[DownloadADOBEsoftware]

It wasn't the LM that was making me cringe, it was the thought of trying to arrest over 150kgs with a hyperextended leg, the thin bar just makes it even more stressful on the leg than if it were on solid ground.

If you had no training or experience in climbing down such a ladder with all that gear on then yes, it would be quite difficult.
If, however, you'd spent years practising and were also backed up by a large team of extremely clever people you could work out all those little problems to make them manageable.

[CULTDIAMONDS]

Wouldn't it be great to make everyone think we'd landed on the moon...

[Kiariitf]

Wouldn't it be great to make everyone think we'd landed on the moon... we did.

;-)

[Buyingtime]

The original Apollo 11 tapes were definitely wiped by NASA for reuse so can't be recovered. What was thought originally to be an unauthorised copy was found to be copy of the wrong tape, a training exercise. One low quality tape was recovered of jetissoning unwanted supplies prior to lift-off. Polaroids of some of the scenes from the lost tapes have been found.

[Voliscietle]

I was asked a few questions today about Apollo, and I thought it might be worth repeating some of it here.

A common misconception regarding the Apollo flights - the lunar landing flights in particular - is that they were trouble free, not having any problems.

Nothing could be further from the truth. All of the flights had problems to some degree; all had minor problems and most had incidents that could of, at a minimum, caused an abort but in the worst case led to utter disaster.

Apollo 11 was no exception. Many people know about the 1201 and 1202 computer alarms. Many people know that the crew had to extend their planning landing site and ran quite low on fuel. But once they were on there surface, they were okay... or were they?

As part of the mission planning, they had Stay / No Stay decision points, ready to leave if there were problems. Almost immediately after landing, a problem did occur: some fuel froze in the fuel lines, leading to a build up of pressure in the lines, threatening to burst and possibly lead to an explosion (Peter B might like to chip in here and go into more detail, explaining why the fuel froze and why it posed a problem).

The astronauts were unaware of this but Mission Control could detect the problem via telemetry. They discussed the problem and were trying to determine the correct course of action: should they "burp" the engine and hope they would free the blockage? Should they abort and immediately lift off?

Whilst they were discussing what to do, the fuel line blockage cleared itself and the mission continued!

[Gulauur]

Yeah, I can't add anything sensible about the Apollo 11 LM fuel anomaly. It was something to do with supercritical helium and a heat exchanger, and the problem was prevented on later flights by a small change in the order in which some activities were undertaken.

But ERB is dead right about how most missions experienced events which could have been show-stoppers.

Other Apollo 11 funnies included:

1. Breaking the circuit breaker on the LM which armed the ascent engine. It was still possible to arm the engine by pushing the circuit breaker in, but it couldn't then be pulled out if it had been necessary for some reason to cycle it. However the LM's wiring was such that its designers were confident they could have achieved the effect by pressing some other combination of circuit breakers, if it had been necessary. On future flights important circuit breakers were covered with simple guards.

2. Poor quality telemetry and voice communication on the LM during the early part of the descent to the Moon. For the first couple of minutes of the descent to the Moon, the quality of telemetry and voice communication from the astronauts was poor, and this made it harder for Mission Control to manage the landing. The reason was that part of the LM got in the way of the direct line of sight between its dish and the Earth. Now the experts at Mission Control had carefully calculated the attitude of the LM at all stages of the descent such that this wouldn't occur. The reason it did occur was that these experts had been given incorrect information about which directions the dish could point without the LM getting in the way. The problem was partly solved on the flight by getting the LM to rotate a small distance around its vertical axis, and ceased to be a problem later in the flight as the LM moved around the Moon and pitched upright, both actions putting the dish in the clear.

3. Lifting off from the Moon without knowing where the LM was located. When the "Eagle" lifted off from the Moon, no one in Mission Control knew exactly where it was located. This meant, in theory, that no one knew what its orbit would be. As a result there are some people who think this is evidence the landing must have been faked - how, they ask, could you possibly put a spacecraft in a stable orbit if you don't know where it lifted off from. The reality was that, while Mission Control didn't know to within more than a few kilometres where the "Eagle" had landed, getting the LM into some sort of orbit was relatively easy. Once it was in space it could be tracked very accurately, and this information could be added to information about the Command/Service Module's orbit to calculate what burns were needed for the two spacecraft to rendezvous and dock.

[Gulauur]

Incidentally, one other issue the earlier Apollo missions had to deal with was avoiding the Service Module during re-entry. Several minutes before hitting the atmosphere, the crew cast off the SM from the Command Module. The SM's retro-rockets were fired continuously to push it well away, as well as giving it a roll. However, a few startled crews reported seeing their SMs drifting in the opposite direction to which they had been despatched, and re-entering the Earth's atmosphere disturbingly close to the CM.

The Apollo Flight Journal for Apollo 15 explains:
Early Apollo missions (Apollo 7 through 12) revealed an unexpected problem with this technique. At first glance, firing the translational thrusters to back the SM away, and using the roll thrusters to stabilize it would seen to be a perfectly adequate solution for this maneuver. Imagine the surprise then, when the crews of the earlier missions looked out the window and saw that the SM had somehow "boomeranged" around and was tumbling alongside the Command Module! After extensive analysis engineers discovered that the residual fuel and oxidizer in the Service Module sump tanks acted as a sort of "spring", taking the energy imparted onto them from the RCS jets, and releasing it against the tank walls as it sloshed about.

In a paper (Prediction of Apollo Service Module Motion after Jettison [J. Spacecraft and Rocket, June 1971]), a chart implies that any minus-X burn longer than about 200 seconds will result in the SM changing direction. Now, the direction reversal is not due simply to propellant sloshing. Because the SM's mass is not symmetrical over it's axis, any translational/rotational firing will start it tumbling. Since it is still tumbling while the minus-X thrusters are firing, eventually it orients itself to where the minus-X thrusters now have a posigrade (towards the CM) component. This, combined with the propellant slosh, was sufficient to cause the SM to reverse direction and head in the direction of the CM.

Remember that the propellants are just floating "loose" in the tank, which of course, is the reason for ullage before most burns. Let's try a simple scenario, where the minus-X thrusters fire for a short time, say 1 second. When the minus-X thrusters fire, the fuel essentially "stands still", and the SM accelerates around it. Now, you have inside the tank, a mass with some velocity. Eventually, the fuel smacks into a tank upper dome, and imparts its kinetic energy to the SM structure.

Now, remember these are the RCS jets, not the SPS, and they are not capable of any serious acceleration. Longer minus-X burns will eventually force the propellants down to the top of the tank, but not as much as you might think. Ullage before burns was enough to settle some of the fuel, but not enough to "pin" it down at the bottom of the tank with any certainty. There is lots of propellant still in the lines to the engine, enough to get a good engine start, which in turn, would provide enough acceleration to ensure that the propellants were always at the bottom end of the tank.

The problem with the SM jettison was twofold - First, the RCS jets created insufficient acceleration to eliminate the bouncing back and forth of the propellants. Second, The offset CG of the SM, along with the roll burn, caused tumbling which worked against any effort to settle the propellants at the "bottom" of the tank.

[Gulauur]

Neil Armstrong on the Moon.

This is the top half of the best photo Aldrin took which happens to show Armstrong on the surface. One of the ongoing arguments in Apollo 11 research (along with whether Armstrong said "...for man..." or "...for a man..." when he stepped on the Moon) is why Aldrin never took a clear photo of Armstrong on the Moon. Was it because no one thought to include such a photo in the moon walk time line, or was it a case of Aldrin snubbing Armstrong for being first on the Moon?