Editing Apollo 15 (section)

== Mission highlights ==

=== Launch and outbound trip ===
[[File:Apollo 15 launch.ogg|thumb|right|alt=Film of a rocket lifting off|Apollo 15 launches on July 26, 1971]]
{{main|Journey of Apollo 15 to the Moon}}

Apollo 15 was launched on July 26, 1971, at 9:34{{nbsp}}am [[Eastern time|EDT]] from the [[Kennedy Space Center]] at [[Merritt Island]], Florida. The time of launch was at the very start of the two-hour, 37-minute launch window, which would allow Apollo 15 to arrive at the Moon with the proper lighting conditions at Hadley Rille; had the mission been postponed beyond another window on July 27, it could not have been rescheduled until late August. The astronauts had been awakened five and a quarter hours before launch by Slayton, and after breakfast and suiting up, had been taken to Pad 39A, launch site of all seven attempts at crewed lunar landing, and entered the spacecraft about three hours before launch. There were no unplanned delays in the countdown.<ref group=ALFJ name=launch>{{cite web |url=https://history.nasa.gov/afj/ap15fj/01launch_to_earth_orbit.html |title=Launch and Reaching Earth 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/20171225233954/https://history.nasa.gov/afj/ap15fj/01launch_to_earth_orbit.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref>

At 000:11:36 into the mission, the [[S-IVB]] engine shut down, leaving Apollo 15 in its planned parking orbit in [[low Earth orbit]]. The mission remained there for 2{{nbsp}}hours and 40 minutes, allowing the crew (and Houston, via telemetry) to check the spacecraft's systems. At 002:50.02.6 into the mission, the S-IVB was restarted for [[trans-lunar injection]] (TLI), placing the craft on a path to the Moon.<ref group=ALFJ name=launch /><ref group=ALFJ name=earthorbit>{{cite web |url=https://history.nasa.gov/afj/ap15fj/02earth_orbit_tli.html |title=Earth Orbit and Translunar Injection |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/20171225234000/https://history.nasa.gov/afj/ap15fj/02earth_orbit_tli.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref> Before TLI, the craft had completed 1.5 orbits around the Earth.{{sfn|Orloff & Harland|p=430}}

[[File:Apollo 15 TandD.ogv|thumb|left|alt=Video showing the final stages of spacecraft docking with lunar module|Astronaut Al Worden maneuvers the CSM to a docking with the Lunar Module ''Falcon'']]
The command and service module (CSM) and the Lunar Module remained attached to the nearly-exhausted S-IVB booster. Once trans-lunar injection had been achieved, placing the spacecraft on a trajectory towards the Moon, [[Detonating cord|explosive cords]] separated the CSM from the booster as Worden operated the CSM's thrusters to push it away. Worden then maneuvered the CSM to dock with the LM (mounted on the end of the S-IVB), and the combined craft was then separated from the S-IVB by explosives. After Apollo 15 separated from the booster, the S-IVB maneuvered away, and, as planned, impacted the Moon about an hour after the crewed spacecraft entered lunar orbit, though due to an error the impact was {{convert|146|km|nmi|sp=us|order=flip}} away from the intended target.<ref group=ALFJ name=translunar>{{cite web |url=https://history.nasa.gov/afj/ap15fj/03tde.html |title=Transposition, Docking and Extraction |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/20171225233953/https://history.nasa.gov/afj/ap15fj/03tde.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref> The booster's impact was detected by the [[seismometer]]s left on the Moon by Apollo 12 and Apollo 14, providing useful scientific data.{{sfn|Mission Report|p=1}}

There was a malfunctioning light on the craft's [[service propulsion system]] (SPS); after considerable troubleshooting, the astronauts did a test burn of the system that also served as a midcourse correction. This occurred about 028:40:00 into the mission. Fearing that the light meant the SPS might unexpectedly fire, the astronauts avoided using the control bank with the faulty light, bringing it online only for major burns, and controlling it manually. After the mission returned, the malfunction proved to be caused by a tiny bit of wire trapped within the switch.<ref group=ALFJ name=sps>{{cite web |url=https://history.nasa.gov/afj/ap15fj/05day2_checking_sps.html |title=Day 2: Checking the SPS |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/20171225233956/https://history.nasa.gov/afj/ap15fj/05day2_checking_sps.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref><ref group=ALFJ name=summary />

[[File:Apollo 15 Earth1.jpg|thumb|upright|alt=Picture of Earth taken from space|Image of Earth taken during the translunar coast]]
After purging and renewing the LM's atmosphere to eliminate any contamination, the astronauts entered the LM about 34 hours into the mission, needing to check the condition of its equipment and move in items that would be required on the Moon. Much of this work was televised back to Earth, the camera operated by Worden. The crew discovered a broken outer cover on the Range/Range Rate tapemeter. This was a concern not only because an important piece of equipment, providing information on distance and rate of approach, might not work properly, but because bits of the glass cover were floating around ''Falcon''{{'s}} interior. The tapemeter was supposed to be in a helium atmosphere,<ref group=ALFJ name=entry>{{cite web |url=https://history.nasa.gov/afj/ap15fj/06day2_enter_lm.html |title=Day 2: Entering the LM |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/20171225233955/https://history.nasa.gov/afj/ap15fj/06day2_enter_lm.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref> but due to the breakage, it was in the LM's oxygen atmosphere.{{sfn|Mission Report|p=153}} Testing on the ground verified the tapemeter would still work properly, and the crew removed most of the glass using a vacuum cleaner and adhesive tape.<ref group=ALFJ name=entry />{{sfn|Orloff & Harland|p=431}}

As yet, there had been only minor problems, but at about 61:15:00 mission time (the evening of July 28 in Houston), Scott discovered a leak in the water system while preparing to chlorinate the water supply. The crew could not tell where it was coming from, and the issue had the potential to become serious. The experts in Houston found a solution, which was successfully implemented by the crew. The water was mopped up with towels, which were then put out to dry in the tunnel between the command module (CM) and Lunar Module—Scott stated it looked like someone's laundry.<ref group=ALFJ name=laundry>{{cite web |url=https://history.nasa.gov/afj/ap15fj/08day3_leak_hilltop.html |title=Day 3: Leaking Water and the Top of the Hill |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/20171225233959/https://history.nasa.gov/afj/ap15fj/08day3_leak_hilltop.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref>

At 073:31:14 into the mission, a second midcourse correction, with less than a second of burn, was made. Although there were four opportunities to make midcourse corrections following TLI, only two were needed. Apollo 15 approached the Moon on July 29, and the lunar orbit insertion (LOI) burn had to be made using the SPS, on the [[far side of the Moon]], out of radio contact with Earth. If no burn occurred, Apollo 15 would emerge from the lunar shadow and come back in radio contact faster than expected; the continued lack of communication allowed [[Christopher C. Kraft Jr. Mission Control Center|Mission Control]] to conclude that the burn had taken place. When contact resumed, Scott did not immediately give the particulars of the burn, but spoke admiringly of the beauty of the Moon, causing [[Alan Shepard]], the Apollo 14 commander, who was awaiting a television interview, to grumble, "To hell with that shit, give us details of the burn."<ref group=ALFJ name=encounter>{{cite web |url=https://history.nasa.gov/afj/ap15fj/09day4_lunar_encounter.html |title=Day 4: Lunar Encounter |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/20171225233956/https://history.nasa.gov/afj/ap15fj/09day4_lunar_encounter.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref> The 398.36-second burn took place at 078:31:46.7 into the mission at an altitude of {{convert|86.7|nmi|km|sp=us}} above the Moon, and placed Apollo 15 in an elliptical lunar orbit of {{convert|170.1|by|57.7|nmi|km}}.{{sfn|Orloff & Harland|p=431}}

=== 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}}

=== Lunar surface ===
{{main|Apollo 15 operations on the Lunar surface}}

==== Stand-up EVA and first EVA ====
{{quote box | align = right | width = 25em | salign = center
| quote = As I stand out here in the wonders of the unknown at Hadley, I sort of realize there's a fundamental truth to our nature. Man must explore. And this is exploration at its greatest.
| source = David Scott, upon setting foot on the Moon.<ref group=ALSJ name=deploying>{{cite web |url=https://history.nasa.gov/alsj/a15/a15.lrvdep.html |title=Deploying the Lunar Roving Vehicle |year=1996 |editor-last=Jones |editor-first=Eric M. |work=Apollo 15 Lunar Surface Journal |publisher=NASA |access-date=September 13, 2018 |archive-url=https://web.archive.org/web/20171225232151/https://history.nasa.gov/alsj/a15/a15.lrvdep.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref>}}

With ''Falcon'' due to remain on the lunar surface for almost three days, Scott deemed it important to maintain the [[circadian rhythm]] they were used to, and as they had landed in the late afternoon, Houston time, the two astronauts were to sleep before going onto the surface. But the time schedule allowed Scott to open the lander's top hatch (usually used for docking) and spend a half hour looking at their surroundings, describing them, and taking photographs. Lee Silver had taught him the importance of going to a high place to survey a new field site, and the top hatch served that purpose.{{sfn|Chaikin|pp=414–415}}<ref group=ALSJ name=landing>{{cite web |url=http://www.hq.nasa.gov/alsj/a15/a15.landing.html |title=Landing at Hadley |year=1996 |editor-last=Jones |editor-first=Eric M. |work=Apollo 15 Lunar Surface Journal |publisher=NASA |access-date=July 14, 2011 |archive-url=https://web.archive.org/web/20110628230652/http://www.hq.nasa.gov/alsj/a15/a15.landing.html |archive-date=June 28, 2011 |url-status=live |df=mdy-all }}</ref><ref group=ALSJ name=seva>{{cite web |title=Stand-Up EVA |url=http://www.hq.nasa.gov/alsj/a15/a15.seva.html |year=1996 |editor-last=Jones |editor-first=Eric M. |work=Apollo 15 Lunar Surface Journal |publisher=NASA |access-date=July 14, 2011 |archive-url=https://web.archive.org/web/20110628231634/http://www.hq.nasa.gov/alsj/a15/a15.seva.html |archive-date=June 28, 2011 |url-status=live |df=mdy-all }}</ref> Deke Slayton and other managers were initially opposed due to the oxygen that would be lost, but Scott got his way.{{sfn|Scott & Leonov|pp=294–295}} During the only stand-up [[extravehicular activity]] (EVA) ever performed through the LM's top hatch on the lunar surface, Scott was able to make plans for the following day's EVA.{{sfn|Beattie|p=231}} He offered Irwin a chance to look out as well, but this would have required rearranging the umbilicals connecting Irwin to ''Falcon''{{'s}} life support system, and he declined.{{sfn|Irwin|p=61}} After repressurizing the spacecraft, Scott and Irwin removed their space suits for sleep, becoming the first astronauts to doff their suits while on the Moon.{{sfn|Chaikin|p=415}}

[[File:Apollo 15 lunar rover EVA2.ogg|thumb|alt=Film taken aboard the lunar rover|Aboard the [[Lunar Roving Vehicle]]]]
Throughout the sleep period Mission Control in Houston monitored a slow but steady oxygen loss. Scott and Irwin eventually were awakened an hour early, and the source of the problem was found to be an open valve on the urine transfer device. In post-mission debriefing, Scott recommended that future crews be woken at once under similar circumstances. After the problem was solved, the crew began preparation for the first Moon walk.<ref group=ALSJ name=eva1wake>{{cite web |url=http://www.hq.nasa.gov/alsj/a15/a15.eva1wake.html |title=Wake-up for EVA-1 |year=1996 |editor-last=Jones |editor-first=Eric M. |work=Apollo 15 Lunar Surface Journal |publisher=NASA |access-date=September 9, 2018 |archive-url=https://web.archive.org/web/20161012014625/http://www.hq.nasa.gov/alsj/a15/a15.eva1wake.html |archive-date=October 12, 2016 |url-status=live |df=mdy-all }}</ref>

After donning their suits and depressurizing the cabin,<ref group=ALSJ name=eva1prep>{{cite web |url=https://history.nasa.gov/alsj/a15/a15.eva1prep.html |title=Preparations for EVA-1 |year=1996 |editor-last=Jones |editor-first=Eric M. |work=Apollo 15 Lunar Surface Journal |publisher=NASA |access-date=September 13, 2018 |archive-url=https://web.archive.org/web/20171225232244/https://history.nasa.gov/alsj/a15/a15.eva1prep.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref> Scott and Irwin began their first full EVA, becoming the seventh and eighth humans, respectively, to walk on the Moon.{{sfn|Harland|pp=89–90, 358–359}} They began deploying the lunar rover, stored folded up in a compartment of ''Falcon''{{'s}} descent stage, but this proved troublesome due to the slant of the lander. The experts in Houston suggested lifting the front end of the rover as the astronauts pulled it out, and this worked.{{sfn|Harland|pp=90–93}} Scott began a system checkout. One of the batteries gave a zero voltage reading, but this was only an instrumentation problem. A greater concern was that the front wheel steering would not work. However, the rear wheel steering was sufficient to maneuver the vehicle.{{sfn|Harland|pp=93–94}} Completing his checkout, Scott said "Okay. Out of [[detent]]; we're moving", maneuvering the rover away from ''Falcon'' in mid-sentence. These were the first words uttered by a human while driving a vehicle on the Moon.<ref group=ALSJ name=deploying /> The rover carried a [[Apollo TV camera|television camera]], controlled remotely from Houston by NASA's Ed Fendell. The resolution was not high compared to the still photographs that would be taken, but the camera allowed the geologists on Earth to indirectly participate in Scott and Irwin's activities.{{sfn|Harland|pp=96–97}}

The rille was not visible from the landing site, but as Scott and Irwin drove over the rolling terrain, it came into view.{{sfn|Chaikin|pp=418–419}} They were able to see [[Elbow (lunar crater)|Elbow]] crater, and they began to drive in that direction.<ref group=ALSJ name=drivingtoelbow>{{cite web |url=https://www.hq.nasa.gov/alsj/a15/a15.elbowtrv.html |title=Driving to Elbow Crater |year=1996 |editor-last=Jones |editor-first=Eric M. |work=Apollo 15 Lunar Surface Journal |publisher=NASA |access-date=September 16, 2018 |archive-url=https://web.archive.org/web/20161012011146/http://www.hq.nasa.gov/alsj/a15/a15.elbowtrv.html |archive-date=October 12, 2016 |url-status=live |df=mdy-all }}</ref> Reaching Elbow, a known location, allowed Mission Control to backtrack and get closer to pinpointing the location of the lander. The astronauts took samples there,{{sfn|Harland|pp=106–107}} and then drove to another crater on the flank of [[Mons Hadley Delta]], where they took more. After concluding this stop, they returned to the lander to drop off their samples and prepare to set up the [[Apollo Lunar Surface Experiments Package]] (ALSEP), the scientific instruments that would remain when they left.{{sfn|Harland|pp=107–114, 315}} Scott had difficulty drilling the holes required for the [[Heat Flow Experiment|heat flow experiment]], and the work was not completed when they had to return to the lander.{{sfn|Harland|p=115}} The first EVA lasted 6{{nbsp}}hours and 32 minutes.{{sfn|Chaikin|p=598}}<ref name=summaryalsj group=ALSJ>{{cite web |url=http://www.hq.nasa.gov/alsj/a15/a15.summary.html |title=Mountains of the Moon |last=Jones |first=Eric M. |year=1995 |work=Apollo 15 Lunar Surface Journal |publisher=NASA |access-date=December 21, 2018 |archive-url=https://web.archive.org/web/20161011044716/http://www.hq.nasa.gov/alsj/a15/a15.summary.html |archive-date=October 11, 2016 |url-status=live |df=mdy-all }}</ref>

==== Second and third EVAs ====
[[File:Apollo 15 Genesis Rock.jpg|thumb|right|alt=A white rock, placed in a laboratory setting|The [[Genesis Rock]]]]

The rover's front steering, inoperative during the first EVA, worked during the second and third ones.{{sfn|Mission Report|p=101}} The target of the second EVA, on August 1, was the slope of Mons Hadley Delta, where the pair sampled boulders and craters along the [[Montes Apenninus|Apennine Front]]. They spent an hour at [[Spur (lunar crater)|Spur]] crater, during which the astronauts collected a sample dubbed the [[Genesis Rock]]. This rock, an [[anorthosite]], is believed to be part of the early lunar crust—the hope of finding such a specimen had been one reason the Hadley area had been chosen. Once back at the landing site, Scott continued to try to drill holes for experiments at the ALSEP site, with which he had struggled the day before. After conducting soil-mechanics experiments and raising the [[Lunar Flag Assembly|U.S. flag]], Scott and Irwin returned to the LM. EVA{{nbsp}}2 lasted 7{{nbsp}}hours and 12 minutes.{{sfn|Chaikin|p=598}}<ref name=summaryalsj group=ALSJ/>

Although Scott had eventually been successful at drilling the holes, he and Irwin had been unable to retrieve a core sample, and this was an early order of business during EVA 3, their third and final moonwalk. Time that could have been devoted to geology ticked away as Scott and Irwin attempted to pull it out. Once it had been retrieved, more time passed as they attempted to break the core into pieces for transport to Earth. Hampered by an incorrectly mounted vise on the rover, they eventually gave up on this—the core would be transported home with one segment longer than planned. Scott wondered if the core was worth the amount of time and effort invested, and the CAPCOM, Joe Allen, assured him it was. The core proved one of the most important items brought back from the Moon, revealing much about its history, but the expended time meant the planned visit to a group of hills known as the [[North Complex]] had to be scrubbed. Instead, the crew again ventured to the edge of Hadley Rille, this time to the northwest of the immediate landing site.<ref name=summaryalsj group=ALSJ />

[[File:Apollo 15 feather and hammer drop.ogv|thumb|alt=Video of an astronaut dropping a hammer and a feather while on the Moon|David Scott's hammer and feather experiment]]
Once the astronauts were beside the LM, Scott used a kit provided by the [[United States Postal Service|Postal Service]] to cancel a [[first day cover]] of two stamps being issued on August 2, the current date.<ref group=ALSJ name=hammer>{{cite web |url=https://history.nasa.gov/alsj/a15/a15.clsout3.html |title=The Hammer and the Feather |year=1996 |editor-last=Jones |editor-first=Eric M. |work=Apollo 15 Lunar Surface Journal |publisher=NASA |access-date=December 21, 2018 |archive-url=https://web.archive.org/web/20181230031714/https://history.nasa.gov/alsj/a15/a15.clsout3.html |archive-date=December 30, 2018 |url-status=live |df=mdy-all }}</ref><ref>{{cite web|title='Moon Mail' and Space Stamps Now on Display in World's Largest Postal Gallery|last=Pearlman|first=Robert Z.|date=September 24, 2013|url=https://www.space.com/22918-moon-mail-space-stamps-on-display.html|publisher=Space.com|access-date=December 21, 2018|archive-url=https://web.archive.org/web/20181221182858/https://www.space.com/22918-moon-mail-space-stamps-on-display.html|archive-date=December 21, 2018|url-status=live|df=mdy-all}}</ref> Scott then performed an experiment in view of the television camera, using a falcon feather and hammer to demonstrate [[Galileo]]'s theory that all objects in a given gravity field fall at the same rate, regardless of mass, in the absence of [[aerodynamic drag]]. He dropped the hammer and feather at the same time; because of the negligible lunar atmosphere, there was no drag on the feather, which hit the ground at the same time as the hammer. This was Joe Allen's idea (he also served as CAPCOM during it) and was part of an effort to find a memorable popular science experiment to do on the Moon along the lines of Shepard's hitting of golf balls. The feather was most likely from a female [[gyrfalcon]] (a type of falcon), a mascot at the [[United States Air Force Academy]].<ref group=ALSJ name=hammer />

[[File:Fallen Astronaut.jpg|thumb|left|alt=A small aluminum statue and a plaque on the lunar surface|The ''[[Fallen Astronaut]]'' memorial, near Hadley Rille, Moon]]
Scott then drove the rover to a position away from the LM, where the television camera could be used to observe the lunar liftoff. Near the rover, he left a small aluminum statuette called ''[[Fallen Astronaut]]'', along with a plaque bearing the names of 14 known American astronauts and Soviet cosmonauts who had died in the furtherance of space exploration. The memorial was left while the television camera was turned away; he told Mission Control he was doing some cleanup activities around the rover. Scott disclosed the memorial in a post-flight news conference. He also placed a Bible on the control panel of the rover before leaving it for the last time to enter the LM.<ref group=ALSJ name=hammer />

The EVA lasted 4 hours, 49 minutes and 50 seconds.{{sfn|Mission Report|p=16}} In total, the two astronauts spent 18{{frac|1|2}} hours outside the LM and collected approximately {{convert|77|kg|lb|abbr=on|order=flip}} of lunar samples.<ref name=summaryalsj group=ALSJ/>

=== Command module activities ===
{{main|Solo operations of Apollo 15}}

After the departure of ''Falcon'', Worden in ''Endeavour'' executed a burn to take the CSM to a higher orbit.<ref group=ALFJ name=preparations /> While ''Falcon'' was on the Moon, the mission effectively split, Worden and the CSM being assigned their own CAPCOM and flight support team.<ref group=ALFJ name=solo1>{{cite web |url=https://history.nasa.gov/afj/ap15fj/13solo_ops1.html |title=Solo Orbital Operations-1 |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/20171225233953/https://history.nasa.gov/afj/ap15fj/13solo_ops1.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref>

[[File:Apollo 15 CSM (14412950693).jpg|thumb|upright=1.3|left|alt=A spacecraft seen with the Moon in background|''Endeavour'', with the SIM bay exposed, as seen from the Lunar Module ''Falcon'']]
Worden got busy with the tasks that were to occupy him for much of the time he spent in space alone: photography and operating the instruments in the SIM bay.<ref group=ALFJ name=solo1 /> The door to the SIM bay had been explosively jettisoned during the translunar coast. Filling previously unused space in the service module, the SIM bay contained a gamma-ray spectrometer, mounted on the end of a boom, an X-ray spectrometer and a laser altimeter, which failed part way through the mission. Two cameras, a stellar camera and a metric camera, together comprised the mapping camera, which was complemented by a panoramic camera, derived from [[Corona (satellite)|spy technology]]. The altimeter and cameras permitted the exact time and location from which pictures were taken to be determined. Also present were an alpha particle spectrometer, which could be used to detect evidence of lunar volcanism, and a mass spectrometer, also on a boom in the hope it would be unaffected by contamination from the ship. The boom would prove troublesome, as Worden would not always be able to get it to retract.<ref group=ALFJ name=summary>{{cite web|url=https://history.nasa.gov/afj/ap15fj/a15summary.html|title=Apollo 15 Flight Summary|year=1998|last=Woods|first=W. David|publisher=NASA|access-date=February 19, 2019|archive-url=https://web.archive.org/web/20171225233958/https://history.nasa.gov/afj/ap15fj/a15summary.html|archive-date=December 25, 2017|url-status=live|df=mdy-all}}</ref>

[[File:Apollo 15 Hadley Rille.jpg|thumb|alt=Part of the lunar surface|The landing area is shown in an image taken by the mapping camera]]
''Endeavour'' was slated to pass over the landing site at the moment of planned landing,<ref group=ALFJ name=preparations /> but Worden could not see ''Falcon''<ref group=ALSJ name=landing /> and did not spot it until a subsequent orbit. He also exercised to avoid muscle atrophy, and Houston kept him up to date on Scott and Irwin's activities on the lunar surface. The panoramic camera did not operate perfectly, but provided enough images that no special adjustment was made. Worden took many photographs through the command module's windows, often with shots taken at regular intervals. His task was complicated by the lack of a working mission timer in the Lower Equipment Bay of the command module, as its circuit breaker had popped en route to the Moon.<ref group=ALFJ name=solo1 /> Worden's observations and photographs would inform the decision to send [[Apollo 17]] to [[Taurus-Littrow]] to search for evidence of volcanic activity. There was a communications blackout when the CSM passed over the far side of the Moon from Earth; Worden greeted each resumption of contact with the words, "Hello, Earth. Greetings from ''Endeavour''", expressed in different languages. Worden and El-Baz had come up with the idea, and the geology instructor had aided the astronaut in accumulating translations.<ref group=ALFJ name=solo2>{{cite web |url=https://history.nasa.gov/afj/ap15fj/14solo_ops2.html |title=Solo Orbital Operations-2 |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 16, 2018 |archive-url=https://web.archive.org/web/20171225233957/https://history.nasa.gov/afj/ap15fj/14solo_ops2.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref>

Results from the SIM bay experiments would include the conclusion, from data gathered by the X-ray spectrometer, that there was greater fluorescent X-ray flux than anticipated, and that the lunar highlands were richer in aluminum than were the mares.{{sfn|Mission Report|p=37}} ''Endeavour'' was in a more inclined orbit than previous crewed missions, and Worden saw features that were not known previously, supplementing photographs with thorough descriptions.<ref name = "moon mountain" />

By the time Scott and Irwin were ready to take off from the lunar surface and return to ''Endeavour'', the CSM's orbit had drifted due to the rotation of the Moon, and a plane change burn was required to ensure that the CSM's orbit would be in the same plane as that of the LM once it took off from the Moon. Worden accomplished the 18-second burn with the SPS.<ref group=ALFJ name=solo4>{{cite web |url=https://history.nasa.gov/afj/ap15fj/16solo_ops4.html |title=Solo Orbital Operations-4 |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 16, 2018 |archive-url=https://web.archive.org/web/20171225233958/https://history.nasa.gov/afj/ap15fj/16solo_ops4.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref>

=== Return to Earth ===
[[File: Apollo 15 liftoff from the Moon.ogg|thumb |alt=Video showing the lunar lander taking off|The liftoff from the Moon as seen by the [[Apollo TV camera|TV camera]] on the lunar rover]]
{{main|Return of Apollo 15 to Earth}}

''Falcon'' lifted off the Moon at 17:11:22 GMT on August{{nbsp}}2 after 66 hours and 55 minutes on the lunar surface. Docking with the CSM took place just under two hours later.<ref name="Apollo 15 CSM">{{cite web|url=https://nssdc.gsfc.nasa.gov/nmc/spacecraft/display.action?id=1971-063A|title=Apollo 15 Command and Service Module (CSM)|publisher=[[NASA Space Science Data Coordinated Archive]]|access-date=December 21, 2018|df=mdy-all}}</ref> After the astronauts transferred samples and other items from the LM to the CSM, the LM was sealed off, jettisoned, and intentionally crashed into the lunar surface, an impact registered by the seismometers left by Apollo 12, 14 and 15.<ref group=ALFJ name=jettison /> The jettison proved difficult because of problems getting airtight seals, requiring a delay in discarding the LM. After the jettison, Slayton came on the loop to recommend the astronauts take sleeping pills, or at least that Scott and Irwin do so. Scott as mission commander refused to allow it, feeling there was no need. During the EVAs, the doctors had noticed irregularities in both Scott's and Irwin's heartbeats, but the crew were not informed during the flight. Irwin had heart problems after retiring as an astronaut and died in 1991 of a heart attack; Scott felt that he as commander should have been informed of the biomedical readings.<ref group=ALFJ name=jettison>{{cite web |url=https://history.nasa.gov/afj/ap15fj/18tunnel_leak_lm_jett.html |title=Leaking Tunnel and Jettison of the LM |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 16, 2018 |archive-url=https://web.archive.org/web/20171225233958/https://history.nasa.gov/afj/ap15fj/18tunnel_leak_lm_jett.html |archive-date=December 25, 2017 |url-status=live |df=mdy-all }}</ref><ref group=ALFJ name=summary /> NASA doctors at the time theorized the heart readings were due to [[hypokalemia|potassium deficiency]], due to their hard work on the surface and inadequate resupply through liquids.{{sfn|Chaikin|pp=446–447}}

[[File: Apollo 15 Worden EVA.ogg|thumb|left|alt=Video of a man working outside the spacecraft|Worden's deep space EVA]]
The crew spent the next two days working on orbital science experiments, including more observations of the Moon from orbit and releasing the subsatellite.<ref name = "moon mountain" /> ''Endeavour'' departed lunar orbit with another burn of the SPS engine<ref group=ALFJ name=jettison /> of 2{{nbsp}}minutes 21 seconds at 21:22:45 GMT on August{{nbsp}}4.<ref name = "Apollo 15 CSM" /> The next day, during the return to Earth, Worden performed a 39-minute EVA to retrieve film cassettes from the service module's scientific instrument module (SIM) bay, with assistance from Irwin who remained at the command module's hatch.<ref name="Drew">{{cite web |url=https://www.drewexmachina.com/2017/12/17/a-history-of-deep-space-evas/ |title=A History of Deep Space EVAs |last=LePage |first=Andrew |date=December 17, 2017 |website=Drew Ex Machina}}</ref> At approximately 171,000 nautical miles<ref group=ALFJ name=wordeneva>{{cite web |url=https://history.nasa.gov/afj/ap15fj/23day11_worden_eva.html |title=Day 11: Worden's EVA Day |last1=Woods |first1=W. David |last2=O'Brien |first2=Frank |work=Apollo 15 Flight Journal |publisher=NASA |access-date=December 26, 2018| archive-url= https://web.archive.org/web/20110629043034/http://www.hq.nasa.gov/office/pao/History/ap15fj/23day11_worden_eva.htm| archive-date=June 29, 2011 | url-status= live}}</ref><ref name="moonworden">{{cite web |url=https://moon.nasa.gov/resources/232/astronaut-alfred-worden-floats-in-space-outside-spacecraft-during-eva/ |title=Astronaut Alfred Worden Floats in Space Outside Spacecraft During EVA  |website=NASA|date=July 9, 2018 }}</ref> (197,000&nbsp;mi; 317,000&nbsp;km) from Earth, it was the first "deep space" EVA in history, performed at great distance from any planetary body. As of {{year}}, it remains one of only three such EVAs, all performed during Apollo's J missions under similar circumstances. Later that day, the crew set a record for the longest Apollo flight to that point.<ref group=ALFJ name=wordeneva />

On approach to Earth on August{{nbsp}}7, the service module was jettisoned, and the command module [[Atmospheric reentry|reentered the Earth's atmosphere]]. Although one of the three parachutes on the CM failed after deploying, likely due to damage as the spacecraft vented fuel, only two were required for a safe landing (one extra for redundancy). Upon landing in the North Pacific Ocean, the CM and crew were recovered and taken aboard the recovery ship, {{USS|Okinawa|LPH-3|6}}, after a mission lasting 12 days, 7{{nbsp}}hours, 11 minutes and 53 seconds.{{sfn|Mission Report|p=3}}