Editing Apollo 15 (section)

=== Lunar orbit and landing ===
[[File:Interior of Apollo 15 lunar module (prior to launch).jpg|thumb|upright=1.2|alt=Control panel of lunar lander|The interior of ''Falcon'']]
[[File:Apollo CSM lunar orbit.jpg|thumb|upright=1.2|The Apollo 15 command and service module in lunar orbit, photographed from ''Falcon'']]
On Apollo 11 and 12, the Lunar Module decoupled from the CSM and was piloted to a much lower orbit from which the lunar landing attempt commenced; to save fuel in an increasingly heavy lander, beginning with Apollo 14, the SPS in the service module made that burn, known as descent orbit insertion (DOI), with the lunar module still attached to the CSM. The initial orbit Apollo 15 was in had its [[apocynthion]], or high point, over the landing site at Hadley; a burn at the opposite point in the orbit was performed, with the result that Hadley would now be under the craft's [[pericynthion]], or low point.<ref group=ALFJ name=orbit>{{cite web |url=https://history.nasa.gov/afj/ap15fj/10day4_lunar_orbit.html |title=Day 4: Lunar Orbit |year=1998 |editor-last=Woods |editor-first=W. David |editor-last2=O'Brien |editor-first2=Frank |work=Apollo 15 Flight Journal |publisher=NASA |access-date=September 5, 2018 |archive-url=https://web.archive.org/web/20171225233957/https://history.nasa.gov/afj/ap15fj/10day4_lunar_orbit.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref> The DOI burn was performed at 082:39:49.09 and took 24.53 seconds; the result was an orbit with apocynthion of {{convert|58.5|nmi}} and pericynthion of {{convert|9.6|nmi}}.{{sfn|Orloff & Harland|p=435}} Overnight between July 29 and 30, as the crew rested, it became apparent to Mission Control that [[Mass concentration (astronomy)|mass concentrations]] in the Moon were making Apollo 15's orbit increasingly elliptical—pericynthion was {{convert|7.6|nmi}} by the time the crew was awakened on July 30. This, and uncertainty as to the exact altitude of the landing site, made it desirable that the orbit be modified, or trimmed. Using the craft's [[Reaction control system|RCS]] thrusters,<ref group=ALFJ name=waking>{{cite web |url=https://history.nasa.gov/afj/ap15fj/11day5_wakeup.html |title=Day 5: Waking in the Descent Orbit |year=1998 |editor-last=Woods |editor-first=W. David |editor-last2=O'Brien |editor-first2=Frank |work=Apollo 15 Flight Journal |publisher=NASA |access-date=September 6, 2018 |archive-url=https://web.archive.org/web/20171225233954/https://history.nasa.gov/afj/ap15fj/11day5_wakeup.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref> this took place at 095:56:44.70, lasting 30.40 seconds, and raised the pericynthion to {{convert|8.8|nmi}} and the apocynthion to {{convert|60.2|nmi}}.{{sfn|Orloff & Harland|p=435}}

As well as preparing the Lunar Module for its descent, the crew continued observations of the Moon (including of the landing site at Hadley) and provided television footage of the surface. Then, Scott and Irwin entered the Lunar Module in preparation for the landing attempt. Undocking was planned for 100:13:56, over the far side of the Moon, but nothing happened when separation was attempted.<ref group=ALFJ name=preparations>{{cite web |url=https://history.nasa.gov/afj/ap15fj/12day5_landing_prep.html |title=Day 5: Preparations for Landing |year=1998 |editor-last=Woods |editor-first=W. David |editor-last2=O'Brien |editor-first2=Frank |work=Apollo 15 Flight Journal |publisher=NASA |access-date=December 15, 2018 |archive-url=https://web.archive.org/web/20171225233954/https://history.nasa.gov/afj/ap15fj/12day5_landing_prep.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref> After analyzing the problem, the crew and Houston decided the probe instrumentation umbilical was likely loose or disconnected; Worden went into the tunnel connecting the command and lunar modules and determined this was so, seating it more firmly. With the problem resolved, ''Falcon'' separated from ''Endeavour'' at 100:39:16.2, about 25 minutes late, at an altitude of {{convert|5.8|nmi}}. Worden in ''Endeavour'' executed a SPS burn at 101:38:58.98 to send ''Endeavour'' to an orbit of {{convert|65.2|nmi}} by {{convert|54.8|nmi}} in preparation for his scientific work.{{sfn|Orloff & Harland|p=432}}

Aboard ''Falcon'', Scott and Irwin prepared for powered descent initiation (PDI), the burn that was to place them on the lunar surface, and, after Mission Control gave them permission,<ref group=ALSJ name=landing /> they initiated PDI at 104:30:09.4 at an altitude of {{convert|5.8|nmi}},{{sfn|Orloff & Harland|p=432}} slightly higher than planned. During the first part of the descent, ''Falcon'' was aligned so the astronauts were on their backs and thus could not see the lunar surface below them, but after the craft made a pitchover maneuver, they were upright and could see the surface in front of them. Scott, who as commander performed the landing, was confronted with a landscape that did not at first seem to resemble what he had seen during simulations. Part of this was due to an error in the landing path of some {{convert|3000|ft}}, of which CAPCOM [[Edgar Mitchell|Ed Mitchell]] informed the crew prior to pitchover; part because the craters Scott had relied on in the simulator were difficult to make out under lunar conditions, and he initially could not see Hadley Rille. He concluded that they were likely to overshoot the planned landing site, and, once he could see the rille, started maneuvering the vehicle to move the computer's landing target back towards the planned spot, and looked for a relatively smooth place to land.<ref group=ALSJ name=landing />{{sfn|Reynolds|p=174}}

[[File:Apollo 15 landing on the Moon.ogg|thumb|upright=1.2|alt=Film showing the lunar surface as the lander descends to it|Apollo 15 landing on the Moon at Hadley, seen from the perspective of the Lunar Module Pilot. Starts at about {{convert|5000|feet|m}}.]]
Below about {{convert|60|ft}}, Scott could see nothing of the surface because of the quantities of lunar dust being displaced by ''Falcon''{{'s}} exhaust. ''Falcon'' had a larger [[Rocket engine nozzle|engine bell]] than previous LMs, in part to accommodate a heavier load, and the importance of shutting down the engine at initial contact rather than risk "blowback", the exhaust reflecting off the lunar surface and going back into the engine (possibly causing an explosion) had been impressed on the astronauts by mission planners. Thus, when Irwin called "Contact", indicating that one of the probes on the landing leg extensions had touched the surface, Scott immediately shut off the engine, letting the lander fall the remaining distance to the surface. Already moving downward at about {{convert|.5|ft}} per second, ''Falcon'' dropped from a height of {{convert|1.6|ft}}. Scott's speed resulted in what was likely the hardest lunar landing of any of the crewed missions, at about {{convert|6.8|ft}} per second, causing a startled Irwin to yell "Bam!" Scott had landed ''Falcon'' on the rim of a small crater he could not see, and the lander settled back at an angle of 6.9 degrees and to the left of 8.6 degrees.<ref group=ALSJ name=landing />{{sfn|Mission Report|p=62}} Irwin described it in his autobiography as the hardest landing he had ever been in, and he feared that the craft would keep tipping over, forcing an immediate abort.{{sfn|Irwin|p=59}}

''Falcon'' landed at 104:42:29.3 (22:16:29 GMT on July 30), with approximately 103 seconds of fuel remaining, about {{convert|1800|ft}} from the planned landing site.{{sfn|Orloff & Harland|p=432}} After Irwin's exclamation, Scott reported, "Okay, Houston. The ''Falcon'' is on the Plain at Hadley."{{efn|[[The Plain (West Point)|The Plain]] was a shoutout to Scott's alma mater, West Point, as that is the name of the [[parade ground]] there.<ref group=ALSJ name=landing />}}<ref group=ALSJ name=landing /> Once within the planned landing zone, the increased mobility provided by the Lunar Roving Vehicle made unnecessary any further maneuvering.{{sfn|Mission Report|p=95}}