Apollo 15, Lunar Surface - Landing

Landing

At 104 hours, 30 minutes and 12 seconds GET the descent engine of Falcon ignited. Burning at about 10% for the first 26 seconds so that the guidance computer could gimbal the engine to direct the thrust through the center of gravity of the LM, it then thrusted up to 100%. Irwin confirmed that the Abort Guidance System (AGS) agreed with the Primary Guidance and Navigation System (PGNS) on their height and rate of descent.

At three minutes the computer rolled the spacecraft so that they were now on their back, with the windows facing away from the lunar surface. This was so the landing radar could acquire the surface. Scott then announced the altitude and velocity lights, indicating the computer was getting acceptable data from the radar. Six minutes into the burn they were 30,000 feet (9000 m) above the surface.

In Mission Control, the Flight Director learned that tracking data indicated they were going to land 3000 feet (900 m) south of the targeted landing site. Although at first he decided not to tell the crew, Ed Mitchell, the CapCom, convinced him otherwise. During this time Scott was trying to see the ground through his window. He thought they were going to land as long as he could see Mount Hadley Delta. He was unable to see the Rille, something that had been possible in the simulators.

Nine minutes and ten seconds into the burn, Program 64 started on the computer and the LM pitched forward and the crew could see the ground. Using scribe marks on the window and angles read to him by Irwin, Scott found where the computer was predicting the landing site to be and then used a hand controller to move the predicted location. He did this 18 times during the landing, moving the target site a total of 338 meters (1110 feet) uprange and 409 meters (1341 feet) north.

Scott's main problem was that there was very little detail on the surface. The best images of the site only had 66 ft (20 m) resolution and photoanalysers had overenhanced the images. The main problem was overestimating the depth of craters, so as to make them have shadows at higher sun angles. Fortunately he was able to see four craters, Matthew, Mark, Luke and Index (the reason it was called Index and not John was due to Madalyn Murray O'Hair, an outspoken atheist who had sued NASA over the reading of Genesis during Apollo 8. Although she lost the case, NASA remained squeamish on overtly religious announcements on later flights).

Irwin began reading the altitude, rate of descent and the projected landing site. At 400 ft (120 m), the computer was switched to Program 66, designed for the landing phase. From now on Scott was flying manually. Irwin stopped reading out the projected landing site. Passing through 120 ft (37 m) Scott said he was picking up some dust. By the time they got to between 60 and 50 ft (18 to 15 m) the view outside would be completely obscured by dust.

Irwin then announced that the contact light had illuminated, indicating one of the landing probes on the LM's feet had contacted the ground. Immediately Scott cut the engine. With the extended engine bell there was a fear that it could touch the ground and cause exhaust to travel back into the engine. It is estimated that they were travelling 6.8 ft/s (2 m/s) when they hit, twice as fast as previous missions. A few seconds later, Scott informed the ground that "Okay, Houston. The Falcon is on the Plain at Hadley." Falcon was tilted nearly 10 degrees to its back left, just 5° below the maximum acceptable angle. It set down on the rim of a crater such that its engine bell was damaged, and with one of the legs in the crater. They were about 600 meters north and about 175 meters west of the targeted landing site. This was of little concern though thanks to the capabilities of the rover.