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Forty-one years ago today, Apollo 15 landed in the Hadley-Appennine region of the Moon.  The fourth manned lunar landing, Apollo 15 was one of the most scientifically successful and geologically diverse of the Apollo Lunar Landing Program.

Apollo 15 lifted-off from LC-39A at Cape Canaveral, Florida at 13:34 UTC on Monday, 26 July 1971.  The all-Air Force flight crew consisted of Commander David R. Scott, Command Module Pilot Alfred M. Worden and Lunar Module Pilot James B. Irwin.  While Apollo 15 was Scott’s third spaceflight, Irwin and Worden were space rookies.

Apollo 15 was the first of the Apollo “J” missions wherein lunar surface stay duration was extended to three (3) days.  This was sufficient time for lunar explorers to conduct a trio of Lunar Extravehicular Activity (LEVA) periods.  Each LEVA was approximately 6 to 7 hours in length.  The Lunar Module (LM) was provisioned with extra equipment and consumables to support these extended stay operations.

Another “J” mission feature was the use of the Lunar Rover (LR).  This electric-powered marvel conveyed astronauts over the lunar surface at speeds up to 8 mph.  It’s range from the LM was limited by a “Walkback Limit” of about 5 miles.  That is, should the LR fail at any point during a lunar excursion, the astronauts had to have sufficient oxygen remaining to permit them to walk back to the LM a distance of up to 5 miles.

The Apollo 15 Lunar Module Falcon, with Dave Scott and Jim Irwin onboard, landed at 22:16:29 UTC in the Hadley-Appennine region of the Moon on Friday, 30 July 1971.  High overhead, Al Worden orbited the Moon alone in the Command Module (CM) Endeavor.

Scott and Irwin conducted 3 separate LEVA’s totaling slightly over 18.5 hours. During these lunar jaunts, they collected 170 lbs of lunar samples.  Their biggest find was the so-called “Genesis Rock” estimated to be 4.1 billion years old.  As per previous Apollo lunar landing missions, the Apollo 15 astronauts deployed an Apollo Lunar Surface Experiments Package  (ALSEP) which permitted monitoring of the lunar environment long after the crew’s return to Earth.

A unique aspect of Apollo 15 was Commander Scott’s conduct of a simple experiment on the lunar surface.  With a geology hammer in his right hand and a Falcon feather in his left, the astronaut released both objects simultaneously.  Television viewers back on Earth witnessed both items striking the ground at the same moment.  This result confirmed Galileo’s assertion that all objects in a vacuum fall at the same rate independent of their mass.

The Apollo 15 lunar explorers’ stay on the Moon lasted almost 67 hours.  Falcon lifted-off from the Moon at 17:11:23 UTC on Monday, 02 August 1971.  For the first time, lift-off of the LM ascent stage was televised back to Earth via a TV camera attached to the LR.  Slightly less than 2 hours later, Scott and Irwin successfully rendezvoused and docked with Worden.

The crew of Apollo 15 started the trip back to Earth at 21:22:45 UTC on Wednesday, 04 August 1971 with a successful Transearth Injection burn of their Service Propulsion System (SPS).  Just before leaving lunar orbit, the astronauts deployed a subsatellite designed to conduct a long duration study the lunar plasma, particle, magnetic and gravitational environments. The next day, Al Worden successfully completed a 39-minute EVA in deep space as he retrieved exposed film from cameras located in a special bay within the Service Module (SM).

Endeavor and her crew successfully reentered the Earth’s atmosphere on Saturday, 07 August 1971.  During descent, one of the CM’s three (3) main parachutes failed to deploy properly and caused the CM splashdown sink rate to be higher than normal.  However, the robust crew survived the subsequent hard landing in the North Pacific Ocean without apparent ill effect.  Crew and craft were safely recovered aboard the USS Okinawa.

Mission elapsed time for Apollo 15 was 295 hours, 11 minutes and 53 seconds. The maturation of lunar surface operations that made an extended stay possible and provided for enhanced exploration activities wrought a substantial scientific bounty.  Indeed, the knowledge and experience gained during the Apollo 15 mission went a long way to helping the Apollo Program make the most of history’s last pair of manned lunar landing missions; Apollo 16 and Apollo 17.

Posted in Aerospace, History

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