Why did "Eagle" land long?

[smartcooky]

Some years ago, an astronaut toured New Zealand on a number of speaking engagements. I can't remember for sure who he was, but IIRC he was a Space Shuttle crew member on one of the earlier shuttle missions (Gordon?)

I any case he spoke at an Astronomical Society meeting in Christchurch in the mid 1980's, where we had a number of computer enthusiasts, and the subject of the 1201 and 1202 alarms came up.

IIRC his explanation was that there were two radars involved in the LM descent; a landing radar which gave the LM pilot accurate height information above the lunar surface, and a rendezvous radar, the primary task of which was to give range indication during lunar orbital rendezvous with the CM after completing of the lunar surface part of the mission, but it also had a secondary role of keeping tabs on the CM in the case of a descent abort being required.

The issue, according to this astronaut, was that there was a procedural flaw in one of the LM checklists that left one of the rendezvous radar's switches in the wrong position during descent. As a result of this, the computer was trying to process too much information, so it kept restarting itself and reporting an error. The astronaut said that the labelling on this switch was ambiguous, and that it was changed on subsequent missions.

The question I have now is, did I understand what he said correctly or incorrectly?

[ka9q]

The boulder field was immediately north of West Crater, so named because it was near the west end of the landing ellipse. The autopilot directed them there precisely because it had been running "long" throughout pretty much the entire powered descent. Armstrong knew it from his visual checks through the front windows before he yawed the LM 180 degrees to its face-up attitude.

West Crater is not to be confused with "little" West Crater, the smaller crater just east (sic) of the actual landing site to which Neil ran and snapped pictures just before the end of the EVA. His footprints there and back are easily seen in most of the LRO images of the site.

[Kiwi]

Armstrong seen that the planned landing site was unfit for doing do and dangerously close to a large crater. He announced that he was going to land long as to say he was going to overshoot the expected LZ...

No, Armstrong announced long before West Crater that they would land long:

To Aldrin:
102:36:11 Armstrong (on-board): Okay, we went by the three-minute point early. We're (going to land) long.

Then to Houston:
102:36:18 Armstrong: (To Houston) Our position checks down range show us to be a little long.

Following this in the ALSJ:
[Armstrong, from the 1969 Technical Debrief - "Our downrange position appeared to be good at the minus 3 and minus 1 minutes points (prior to ignition). I did not accurately catch the ignition point because I was watching the engine performance. But it appeared to be reasonable, certainly in the right ballpark. Our crossrange (north/south) position was difficult to tell accurately because of the skewed yaw attitude that we were obliged to maintain for comm. However, the downrange position marks after ignition indicated that we were long. Each one that was made indicated that we were 2 or 3 seconds long in range. (That is, they were reaching landmarks 2 or 3 seconds early. One second corresponds to about a mile of miss distance.) The fact that throttle down essentially came on time, rather than being delayed, indicated that the computer was a little bit confused at what our downrange position was. Had it known where it was, it would have throttled down later (to kill a little velocity). Landmark visibility was very good. We had no difficulty determining our position throughout all the face-down phase of powered descent. Correlating with known positions, based on the Apollo 10 pictures, was very easy and very useful."]

West Crater wouldn't have been visible at this stage and they didn't see it until after pitchover about six minutes later:

102:42:33 Armstrong: (With some urgency in his voice, possibly as he sees West Crater) Give me an LPD (angle).

[Armstrong, from the 1969 Technical Debrief - "In the early phases of P64, I did find time to go out of Auto control and check the manual control in both pitch and yaw and found its response to be satisfactory. I zeroed the error needles and went back into Auto. I continued the descent in Auto...We proceeded on the flashing 64 and obtained LPD availability, but we did not use it because we really weren't looking outside the cockpit during this phase. As we approached the 1500-foot point, the program alarm seemed to be settling down and we committed ourselves to continue. We could see the landing area and the point at which the LPD was pointing, which was indicating we were landing just short (and slightly north) of a large rocky crater surrounded with the large boulder field with very large rocks covering a high percentage of the surface. I initially felt that that might be a good landing area if we could stop short of that crater, because it would have more scientific value to be close to a large crater. (However), continuing to monitor the LPD, it became obvious that I could not stop short enough to find a safe landing area."]

[Armstrong and Aldrin, from the Crew Observations chapter of the Apollo 11 Preliminary Science Report - "This crater was later identified as one we had informally called West Crater during our prelaunch training."]

Once you know where to look, it's easy to find West Crater in the wonderful AS11-40-5882HR.

This site helps:
http://www.boulder.swri.edu/~durda/Apollo/landing_sites.html

[ka9q]

Once you know where to look, it's easy to find West Crater in the wonderful AS11-40-5882HR.

That can't be the rim of West Crater because the view is down-sun, i.e., looking to the west, so West Crater was almost directly behind the photographer (Armstrong?) This is the rim of some other crater even farther downrange in the landing ellipse or beyond it, to the west of the actual landing site.

[Echnaton]

Some years ago, an astronaut toured New Zealand on a number of speaking engagements. I can't remember for sure who he was, but IIRC he was a Space Shuttle crew member on one of the earlier shuttle missions (Gordon?)

I any case he spoke at an Astronomical Society meeting in Christchurch in the mid 1980's, where we had a number of computer enthusiasts, and the subject of the 1201 and 1202 alarms came up.

IIRC his explanation was that there were two radars involved in the LM descent; a landing radar which gave the LM pilot accurate height information above the lunar surface, and a rendezvous radar, the primary task of which was to give range indication during lunar orbital rendezvous with the CM after completing of the lunar surface part of the mission, but it also had a secondary role of keeping tabs on the CM in the case of a descent abort being required.

The issue, according to this astronaut, was that there was a procedural flaw in one of the LM checklists that left one of the rendezvous radar's switches in the wrong position during descent. As a result of this, the computer was trying to process too much information, so it kept restarting itself and reporting an error. The astronaut said that the labelling on this switch was ambiguous, and that it was changed on subsequent missions.

The question I have now is, did I understand what he said correctly or incorrectly?

That is pretty close to my understanding although I have also read accounts that put more emphasis on Aldrin.  Thankfully the ground crew was prepared. 

[smartcooky]

There are many good lessons in software engineering from the Ariane 501 failure. Most of them were immediately obvious in hindsight, and the fact that they weren't obvious prior to the flight is one of those lessons.

I once read the following on a forum in which the discussion was about the STS51-L, and the systemic failures that lead to the disaster, although this particular post related more to the Colombia disaster.

This text was part of a post by a member of that forum, and I liked it so much that I saved it for future use. I do quote it from time to time in relation subjects other than Apollo / Spaceflight

The value of failure is that you almost always learn something new about what your system can or cannot tolerate, plus you are forced to look at all of the potential failure modes as part of a disciplined failure review process.

Every time you succeed, all you learn is that you were some combination of good and lucky, and you never really know the ratio of one to the other.

When you fail, you generally have a good idea of just how unlucky you were that day, and how to improve your odds tomorrow.

- Stranger-on-a-Train (straightdope.com) 7 December 2011

[Kiwi]

Once you know where to look, it's easy to find West Crater in the wonderful AS11-40-5882HR.

That can't be the rim of West Crater because the view is down-sun, i.e., looking to the west, so West Crater was almost directly behind the photographer (Armstrong?) This is the rim of some other crater even farther downrange in the landing ellipse or beyond it, to the west of the actual landing site.

Oops, my apologies, I pasted the wrong photo number from the wrong film.  The correct one is
AS11-37-5447HR.

This site helps:
http://www.boulder.swri.edu/~durda/Apollo/landing_sites.html

[RedneckR0nin]

Armstrong seen that the planned landing site was unfit for doing do and dangerously close to a large crater. He announced that he was going to land long as to say he was going to overshoot the expected LZ...

No, Armstrong announced long before West Crater that they would land long:

To Aldrin:
102:36:11 Armstrong (on-board): Okay, we went by the three-minute point early. We're (going to land) long.

Then to Houston:
102:36:18 Armstrong: (To Houston) Our position checks down range show us to be a little long.

Following this in the ALSJ:
[Armstrong, from the 1969 Technical Debrief - "Our downrange position appeared to be good at the minus 3 and minus 1 minutes points (prior to ignition). I did not accurately catch the ignition point because I was watching the engine performance. But it appeared to be reasonable, certainly in the right ballpark. Our crossrange (north/south) position was difficult to tell accurately because of the skewed yaw attitude that we were obliged to maintain for comm. However, the downrange position marks after ignition indicated that we were long. Each one that was made indicated that we were 2 or 3 seconds long in range. (That is, they were reaching landmarks 2 or 3 seconds early. One second corresponds to about a mile of miss distance.) The fact that throttle down essentially came on time, rather than being delayed, indicated that the computer was a little bit confused at what our downrange position was. Had it known where it was, it would have throttled down later (to kill a little velocity). Landmark visibility was very good. We had no difficulty determining our position throughout all the face-down phase of powered descent. Correlating with known positions, based on the Apollo 10 pictures, was very easy and very useful."]

West Crater wouldn't have been visible at this stage and they didn't see it until after pitchover about six minutes later:

102:42:33 Armstrong: (With some urgency in his voice, possibly as he sees West Crater) Give me an LPD (angle).

[Armstrong, from the 1969 Technical Debrief - "In the early phases of P64, I did find time to go out of Auto control and check the manual control in both pitch and yaw and found its response to be satisfactory. I zeroed the error needles and went back into Auto. I continued the descent in Auto...We proceeded on the flashing 64 and obtained LPD availability, but we did not use it because we really weren't looking outside the cockpit during this phase. As we approached the 1500-foot point, the program alarm seemed to be settling down and we committed ourselves to continue. We could see the landing area and the point at which the LPD was pointing, which was indicating we were landing just short (and slightly north) of a large rocky crater surrounded with the large boulder field with very large rocks covering a high percentage of the surface. I initially felt that that might be a good landing area if we could stop short of that crater, because it would have more scientific value to be close to a large crater. (However), continuing to monitor the LPD, it became obvious that I could not stop short enough to find a safe landing area."]

[Armstrong and Aldrin, from the Crew Observations chapter of the Apollo 11 Preliminary Science Report - "This crater was later identified as one we had informally called West Crater during our prelaunch training."]

Once you know where to look, it's easy to find West Crater in the wonderful AS11-40-5882HR.

This site helps:
http://www.boulder.swri.edu/~durda/Apollo/landing_sites.html

Thank you sir