Hoax? - Lunar Launches - Too Fast

[JayUtah]

The question has had an answer two hours ago, 12/31/2024 1056 CDT.

And it's quite a good answer, albeit misdirected for the purpose of this thread. Najak asked that forum a different question than he asked this one. He asked that forum for a clarification of steady-state operation only, and got one—along with the standard simplifications. He asked this forum to explain a transient observation, which naturally requires us to consider transient phenomena that the simplifications don't cover. So any dreams he might have had of cribbing that answer for the question here falls into the same pitfall as demanding that simplified, straightforward rules explain the uncommon.

At least in that forum, where he's not overtly peddling conspiracy theories, he's willing to confess his ignorance. And there, as here, people first have to disabuse him of the wacky notions he's concocted from his desire to build his own Chartres from children's wooden blocks. Here he stomped and whined until I reminded him of the list of factors we can consider for LM liftoff performance. As usual he's latched onto a new one, conjured up a new straw man, and Gish-galloped it down a completely new rabbit hole that we're going to have to undo when we get there.

The endorsed answer accurately depicts nominal steady-state thrust in three escalating degrees of complexity. The first, 𝐹 = 𝑐_𝑓𝑃_𝑐𝐴_𝑡 is, as stated, the first-order approximation: throat area times chamber pressure, scaled by a coefficient. As explained—and as is the case any time "coeffiicient of ____" appears in engineering, the coefficient is the first-order approximation for a number of factors that under other circumstances may behave in complex ways, but under the conditions appropriate to the use of this simplification they may be approximated by a single number. One of the conditions given as being hidden behind this approximation is unideal expansion. That's exactly part of the transient phenomena we're considering in this thread, which is not about normal, steady-state operation but rather something that occurs under very rare conditions where fluid expansion can produce a number of uncommon effects. Rocketry has traditionally assiduously avoided those conditions, which is why they're not part of the standard canon.

The second form, 𝐹 = 𝑚˙𝑣_𝑒+(𝑃_𝑒−𝑃_𝑎)𝐴_𝑒 (where m-dot doesn't seem to want to paste accurately) is a second-order approximation that allows two important terms to vary separately. The author was kind enough to provide a bolded clarification that disabuses Najak of his conflation between thrust chamber pressure and pressure thrust (as considered collateral with momentum thrust). This equation is especially important where 𝑃_𝑎 varies significantly. It's the classic form because it gives the most accurate answer for the least math.

The third form, ∫𝑃_𝑥 𝑑𝐴, is the ultimately correct answer in the sense that it correctly and completely expresses the actual physics. Calculus is entitled to make people's eyes glaze over, but this is just a mathsy way of saying "The vector sum of all pressure parallel to the direction of travel." 99 times out of 100 that's overkill, and one of the approximations would be simpler and safer. LM liftoff is that hundredth case, and why we have to belabor the solution. The author of the answer basically gives away the method we're reaching for here; we'll see if Najak can think outside the box. That's why we're working with the underlying thermodynamics: because the unconventional ways in which the pressures act require us to start with the basic elements of pressure-volume work. And that's why we started with understanding the gap through which exhaust gases will escape while the LM is just lifting off. ∫𝑃_𝑥 𝑑𝐴 is the solution we need, and as the author warned, it's a "nasty integral." It's about to get monumentally more nasty, which is why we're approaching with caution and ensuring that we have solid footing in every step of that approach.

LM stability is only tangentially part of this thread, and it's indeed gratifying and amusing that someone linked to my explanation (which seems to be missing a key diagram). I understand why that forum downvoted it in their context, but the endorsed answer hints at the solution I invited the reader to consider by looking at the front view of the LM with its principal mass elements collocated. The general form of the solution to finding center of mass, center of gravity (which in terms of orbits can be different), center of pressure, and moment of inertia are "nasty integrals." But there are some coarser techniques that apply such as considering the moments provided by only the high-order masses. It's still math, but less nasty.

[bknight]

I believe that I mentioned in the thread a couple of times, that the engineers at NASA knew all this and gave Fendell a table of camera angles to be at specific times.  It was not breaking physics because they knew more physics than najak knows.  But thanks for the expansion of the answer and since those integrals are nasty, I won't even bother to attempt them.

[JayUtah]

I believe that I mentioned in the thread a couple of times, that the engineers at NASA knew all this and gave Fendell a table of camera angles to be at specific times.  It was not breaking physics because they knew more physics than najak knows.

To that point, I've been stepping through frames of YouTube videos that have nothing to do with Apollo, but which do involve frame-rate conversions and other interloping factors such as conversion from file-sequential color. As a result, I'm decreasingly convinced that Najak's removal of "duplicates" did not result in dropped frames and, consequentially, a compressed time line. He's going to have to convince me harder that he's getting that part of his presentation right. With any luck we can impose upon Dwight to offer some insight.

But thanks for the expansion of the answer and since those integrals are nasty, I won't even bother to attempt them.

If this goes the way I plan, we won't actually need to solve the whole integral. But you can't understand the estimation process without understanding why you need to integrate axis-aligned pressure over area, and over what area. This is why we need to get the essentials underfoot first, otherwise it comes across as appealing to magic. Experience has shown that Najak will just dismiss the "magic" answer with bluster because he doesn't understand it—because it's not expressible in the simplistic building blocks of "basic physics" he insists we must limit ourselves to. That understanding cannot be conveyed accurately in the coefficient-of-thrust formulation. Understanding why you can decompose the agents into a momentum component and a (supposedly negligible) pressure component is the important conceptual leap—hence the classic formulation that gives us just enough of the calculus (albeit hidden). Remember, before Newton could properly express the mathematics that describe physics, he had to invent calculus to do it. (Yes, yes, Leibniz.) Physics is applied calculus, not applied Excel—hence the integral formulation.

You're right in imagining that solving the integral over the geometry of the thrust chamber, nozzle, etc. would be heinous. If doing it analytically, I'd be tempted to toss out the power basis functions; I'd use something like the Bernstein or Bezier basis functions to describe the geometry, but then I'd lose the primacy of the thrust axis—sigh. In the real world we'd do it discretely using a fine planar mesh and a Taylor series in a computer. That's less analytical work and therefore probably less error-prone. But even that would be just another approximation to the actual physics. To bring this back down to Earth, so to speak, we won't be plodding through any of that. No one ever wants to actually do it, but understanding why that's the theoretically pure and correct answer is vital to understanding how and why you can sometimes approximate—and how and why certain unexpected things might happen under curious circumstances.

Now to be fair, I don't think Najak was asking that forum about the question in this particular thread. He didn't mention LM liftoff at all—to the contrary, he asked his readers to assume fully nominal conditions. To me it seems like he was trying to address the LM stability question, which he has pursued chiefly by trying to estimate the length of the moment arm from center of pressure (thrust) to center of mass. That the good answer he got bears upon this thread may just be an accident. The answer applies here, but it's not clear that Najak asked the question with the express intent of applying it here. I feel we need to acknowledge this in order to avoid the straw man.

[dwight]

Hi everyone, I've been loosely following this from the sidelines, but I'll give my best given that lack of depth I have read into this discussion.

The color-sequential cameras operated at 30 frames per second, and were, essentially, black and white cameras, with the Red, Blue, Green color-wheel providing the color information for each field sequentially. And here goes the explanation I did in "Live TV From the Moon".

A normal NTSC TV frame occurs 30 times per second which is made from two fields containing half of the image information occurring 60 times per second. As mentioned earlier, the first
field contains every odd line (1, 3, 5 and so on) of information, while the second field contains every even line (2, 4, 6 and so on). The disc recorder recorded each incoming video field (1/2 of a complete frame) onto one of six available tracks.

As field 1 was being written, 3 were being played back, and 1 was left blank. In order to recreate a full NTSC frame, there must be 3 even fields and 3 odd fields in the disc recorder. Due to the manner in which the fields were recorded in the first place, the field combination would always be wrong, that is the combination would always be either 2 odds and 1 even, or
2 evens and one odd. To rectify this, the incorrect field was always delayed by half a line, and thus it conformed to the other two fields.

The signal was then fed to an encoder made by Cohu which combined the fields of the respective red, green and blue fields to create a complete full frame of color video completely compatible with standard NTSC television sets. This signal could be sent on to any television station. In the case of non-NTSC format countries, the signal was converted one more time into either PAL or SECAM, although this occurred in the respective countries and was not performed by NASA. An additional problem had to be overcome as the spacecraft was travelling
either to or from the earth. The Dopplereffect, whereby the frequency of the radio waves increase or decrease depending on the direction of travel of the transmitting spacecraft from the earth, could potentially cause timing problems to the incoming TV signal. In order to overcome this, a series of two video tape machines were linked together with one recoding the signal onto 2” tape and synchronized to the spacecraft signal. This tape was then wound onto the second machine synchronized to ground-based equipment and played back. The resultant signal was a fully compliant TV signal which would cause no problems in re-transmission.

There was however a 12 second delay introduced for the color signal, which is often referred to in ground-to-spacecraft communications.

An important aspect to this signal. At any given time, there was always fluid motion. The buffering system repeated the respective color fields, but motion was always live, per se. The buffered fields present themselves as the "confetti" artifacts when fast motion is present. It is not possible to remove "redundant" frames, as there are none. If you attempt to remove fields/frames, you are removing the fluid 30 fps motion.

[najak]

Before my vacation and shortly after my banning, I completed the Static Pressure Analysis spreadsheet.   And then refigured my 30 FPS screenshots trying to make it work for the Apollogy, and succeeded in being able to present a possible launch acceleration that could be skewed to what we see.

The introduction of Static Pressure concept was enough to bring the theoretical acceleration curve closer to what we saw in the videos, such that if I also introduced some possible frame skew, it would at worst make it "ambiguous enough" to not be a smoking gun.

I posted my conclusion on Facebook, Dec 22nd.  This wasn't a difficult proof, and only required Fluid-Dynamics (first week) type math to make this proof.

https://www.facebook.com/share/p/14wR9aCqaF/

==
Jay you have a smoke-screen manner of making something not-so-difficult sound as complex/difficult as possible, to slow down the process.   I could have completed this work along ago with a few-minute explanation.   Either you really really stink at teaching, or were simply trying to slow down the process keeping it stuck in the mud.

My question on Stack-Exchange had NOTHING to do with takeoff.  Dec 22nd, I dropped this topic, as "not a smoking gun".  My conclusion is that "the Apollogy has a sufficient counter argument" to at best make this ambiguous.  And this counter-argument wasn't even tough to make.   I could teach someone with decent high school trig/calculus skills how to calculate the "theoretical thrust" from this special-case static pressure thrust at take-off.

===
It goes like this: 
1. Use Fluid Dynamics simple equation for Pressure, Flow, Restriction - to figure out the Pressure inside of the Nozzle based upon the size of exit aperture as it takes off (which increases).
2. Multiply this pressure by the surface area of the nozzle exit -- this is approximate of Static Pressure thrust.
3. Then figure the Combustion chamber's contribution by 130 psia (assumed max) by 16.4 sqIn to produce the other 2130 lbF.

Then as it gets further from the ground, this transitions to Steady state (close enough) above 33 cm.   But by this point, the Static Pressure Thrust has provided enough EARLY acceleration to help explain the full second.

Note, that it STILL falls short by 7 inches at the 1 second mark.

My conclusion is that, if faked, NASA modeled the ascent accurately enough.  This was not a blatant mistake.

This thread can be closed as "Sufficiently Debunked" ... at least for non-rocket-scientists.   It's possible that a skeptical rocket scientist might disagree with my conclusion.  But for me, this proof is done.  I concede, this acceleration rate does NOT appear to be proof of a Faked Landing.

[najak]

My question on Stack Exchange has to do with another concern entirely, although his single answer was more educational than all of Jay's combined.  I'd like to get him to come to these forums for discussion, and see where he lands on various evidences.

[JayUtah]

Before my vacation and shortly after my banning, I completed the Static Pressure Analysis spreadsheet.

..which, as was explained to you, isn't correct physics.

I posted my conclusion on Facebook, Dec 22nd.  This wasn't a difficult proof, and only required Fluid-Dynamics (first week) type math to make this proof.

Hilarious. You up and decided all on your own that your pidgin analysis was enough. It doesn't matter that you had to abandon your claim, so long you can continue to believe you're the genius.

Jay you have a smoke-screen manner of making something not-so-difficult sound as complex/difficult as possible, to slow down the process.   I could have completed this work along ago with a few-minute explanation.   Either you really really stink at teaching, or were simply trying to slow down the process keeping it stuck in the mud.

Your obsession continues unabated, I see. All you've done is is convert your claim from "Basic physics proves that the LM liftoff was faked," to "Basic physics is insufficient to solve the problem." What remains constant throughout is your firm belief that you are the brains behind the answer.

My question on Stack-Exchange had NOTHING to do with takeoff.

I agree. However, the answer did. I've explained at length how, and even provided you with your much-desired hints into where I was going with it.

I could teach someone with decent high school trig/calculus skills how to calculate the "theoretical thrust" from this special-case static pressure thrust at take-off.

Except that in your haste to declare victory, you've missed out on the part that was truly different in this launch. I was leading you to it, and you could have shared in a truly a-ha! moment. Too bad you'll never know how wrong and incomplete your answer is.

Then as it gets further from the ground, this transitions to Steady state (close enough) above 33 cm.   But by this point, the Static Pressure Thrust has provided enough EARLY acceleration to help explain the full second.

Too bad you missed the most important and unique element.

This thread can be closed as "Sufficiently Debunked" ... at least for non-rocket-scientists.   It's possible that a skeptical rocket scientist might disagree with my conclusion.

Every single rocket scientist agrees that the Apollo missions were real, and they have the expertise to know how. The issue is not that the rocket scientists haven't sufficiently grasped the genius of your claims. The issue is that the rocket scientists speak in unison when they tell you you don't know what you're talking about.

But for me, this proof is done.  I concede, this acceleration rate does NOT appear to be proof of a Faked Landing.

And with that, you can maintain the illusion that you figured it out all by yourself. When you're talking with someone else, your spiel is, "Please help me, I don't know what I'm doing!" But as soon as you get back here, the story changes to, "I've figured it out all by myself, no thanks to you." Could you be any more transparently dishonest? You think you've precluded the examination of your claims by conceding the conclusion. I think we'll keep going and just see how committed you are to a proper physics solution.

[najak]

For reference, here is the spreadsheet showing the maximum Static Pressure Thrust concept, coupled with the force exerted at the top of the combustion chamber.

https://docs.google.com/spreadsheets/d/1qYtfrOghTwQ-C3sxMIerEGokdxFqFdM32_NX-TmpELs/edit?usp=sharing


This Static Pressure concept adds enough early acceleration to produce a result that is close enough.   This topic has been concluded.

[JayUtah]

For reference, here is the spreadsheet showing the maximum Static Pressure Thrust concept, coupled with the force exerted at the top of the combustion chamber.

https://docs.google.com/spreadsheets/d/1qYtfrOghTwQ-C3sxMIerEGokdxFqFdM32_NX-TmpELs/edit?usp=sharing


This Static Pressure concept adds enough early acceleration to produce a result that is close enough.   This topic has been concluded.

An important aspect to this signal. At any given time, there was always fluid motion. The buffering system repeated the respective color fields, but motion was always live, per se. The buffered fields present themselves as the "confetti" artifacts when fast motion is present. It is not possible to remove "redundant" frames, as there are none. If you attempt to remove fields/frames, you are removing the fluid 30 fps motion.

Thanks, that confirms my recollection of your description in the book.

The LM liftoff provides us with good examples of the "confetti" effect, since the ejecta is moving rapidly and the single-color frames are captured while the subject shifts markedly in the frame. It would be interesting to see how much the motion of the ascent stage bulk exhibits this motion shifting effect. Depending on how the luminance is accumulated in the field combination process, it might be difficult to accurately locate any given feature on the LM by which to measure its height above a reference point.

But the more perplexing effect is what is seen in the convenience video obtained from YouTube by which the apparent lack of motion in the launch "confetti" suggests that the YouTube-presented frame is a duplicate of a previous frame. I think the speculation was that this was an effect akin to frame-rate conversions such as between 24 fps systems and 30 fps systems where it is often satisfactory to duplicate every fourth frame. I wonder if this apparent effect can be attributed to the peculiar odd-even field combination. Or it may be just some unknown artifact in the unknown workflow that got us from the NTSC format to whatever ended up on YouTube.

The concern is that Najak seems to have used this apparent duplication as an excuse to remove frames from the video and close the gap, resulting in an ascent profile he argues is too fast. I wonder how much of the purported overspeed effect would vanish if the "duplicate" frames were replaced with placeholder frames and the ascent profile recomputed accordingly.

[JayUtah]

This Static Pressure concept adds enough early acceleration to produce a result that is close enough.

According to you.

This topic has been concluded.

According to you.

I say you're bailing because you've realized just how in over your head you are. You now accept an error margin in your own offering that you were unwilling to accept from us at the beginning of the thread, and you abandon your hoax proposition—not as fully debunked but as sufficiently muddy that some rogue rocket scientist might still come along and agree with you. It doesn't even matter in the slightest to you that you got the wrong answer using the wrong method and that two professional rocket scientists have said as much to you.

You aren't even remotely concerned anymore what the right answer is, so long as you can believe that you and your unassailable spreadsheets have conquered the problem. In your haste to declare yourself the sovereign of pressure thrust, you forget that it took me pages and pages just to get you to figure out that pressure thrust even existed. And now that you think you've mastered it at last, you're desperate to avoid any more discussion that might further expose the ignorance you admitted when you thought no one was watching.

[smartcooky]

najak, I warned you when you first got here that this site is not like Aulis or GLP, that the people here are actual, certified experts in their fields, not self-proclaimed braggers like those at the sites I mentioned above... braggers who have done little more that attend Googleversity. I warned you that if you tried to BS people here, that you would be found out and handed your arse.

You are utterly out of your depth here. Jay has run rings around you without really trying. So have a couple of others. You have also failed to bring anything new to the table - your claims are just  moderately varied rehashes of previously debunked claims that were presented with more skill and clarity by other HBs such as AWE130, Neil Baker et al.

IMO, you're a fine example of Dunning-Kruger... you are nowhere near as smart as you imagine.

[Luke Pemberton]

The crux of all this:

• Claimant applies F = ma to YouTube video.
• Everyone but claimant knows that this is not possible because frame rate conversion has artifacts. which then gives spurious results: even if high school physics is a good first term approximation.
• In any case, applying high school physics to real world problems has pitfalls because of transient behaviour.
• Therefore we have this branch of study called engineering where specialists use calculus/applied numerical analysis to apply physics to non-linear problems.
• Claim falls over.

[Luke Pemberton]

Remember, before Newton could properly express the mathematics that describe physics, he had to invent calculus to do it. (Yes, yes, Leibniz.)

Glad you got Leibniz in there. As someone who has taught physics beyond high school, I tear my hair out with Leibniz and his narrow minded views of calculus and how that impacts on teaching math. Students are so used to being taught dy/dx, they cannot make the leap and differentiate functions that are not described by y = f(x).

Physics is applied calculus...

I object. We use other branches of maths, not just calculus. 

[Mag40]

And then refigured my 30 FPS screenshots trying to make it work for the Apollogy

Three launches of Apollo ascent stages, from the lunar surface. All videoed from their respective lunar rover cameras and as far as anyone watching was concerned, absolutely no need to even do this. It's almost as though it was authentic and they weren't worried 50+ years later that some internet nobody would be jumping up and down for 30 pages of hoohah, making ignorant, uninformed claims about it!

It was not a bloody "Apollogy" and the continued antagonistic labelling of this footage is needless and childish.

This thread can be closed as "Sufficiently Debunked" ... at least for non-rocket-scientists.   It's possible that a skeptical rocket scientist might disagree with my conclusion.  But for me, this proof is done.  I concede, this acceleration rate does NOT appear to be proof of a Faked Landing.

All the non rocket scientists already knew this! Imagine how massively less of an arse you would have looked had you raised the issue as a neutral without the posturing and goading?

[JayUtah]

I warned you that if you tried to BS people here, that you would be found out and handed your arse.

To continue the saga, Najak went back to Stack Exchange to continue the discussion, revealing there that he's been dealing with apollohoax.net on the question of ascent engine thrust. So while he tells us here that his question had nothing to do with this thread, he tells them there that it does. During the brief exchange, his respondent assures him that the LM ascent engine "checks out," which we here agree it most certainly does. The issue is that Najak didn't tell them there that he was the hoax claimant, and that all the regulars here are the ones trying to fix his mistakes. Brazenly dishonest.

Hint 1: The nozzle isn't the only thing that exhaust gas static pressure is acting against in this problem, and therefore not the only thing that must be included in the integral.

Hint 2: There are photographs showing a reflected shock wave from the ascent engine plume during LM staging tests in a vacuum. Can shock waves exist in a vacuum?