Tuesday, December 11, 2012

Apollo+40: The Sixth Lunar Landing

The Apollo Lunar Module (LM) was the first true spacecraft - it was only designed for and able to fly in space, in a vacuum. Grumman completed twelve of them. Ten of the twelve flew, and eight made the journey to their intended environment: the Moon.

Apollo 17's LM Challenger was the 12th produced and would be the last craft to carry humans to the surface of Earth's Moon. She was built by hand in Grumman's plant in Bethpage, New York. When LM-12 was delivered to NASA, hundreds of men and women who built the crafts that had delivered ten Americans to the lunar surface - and which had saved the lives of three - had lost their jobs. It's a tribute to them all that Challenger was as ready, and performed as flawlessly, as her predecessors Spider, Snoopy, Eagle, Intrepid, Aquarius, Antares, Falcon, and Orion.

The date was December 11, 1972. Forty years have passed since a human prepared to land their craft and set foot on another world.

As Challenger, docked to the Command/Service Module (CSM) America, completed its 10th revolution of the Moon since entering lunar orbit, Commander (CDR) Gene Cernan, Command Module Pilot (CMP) Ron Evans, and Lunar Module Pilot (LMP) Jack Schmitt, clambered back into their pressure suits and prepared their two spacecraft for undocking.

During the 11th revolution, all the final checks were completed and both America and Challenger were given the go ahead for undocking, which would take place on the far side of the Moon, out of communication with Earth. The crew completed the undocking at 110:27:56 Ground Elapsed Time (GET)/12:20 EST. When contact was regained with Mission Control in Houston, the two ships were flying independently.

On this frontside pass, America and Challenger were given a "GO" for their next major maneuvers. America burned its large motor to both raise and circularize its orbit to prepare for the rendezvous and return of Challenger from the surface, hopefully in a little more than three days, but sooner if an abort was required. Challenger fired her reaction control jets for about 20 seconds to set the LM on the trajectory for the point 6.5 miles above the surface where Cernan and Schmitt would light their Descent Propulsion System (DPS) for Powered Descent Initiation - "PDI" in Astronaut parlance.

Once again, the astronauts on board America and Challenger, and the engineers and flight controllers back at Mission Control, made sure all was in readiness. Challenger was given a go for PDI.

The DPS ignited on schedule at 112:49:53 and Cernan and Schmitt began their approximately 12 minute descent to the surface. Their target was a central location in what had been called by NASA's lunar scientists the Taurus-Littrow valley on the edge of the Sea of Serenity. It was one of the most complicated and yes, challenging, landing approaches as the LM had to cross a mountain range before it could descend towards the target area. 

Cernan and Schmitt saw their altitude readings change right on schedule at 112:56:07 when they crossed the mountain ridge that blocked their approach. They were flying blind at this point, with their windows pointed skyward. They flew the remainder of their approach to Taurus-Littrow perfectly, and when they were 5,000 feet above the surface at 112:59:32, they received the word that only ten had received before, and none have since:
Challenger, you're GO for landing!
This film, taken out of the LMP window with a 16mm movie camera, shows the last four minutes of Challenger's descent along with the voices of CDR Cernan, LMP Schmitt, and CAPCOM Gordon Fullerton:

Challenger came to rest at Taurus-Littrow at 113:01:58 GET, 2:54 PM Eastern Standard Time - exactly 40 years ago from the time of this post.

Cernan and Schmitt readied Challenger for a quick take-off should any problems be discovered, but none did. After about 30 minutes, the pair began configuring their ship for its three-day lunar stay by powering down the flight systems.

The day's work was far from over though. In about three and a half hours, the eleventh and twelfth - and thus far final - men to walk on the moon would get their first chance of three during their lunar stay to do so.

Blogger's note: as with previous posts, in addition to linked material, it draws upon content from the Apollo Lunar Surface Journal and The Last Man on the Moon.

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