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  Apollo 11: Biggest myth about first moon landing

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Author Topic:   Apollo 11: Biggest myth about first moon landing
Robert Pearlman
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Posts: 27682
From: Houston, TX
Registered: Nov 1999

posted 09-06-2013 09:54 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Space artist Paul Fjeld contributes the cover article (and art) for the May/June 2013 issue of AIAA Horizons newsletter, "The Biggest Myth about the First Moon Landing."
We all know the Apollo 11 story. Many of us were "there." If you're older than 44 years, you were watching TV that summer of '69, even if you were a baby, though babies didn't understand what all the fuss was about. Neil Armstrong was guiding himself and his crewmate, Buzz Aldrin, in that odd creation of the early space program, Eagle, the Lunar Module (LM), nearer and nearer to the Moon's surface. It was very exciting to listen.

Aldrin was calling out numbers relating to where they were and how fast they were going as they worked to make that final first touch by humanity on a celestial object. The other voice was that of Houston (NASA Mission Control), CAPCOM (capsule communicator) Charlie Duke, mostly saying that things were going okay, but, at the end, doing a countdown.

"Sixty seconds." Then, "Thirty seconds!" Finally we heard, "Contact light!"

Ever since then the story headline has been, "The dramatic first Moon landing of Apollo 11 succeeded with only twenty seconds of fuel remaining!"

No! The biggest myth about the first Moon landing is those twenty seconds. Armstrong and Aldrin could have stopped their approach a few feet above the lunar surface and stayed there for more than a minute before letting Eagle drop safely to the surface...

moorouge
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From: U.K.
Registered: Jul 2009

posted 09-06-2013 10:41 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
Really!!! I'd like some evidence to support this contention. My understanding is that there was a margin of error in the fuel quantity light gauges, but a minutes worth of error?

Robert Pearlman
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From: Houston, TX
Registered: Nov 1999

posted 09-06-2013 10:48 AM     Click Here to See the Profile for Robert Pearlman   Click Here to Email Robert Pearlman     Edit/Delete Message   Reply w/Quote
Fjeld provides the details in the full article. To excerpt the basic details:
...the mission planners saved five seconds of descent engine burn time at full throttle to loft them to a safer altitude. During those five seconds, they would have time for staging, pressurizing of the ascent tanks, and ignition of the ascent engine.

Five seconds of thrust at full throttle corresponds to twenty seconds of thrust at 25% of full throttle.

...that adds another twenty seconds to the mythical twenty seconds, getting us to forty seconds of flight time left at landing. The remaining part of that "more than a minute" is a tale of slosh in the propellant tanks.

...after the flight, engineers concluded the low-propellant-level light was turned on between 30 to 45 seconds early!

So we now know that Armstrong had at least 20 + 20 + 30 = 70 seconds of flight time remaining (even though the LM crew and Houston could only count on 40 of them) before he would have crashed into the Moon in an Eagle LM starved of vital fuel.

garymilgrom
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From: Atlanta, GA, USA
Registered: Feb 2007

posted 09-06-2013 12:28 PM     Click Here to See the Profile for garymilgrom   Click Here to Email garymilgrom     Edit/Delete Message   Reply w/Quote
Most know the countdown was to the abort point, not to crashing. Giving this more thought it makes sense they had additional fuel to position themselves for the abort. But that doesn't mean (to me) that they could have used said fuel to extend the landing phase.

I'm confused by this part of the article:

This is why the bingo call was actually a “Land in twenty seconds or abort now!” decision point. For example, if Armstrong had been flying when Duke’s countdown reached zero and Armstrong was still 60 feet above the lunar surface, but coming down smoothly with a three-feet-per-second velocity to a safe spot, his decision would definitely have been to continue with the landing.
If the LM could continue a safe descent after the abort now point, as this seems to say, then the bingo call was not land in 20 seconds or abort now. The author seems to be arguing both sides of that statement (abort now, continue landing) as true.

moorouge
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From: U.K.
Registered: Jul 2009

posted 09-07-2013 01:57 AM     Click Here to See the Profile for moorouge   Click Here to Email moorouge     Edit/Delete Message   Reply w/Quote
This confused me also. Surely, if mission rules stated that abort at this point, then the crew would abort regardless of how much fuel there theoretically remained. Otherwise we have a discussion on when is a mission rule not a mission rule.

On a related point - if an abort had taken place would the ascent stage engine be fired whilst the descent engine was still firing? Or would it have to be shut down before the abort took place?

David C
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From: Pasadena
Registered: Apr 2012

posted 09-07-2013 05:09 AM     Click Here to See the Profile for David C     Edit/Delete Message   Reply w/Quote
quote:
Originally posted by moorouge:
This confused me also. Surely, if mission rules stated that abort at this point, then the crew would abort regardless of how much fuel there theoretically remained.
It's not that simple. An abort, like a bale out or ejection is a course of action that is not available in all situations and in itself rather risky. Remember, that in an an analogous manner to a single engine helicopter or an ejection seat the LM was subject to a low level "avoid curve" defined by height, sink rate and mass, within which assured abort was not possible.

I'm not commenting directly on Fjeld's article, and I'm afraid that my copies of Apollo Mission Techniques for Mission G are stored away.

"AMT Mission H-2 And Subsequent: Lunar Descent" states:

3.3 ABORT OR ABORT/STAGE DECISION

An abort or abort/stage decision is made when a malfunction has been detected that will affect crew safety or the capability of the LM to abort from powered descent... The decision to abort is based on the occurrence of one of the following:

  • (a) Propulsion... Impending DPS propellant depletion
  • (c) Trajectory constraints: Violation of specified abort limits on MCC-H displays
4.3.7 Low Level Propellant Monitoring

...the ground will assume the prime responsibility for warning the crew of impending DPS fuel depletion. Using the time at which the ground observes the DPS propellant-level low (DES QTY) "light on" signal as a zero reference point, MCC-H will give voice cues to the crew indicating 30 and 60 seconds elapsed time, and fuel depletion. The timing Of these cues will be biased (to account for transmission delay, fuel usage prediction errors, and sensor errors) so that the crew will hear "fuel depletion" when there will actually be 20 seconds of hover thrust (6 seconds of full thrust) remaining for an immediate landing or DPS abort.

"AMT Mission H2 And Subsequent: Abort From Lunar Powered Descent And Subsequent Rendezvous" states:
3.1 GROUND RULES

...the DPS should be used in abort situations whenever possible, even if there is only a few seconds burn available, to aid in establishing a positive radial rate and to improve propellant margins.

The "Final Flight Mission Rules: Apollo 11" document dated 16MAY69 states:
1-23 The Command Pilot may initiate such inflight action as he deems essential for crew safety.

2-25 LM Powered Descent: If a systems failure occurs and a choice is available:

  • Early in powered descent... (up to PDI +5 minutes)
  • During the remainder of the powered descent, it is preferable to land and and launch from the lunar surface than to abort. Only those systems failures and trends that indicate impending loss of the capability to land, ascend and achieve a safe orbit from the lunar surface, or impending loss of life support capability will be cause for abort during this period.
5-90 Powered descent will be terminated for: (H) Violation of the time biased (20 sec) DPS abort boundary.

5-91 There are no trajectory or guidance constraints which are cause for abort after crew take over of powered descent.

25-12 The total continuous burn time of the descent engine shall not exceed 910 seconds of continuous operation independent of thrust level (based upon a lunar mission duty cycle).

25-18 If possible the DPS will not be burned to propellent depletion, where ever possible the abort stage sequence will be initiated at low level plus 20 seconds during an abort from powered descent, however, at crew option abort stage sequence may be initiated at low level if a safe abort stage capability exists.

25-37 Low level confirms insufficient propellant to land - (B) Powered descent: Abort stage 20 seconds after low level

So what does all that mean? At low level there was no absolute hard "you must abort now" for propellant quantity. Propellant was only one part of the equation, and it all came down to the judgement of the command pilot. Frankly, any other "rule" would have been pointless. No stick - no vote. Arrogant perhaps, but ultimately true. Mission Rules in an area like this are more like guidance to assist the command pilot in exercising sound judgement.

BBlatcher
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Posts: 48
From: Savannah, GA, USA
Registered: Aug 2011

posted 09-07-2013 10:12 PM     Click Here to See the Profile for BBlatcher     Edit/Delete Message   Reply w/Quote
In his autobiography, Armstrong makes clear that he was going to be the final decider on whether to land or not.

Lou Chinal
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From: Staten Island, NY
Registered: Jun 2007

posted 09-09-2013 03:34 PM     Click Here to See the Profile for Lou Chinal   Click Here to Email Lou Chinal     Edit/Delete Message   Reply w/Quote
After all was said and done, it came down to one guy's hand/eye co-ordination.

OV-105
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From: Ridgecrest, CA USA
Registered: Sep 2000

posted 09-10-2013 12:32 PM     Click Here to See the Profile for OV-105   Click Here to Email OV-105     Edit/Delete Message   Reply w/Quote
I thought the biggest myth was that it was fake.

Headshot
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Posts: 197
From: Streamwood, IL USA
Registered: Feb 2012

posted 09-10-2013 03:38 PM     Click Here to See the Profile for Headshot   Click Here to Email Headshot     Edit/Delete Message   Reply w/Quote
OV-105, you hit a grand slam with that observation!

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