Author Topic: Questions concerning Apollo  (Read 11910 times)

Offline profmunkin

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Questions concerning Apollo
« on: May 07, 2012, 08:31:22 PM »
When Apollo 11 landed on the moon, was The Eagle piloted by Armstrong or remote controlled from Mission Control or by Computer Guidance system on board?
And or at what times during the landing was each system utilized?

Offline Laurel

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Re: Questions concerning Apollo
« Reply #1 on: May 07, 2012, 08:51:30 PM »
Armstrong took manual control of the LM during the landing because the guidance system was leading them into a boulder field and he needed to find a safer landing site.

What hoax theory are you asking this in relation to?
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Offline profmunkin

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Re: Questions concerning Apollo
« Reply #2 on: May 07, 2012, 09:53:05 PM »

What hoax theory are you asking this in relation to?

I was wondering how the eagel was controlled.
If they could have remote controlled the the eagle most or all the way to the moons surface, why did they not do it on an earlier apollo mission as a test run to make sure it was possible?

Was the Eagle controlled from Mission control or computer before Armstrong took over?
When the landing sequence was started, how was it controlled till Armstrong.

Offline sts60

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Re: Questions concerning Apollo
« Reply #3 on: May 07, 2012, 10:08:29 PM »
The LM was not and never could be flown from the ground.

Offline Grashtel

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Re: Questions concerning Apollo
« Reply #4 on: May 07, 2012, 10:17:02 PM »
I was wondering how the eagel was controlled.
If they could have remote controlled the the eagle most or all the way to the moons surface, why did they not do it on an earlier apollo mission as a test run to make sure it was possible?
Earlier missions had performed unmanned and manned testing of the LM so they knew that it would work.  Probes had landed on the Moon before Apollo using the same technique as the LM so they knew that would work.  All that was left to test was the actual landing of the LM on the Moon which as Apollo 11 demonstrated needed a pilot to be a proper test due to needing to make sure that the landing site was suitable.  An unmanned version of Apollo 111 would have failed due to not being able to see that the landing site was unsuitable and choose another as Neil Armstrong did.
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Offline Count Zero

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Re: Questions concerning Apollo
« Reply #5 on: May 07, 2012, 10:46:12 PM »
The onboard Apollo Guidance Computer (AGC) autopilot controlled the powered descent until ~2 1/2 minutes before landing.  At that point, Armstrong saw that the area the autopilot was bringing him down into was too rough, so he switched from automatic guidance to "attitude hold", which enabled him to manually control the attitude and thus the speed & direction of travel.  12 seconds later he flipped the "rate of descent" switch (R.O.D.), which enabled him to control how fast the LM descended.  He levelled-out, allowing the LM to fly down-range past the debris field.  Then he pitched back to kill his horizontal velocity (much the same way that a helicopter flares before landing) and used the ROD function to bring it down to a soft landing.

Here is an excellent detailed description of how the AGC and Armstrong worked together to make a safe landing, written by Don Eyles, the guy who programmed the AGC (note that there's a link to contact Eyles by e-mail).  You can follow his narrative while watching this film of the landing.

Left to its in automatic, the AGC would have tried to bring the LM to zero horizontal velocity & zero rate-of-descent at zero altitude.  However it had no way of knowing what the terrain was like, and would have crashed had it been allowed to come down in or near West Crater.  The astronaut-pilot was essential to safely landing an Apollo Lunar Module.
« Last Edit: May 07, 2012, 10:48:10 PM by Count Zero »
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Offline JayUtah

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Re: Questions concerning Apollo
« Reply #6 on: May 08, 2012, 12:36:56 AM »
I was wondering how the eagel was controlled.

Manually, with computer assistance.

Quote
If they could have remote controlled the the eagle most or all the way to the moons surface, why did they not do it on an earlier apollo mission as a test run to make sure it was possible?

First, because the point was to land a man on the Moon.  And second, it's a much harder task to land by remote control.  It's not a faithful test of whether a manned spacecraft could land on the Moon, which was the goal of the program.  Manned flight test occurs all the time.  When you go up, you're committed to a safe landing or a Bad Day, whether you're 200 feet above the Earth's surface or 240,000 miles above it.  In other words, Apollo 11 was the test flight.  There's absolutely no point to a remote-control "test" flight.

Quote
Was the Eagle controlled from Mission control or computer before Armstrong took over?

Mission Control never flew it.  Armstrong flew it with computer assistance.  There are three principal computer programs that control the LM during the descent, and all require pilot input (if at least to confirm transferring from one program to another).

P63 operates the LM from PDI (powered-descent initiation) to "high gate," a pilot's term for the end of the initial approach.  Little pilot input is needed here; the ship is mostly just bleeding off forward velocity in a controlled manner.

P64 operates the LM from "high gate" to "low gate."  It flies a predetermined profile designed to leave the LM about 200-300 feet above the selected landing site with a vertical descent rate of 10-15 fps.  The pilot places the landing site by means of the rotational hand controller, using marks on the LM window as a sort of gunsight.  "Pitch forward" means move the landing point long (i.e., downrange); "pitch back" means to move it short (i.e., uprange).  Lateral movements move the landing site left or right.

P65 was supposed to be an automatic terminal descent program, but was never fully implemented, tested, or used.  Because of the coupling and the non-orthogonal control axes, the program never worked right.  Elements of it were eventually incorporated into P66 (see below).

P66 is "manual" control, meaning the pilot has attitude control with the attitude hand controller, and control over the descent rate.  The computer converts the commanded descent rate into a throttle setting.  In later versions of P66, zeroing the lateral velocities was an automatic feature.

The ground had limited control over the LM computer remotely by means of the ability to send virtual keystrokes via telemetry.  However, the hand controllers are not addressable telemetrically, and the PRO key (the keypress required to confirm transition from program to program in the descent guidance sequence) is explicitly not available remotely.  The onboard crew must be present to press that button and confirm any program changes that the ground could conceivably order.
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Offline ka9q

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Re: Questions concerning Apollo
« Reply #7 on: May 08, 2012, 12:48:39 AM »
When Apollo 11 landed on the moon, was The Eagle piloted by Armstrong or remote controlled from Mission Control or by Computer Guidance system on board?
And or at what times during the landing was each system utilized?
Piloted by Armstrong, with Aldrin as his flight engineer. That's why they were there. They were also there to deploy the scientific experiments and take pictures around the landing site, but that was secondary on Apollo 11. Surface EVAs became far more elaborate and important on the later landings.

How could the LM be remote-landed from Mission Control? The only TV camera on board was packed away in the side of the descent stage, and you know how crappy its pictures were. How would Mission Control have seen where they were going?

That was the whole point of having a crew on board. They had eyes to see where they were going, so they could find a good landing spot in the limited time available. And they could do it without the 3 second round trip delay to earth that will always be there no matter how good our technology gets.

One of the major tasks of today's LRO with 50cm (or better) resolution is to map prospective landing sites well enough that safe landing spots can be pre-identified. If you know where the safe spots are and you can accurately navigate to them, then certainly with today's technology you can reliably land without local eyeballs and skilled judgment. And even when you do have a crew, you improve their safety by eliminating as many unknowns as possible.

But there was no LRO with 50cm resolution in those days. There was Lunar Orbiter, whose primary job was to image the prospective Apollo sites at the highest resolution possible, but even it could not spot every boulder and crater large enough to cause a problem for a LM. Each landing was a trip into unknown (at high resolution) territory. The planners picked areas that, from the medium resolution LO images, looked flat and clean, but they were often surprised (as on Apollo 11).

Navigating a lunar landing is a big issue. The moon doesn't have GPS, and its detailed gravity field is only now being worked out. The incomplete lunar gravity model (especially for the farside) inherently limited the accuracy of the LM's onboard guidance system no matter how good the hardware and software were. These errors in the gravity model are the favored explanation for Apollo 11 landing so far downrange.

These errors were tolerable in orbital flight, and Mission Control did have a limited ability to remotely command simple LM maneuvers (e.g., the final deorbit of the ascent stage into impact after jettison, and the entire Apollo 5 mission). But landing is an entirely different problem.  Because of the inherent accuracy of the unaided guidance system was nowhere near good enough, the Apollo LM carried a landing radar to tell how far away the surface really was and how fast they were really moving over it. They simply couldn't have landed without it, though Alan Shepard probably would have given it a really good try. And the LM simply wasn't designed to land without a crew, though there were proposals to create cargo versions that could.




Offline raven

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Re: Questions concerning Apollo
« Reply #8 on: May 08, 2012, 12:51:56 AM »
It wouldn't surprise me if Soviet LK control would have been a bit different, seen how they favoured much more the spam in a can approach to cosmonaut flight.
Can any confirm or deny this?

Offline Glom

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Re: Questions concerning Apollo
« Reply #9 on: May 08, 2012, 03:30:11 AM »
In case it gets brought up. Apollo 5 didn't involve any sophisticated control and navigation. It was just a firing of the engines. It was over before dinner.

Offline sts60

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Re: Questions concerning Apollo
« Reply #10 on: May 08, 2012, 10:32:10 AM »
The LM was not and never could be flown from the ground.
So much for hasty replies typed on a PDA.

The LM could not be landed from the ground. 

Offline ka9q

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Re: Questions concerning Apollo
« Reply #11 on: May 08, 2012, 02:21:41 PM »
In case it gets brought up. Apollo 5 didn't involve any sophisticated control and navigation. It was just a firing of the engines. It was over before dinner.
Correct. That's why I distinguished between orbital flight of an LM (Apollo 5 was earth orbital) and a lunar landing, which is far more difficult and can only be done with a human crew at the controls.

Apollo 5 had planned to exercise the Apollo Guidance Computer much more than it did. But an incorrect parameter given the programmers resulted in a shutdown of a planned burn, so the burns were done manually. I guess it was mostly important to check out the various hardware systems (especially propulsion) in vacuum and 0g, as that's hard to do on the ground. On the other hand, the computer operates just as well in both places.

« Last Edit: May 08, 2012, 02:23:43 PM by ka9q »

Offline profmunkin

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Re: Questions concerning Apollo
« Reply #12 on: May 08, 2012, 10:15:31 PM »
How could the LM be remote-landed from Mission Control?

Navigating a lunar landing is a big issue. The moon doesn't have GPS, and its detailed gravity field is only now being worked out.

I was guessing that it could not be controlled from earth because of the time delay for signals.

I found the gravity anomalies (if that is the right word ) to be fascinating, is the cause understood?

Offline Echnaton

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Re: Questions concerning Apollo
« Reply #13 on: May 08, 2012, 10:57:16 PM »
Mass concentration within the moon that was not understood and incorporated into the computer model. 

Gravitation of the Moon
« Last Edit: May 08, 2012, 11:01:39 PM by Echnaton »
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Offline Chew

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Re: Questions concerning Apollo
« Reply #14 on: May 08, 2012, 10:58:06 PM »