shows the detail of the projected impact point:
The scale of an entire framelet is ~200 meters. While the full framelet is not shown here, the ragged overlap between two framelets from the film version of the image has lead to a misleading conclusion regarding the size and the shape of the crater. Crater C1 was disputed as the location of the impact in another NASA document (SP-315). The Apollo 16 preliminary science report (SP-315) identifies crater C2 as the impact point of
Ranger 8 because it is consistent with other craters photographed by the later Apollo missions. The central mound is a distinctive signature of these impacts. Figure 3 is a low resolution version of our updated image from the LOIRP scans.
Figure 4 shows the enhanced detail available from the LOIRP analog data tapes. Since the contrast is muted due to the nature of the site, the dynamic range improvements are not as noticeable. In the digital domain the framelet edges can be repositioned to generate a super-resolution version of the image by scanning the tape multiple times. The central mound, which seems to be an indicator of these small craters (as discussed in NASA SP 315 for the SIV-B impacts) is clearly evident here. The dark surrounding ejecta blanket was not expected, which drove the early identification of crater C1 as the impact point. However, it is unclear if the light colored ejecta to the lower left is associated with crater C1 or C2.
From a science perspective we are able to discern the size of the crater to a precise number (12.5 meters), which can give the LCROSS team a ground truth for similarly sized spacecraft.
Posted by: Soderman/NLSI Staff
Source: D. Wingo/ LOIRP