This is how we land on the moon

The Eagle has wings

A prose poem to Apollo 11’s landing

Grab a beer and take a seat.  I’m going to tell you, one pilot to another, what it was like.  OK, ready?  Let’s start with DOI, Descent Orbit Initiation, our first taste of the Descent Engine to take us into a low orbit, call it the staging point for descent.  We go around the backside of the moon, out of contact with Houston, of course, and about eight minutes later, fire that engine — the DPS — for 29.8 seconds, first at 10 percent and then throttling up at 40 percent thrust.  At 10 percent, I can’t hear or feel the engine, only know it’s firing by watching the readouts on chamber pressure and acceleration.  A perfect burn, and in thirty minutes we come around to the frontside of the moon, on the way down to 50,000 where PDI — Power Decent Initiation starts our 12-minute descent to the surface.  PDI occurs less than twenty minutes after we come around, so things are moving fast.  Houston gives us a, “You are go for PDI”  The LM is oriented face down, the Descent Engine leading the way.  I’m tracking landmarks.  If we pass them at the prescribed time, that means were on course.  Our position checks three minutes prior to PDI are on time.  Checks at one minute — on time.

Ignition — 10 percent thrust.  “Just about on time.”  I’m watching the readouts and so don’t make a landmark check.  Data from our two guidance systems The Primary Guidance and Navigation Control System, PGNCS (pronounce “Pings”) and the backup Abort Guidance System (Ags”) match — as they must.  We’re now 2 minutes 20 seconds into the descent, at 47,000 feet.  At the three minute mark, I’m eyeballs out the window making a position check — looks like where hitting the landmarks about three seconds early — we’re going to be landing long, beyond the designated touchdown point.  That’s fine — it’s not like there’s a welcoming committee waiting for us.  Houston gives us a “You are go to continue powered descent.”

OK, we hit 40,000 ft. altitude, and it’s time for me to roll the LM on its back — actually a right yaw of 180 degrees.  We begin to to rotate, but slow.  Damn if I haven’t left the rate switch in low, only a degree or two per second.  I flip it to high, and we turn at a crisp five-degrees a second.  We have to make this flip, which leaves us staring up into the blackness of space, so that the landing radar at the LM’s bottom can gain a good lock on the surface, a must for landing.   We’re four minutes into the descent, one-third of the way, measured by time.  Sure enough, an immediate radar lock.   Look at that — we have the Earth out the window in front of us.

At five minutes, we’re down to 33,500 feet altitude.  Everything going fine, even if we’ll be landing long.  Then at five minutes, our ears are blasted by a master alarm.  It’s a computer warning — flashing a code, a 12-02 alarm.  We have no idea what that means.  I call it to Houston.  Wait a couple seconds and just with just a touch of urgency, “Houston, give us a reading on that twelve-oh-two alarm.”   They comes back, “We’re go on that alarm.”   We’re now six minutes into the descent, 27,000 feet.  The alarm sounds again.  Same alarm.  Same go.  It keeps coming back, but I’m not totally alarmed.  I’m watching the readouts that show the vehicle is flying just fine.  That’s all that matters.  As long as that’s the case, we’re go, as far as I’m concerned.  We’re not going to abort because some computer is coughing.

Seven minutes and 21,000 feet.  Ags and Pings look good.  The DPS throttles back right on time.  We’re still in what’s called the braking phase.  At 18,000 feet, the lunar horizon begins to appear in our triangular windows.  The alarms are still sounding, drawing me from the window.  Gotta keep an eye on the readouts, make sure the bird is flying properly.  It is.  We continue.  Eight minutes.  “Give us an estimated pitchover time.”  When we pitch upright — with a good view out the windows, steepening our descent, the Approach Phase begins.  This point is called “High Gate.”

At 8.5 minutes, 9,200 ft. — pitchover begins.  Nine minutes — High Gate, the Approach Phase, just over 7,000 ft. altitude.  I test manual control.  “Manual attitude control is good,” I report.  Back to auto.  We reach 4,200 ft. and Houston calls, “You are go for landing”    Just as they do, there’s that damn master alarm again.  It’s a 12-01 computer alarm.  Houston calls, “We’re go.  Hang tight — we’re go.”  We’re now just at 3,000 ft.

Two-thousand feet. Finally those damn alarms seem to settle down.  Much later than I would have liked, I put my eyeballs out the window.  Give me a LPD number.   The Landing Point Designator.  The computer-generated number corresponds to a number on a grid etched in my window and shows our touchdown point.  Damn — taking us right into a big crater, boulders the size of small cars in and around it.  Of course, all I say is, “Pretty rocky area.”  At 500 ft., we hit what is called Low Gate — the Landing Phase begins.

We’re at 350 feet and it’s decision time.  I could try to land short of the crater, maybe even jitterbug around those boulders.  Naw, I don’t want to be that aggressive flying this thing.  And now the LPD shows I won’t be able to stop short.  Best anyway to fly long, keep the landing spot ahead of you so you’ve got a clear view of any obstacles.  I pitch the LM nearly vertical, which halts the descent and starts us over the crater.  I’ve only got 163 seconds of hover time.  We fly over the damn crater at 220 feet altitude.

OK, up ahead — the area between those two craters and that boulder field.  That looks good.  We’re at 100 feet and picking up a transparent sheet of dust.  No problem.   Descending slowly, carefully.  Houston calls “Sixty Seconds.”   Meaning sixty seconds of fuel.  But I’m not worried now.  We’re at 50 feet.  I figure I can get this thing down below 20 feet, and if we ran out of fuel that low, it’s tough enough to survive the fall in the moon’s one-sixth gravity.   And if we try to abort this low, we’re in what we call “The Dead Man’s Zone” — we’d likely crash before we could pull away.

I’m concentrating on nulling out our rates — coming in straight down.  But we drift to the right, backward a bit.  Don’t want that.  Forwards, forwards.  Now drifting left.  Damn — I overcompensated.  Houston calls, “Thirty seconds.”   I wish I was doing a better job of flying this thing.  It’s hard — we’re really kicking up the dust which is moving out in ray-like streams.  I’m trying to judge my motion by rocks poking through the dust.  It’s like looking through ground fog.  I’m concentrating so hard, I don’t hear the call, “Contact.”  By muscle memory, I switch off the engine. 

We settle gently on the surface of the moon.   It takes a moment, a few switch reconfigurations, a few breaths.  Finally there is time to say it:  “Houston, Tranquility Base here.  The Eagle has landed.”

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