July 30, 1971: Apollo 15 lands in the mountains of the moon

Falcon on the plain at Hadley — note how far it is leaning back and to the side.

****

1.  Floating through the mountains

            “Take care of home, Al.   We’ll be back in three days.”  It’s time to go exploring. We close the hatches, four-and-a half hours before landing, June 30, 1971.  Don’t worry, Al Worden won’t be bored in the Apollo 15 command ship — he has a full program of science to perform from his orbiting base while while we range the surface. 

            We’re go, if we can pull it off — about to attempt the most difficult landing ever, descending at a steep angle through a gap in the Himalaya-size Apennine mountains to our target near the gorge-like Hadley Rille.  To make it even harder, we only have maps made from medium-resolution Lunar Orbiter photos.  They only show features of about 60-ft. in size.  The site could be strewn with boulders. 

            Coming up on undocking. Release the latches, Al.   And nothing happens.  A failure now ends the mission.  

            Houston says we have 40 min. before they’ll have to call a “wave off” for at least one orbit. Quickly, Al opens the hatch on his side, checks the power cables to the latch mechanism.  Sure enough, one is loose.  He buttons everything up.  Try again — release.  And bingo — we’re free.  And the entire incident has only taken 15 min. 

            Al radios, “You’re on your own.”  He looks over our Lunar Module, Falcon— landing legs locked and ready.  Falcon looks good.  He makes a small separation burn, the command ship slowly shrinking. He’s below us, pointed straight up, as we pass over the landing site, the cone of the Command Module tiny against the backdrop of ranging mountains.  My God,  we’re going to land in those mountains? 

            An hour after undocking, Al goes his way, fires that big engine to lift himself into a higher, circular orbit, he’ll be overhead at landing — ready should we have to abort. Less than two orbits, all elements in position, it’s our turn.  Approaching PDI — Powered Descent Initiation — the start of our swift 12-min. ride to the surface.  We’re anchored standing at our windows.   

            We come around to the moon’s nearside, hoping we won’t leave it for three days.  And Houston gives the word, “Go for PDI.”

            Mark, one minute until ignition of the Descent Propulsion System.  

            “Stand by for ullage.”  A thruster nudge to settle the propellants in their tanks.

            Ullage — and go for the burn.

            “Ignition.” Eleven percent thrust on the throttle.  

            After 31 sec, “Throttle up.”  Full power. We keep our roving the instruments, looking for any deviations from what we love to call “nominal.”

            “Falcon, Houston, you’re go at 2 min.”  We’re at 46,000 ft.   We call “Pings and Ags agree.”  Those are our two guidance systems, The Primary Guidance and Navigation System (PGNS) and the Abort Guidance System (AGS).  It’s always a good day when Pings and Ags agree — meaning both are working.

            At 3 min. — and we’re at 42,000 ft., about 58 mi. from the target.  We’re anchored standing at our windows.  We yaw until we are facing upwards, engine forward, to give the radar a good lock on the surface.  We won’t see anything until we pitch upright in the approach phase in 6 min.  

            Data begins streaming from our landing data.  Is it accurate?  Houston calls to accept the radar — we’re 3 min. 41 sec.  We show we’re about 2,000 ft. higher than planned.  It’s actually an error in the readings that should correct itself, Houston says.

            “Pings and Ags look good,” we call.

            “Falcon, Houston. You’re go at five.”  A minute later, we’re down to 19,000 ft., still flying blind, about 19 mi. from the landing point.

            And 7 min., 22 sec., we throttle down to 57 percent — or I should say our computer does.  And two minutes later, we hit what we call “high gate,” the beginning of the approach phase, Falconbeginning to tilt upright, the surface just beginning to slide into view at the the bottom of our triangular windows.  Straining to see the sinuous rille.   Where is it? 

            We see Hadley-Delta float by our left side — we’re at 11,000 ft. — and Mount Hadley pass to the right.  It’s like we’re flying through a mountain pass.  We have the impression that we’re going to land long.  Land too long and we’ll end up putting down on the other side of the rille, cutoff from the territory we want to explore.  Still can’t see the rille, looking for it out the forward corner of the window. 

            Houston calls, “Falcon, Houston.  We expect you may be a little south of the site, maybe 3,000 ft.”  So we quickly begin nudging our landing point to the north. 

            We reach the landing phase, not quite 11 min. into the descent, Falcon swinging vertical, 7,000 ft. And there it is — there’s the Rille ahead of us.   We’re headed toward the right area.  Where’s Index Crater? — that’s sorta our reference point for landing.  We can’t identify the craters, find our landing target, which is 1.25 mi. east of the rille.  Seeing a confusion of secondary craters.  The craters are soft and shallow, without defining shadows, a blur of craters — whereas the maps showed well-defined craters.  Because the Lunar Orbiter photos weren’t the best, the topographic experts pumped up the contrast to bring out detail, but that had made the craters stand out.

            Calling out the numbers, altitude and rate of descent. 

            “Four-thousand feet. Three thousand feet.”  Rate of descent, “four-seven, four-eight . . . “

            I see a couple craters I think I can recognize, but they’re quite subdued.

            “Falcon, Houston.  We’re go at 1,000.”

            We’re’ busy trying to select a landing spot.  Descending through 400 ft. altitude, assuming manual control.  Se a spot that looks relatively flat and head for it, down to 250 ft. altitude, 9 percent fuel remaining 

            OK, 150 ft., coming down. At 100 ft., “There — got some dust. “

            “80 [ft.] at 5 [feet-per-second descent rate].”

Wow — at 50-60 ft., it’s a dust storm radiating from under us. Can’t see the surface.  Gonna have to land on instruments.  It’s Instrument Flight Rules all the way in, using the numbers called from the computer display.  

            “60 at 3.”

            “50 at 3”

            “40 at 3”

            Bringing her down at a nice steady rate.  Fuel remaining at a healthy 6 percent.  

            “15 at 1”

            Close above the sandstorm, hovering.

            “Eight feet” 

            “Contact.” The blue contact light blinks on. Cut the engine — if left running against the surface, especially with our long engine bell, the back pressure could cause an explosion.

            We’re braced for a hard landing, as our LM weighs a ton more than previous ones.   In a half second, we hit.  “Bam!”   Hit and heave with a big rattle, jump to the left, 17 degrees over, then roll back, equipment shaking, settle with a tilt back and to the side of about 10 degrees — all in about two seconds.

            In the Eastern U.S., the time is 6:16 p.m. — and 29 seconds.  The nominal plan had the decent lasting 12 min. 2 sec.  In reality, we took 12 min. 20 sec.

            Take a breath and then give the word.  “Falcon is on the plain at Hadley.”

            But where exactly are we? Turns out, Houston had miscalculated that we were straying to the south.  So our “corrections” put us 1,500 ft. to the northwest of the the target.  Not a pinpoint landing, but well within the neighborhood.  And it’s time to take a look at our neighborhood.

*          

2. “Trafficability”

            Here’s the plan: We want to be rested, a night’s sleep before attempting the world’s first extended moonwalk of 7 hrs.  But we knew we’d be too keyed up to go right to sleep. And it’d be a good idea to take a look around, especially as the site isn’t well mapped, familiarize ourselves, minimize the problems Apollo 14 had with knowing where they were on their long traverse up Cone Crater.  Most importantly, see if obstacles will hinder our use of the first moon car, the Lunar Roving Vehicle.  And do something every geologist does — make a visual survey of the worksite.  

            So two hours after landing, still in our suits, we depressurize the cabin, open the circular overhead (rendezvous) hatch and stand on the can-like cover of the ascent engine. We’re looking out from 25 ft. above the surface. 

            Oh, boy, what a vista — soft, rolling mountains flowing against the short horizon — no sharp, jagged features as depicted in science fiction.  Surfaces worn down by eons of solar and meteorite bombardment, and yet unchanging — undisturbed by wind and water as on Earth.  Every feature soft, flowing, almost liquid, golden.

            And familiar to us, too. Hadley Mountain, the primary peak in this range, rising 15,000 ft., draped in shadow except for a wedge of its eastern flank.  And the mountain destination for two of our moonwalks, the slightly smaller Hadley-Delta, fully illuminated to the south, the huge hole of St George Crater on its right flank.  Good news, yet puzzling — no boulders visible on the mountain’s slopes.   Some thought it’d be covered with them. Indeed, we’d like a few to sample, perhaps deep bedrock tossed up by crater impacts.  No large boulders anyway along the hummocky ground from here to there, just a field of small craters, right up onto the flanks of the mountains. Looks like they were tossed out by large impacts to the north.

            We inform Houston, “The whole surface of the area appears to be smooth.  It’s gently rolling terrain 360 degrees around.”

            And here’s the key report — on trafficability, the ability of the Rover to negotiate the terrain. “Trafficability looks pretty good. It’s hummocky, but I think we can maneuver the Rover in a straight line.”

            “Sounds like we’re in business, old friend,” Houston calls.

            After a half hour, we close the hatch, pressurize and perform another first.  Our new suits, in addition to increased mobility, can be more easily removed.  We become the first to take them off, comfort important if we are to sleep well. Previous crews could gut it through for their short stays without good sleep.  If we’re to remain productive, sleep is imperative.

            Good night from the plains of Hadley.

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