Tranquillity Base


NASA recently released a remarkably precise reconstruction of the Apollo 11 descent to the Sea of Tranquillity using footage taken by the Lunar Reconnaissance Orbiter. The result is a side-by-side view of the original footage taken out the window of the Eagle and a high-resolution wide-field view of the lunar surface as Armstrong and Aldrin would have seen it in 1969.

The Apollo program stands as the greatest endeavour of exploration in history of mankind, particularly as the program stretched the existing technology well beyond what was realistic at the time, so much so that in forty years this feat has not been repeated by any country, or even by the US itself. To call the Apollo program herculean does not do the program justice.

When watching the following video, there’s a few points to note:

  • I recommend watching this video on the NASA website, where you can click the CC (Closed Caption) button to see precisely what the astronauts are saying, as the audio is coarse, making it hard to pick out their words.
  • The clear voice is mission control, while the astronauts, unsurprisingly, sound more distant.
  • Note how calm and routine their comments are. Their professionalism is astounding given the pressure they were under.
  • Prior to the start of the video, and at several points during this video, Armstrong and Aldrin are hit with numerous computer alarms. Although they’d faced alarms in the simulators, in the heat of the moment these alarms suggested serious problems with the computer systems on the Eagle. A problem in the rendezvous radar program stole 13% of the duty cycle, overloading the computer and forcing several restarts (this is the 1202 error you can hear them talking about). In addition to this, erroneous computer data caused the LM descent engine to fluctuate wildly, and the throttle control algorithm was only marginally stable. 240,000 miles from Earth, there’s no hint of panic or concern from the astronauts.
  • Because the moon reflects sunlight off the surface, and as the surface is so strange and featureless, it is difficult to gauge the distance to the moon’s surface and the speed with which the Eagle is descending. Listen carefully and you’ll hear them go from 5000 feet to 3000 feet in less than thirty seconds, highlighting their rapid descent into the moon’s gravity well. As they get closer to the surface, Armstrong fires the descent engine to slow the rate of descent down considerably, but at the start of the video it is fair to say they are plummeting toward the surface of the moon.
  • At 750 feet they’re descenting at 23 feet per second, in the next breath Buzz adds 700 feet at 21 feet per second, and you get a feeling of how they’re timing their descent. This is critical, as by the time they land they’re running on vapour
  • You’ll miss this if you don’t have the captions on, but at this point Armstrong notes “pretty rocky down there.” Watch the shadows over the next few minutes and you’ll see that there’s not just a bunch of craters, there’s a debris field full of massive rocks, casting long shadows that are visibly different to the crater shadows. Given the height of the Eagle, these rocks are anywhere from the size of a car to the size of a house. From this point, you’ll notice Armstrong increases their lateral thrust, moving them sideways away from this region, burning a considerable amount of fuel in the process. To NASA’s credit, they don’t question his decision, they let him run with it, trusting his judgement in the moment. Armstrong later spoke of this moment, saying because he couldn’t see directly below the LM at the point of landing, he wanted to be well clear of any boulders and land in a clear field, as clipping even a small boulder could have toppled the LM and made ascent impossible. When Buzz notes, “pegged on horizontal velocity” he’s telling Armstrong the Eagle is now hovering, no longer descending as it drifts sideways, using its dwindling fuel as Armstrong looks for a spot to land.
  • When Armstrong asked, “OK, how is the fuel?” watch how quickly it is being consumed. Buzz notes they’re at 8% (ie, 92% of what they had when they started their descent is gone)
  • “I’ve got a shadow out there,” is Armstrong noting that he’s low enough that he can see the shadow of the Eagle on the surface of the moon.
  • At a hundred feet, they’re down to 5% of fuel remaining
  • “60 seconds” is mission control informing the crew they have a minute before they have to either land or abort because the descent fuel is too low to continue
  • “30 seconds” from mission control would have put a phenomenal amount of pressure on Armstrong to touchdown. They were 20 feet from the ground and trying to touch down lightly, not just in terms of their rate of descent but in terms of reducing any lateral motion.

Top ten things you may not have known about the Apollo flights:

1. The Apollo’s Saturn rockets were packed with enough fuel to throw 100-pound shrapnel three miles, and NASA couldn’t rule out the possibility that they might explode on takeoff, so NASA seated its VIP spectators three and a half miles from the launchpad.

2. The Apollo computers had significantly less processing power than a cellphone.

3. Drinking water was a fuel-cell by-product, but Apollo 11’s hydrogen-gas filters didn’t work, making every drink bubbly. Urinating and defecating in zero gravity, meanwhile, had not been figured out; the latter was so troublesome that at least one astronaut spent his entire mission on an anti-diarrhea drug to avoid it.

4. When Apollo 11’s lunar lander, the Eagle, separated from the orbiter, the cabin wasn’t fully depressurized, resulting in a burst of gas equivalent to popping a champagne cork. This reaction threw the module’s landing four miles off-target.

5. As noted, Neil Armstrong nearly ran out of fuel landing the Eagle, and many at mission control worried he might crash. Apollo engineer Milton Silveira, however, was relieved: His tests had shown that there was a small chance the exhaust could shoot back into the rocket as it landed and ignite the remaining propellant.

6. The “one small step for man” wasn’t actually that small. Armstrong set the ship down so gently that its shock absorbers didn’t compress. He had to hop 3.5 feet from the Eagle’s ladder to the surface.

7. When Buzz Aldrin joined Armstrong on the surface, he had to make sure he did not lock the Eagle’s door because there was no outer handle.

8. The toughest moonwalk task? Planting the flag. NASA’s studies suggested that the lunar soil was soft, but Armstrong and Aldrin found the surface to be a thin wisp of dust over hard rock. They managed to drive the flagpole a few inches into the ground and film it for broadcast, and then took care not to accidentally knock it over.

9. The flag was made by Sears, but NASA refused to acknowledge this because they didn’t want “another Tang,” where a company made commercial profit from the space program

10. The inner bladder of the space suits—the airtight liner that keeps the astronaut’s body under Earth-like pressure—and the ship’s computer’s ROM chips were handmade by teams of “little old ladies.”

Craig Nelson uncovered these facts in various NASA archives while researching his book, Rocket Men (Viking; $28).

The full journal of the descent can be found in the NASA archives.

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7 thoughts on “Tranquillity Base

  1. its amazing that people will still find reason to call moon landings a hoax. appreciate the math it takes to fly from one point to another in a straight line using minimal correction.

  2. Pingback: Farewell, Neil Armstrong « THINKING SCI-FI

  3. Pingback: Farewell, Neil Armstrong « Scatch の 窝

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