Author Topic: Apollo 11 Lunar Lander Pre-Launch  (Read 8333 times)

Offline nomuse

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #15 on: December 13, 2018, 11:27:10 AM »
Spacecraft pretty much never get t-boned, no matter how many driveways they might have to back out of.

How is the size of the windows an indicator of anything other than design trade-offs? Have you ever been inside a buttoned-down tank? Heck, have you ever played drums in a crowded orchestra pit? The LM cockpit was mocked up and flown in sims and the astronauts signed off on the idea that they could adequately perform the necessary piloting tasks with viewports that didn't negatively impact the structural strength and other flight considerations of the spacecraft.

Offline bknight

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #16 on: December 13, 2018, 11:36:33 AM »
Hi Everyone, I appreciate your responses. And yes I am not a naïve guy who just wandered in. But I am not a "hunchbacked" either. To be honest I don't know what to think anymore. I don't have a agenda. But having immersed myself in the subject over the years, some things continue to nag at me. I don't have blinders on and I am sure there are reasonable answers to many of my concerns.

With regards to backing up in your driveway. I was just being a bit cynical to illustrate the visibility we require today. But to suggest, as some here have, that two small windows on the LM were adequate for the job shows people have certain predisposed views. Those windows were in no way adequate, let alone ideal, in maneuvering that craft. I would suggest, if we could, ask the crew of Apollo 17 if those windows were adequate. They literally landed 2 feet away from almost certain death. Not only did one pad land in a small crater, the entire craft missed a very large crater by 2 or 3 feet which would have resulted in the craft tumbling over and death. I am 100 percent certain they had no intention of landing that close. But they did because they had zero visibility below. It was a complete miracle the crew did not perish. If I were Cernan and Schmitt I would be irate that I was nearly killed because I was given a craft in which I am flying blind. So to suggest, on anyone's part, the LM's design regarding visibility isn't, at very least, a bit puzzling demonstrates people may have blinders on. Again, just look at the DAC footage from these windows. You can't see directly below and your view is limited to maybe 15-20 percent of the horizon.

With regards to LM pre-flight, I was hoping I would get an honest discussion about this. Literally someone said "I see the differences but I don't question them" I don't get it. Does no one care? I show a photo that explicitly shows a different looking LM already inserted in the Saturn stage, mated to the CM and being hoisted to be mated to a lower stage. Everything is different right down to the tape job on the ladder. And then there are the plume deflectors. The engine thrusts are pushing directly against the body of the craft. Does this not raise even the simplest of questions? ie How do you maintain stability??? Is there even one craft/ship/vehicle in existence in which its engines thrust back into itself??? I would love to have a good debate on this (rather than whether you need a back up camera in your driveway). (and btw onebigmonkey I see no documentation on how the plumes would work. There is documentation of them on the LM)

Concerning the bolded text notice from the landing site diagram, Gene landed between two smaller craters  between two larger craters  I don't have a scale on that drawing so I can't make a comment on how far they were.  But again Gene guided the LM to where it landed and yes he could see them out the windows, until he was directly above them.  To make a statement that landing in a crater would resulted in a tumbling over resulting n death.  If you would have researched that comment you would see that the amount of list was taken into consideration.  The construction increased the chances of tumbling over were greatly decreased.


You really need to research the LM, weight was a major concern and the window size was designed to give the optimal view versus weight.  So:"If I were Cernan and Schmitt I would be irate that I was nearly killed because I was given a craft in which I am flying blind."  They were given a craft with the windows and their mission was to land.  You presume a feeling without clear knowledge of any of the astronauts.
https://airandspace.si.edu/multimedia-gallery/12965640jpg

Concerning the RCS system the force is developed at the nozzle throat, not the deflectors.  the exhaust will make a smaller force but the accelerometers would detect any motion not intended and fire thrusters to stop that movement. No problem or concern here unless the system stopped working which did not happen during the six landings.
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Offline JayUtah

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #17 on: December 13, 2018, 11:49:26 AM »
In my decidedly unprofessional experience, you don't need to be a rocket scientist to think things look odd, but sometimes, you do need to be one to understand why they're not.

Indeed, there are questions and then there are questions.  Any well-developed body of specialized understanding is likely to manifest things that look odd or seem counterintuitive to the layman.  Layman's questions intended to learn more about the field are honest and good.  Rhetorical questions that hide intuitive (but wrong) assumptions and attractive (but wrong) conclusions are less honest and less productive.

Things that seem "odd" about reaction control systems are often based on idealized depictions of such systems for lay audiences.  Certain jets fire for roll, others for pitch, etc.  In practice this is never the case.  Which is to say, in practice there is no ideal positioning of RCS thrusters on any spaceframe such that only the expected cardinal axis is affected by some control command.  It is essentially impossible to achieve such an elegant arrangement in actual design and practice.  Given this limitation, the control system for an RCS has the task of translating (auto-)pilot commands such as "roll 30 degrees clockwise" into actual on-off commands for control jets as they are actually constituted, which will inescapably generate residuals.  It must accommodate stuck or stuttering valves, broken or bent jets, and the ubiquitous condition that control moments are never exactly confined to any of the cardinal axes.  To that effect, the common solution is understandably generalized and based heavily in linear algebra.  Then, because this type of solution exists, all the other unwanted moments (fuel slosh, etc.) are also rendered according to this same generalized model.  To make matters even more interesting, the control axes for the LM weren't even orthogonal!  The generalized solution for RCS control accommodates all this, and does so dumbly with a single set of abstract control laws instantiated for each RCS channel.  In other words, engineers who do this are far smarter than lay critics give them credit for.
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Offline jfb

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #18 on: December 13, 2018, 12:26:24 PM »
And yet they go to the launch pad last second and add all this. It defies reason.

Not necessarily - fiddly, sticky-outy bits like plume deflectors could easily be damaged during the mating process, so it makes sense to install them after mating is complete.  Same with things like thermal blankets.  Yeah, the workspace would have been cramped, but flying to the moon isn't for sissies. 

Then you have all the protective wrappings that need to be there for transport and mating, but has to be removed before flight.  It's not at all surprising to me that some work had to be done after the LM was encased in adaptor. 

Offline JayUtah

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #19 on: December 13, 2018, 12:28:02 PM »
Concerning the RCS system the force is developed at the nozzle throat, not the deflectors.  the exhaust will make a smaller force but the accelerometers would detect any motion not intended and fire thrusters to stop that movement. No problem or concern here unless the system stopped working which did not happen during the six landings.

Let's elaborate on that.  The principal reactive thrust is generated in the throat of the deLeval nozzle, to be sure.  There is another model which locates it at the top of the thrust chamber, but that's for another purpose.  But plume impingement is a separate conservation-of-momentum event.  If any momentum change occurs, a reaction must occur to conserve the momentum.  When the plume hits the planted flag, the flag reacts inertially by moving.  Other reactions possible in other kinds of objects would include stress and strain effects (e.g., if the object were solid and fastened down).  The LM plume deflectors are attached to the LM structure, so they react inertially by a combination of absorbing and transmitting mechanical loads to the structure.  The resultant moment for stability purposes depends on the precise moment diagram for each plume deflector, and how they combine during actual operation.

Now whereas the thrust generated by the LM RCS was on the order of 400 N -- that's what I recall the rated vacuum thrust is of the the particular Marquardt jet I'm thinking of -- the reaction in the plume deflector is going to be much, much less.  It depends on the angle of deflection, and how much of the plume actually hits the deflector.  Reckoning the reaction force -- i.e., the nominal force coupled back to the LM frame -- is suitably analogous to angle-of-attack for a conventional airplane's airfoil.  The less angle of attack, the less force that aerodynamicists solving the airfoil problem decompose into flow-deflection lift, drag, and so forth.  If the plume gases deflect by only a small number of degrees, the flow-deflection reaction is small because the change in velocity vector is small.  Yet it would be the biggest force in the problem; drag from the plume would be negligible.  In this case it acts in the plane defined by the longitudinal axis of the deflector and the plume axis, perpendicular to the deflector axis.  That's inward, toward the center of the LM.

The fully integrated lunar module's center of mass is in the descent stage, and moves upward dramatically during powered descent.  With a nearly empty descent stage, the center of mass is closer to the interstage connection.  From photographs of the landed LM, we can see that the impingement point was biased high on the deflector surface.  And from appropriate drawings, we can see that the deflectors are angled and fastened such that the net force would point directly at the center of mass in the DPS-powered, low-fuel condition.  The deflectors were aimed precisely so as to create as small a residual as possible.

Now consider when the affected jets would be used.  In orbital flight, the x-axis thrusters provide small translations by firing all four together.  If you decompose the plume deflector reaction vectors into moment and non-moment components, you see that the moment-producing components add to amplify (or possibly reduce) the combined thrust in the desired direction, not produce a roll, pitch, or yaw moment.  It reads in the DAP simply as thrusters firing a little more or less energetically than designed.  As you say, that's just picked up by the accelerometers and accommodated in the state vector.  The x-axis thrusters also participate in roll and pitch control.  Here the residuals would produce a slight tendency to translate in the direction of the roll or pitch.  In landing, this is not at all a problem, since pitch and roll are most commonly effected in order to angle the DPS and produce lateral movement above the surface.  The sympathetic residuals contributed by plume deflectors would be lost in the DPS thrust.  And it's not a problem at all for docking, since the plume deflectors get left behind before that's necessary.

So no, an analysis of the problem with a proper knowledge of spacecraft dynamics and control and the precise design characteristics of the LM's plume deflectors reveals no stability issue that rises to the level of concern.
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Offline JayUtah

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #20 on: December 13, 2018, 12:30:22 PM »
It's not at all surprising to me that some work had to be done after the LM was encased in adaptor.

It's absolutely standard.  The notion that any vehicle and its payload are rolled out the launch pad with all the parts installed is laughably naive.
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Offline bknight

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #21 on: December 13, 2018, 12:48:06 PM »
It's not at all surprising to me that some work had to be done after the LM was encased in adaptor.

It's absolutely standard.  The notion that any vehicle and its payload are rolled out the launch pad with all the parts installed is laughably naive.

In addition the images that have been posted are far apart to do an analysis you need a series of sequential operation to make a better evaluation.  Maybe one does not exist, but to even ask a question of the LM assembly during the mating operations without knowledge of the process is laughable.
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
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Offline bknight

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #22 on: December 13, 2018, 12:49:14 PM »
Jay: Great elaboration of my post!  :)
Truth needs no defense.  Nobody can take those footsteps I made on the surface of the moon away from me.
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Offline JayUtah

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #23 on: December 13, 2018, 01:07:56 PM »
...but to even ask a question of the LM assembly during the mating operations without knowledge of the process is laughable.

There is nothing magical about rollout and/or erection.  Those are simply single steps in a long, elaborately coordinated procedure of fabrication, assembly, integration, and checkout, and safing that occur as part of any rocket launch.  There's a certain ceremonial significance to rollout, chiefly for those who paid for the mission, but to engineers it's just another procedure to worry about.  It does not signal the end of their work.  Their work continues after the rocket is integrated with launch and ground-support facilities.  I'd have to check the regs to be sure, but it might even be illegal to install things like pyrotechnics until literally hours before launch.  You certainly can't have them installed when people are working in and around the equipment that needs it.

As I said, there are questions and then there are questions.  If someone wants to learn about the intricate details of payload integration, they should find well-qualified people and ask them questions.  But when questions are paired with presumptuous declarations like something "defy[ing] reason," we gather then that the question is intended to be rhetorical, not inquisitive.
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Offline jr Knowing

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #24 on: December 13, 2018, 05:05:35 PM »
I think people need to consider the deflector was 6 inches away from the nozzle and not 5 feet. To suggest the thrust would have little impact is a supposition I have seen nowhere (from a technical standpoint). And regarding the comments about the DAP, it is the partial reason why the craft may go into an uncontrollable spin. If the thrusts start to cause instability, the system may call for more thrusts in what will lead to an almost negative feedback loop. I will dig up one of the MIT papers which suggests this is a real possibility short of perfect conditions. Thanks to posters for taking the time to respond.

Offline Zakalwe

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #25 on: December 13, 2018, 05:42:27 PM »
I think people need to consider the deflector was 6 inches away from the nozzle and not 5 feet. To suggest the thrust would have little impact is a supposition I have seen nowhere (from a technical standpoint).

Why would it have an effect?
Do you even know how rocket motors work?
Do you think that a rocket motor works by "pushing" against something?
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Offline Jason Thompson

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #26 on: December 13, 2018, 06:23:19 PM »
I don't have blinders on and I am sure there are reasonable answers to many of my concerns.

Are you willing, as Jay has asked, to concede that one of the 'reasonable answers' is that your expectations and suppositions are wrong? So far you have produced a lot of 'seems odd' or 'defies reason' arguments, but that is subjetive. No professional individual or organisation is obliged to share your incredulity at how things are done.

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With regards to backing up in your driveway. I was just being a bit cynical to illustrate the visibility we require today.

And we were pointing out that the requirements for backing out of a driveway are totally different from those of landing on the Moon. If you wish to use illustrative examples then ensure they actually fit.

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But to suggest, as some here have, that two small windows on the LM were adequate for the job shows people have certain predisposed views.

To suggest, as you have done, that two small windows that were the result of years of design work and design trade-offs (weight versus the need to see out of the craft) by several experienced professionals including the astronauts who would actually land the thing were inadequate demonstrates your predisposed views. The crews were not simply handed this craft and told to fly it. Astronauts had involvement in all stages of spacecraft design.

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They literally landed 2 feet away from almost certain death. Not only did one pad land in a small crater, the entire craft missed a very large crater by 2 or 3 feet which would have resulted in the craft tumbling over and death.

Please tell us how you conclude the craft would tumble over, taking into account the span of the footpads and the location of the centre of mass of the craft, and any information you can find about the possible slopes it could land on.

ALso please point out this 'very large crater' in this LRO image of the landing site.

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Again, just look at the DAC footage from these windows. You can't see directly below and your view is limited to maybe 15-20 percent of the horizon.

Or it would be if your eyes were locked in that position. Why do you think a fixed mounted camera (specifically put up out of the way to avoid blocking the window) in any way represents the experience of a person with a mobile head and eyes who could change his position in regard to the window?

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With regards to LM pre-flight, I was hoping I would get an honest discussion about this.

You've had one.

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Literally someone said "I see the differences but I don't question them" I don't get it. Does no one care? I show a photo that explicitly shows a different looking LM already inserted in the Saturn stage, mated to the CM and being hoisted to be mated to a lower stage. Everything is different right down to the tape job on the ladder.

And plenty of people have shown you how much work was done as a matter of routine after that stage. Once again, are you willing to concede that your naive assumption that once it was mated it was all done might be wrong?

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And then there are the plume deflectors. The engine thrusts are pushing directly against the body of the craft. Does this not raise even the simplest of questions? ie How do you maintain stability???

Here's a thought: the thrust at the engine nozzle will be a fair bit more than any incidental impingement on the plume deflectors would generate, and in any case fire them in pairs and use an active control system that can detect and resond to instability. That way any thrust generated by one thruster plume impinging on the defelctor is cancelled by an equal thrust on the opposite deflector. This is in fact exactly what they did, but not for any reason to do with any small amount of thrust that might impinge on them but simply because that's how you use an RCS thruster quad system anyway. The plume deflectors are only impinged on by the engine exhaust if the LM pitching up (two forward thrusters firing down while two rear ones fire up), pitchng down (two forward thrusters firing up with two rear ones firing down) or translating 'upwards' (all four firing down).

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Is there even one craft/ship/vehicle in existence in which its engines thrust back into itself???

A helicopter for starters. Rotors above the body generate downward thrust over the entire body of the craft. It still flies OK.

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I would love to have a good debate on this

That presumes there is actually cause for debate.

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and btw onebigmonkey I see no documentation on how the plumes would work. There is documentation of them on the LM

'There is no' or 'you have found none'? Two very different propositions.
« Last Edit: December 13, 2018, 06:32:58 PM by Jason Thompson »
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Offline Jason Thompson

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #27 on: December 13, 2018, 06:27:09 PM »
I think people need to consider the deflector was 6 inches away from the nozzle and not 5 feet. To suggest the thrust would have little impact is a supposition I have seen nowhere (from a technical standpoint).

Rockets don't work by pushing against things outside the rocket nozzle, and the RCS thrusters were used in pairs.

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If the thrusts start to cause instability, the system may call for more thrusts in what will lead to an almost negative feedback loop.

In a negative feedback loop you get the result you want. Instability leads to more thrust opposed to the instability, thus cancelling it. In fact ths is just how the RCS was used. The scenario you describe is a positive feedback loop, where the system demands more, which leads to more demand, leading to more and increasing the problem.

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I will dig up one of the MIT papers which suggests this is a real possibility short of perfect conditions.

Please do, it will be interesting to read.

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Thanks to posters for taking the time to respond.

You're welcome.
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Offline Jason Thompson

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #28 on: December 13, 2018, 06:45:41 PM »
And yet they go to the launch pad last second and add all this. It defies reason.

Not necessarily - fiddly, sticky-outy bits like plume deflectors could easily be damaged during the mating process, so it makes sense to install them after mating is complete.  Same with things like thermal blankets.  Yeah, the workspace would have been cramped, but flying to the moon isn't for sissies. 

Then you have all the protective wrappings that need to be there for transport and mating, but has to be removed before flight.  It's not at all surprising to me that some work had to be done after the LM was encased in adaptor.

The amount of work that had to be done on the entire vehicle after stacking is obvious when you consider this:



That large scaffold to the right of the Saturn V is the mobile service structure. Parked at that point in rollout but after the launch platform was desposited on the pad the crawler transporter would trundle back down the crawlway and pick up the structure and bring it alongside the LUT and vehicle. They built an entire service structure that's actually bigger that the LUT specifically for the purpose of doing stuff on the craft after rollout that was either impractical, unsafe or simply not convenient to do while the craft was in the VAB in the overall process of getting the vehcile ready for launch.
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Offline JayUtah

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Re: Apollo 11 Lunar Lander Pre-Launch
« Reply #29 on: December 13, 2018, 07:28:23 PM »
I think people need to consider the deflector was 6 inches away from the nozzle and not 5 feet. To suggest the thrust would have little impact is a supposition I have seen nowhere (from a technical standpoint).

If you didn't understand my explanation of the forces resulting from flow deflection, then you probably don't know enough about spacecraft dynamics and control to have this discussion.  Your response displays a fundamental misunderstanding of basic Newtonian dynamics.
« Last Edit: December 13, 2018, 07:34:02 PM by JayUtah »
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