Hoax? - Lunar Launches - Too Fast

[JayUtah]

How do you believe they could calculate the "required RCS thrust time" without knowing the Weight/Balance/Inertia information?

What makes you think that was something they calculated, or needed to calculate?

How would they be able to predict the impact of "variance in the thrust output/timing of each RCS thruster"?

What makes you think it needed to be predicted on the fly in order to achieve attitudinal control?

This is MANDATORY BASIC CORE information they'd have to derive, share, and use for Attitude Control system.

Or so you think, because apparently you're unable to conceive of any way to do it that transcends your basic-only concept of physics. The LM's digital autopilot (DAP) is one of the most copiously documented features, right down to the program code being available on GitHub. Not surprisingly, it doesn't work by timing the RCS firings ahead of time, or by deriving control moments from a static understanding of the LM's aggregate mass properties. You simply assume you know how it works, or should work, and imagine that everything that doesn't fit that understanding must be a cause for suspicion.

[najak]

I hinted that the initial conditions would be a static pressure problem in which a compressible fluid is introduced into a partially closed vessel. The fact that you can't even venture a guess at what any of the next steps should be in the process indicates you don't know what you're asking for. Maybe the inflow mass flow rate? Maybe the compressibility of the combustion products?

Move forward more quickly.  Your manner is designed to stall, and drag it out.   Just make your proof (which no one else seems to be able to do) - then it can be assessed.

The direction you were headed in, has to do with "Pressure Force".  So go ahead, and describe the process by which you'd estimate the range of "Pressure Force".  But as you do this, it won't be complete unless you also:
1. Talk about the correlated LOSS of Momentum Thrust.
2. The extreme immediate fall off in Pressure Thrust as we begin to rise...
3. Your math needs to account other gaps in the platform... were they any?  How much gap?   Where is the top level document that simply "states it" (e.g. 40 square inches of gap to allow more exhaust to escape on ignition).

There are NUMEROUS articles from Rocket Scientists which all agree that "Thrust is normally LOWER at launch" because the Loss in Momentum Thrust (because the exhaust is constrained/compressed) is more than the Gain in Pressure Thrust.

This has ALREADY BEEN STATED BY ROCKET SCIENTISTS.

So there's no reason for ANYONE to think there is a "pot of gold" at the end of this proof -- unless you are suggesting that you can "do what has never been done in 40 years" (that we know of) while proving the existing rocket scientists wrong -- to reveal some magic solution that provides the AM an added 72% boost in a steady fashion for 1 second.


But if you insist, I'll go through your proof with you, but please go faster - there will be hundreds of steps in this Rocket Science proof, so we can spend 4 posts per mini-step.  Get to your point faster - I'll keep up.

[JayUtah]

I get it quite clearly.  Perhaps YOU can show me ANY science article which indicates that they can justify the added 72% of boost for the first 1 second...

"Unless you can show me an external source that expressly refutes my exact question, I'll continue to claim it's unrefuted." That's not how knowledge works.

Here's a start. It doesn't directly address thrust, but it does address the proxy value of chamber pressure. "The maximum allowable combustion chamber pressure during start transients was 177 percent of the nominal combustion-chamber pressure." C.E. Humphries, R.E. Taylor. Apollo Experience Report - Ascent Propulsion System, NASA Technical Note TN D-7082 (Houston, TX: 1973), p. 2. You maintain that thrust is uniformly lower during ignition transients. But from your own sources: "Single engines or different engines of the same design also exhibit variations of thrust input, and consequently have significant differences in thrust-buildup curves. As discussed in Section 2.1.4, the usual procedure is to conduct many static firings to establish the statistical nature of the ignition thrust input." Transient Loads from Thrust Excitation. NASA Space Vehicle Design Criteria, NASA SP-8030, p. 2. The reference says, "Data for obtaining dynamic input curves of thrust buildup and thrust decay should be obtained directly from static firings of the actual engines, with care taken to correct the data for test-stand motion." (internal references omitted) Id. p. 15. There's no one-size-fits-all concept of ignition transient.

He's stalling here for a reason.

I'm just not running the play the way you want me to, the way you expect me to, the way that plays into your plan of always keeping the ball in everyone else's court while sidestepping everything that's explained to you. Again, you're not the first person to come here and demand extensive refutations of poorly-supported claims, only to discard them and move on to the next "Here's why it's still fake."

You are safe within an echo chamber here.

This forum exists primarily to invite hoax claimants to come here and make their cases.

You wouldn't last 2 seconds in the realm of friends that I keep.

And the company you keep seems to have a persistent problem making their case to anyone who knows the science, a problem you dismiss by pretending the vast internet powers that be are suppressing you and that your critics must be the equivalent of religious fanatics for not bowing to your superior wisdom.

I'd like to see that changed.

What part of that was served by you arriving here assuming you were the smartest person in the room?

[JayUtah]

Move forward more quickly.

We'll do it my way, for the reasons I already gave. If the ball's in my court, that means I call the play.

The direction you were headed in, has to do with "Pressure Force".

No. This has nothing to do with pressure thrust. That's a problem of static pressure at the exit plane, irrelevant to anything that might be occluding or partially occluding the engine nozzle. But thanks for proving why we need to move step by step instead of one single big-bang estimation. Pressure thrust is already included in the rated thrust of the engine. That represents the final state of our estimation: the LM flying under nominal thrust, free of any ephemeral or transient phenomena.

Your math needs to account other gaps in the platform... were they any?  How much gap?

I promise that will come into it. But you're getting ahead of the process.

Where is the top level document that simply "states it" (e.g. 40 square inches of gap to allow more exhaust to escape on ignition).

Are you really so naive as to demand that everything we look at, derive, estimate, or compute along the way must have a "top-level document" that just comes right out and hands it to us?

[najak]

#1: What makes you think that was something they calculated, or needed to calculate?
#2: What makes you think it needed to be predicted on the fly in order to achieve attitudinal control?
#3: Or so you think, because apparently you're unable to conceive of any way to do it that transcends your basic-only concept of physics. The LM's digital autopilot (DAP) is one of the most copiously documented features, right down to the program code being available on GitHub. Not surprisingly, it doesn't work by timing the RCS firings ahead of time, or by deriving control moments from a static understanding of the LM's aggregate mass properties. You simply assume you know how it works, or should work, and imagine that everything that doesn't fit that understanding must be a cause for suspicion.

#1/2: What makes you think it's not?  Do you think the AGC/DAC are going to fire the thrusters without at least having a "predicted estimate" for acceleration impact?

[JayUtah]

What makes you think it's not?

Because I know how the digital autopilot actually worked, and in the broader sense I understand how a proportional-differential control system works.

Do you think the AGC/DAC are going to fire the thrusters without at least having a "predicted estimate" for acceleration impact?

Yes. In fact, I not only think so, I know so.

[najak]

The direction you were headed in, has to do with "Pressure Force".

No. This has nothing to do with pressure thrust. That's a problem of static pressure at the exit plane, irrelevant to anything that might be occluding or partially occluding the engine nozzle.?..

I said "Pressure Force" - in this case that pressure can be considered "Static pressure" because the object pushing back is the stationary platform.  Is this not what you are about to "calculate?"  (the collective pressure at Nozzle exit - then Newtons law indicates that equal force is pushing up on the AM.   Is this NOT where you are headed with this?

So let's quickly calculate this estimated "Static Pressure Force" - and lets' move on.

You'll also need to figure out the "Loss of Momentum Thrust", unless you are suggesting that it's constant and not impacted by "blocking the escape of exhaust".

[najak]

Do you think the AGC/DAC are going to fire the thrusters without at least having a "predicted estimate" for acceleration impact?

Yes. In fact, I not only think so, I know so.

It seems that your "knowledge" doesn't match that of the Apollo flight journal:
https://www.nasa.gov/history/afj/ap15fj/12b-day5_lm_activation.html

"098:36:21 Mitchell: All right, your LM DAP [Digital Auto Pilot] data first. CSM weight, 37679; LM weight, 36630. Your GDA [Gimbal Drive Actuator] drive angles onboard are good. [Pause.]
Spacecraft weight, or more accurately, its mass is very critical in calculating what is known as the "Moment of Inertia". This changes significantly as a function of mass and is used to calculate the firing times of the thrusters needed to establish known rates of rotation. Of course, all of these functions are under the control of the DAP (Digital AutoPilot), a set of algorithms in the CMC which are calibrated to accept values for vehicle mass in pounds. In metric units, the values loaded in the DAP are 17,091 kg for the CSM and 16,615 kg for the LM."

[JayUtah]

I said "Pressure Force" - in this case...

Yes, you're combining words and concepts from various elements of the problem and trying to give a name to the horribly confused mish-mash that seems to constitute your understanding of the problem you think is a slam-dunk.

...(the collective pressure at Nozzle exit - then Newtons law indicates that equal force is pushing up on the AM.   Is this NOT where you are headed with this?

No.

So let's quickly calculate this estimated "Static Pressure Force" - and lets' move on.

No, it appears we still have to disabuse you of the conflation of effects that you have carried forward from the first page. Bob Braeunig initially spoke of the effect of the exhaust being somewhat contained at launch. That is one effect, and it is fairly particular to the lunar module ascent stage. They were really only concerned with whether firing the engine under those circumstances would blow up the engine. No one cared about thrust excursions. And in every other case we take pains not to let that effect happen at all. There is also the normal component of pressure thrust. That has nothing to do with whether there's something near the nozzle exit, although as you suspect, it will be convolved with the previous effect (and we'll get to that). There is momentum thrust, which is the component we like most. We aren't concerned with that for this stage of estimation. You want to compose these two effects together and say that additional pressure thrust results in lower exhaust velocity and therefore less momentum thrust (or at least that what you seem to be claiming). That's not relevant at the moment, and in any case is subsumed into the rated engine thrust. Then there is the ignition transient, which varies greatly from engine to engine and applies whether or not there is anything near the engine. Bob Braeunig added that to his page after discussing with me. It seems almost impossible to even start to discuss any of these in isolation for estimation purposes without you flailing your hands about how we have to consider this or that from all the stuff you've Googled up and tried to understand. Then there is the component of the rebound shock wave from the descent stage deck. Someone lately reminded me of that. That's not just Newtonian action/reaction. We haven't considered it up until now, but we should.

On a related note, you indicated that combustion would be inefficient owing to evidence or inference of unburnt propellants at ignition. It is true that oxidizer is pre-injected to smooth the ignition process. It is also true (but not widely known) that the APS used a kind of film cooling that allowed suboptimally mixed propellant to slide down the inside of the nozzle to form a film that is partly opaque to the radiant heat transfer from the main fluid flow. This does not affect rated thrust or the combustion that produces the various effects we wish to contemplate.

You'll also need to figure out the "Loss of Momentum Thrust", unless you are suggesting that it's constant and not impacted by "blocking the escape of exhaust".

No, we don't need to consider momentum thrust in any way, shape, or form for this part of the estimation.

You insist that many rocket scientists have assured you of some certain law. But I'm having trouble tracing this to any particular documentation you've presented. I find this :—

When I look up the concepts of "Ignition Transient" it's a phase with LESS THRUST, not more. I think this statement might be misconstruing the phrase "over pressured Ignition"...

...but then nothing until this...

Braeunig (smartly) removed his prior explanation, because it was unfounded/unsubstantiated, and goes against what most other articles have said about the "net result on thrust when the rocket engine is too close to the ground". Even if Pressure Thrust increases, it is ususally MORE-THAN-OFFSET by a reduction in Momentum thrust -- resulting in LESS NET THRUST (not more).

...which I'm not sure is related, but is the only other place where you allude to many sources that allegedly confirm your beliefs. Would you care to be more specific about which constitute the "most other articles" that establish these various concepts in your mind, and which source applies to which concept? You seem to be confused about what constitutes the elements of rated thrust in a nominal engine operation, much less what might hold under the special conditions of launching from just slightly above a surface.

[JayUtah]

It seems that your "knowledge" doesn't match that of the Apollo flight journal...

As usual, the concepts at work are not as simple as you wish. Yes, there is a mode in which the LM autopilot can make use of moment-of-inertia data to estimate acceleration rates. And because the DAP has to be able to fly the LM/CSM docked, undocked, and separated, these are grouped into different control laws for each case, not all of which need the moment of inertia. Ask yourself why the lunar module pilot would give a flying frack about the mass of the CSM: it's because they're setting up for the contingency in which the LM might have to fly the whole stack, not because knowing these masses is essential to solving the guidance problem.

Because the LM RCS has to be able to fly the whole stack (very massive) and the ascent stage alone (something like two orders of magnitude less massive), the control axes are not purely orthogonal, the jet firing logic is not straightforward, and the jets are oversized. It is the need to accommodate these highly varying spacecraft masses and flight regimes that requires a separate step of estimating rotation rates, angular acceleration, and thus whether to fire the jets continuously or "pulse" them. But this is not a requirement of the attitude control problem. It is an artifact of how the LM designers chose to solve it.

You bring up weight-and-balance charts, which are critical for determining the center of gravity for a winged airplane. You compute the moment arms of passengers and baggage primarily in the pitch axis (but perhaps also in the roll axis) and position them so that the center of gravity thus computed lies within a particular envelope that permits flight control. That relates to spacecraft design only insofar as the gross center of mass and the gross placement of reaction controls should be coordinated in the design. In most practical spacecraft designs, stability cannot depend on real time control or knowledge of the center of mass. It will simply be where it is.

In the case of a docked LM/CSM, the combined center of mass doesn't lie anywhere close to the ideal position for the LM RCS. Control is still possible. This problem was solved by a mathematical indirection whereby a notional set of control axes was devised, and the practical control axes were mathematically mapped to them via linear algebra depending on which flight mode was in force and which control laws governed. Again, this is not endemic to the problem of attitude control. It is merely the way Apollo decided to solve it.

The values being passed to the lunar module in the transcript are merely the spacecraft masses, not information that has anything directly to do with center of mass. We want the moment of inertia in one case because we want to estimate our angular acceleration and decide whether to fire the jets continuously or pulse them. You can see the LM ascent stage operating in "pulse mode" in the ascent film. The moment of inertia changes extremely dramatically over the mission. This doesn't affect the essential nature of the guidance problem, but it relates to one possible way to solve it.

In general, if you can measure the error and error rate (which any IMU in the 1960s could do), then you have the basis for a proportional-differential controller in that channel, which is at the heart of MIT's design. There is no need to estimate or precompute the application of a corrective moment, and in fact the accuracy of the solution isn't increased by doing so. If the error and error rate are cross-signed, you merely have to zero out the error rate when the error falls inside the deadband. You don't need to time anything; you just apply the control until the rate reaches zero, however long that takes.  You might know this as closed-loop control. If the error and error rate are same-signed, you need to apply a control moment to oppose the rate and drive it to a preset corrective value in the opposite direction. Then the previous logic takes over. Do this separately for the roll, pitch, and yaw channels and you have a working autopilot with no need to compute (or even know)  the center of mass or to incorporate the moment of inertia.

[najak]

....

In the time you spend writing, you could have just done some ballpark math to derive what you believe are the ballpark contributors that boosted acceleration.  To date, after 40 years, there still exists no such presentation (that anyone here seems aware of) -- so this is exciting new ground.  Perhaps we can name it after you -- the only one to be able to do this.

I'm just one person.  My education is not your concern here.  The concern is debating this LONG-TERM WIDELY KNOWN MLH CLAIM... 
"How did it generate 27,000 Newtons of steady upwards force for the first full second?"

If you want to educate people -- START WITH THIS NON-EXISTENT PROOF - then you can educate people on "the math/science behind it".

I will simply document the state of affairs... if you want to change this state of affairs -- great.  Do it.  Show us.

[JayUtah]

In the time you spend writing, you could have just done some ballpark math to derive what you believe are the ballpark contributors that boosted acceleration.

...which you will then nitpick, sidestep, and dismiss as merely a ballpark figure. You do not get to dictate what must be the method to answer your questions. And your ongoing insistence that the answer must be simple, or simply arrived at, is at odds with the nature of the problem you present.

I'm just one person.  My education is not your concern here.

You have made many claims to having off-the-charts intelligence, and upon that basis to be well versed in the physics problems with Apollo, and upon that basis to have rationally concluded it did not happen. You have challenged your critics to provide arguments and estimates to dispute your findings. But what are we to do with such challenges when your understanding of the problem is so very muddled? What confidence can we have in your ability to understand the answer and your willingness to accept its findings? The goal is not to prove that you are unintelligent or not as knowledgeable as you claim. But as long as you keep failing to understand the problem, your demands that we "get on with it" according to your preferred schedule and method carry little weight.

We have identified the components of thrust that likely acted over the first second of flight. I am taking them one at a time, applying a defensible estimation procedure, and engaging you along the way in order to ensure the sincerity of your interest and your eventual buy-in to the findings. If we introduce a compressible fluid at a known mass flow rate into a vessel that has an aperture of known size, what will happen?

[najak]

#1: your ongoing insistence that the answer must be simple, or simply arrived at..
#2: You have made many claims to having off-the-charts intelligence...
#3: We have identified the components of thrust that likely acted over the first second of flight. I am taking them one at a time, applying a defensible estimation procedure, and engaging you along the way in order to ensure the sincerity of your interest and your eventual buy-in to the findings. If we introduce a compressible fluid at a known mass flow rate into a vessel that has an aperture of known size, what will happen?

#1: Be as complex as you like.  But in the end, it MUST ALSO satisfy Newtonian math too.   Your complexity still cannot BREAK newton's laws, until you reach much higher speeds where things get weird.
#2: I withdraw my statement.  It was an overstatement to begin with hastily typed, and inaccurate.  It is now withdrawn; I stand corrected.   Thank you.

#3: "If we introduce a compressible fluid at a known mass flow rate into a vessel that has an aperture of known size, what will happen?"
I don't think the question is fully qualified.   It seems like "existing pressure of the liquid", "forward pressure" and "flow rate" need to be known to figure out if the liquid will either compress or expand.  You also have to know the "existing pressure inside the aperture" and what is beyond it?  Was it previously closed, then opened?

OR - just make the darned proof start-to-finish, as ONE DOES NOT YET EXIST, leaving the MLH claim without a debunk.

Or at least make HALF your proof about the "static pressure" contributor - and present it.   Then you can see if I'm keeping up or not.

[JayUtah]

Be as complex as you like.  But in the end, it MUST ALSO satisfy Newtonian math too.

The ultimate answer is not required to submit to your limited understanding.

I don't think the question is fully qualified.

You're right. Your ability to understand what's missing helps you buy into an ultimate estimate.

It seems like "existing pressure of the liquid"

Who said anything about a liquid?

"forward pressure" and "flow rate" need to be known to figure out if the liquid will either compress or expand.

Compressible flow is not really where I'm going.

You also have to know the "existing pressure inside the aperture" and what is beyond it?  Was it previously closed, then opened?

Well, we're talking about vacuum both inside and outside the vessel until the fluid begins to fill the vessel. We propose a fixed mass flow rate into the vessel, but the flow out of the vessel is determined by the fluid properties and the area of the aperture through which it flows. Since it's flowing out into space, and we're just estimating, we can assume an infinitely capacious vacuum into which the fluid flows. Ignore forward pressure for now.

Or at least make HALF your proof about the "static pressure" contributor - and present it.   Then you can see if I'm keeping up or not.

So far you are not keeping up, as you refuse to separate the various effects we have mentioned and don't seem to understand where one leaves off and the other starts.

[najak]

#1: The ultimate answer is not required to submit to your limited understanding.
#2: Well, we're talking about vacuum both inside and outside the vessel until the fluid begins to fill the vessel. We propose a fixed mass flow rate into the vessel, but the flow out of the vessel is determined by the fluid properties and the area of the aperture through which it flows. Since it's flowing out into space, and we're just estimating, we can assume an infinitely capacious vacuum into which the fluid flows. Ignore forward pressure for now.

#1: My "limited understanding" says "the AM's acceleration can be used to determine the NET FORCE acting on it".   Do you really disagree with this?
#2: OK, so the fluid will expand, likely into gas form.  If this is the ignition chamber, then ignition will happen over a period of X msec with some variance and transients.   Quickly it should reach steady state.  Starting out, portions of this fuel will be expelled from the nozzle before it's burned.

The combusted (and un-combusted) fuel will be expelled from the nozzle.  The combustion process, which seems to produce about 3000+ C heat, along with bright light - will dramatically increase expansion, as expansion is a function of temperature.

Transient behaviors can vary, as it reaches steady state.  Pressure against the front of the ignition chamber as well as the exhaust cone, is known as "Pressure Thrust" (per Newton, will be the same as the equivalent imbalance in gas pressure as it leaves the nozzle).   The Momentum Thrust is calculated by "fuel flow rate * exhaust velocity".. 

So what's next?