Sunday, July 19, 2009

Revisiting the Moon Landing

I've decided not to jump the gun like so many news stories, and hold off on posting my personal photo of the moon walk until roughly the anniversary of when it was taken (about quarter after 11 EDT on the night of 20 July). Today I will just reflect on the events themselves and some articles I feel are worth mentioning.

Looking back, we knew what was going to happen, in detail. Maybe in more detail than you can find in all of the Wiki articles put together, because we had been raised on the space program. We (meaning my brother and I) had read every National Geographic article about moon missions going back to the first high-resolution pictures taken by Ranger 7. And we had read everything in Popular Science, books, Life magazine, you name it.

In addition, there had already been several missions to the moon, and the dangers were clear. We had seen plenty of launch attempts fail in the early days, so we knew every launch was dangerous. We had seen quite a few early moon missions actually miss the moon, so we knew navigation was not a trivial detail. We knew the rocket on the Service Module had to work correctly several times. Once you slowed into orbit around the moon, you were stuck there unless it fired. We knew there was a very narrow window for reentry. You didn't aim for the earth, you aimed at the edge of the earth to just barely catch the atmosphere. Too little and you skipped off into oblivion, too much and you would be crushed by the g forces. And we knew that there was a lot of kinetic energy to burn off by the heat shield, because you were coming in at 25,000 miles per hour.

Worse, we knew that both the descent and, in particular, ascent engines on the LM had to work or you would be stuck on the moon - leaving one man to go home alone. And, unlike the main engine (which was used for mid-course corrections), that ascent engine was never tested. Sure, they had used one on Apollo 10 when the LM had descended to less than 10 miles above the moon, but that was a different spacecraft. You had one shot to get home.

Best of all, it was summer. We knew when it was going to happen and we could watch it all as it happened. It was like riding along with Columbus to the New World. And that is what we did, went along for the ride via television.

One news item out there that I really enjoyed was this Audio slide show from the BBC. The music is from the top songs at that time: "In the year 25-25", "Age of Aquarius", and "Something in the Air". However, the newsman narrating is wrong about just how much chance was involved in the selection of Armstrong for that flight. The only way he would have missed is if an earlier mission had failed in its objectives, and even then one suspects that the crews might have shifted so he was flying the LM with the same skill that he showed flying an X-15.

Another news item of note was this video interview with a self-styled beatnik who programmed the computers on the Apollo mission. I'll bet The Thomas will enjoy this, with its discussion of worrying about every byte of code that had to be squeezed into that box, even more than I did. No bloatware back then!

Videos and pictures:
I suppose everyone has seen the partial set of cleaned up video (BBC version here), but I'll also link in my blog from last year that includes comments about the edits of the audio-video sync (concerning Armstrong's jump down, up, and then down again) in many of the older "first step" versions out there. By the way, the picture I will post on 20 July was taken just a bit after the part shown at the 3:00 mark of the first YouTube video.

For that matter, I think the coolest photo of all isn't on the moon, it is this one of Neil Armstrong doing his best Jack Nicholson impression after returning to the LM after walking on the moon. That look of tired joy, and the twinkle in his eye, says more than his words did.

Side remark:
The one thing I would like to see that has never been on any program is a side-by-side comparison of the Saturn launch to the moon and a Space Shuttle launch. The Saturn just crawls off of the pad. Why? The shuttle has a thrust to weight-at-launch ratio of 6.8 to 4.5 (in millions of pounds) while the Apollo rocket had a ratio of 7.6 to 6.7. Apollo didn't get going until it had burned off a lot of fuel from the first stage. A friend who watched them all as a kid was stunned when he saw the first Shuttle launch. It went up like an Estes rocket, and the roll maneuver it did early in flight looked like one of those early rockets just before they blew up.

Cranks and crackpots:
I really enjoyed some of the articles about the silly people who think a friend of mine (who witnessed the launch in person) and even the Soviets (who tracked the mission and congratulated us on kicking their butts in the biggest competition of the entire Cold War) were pathological liars and/or part of a conspiracy to fake the landing. Matt laid out part of the answer to some complaints, but posted a few days before new photos (pointed out by Astroprof) showed up that allow us to see the base of the LM at the Apollo 11 landing site. Even better, the LRO photos also include a cool image of the Apollo 14 site where you can see the disturbed lunar dirt (I was going to write "earth"!) where the astronauts hiked back and forth to set up a science experiment. However, as a BBC article explains, they won't get the resolution down to 50 cm per pixel (twice what is in the images linked above and shown in Astroprof's article) until August. They will eventually orbit even lower, giving sharper images for the reasons Matt explained, but that will be some time next year.

One thing those cranks never deal with is the 3 foot jump needed to get up on the ladder to get back in the LM. If you were faking it you would have steps all the way down. No one, not even a basketball star, could do a 36" vertical jump with all of that equipment on in full gravity, but it is easy in 1/6 gravity. And why the big gap? The legs on the LM were collapsible, to take up the impact when they shut off the engine and dropped the last meter or two to the moon. The ladder could not go all the way down; it had to allow for the possible compression of the lander legs.

PS - Every news feed has their version of this info, but CBS deserves mention because their video archives helped make up for the landing videos that NASA destroyed or simply lost. I like the BBC versions because they seem to provide better bandwidth, particularly for video.

Here is today's story about Pres Obama honoring the Apollo 11 astronauts. The sidebar has a number of additional new stories related to the 40th anniversary of the landing.


The Thomas said...

That interview with Don Eyles is a hoot. The AGC had 76Kb of memory. That was 9 times what I had to work with on my first guidance system.

There exists a group devoted to retaining the knowledge of the AGC. They found the drawings and the code. Recreated the assembler and built a simulator. See:

Seeing as this was a "space" application and PROMs/ROMs weren't quite there yet, the AGC was probably programmed by stringing core rope. As in stringing drive lines through the "ones" of the program memory so that the sense lines would indicate ones when the locations were read. Space has all those nice cosmic rays that do nasty things to most types of memory, so really rugged memory was necessary. The ugly part is that someone had to string the core rope and that someone would get really annoyed if some dumb engineer made a mistake and the core rope had to be re-strung, losing a week or two of work.

Ah, the memories of DTL technology and punched cards.

The Thomas said...

I notice also that Don looks strikingly familiar, although my hair was never quite that long.

Doctor Pion said...

Heh heh. Yeah, it did cross my mind that he looked like a code madman I knew back in the day ... but that one had quite an interesting beard until he shaved half of it off.

Doctor Pion said...

Interesting bit about "core rope". I'd guess that this is what we see in one of the frames of the video.

Doctor Pion said...

One addition:

I realized when commenting on Matt's blog that I had not mentioned the fact that the LM was the first and only manned SPACE craft - a vehicle designed to travel somewhere that would only work in space.