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Post by ka9q on Feb 13, 2010 9:49:11 GMT -4
Hi. I recently learned of a hoax claim by a Russian named Stanislav Pokrovsky based on his allegation that the S-IC lacked the performance that NASA claimed it had. Specifically, at S-IC/S-II staging, the stack was moving at only 1200 m/s (relative to the earth), not 2400 m/s as given in the mission reports.
His paper is in Russian. I cannot find an English translation, but using Google Translator I was able to get the gist of it. Basically, his entire case seems to rest on the assumption that the smoke from the solid fuel retro rockets on the S-IC and ullage rockets on the S-II came to an instant halt in the surrounding air so it could be used as a reference for the motion of the rocket.
The big problem with his analysis is that S-IC/S-II separation occurred at an altitude of 67 km where air is about 0.0001 times as dense as at sea level, i.e., about 100 milligrams/cubic meter instead of 1.2 kg/cubic meter. Even sea level air isn't especially effective at instantly stopping something - even smoke - moving at 2.4 km/sec, so this certainly seems doubtful.
I heard about this argument when I asked straydog02, one of the more vociferous hoax proponents on YT, if he had any NEW hoax claims as it was getting quite tiresome having to repeatedly debunk the same old tired claims about no stars and waving flags. So he mentioned this one. The really funny part is how confident he is that the analysis is correct, even though he can't read Russian and can't begin to describe Pokrovsky's analysis in his own words.
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Post by grashtel on Feb 13, 2010 11:52:24 GMT -4
Of course he is confident about it, in Straydog02's mind Apollo being a fake is a FactTM and therefore any research supporting that position must also be true. Of course in the universe that the rest of us live in that line of reasoning doesn't actually work.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Feb 14, 2010 4:44:53 GMT -4
Hi. I recently learned of a hoax claim by a Russian named Stanislav Pokrovsky based on his allegation that the S-IC lacked the performance that NASA claimed it had. Specifically, at S-IC/S-II staging, the stack was moving at only 1200 m/s (relative to the earth), not 2400 m/s as given in the mission reports. I'm currently in the process of analyzing and simulating the Saturn V. I did a simulation about 15 years ago, but I'm updating it with better data. I'm not having any problem at all getting it to 2,400 m/s by S-IC/S-II separation. |
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Post by scooter on Feb 14, 2010 9:49:32 GMT -4
I remember a certain JW video that complained that there were sounds from the shuttle's jettisoned SRBs when they were supposedly in "vaccuum". Being jettisoned at around 46km (and climbing), well within the atmosphere was presented. The STS MECO occurs around 100km (still climbing), which explains the visible slipstream appearance as the thrusters fire at tank separation. Still some atmosphere even up there.
The idea that "smoke" particles, with the mass/drag properties of...smoke, should somehow travel along with the heavy, streamlined Saturn stack around 42 miles up is just wrong.
But it's not like they're at 20,000 feet either.
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Post by Daggerstab on Feb 15, 2010 5:02:56 GMT -4
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Post by ka9q on Feb 15, 2010 19:28:29 GMT -4
Ah, thanks. I just read that thread. Somehow I missed it when I looked before posting my message. I do wish a good English translation existed of his paper so we could give it a proper debunking... |
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Post by ka9q on Feb 15, 2010 19:31:08 GMT -4
I'm currently in the process of analyzing and simulating the Saturn V. I did a simulation about 15 years ago, but I'm updating it with better data. I'm not having any problem at all getting it to 2,400 m/s by S-IC/S-II separation. I'd love to see your simulation when you're done. Seems to me the hardest part of simulating the Saturn V would be in calculating the effects of aerodynamic drag and high altitude winds during S-IC flight. I take it you have all of the Saturn V manuals and flight reports? |
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Bob B.
Bob the Excel Guru?
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Post by Bob B. on Feb 15, 2010 21:27:35 GMT -4
I'd love to see your simulation when you're done. I'll post it on my website when it's done. I'm just doing a one-time simulation to verify the Saturn V operation to debunk the claims it couldn't work. It won't be anything interactive. I got the drag thing pretty much figured out. Wind I'm neglecting because I don't think it's necessary for my purpose. I don't know if I have them all but I have a lot of them. I think I have all the information I require. |
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Post by scooter on Feb 15, 2010 22:47:46 GMT -4
www.youtube.com/watch?v=-rM1RA2Jmh8&feature=relatedHere's an A-15 airborne tracking camera view of the launch...if he's just looking at relative motion of "smoke", it would need to account for the view angle from behind the rocket. There's a nice white puff of something after engine cutoff that shows pretty clearly the Saturn was really moving along.
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Post by JayUtah on Feb 17, 2010 15:29:38 GMT -4
if he's just looking at relative motion of "smoke"...Not really, but close. He's looking at the geometry of the plume in a very limited way, in photographic data. He proposes to fit that plume geometry into an aerodynamic and thermodynamic model that, according to him, predicts that plume geometry only for lower temperature and therefore lesser thrust. Now there is a whole bunch of unstated stuff we need to examine about that, mostly regarding the applicability and validity of the model he's using. But what concerns me most is... ...it would need to account for the view angle from behind the rocket....which his paper does not do. Which is to say, the paper mentions that a geometric transformation must apply to convert the visual plume spread angle (i.e., in image space) to the actual plume spread angle (i.e., in affine or real-world space), but it does not say how that transformation was accomplished or give the math for it. As I mentioned in the other thread, Pokrovsky simply mentions that it was "taken into account." It is a very conspicuous omission. The principal parameter to Pokrovsky's model is the angle formed by the plume as it spreads at a given altitude. That angle derives solely from Pokrovsky's analysis of a photograph taken from a ground camera with the Saturn V progressing substantially along the line of sight and therefore presenting a foreshortened plume. So Pokrovsky spends all his time manipulating the physics models, he spends no time proving that the numbers he's plugging into them reflect reality. Most of his intended audience won't understand the physics, but they'll be impressed at all the diagrams and equations. The paper does a good job of mimicking science for the non-scientist. There's a nice white puff of something after engine cutoff that shows pretty clearly the Saturn was really moving along.Yes, there is much more evidence of the Saturn V's real speed. Pokrovsky's over-arching fault is the fallacy of limited scope. He latches onto one tortuously derived value and considers it the sole definitive value of the vehicle's speed. He ignores all other evidence.
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Bob B.
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Post by Bob B. on Feb 17, 2010 19:46:16 GMT -4
Pokrovsky’s study results in such absurd consequences for the Saturn V that it forces one to question the veracity of Pokrovsky’s work rather than the capability of the Saturn V.
Had the Saturn V been able to reach only that velocity calculated by Pokrovsky, than one of two things must be true: (1) the F-1 engines were far less powerful than reported, or (2) the Saturn V was far more massive than reported. If either were true, then the Saturn V couldn’t have lifted off the launch pad, at least not until a large amount of propellant had burned off. (The Saturn V had a very low initial thrust-to-mass ratio, so there was little margin to work with.) Since the Saturn V lifted of the pad with acceleration consistent with the known thrust-to-mass ratio, we can dismiss this.
Knowing the liftoff thrust-to-mass ratio, one can easily calculate how much of the rocket’s mass should be consumed per second in the form of propellant. From this one can calculate the theoretical S-IC cutoff velocity. It is also possible to perform a computer simulation of the launch. I have done both the theoretical calculations and the simulation, and in both cases the results support NASA and not Pokrovsky.
There is only one scenario I can think of that could possibly give us both the observed liftoff acceleration and the cutoff velocity calculated by Pokrovsky. That is, the rate of propellant burn-off was far less than reported and expected. In this scenario the Saturn V would liftoff as observed, but because it is retains much more of its mass due to the lower propellant consumption rate, it is unable to reach the higher velocity.
This last scenario is, of course, absurd for a couple reasons. First, for the F-1 engine to give us the necessary thrust at the lower propellant consumption rate, its efficiency would have to be ridiculously high. Second, if the F-1 engine were so efficient, then why are we carrying so much propellant in the first place? This scenario requires the Saturn V to carry a large amount of unused and wasteful mass.
The bottom line is that Pokrovsky calculation makes no sense whatsoever from a rocketry perspective. The ridiculousness of what Pokrovsky’s findings suggest makes it pretty clear, to me at least, that the error lies with Pokrovsky and not the Saturn V.
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Post by randombloke on Feb 17, 2010 20:05:14 GMT -4
What amuses me about all this is that, to a True Hoax Believer™, the totally different approaches you both used to throw doubt on Pokrovsky's hypothesis indicate that you (the CIA/denialist hegemony) can't decide which story to use; as opposed to the actual case which is that Pokrovsky's paper is so full of holes that multiple approaches to the same problem keep finding their own sets...
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Post by ka9q on Feb 18, 2010 19:52:41 GMT -4
I've also given some thought to how the observed behavior of the Saturn V (as observed by millions of people in person and hundreds of millions more on TV) could still be consistent with Pokrovsky's claims. And it is indeed difficult.
For a rocket engine to "underperform" it must either produce less thrust at a given propellant flow rate or require more propellant flow for the same thrust. Yet as Bob just pointed out, we know the Saturn V took off with a thrust/mass ratio only slightly more than 1, so any less thrust would have meant that it wouldn't take off at all.
Yet if it produced nominal thrust while consuming more propellant, it would have emptied its tanks sooner than it was observed to do by hundreds of millions of people. Those tanks were visible to everyone, and their dimensions are easily determined. They could not have been more than full, because there would be no other place to put the excess propellant -- we saw it separate from the upper stages right where it was supposed to -- and the extra weight would also have kept the stack from leaving the ground.
So we have to assume that its propellant flow rate was as stated.
That leaves only one possibility: that the upper stages were lightened, e.g., by offloading propellants so that the first stage would seem to fly normally for the proper period of time.
I haven't worked this one further, but it already seems obvious that offloading the upper stages would have had other visible consequences, such as a different acceleration vs time profile - and there are numerous photos, taken by non-NASA cameras, showing a nice shock cloud forming around the interstage just as the stack went transonic.
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Bob B.
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Post by Bob B. on Feb 19, 2010 1:34:35 GMT -4
Pokrovsky’s claims are just plain wrong, which can be demonstrated computationally.
The total liftoff weight of Apollo 11 was about 6.4 million pounds. The thrust-to-mass ratio at first motion was about 1.185, which is easy enough to confirm. (The T/W ratio must be >1 or the rocket won’t lift off the launch pad.) Based on these numbers, the thrust is
6,400,000 x 1.185 = 7,584,000 lbs
The specific impulse of the engines was 260 seconds, which is typical for engines of this type. Therefore the propellant flow rate is
7,584,000 / 260 = 29,169 lb/s
The center engine burned for 135 s and the outboard engines for 164 s, but it is simpler if we just say all five engines burned for 158 s, which is equivalent. The total propellant consumed is
29,169 x 158 = 4,608,702 lbs
Thus, the rocket mass at S-IC cutoff is
6,400,000 – 4,608,702 = 1,791,298 lbs
Using Tsiolkovsky's rocket equation, the rocket delta-v is
260 x 32.174 x LN(6,400,000 / 1,791,298) = 10,652 ft/s (3,247 m/s)
Of course the rocket won’t actually reach this velocity because there are losses due to gravity and drag. My simulations (which are still a work in progress) show that a velocity of about 2,600 m/s is attained.
Pokrovsky says the F-1 engines were not as powerful as claimed, but the engines must provide a thrust of 1.185 times the Saturn V’s liftoff mass to match the observations. If the engines were less powerful, then the Saturn V was proportionately less massive. Assuming the specific impulse is unchanged, the same velocity is achieved because everything is simply factored down in size.
If Pokrovsky is claiming the F-1 engines were less efficient, i.e. lower specific impulse, then his velocity estimate is still wrong. We simply can’t get around the 1.185 thrust-to-weight ratio because this is verified by direct observation. The engines still must produce the thrust to get the vehicle off the ground, so if they are less efficient, they must consume propellant at a greater rate.
Let’s say the specific impulse is only 240 seconds instead of 260 seconds. The propellant flow rate is now
7,584,000 / 240 = 31,600 lb/s
If the rocket carries the same propellant load as previous, it will burn off its load in
4,608,702 / 31,600 = 146 seconds
Of course the burn time is not something that can be fudged – we know how long the engines burned. This means that more propellant has to be burned, as follows
31,600 x 158 = 4,992,800 lbs
Burning more propellant means we have less mass remaining at cutoff
6,400,000 – 4,992,800 = 1,407,200 lbs
Calculating the rocket delta-v we get
240 x 32.174 x LN(6,400,000 / 1,407,200) = 11,696 ft/s (3,565 m/s)
Surprisingly, the delta-v with the less efficient engines is actually higher. This is because we have a greater mass ratio (i.e. beginning mass divided by ending mass) resulting from the need of the engines to gulp more fuel.
There is no way Pokrovsky’s claims can be reconciled with observations of the launch. The numbers just don’t add up. We can’t have the thrust and propellant flow rate needed to get the vehicle off the ground, burn the engines for more than two and one-half minutes, and be traveling only 1,000 m/s at the end of it all.
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Post by bazbear on Feb 19, 2010 1:37:34 GMT -4
The Saturn V worked. I have no evidence I can point at to prove it staged and had the thrust it needed, other than that it worked as advertised, but I don't personally need it. Stanislav Pokrovsky is obviously the one with the burden of proof in any case.
Thanks for the great tracking vid link, Scooter!
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