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  Moon landings "dead man's zone" altitude

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Author Topic:   Moon landings "dead man's zone" altitude
moorouge
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posted 03-29-2010 08:54 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
One of the major difficulties during the landings for the flight controllers was how to cope with what was known as the 'dead man's zone' - a term NASA didn't like and tried to discourage.

This was defined as the period towards the end of the descent when there was no way of aborting the flight in the event of a mishap. Lasting for about ten seconds, it was that time when the combination of low altitude and high rate of descent made it impossible for the ascent engine to overcome the downward inertia of the LM.

Though steps were practiced to counter this, nowhere have I been able to find exactly the parameters of this in terms of altitude above the lunar surface. My initial thoughts are that this happened at or shortly after 'low gate'. Any ideas anybody?

Byeman
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posted 03-29-2010 10:25 AM     Click Here to See the Profile for Byeman   Click Here to Email Byeman     Edit/Delete Message   Reply w/Quote
There wasn't an exact altitude. It was a function of vertical velocity, altitude and ascent stage weight.

moorouge
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posted 03-29-2010 02:46 PM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
I thought that was what I said. However, there had to be a range of parameters when these factors combined to create the 'dead man's zone'. Was it at between 500-300 feet, 450-250 feet and with what descent rates that were crucial? Perhaps a time before landing came into the equation also. I did say that it lasted for about 10 seconds.

So, again - at what stage?

SpaceAholic
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posted 03-29-2010 03:34 PM     Click Here to See the Profile for SpaceAholic   Click Here to Email SpaceAholic     Edit/Delete Message   Reply w/Quote
Have you reviewed the flight plan?

Blackarrow
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posted 03-29-2010 04:52 PM     Click Here to See the Profile for Blackarrow     Edit/Delete Message   Reply w/Quote
During the build-up to Apollo 11, I remember seeing the term "dead man's gulch" being used to describe that point in the landing-approach when stage-separation and abort would have taken too long to prevent a crash. I can't ever remember seeing that term used again.

Lou Chinal
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posted 03-29-2010 06:08 PM     Click Here to See the Profile for Lou Chinal   Click Here to Email Lou Chinal     Edit/Delete Message   Reply w/Quote
"Dead Mans Gulch" or "Dead Mans Zone", was a term used by NASA sparingly. Rather than look at the flight plan, I would look in Bill Tindall's notes. I think he was one of the first to coin the term. Also see "Chariots of Fire" by Josh Stoff.

moorouge
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posted 03-30-2010 06:45 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
My thanks to the responses thus far. But we're still no nearer to giving an approximate point where in the final descent this was. I still favour at, or shortly after, 'low gate' was reached, but stand to be corrected.

I don't think the flight plan would have in it - "We've had a problem and you're going to crash. Oh dear! What a pity! Never mind!"

Byeman
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posted 03-30-2010 07:37 AM     Click Here to See the Profile for Byeman   Click Here to Email Byeman     Edit/Delete Message   Reply w/Quote
Air&Space Magazine: Called It 'The Bug'"
"Below the 200-foot level, you are in the dead man’s curve," says Cernan. "Past that point, if the descent engine quit burning for any reason, you would fall to the surface and crash before you could manually abort."
Honeysuckle Creek: Apollo 11
At an altitude of 15 metres they entered what was referred to as the deadman zone. In this zone, if anything had gone wrong if for example, the engine had failed it would probably have been too late to do anything about it before they crashed on the moon. There were no fail-safe abort systems available until after the landing.

moorouge
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posted 03-30-2010 03:42 PM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Is the 'dead man's zone' the same as the 'dead man's curve'?

This from 'Chariots for Apollo' would seem to suggest that the two things were different -

Tindall's group also found guidance system faults that might result in unwanted excursions. Flight controllers would have to help the crew decide whether to go on or return to the command module. But returning to the mother ship would be tricky, Tindall said. Dispersions had to be severely contained to prevent the crew from flying a "dead man" curve - an aimless trip across the lunar sky far out of range of the command module's rescue capability.

MadSci
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posted 05-22-2010 10:00 PM     Click Here to See the Profile for MadSci     Edit/Delete Message   Reply w/Quote
The term "Dead Man's Curve" has a lot of meanings. Celebrated in song as a dangerous piece of road, it also has a meaning in aviation.

Normally, when flying an aircraft, to fly slower you need less power. However, while in certain parts of the flight envelope, particularly in a landing configuration, you actually need MORE power to fly slower.

This counter-intuitive situation is caused by the need for additional power to overcome the increasing drag associated with the high angle of attack needed to generate enough lift at low speeds.

It is sometimes called the "back of the Power Curve", but I've also heard that part of the Power Curve referred to as the "Deadman's Curve". The reason being, that while adding power allows you to slow down, you also get closer to the critcal angle of attack at which the wing will stall. If you feel yourself getting into a near stall situation, you usually get some relief from adding power, which will increase airspeed, but not in this situation. You may already be using all or almost all of your avaialable power to fly so slowly, so ther's nothing more to help you. The only solution is to lower the nose of the aircraft to lower the angle of attack. Unfortunatly, this tends to lead to a loss of altitude in this high drag configuration.

In conventional flight, the most likely times to flirt with the "Deadman's Curve" are on take off and landing. So lowering the nose tends to lead to contact with Mother Earth.

Welcome to the Deadman's Curve.

Ian Limbrey
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posted 11-13-2012 02:22 PM     Click Here to See the Profile for Ian Limbrey   Click Here to Email Ian Limbrey     Edit/Delete Message   Reply w/Quote
How quickly would it take for the Ascent Engine to fire once the abort button had been pressed?

Having reviewed the procedures for a normal lift-off from the moon's surface which include the helium tanks valves being opened to pressurize the oxidiser and propellant etc etc, this would appear to take some time and hence an abort would not be immediate?

Editor's note: Threads merged.

Lou Chinal
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posted 01-12-2014 09:58 AM     Click Here to See the Profile for Lou Chinal   Click Here to Email Lou Chinal     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by MadSci:
Welcome to the Deadman's Curve.
You put it far better then I did. An excellent explanation.

As far as an abort time lag, all the tanks were pressurized during the decent.

All times are CT (US)

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