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21
The Reality of Apollo / Re: Any truth to these two stories during Apollo development?
« Last post by ka9q on September 18, 2017, 08:34:30 PM »
I guess when you're dealing with millions of pounds of vehicle going at thousands of miles an hour with three people on it
Actually, the problem is that it's not millions of pounds of vehicle. Or at least not nearly as many millions of pounds as at liftoff. Nearly all your propellant is gone so you're much lighter, so for a constant engine thrust they're producing much more acceleration (F=ma -> a = F/m). Any vibration or unbalanced thrust will have that much more effect on you than when you left the pad.

Remember the Saturn V shut down its inboard F-1 engine early, despite the decrease in performance from the resulting increase in gravity loss, to keep acceleration from exceeding 4 g and overstressing the vehicle. It was only about 1.1 g at liftoff...
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The Hoax Theory / Re: Question: how did they slow down in space?
« Last post by ka9q on September 18, 2017, 08:24:50 PM »
Thinking that the LM would pass through its own exhaust is the same thing as thinking you can shoot yourself simply by firing a bullet in the same direction as you are traveling.
Well, you could if you were facing a very strong wind. Like if you were sitting on the nose of the space shuttle during early launch.

I remember grimacing when I heard, during a live Columbia post-accident press conference, one of the mission managers claim that a piece of mere foam was much too light to possibly damage the orbiter during launch. Even engineers who should know better can suffer failures of intuition.

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The Hoax Theory / Re: The Physics of jumping
« Last post by ka9q on September 18, 2017, 08:15:04 PM »
If you have initial velocity (which you would have to if your jump leaves the ground), then that velocity is a result of a NET force upwards.  This is the sum of all forces - including gravity - which is six times stronger on the Earth.
You are correct. In the limit of a very sudden, instantaneous jump, the momentary upward force of your muscles swamps your downward weight on both the earth and moon, so you'd rise 6 times as high on the moon. But you are correct that when you consider the upward force to be of finite duration, some of it is required to overcome weight, so the difference would be greater.

It's the same thing as "gravity loss" in a rocket, the reason why lots of liftoff acceleration is much better than just a little more than that required to overcome gravity, even if the total impulse (thrust times time) is the same.

I had to explain this once to my significant other after she put an low thrust engine in one of my rockets at a launch event. Despite having the same total impulse as a correctly sized engine, it valiantly struggled off the pad and made it to only maybe 100' before burning out and nosing over into (into) the earth before the ejection charge could fire...

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General Discussion / Re: ISS sightings
« Last post by ka9q on September 18, 2017, 08:01:39 PM »
The brightest Venus gets is magnitude -4.6....
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The Reality of Apollo / Re: Digitizing my Apollo audio tapes.
« Last post by ka9q on September 18, 2017, 07:43:55 PM »
The more I listen to your tape and read the documentation, the more strongly I suspect that you've captured PLSS telemetry. Caveat: I haven't yet run any formal analysis on these signals other than looking at the waveforms, spectrum and autocorrelation with Audacity.

But if I understand the system correctly, I should be able to extract and plot the actual telemetry waveforms. The documentation gives the channel assignments, though without unit-specific calibration records they would be uncalibrated.

I hear occasional sudden changes in the recorded audio that make me think this was recorded from a selector switch manually set to one of the PLSS composite signals and shifted down from the actual VCO frequency to about 1600 Hz (within the audio range and easily recorded).

It is even possible that the switch settings include EKG (electrocardiogram) data, though there seems to be much less detail on that part of the subsystem than on PLSS internal telemetry (O2 pressure, water temperature, etc, etc). I don't yet hear anything that sounds like a *direct* connection between EKG electrode amplifiers and the associated voltage controlled oscillator, but it's possible that the waveform was interrupted with sync and calibration signals as were the commutated hardware analog telemetry channels.
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The Reality of Apollo / Re: Digitizing my Apollo audio tapes.
« Last post by ka9q on September 18, 2017, 06:32:05 PM »
This is looking more and more interesting.

The Apollo Operations Handbook for the Extravehicular Mobility Unit, Volume I (system description) for Apollo 14 (which covers the early pre-J missions) says that each PLSS generated two subcarriers, one for PLSS telemetry and the other for an electrocardiogram. EVC-1 (worn by the commander) put the EKG on a 5.4 kHz subcarrier and telemetry on 10.5 kHz. EVC-2 (worn by the LMP) put the EKG on 3.9 kHz and telemetry on 7.35 kHz.

The LMP's PLSS transmitted the two subcarriers, plus the LMP's voice, via VHF-FM to the CDR's PLSS, which mixed in the CDR's voice and his two subcarriers, transmitting the whole thing (combined voice + 4 subcarriers) to the LM by VHF-AM.

The block diagrams show the subcarrier oscillators as VCOs (Voltage Controlled Oscillators), which means the telemetry frequency modulated these subcarriers. The modulating signal commutated among 30 analog channels 1.5 times per second. 26 channels were used for actual telemetry and the rest for synchronization and calibration. Your mystery signal sounds exactly like a frequency modulated tone (though lower than any of the frequencies listed above) and repeats 1.5 times per second (rather than 1.0 times/sec as you'd expect for most time codes).

So my very VERY initial take is that you've found one of the two PLSS telemetry streams, shifted down in frequency to make it easier to record on one channel of an audio tape recorder. It's probably not one of the EKGs, which was transmitted on its own subcarrier, and in any event would not repeat at such a fixed rate given the astronauts' physical exertion (not to mention excitement).

Got any more like these?
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The Reality of Apollo / Re: Digitizing my Apollo audio tapes.
« Last post by ka9q on September 18, 2017, 06:06:57 PM »
The more I listen to this, the more I'm inclined to think that this is NOT a time code but rather some form of low bandwidth telemetry. Time codes are digital but this appears to be multiplexed analog frequency modulating an audio subcarrier.

The PLSSes transmitted multiplexed analog telemetry on several subcarriers above the voice. I believe medical telemetry was in there as well, probably on a separate subcarrier.

If this is what it is, this may be a find of some importance. Time to hit the references...

The FLAC files are digitized at 22050 Hz, which means they're probably filtered at 10 kHz. Can you ensure there isn't anything you might have missed higher in the spectrum? What is the tape speed?

 
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General Discussion / Re: Searching for Skylab
« Last post by dwight on September 18, 2017, 06:01:10 PM »
I will be doing a remote interview with someone who was in MOCR and recorded the final hour of Skylab's life. We have interviewed the following people:

From Huntsville: Roy Logston, Wille Weavers, John Reaves
From Honeysuckle: Phil Maier, Cyril Fenwick, Hamish Lindsay, John Saxon, Colin Cochran, Bernard Smith, Phil Rutherford.
From Skylab: Joe Kerwin, Paul Weitz, Jack Lousma, Owen Garriott, Ed Gibson, Dr Lubos Kouhoutek
From exclusive rights with GNAT TV, Jerry Carr.
The widow Sylvia and son James of Jack Kinzler (who came up with the idea of the parasol), Paul Weitz's son Mathew and Jack Lousma's wife Gratia and daughter Mary, and Herb Baker, whose Mum was seamstress on the sun shade for Skylab.
From: backup crews: Bruce McCandless and Vance Brand
From history alumni: Glen Nagle, Emily Carney, David Hitt and Andy Chaikin. Plus archive footage which does have truly the claim of being Ultra rare. We went to town on this.
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The Reality of Apollo / Re: Digitizing my Apollo audio tapes.
« Last post by ka9q on September 18, 2017, 05:46:22 PM »
My first thought is that the weird left-channel sound is probably a time code, probably one of the IRIG codes.

But what's really interesting is that it changes as soon as the crew turns on the TV and the ground confirms a picture.

Where did you get this??

I'm pulling down the FLAC images and will take a closer look. If it's one of the IRIG time codes I should be able to tell which one.


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The Hoax Theory / Re: Gardum's thread
« Last post by ka9q on September 18, 2017, 05:16:41 PM »
If I am walking around at high Moon noon, and find myself getting too hot from the Sun, I can duck into the shade of a big rock, but still be heated by the solar energy reflected from the lunar surface (albedo heating), as well as the solar energy absorbed and re-emitted from the surface (infrared heating), even as my suit is radiating heat to deep space. 

But I'm also radiating heat toward the lunar surface, and a (very small) amount of heat energy from deep space is impinging on my suit.  There's no one-way switch depending on your view to certain objects.
There is a "one way switch": possibly different optical properties at different optical wavelengths, as I explained in my last message.

But there's no one way switch that can operate at the same optical wavelength. If there were, you'd have a violation of the Second Law of Thermodynamics.

This is a bigger factor on the moon than you might think. A thermal radiator can work efficiently even in direct sunlight because the low absorptivity (high optical reflectivity) rejects the lion's share of the sun's radiation that arrives as visible and near-IR light. While the sun also radiates in the far IR, which the radiator cannot reject, the sun is very small (0.5 deg diameter) compared with the cold dark sky around it. So it doesn't have much effect.

But a thermal radiator on the moon cannot function effectively if it sees much of the hot lunar surface. Despite being much cooler than the sun, and therefore radiating less per square degree of apparent size even in the far IR, the lunar surface could easily occupy a lot more of the radiator's "sky" than the sun and thereby radiate considerably more heat into it. This was a very real problem for the ALSEP experiments left by the last three Apollo missions where the radiators, despite being pointed straight up, "saw" quite a bit of the warm mountains surrounding the landing sites. (It also didn't help that it was almost impossible to keep them free of lunar dust.)

The warm lunar surface was a significant source of heat even to the well-insulated Apollo pressure suits. The Apollo 12 crew, being the first to make two EVAs, commented on how much warmer things seemed during their second EVA even though the sun's direct thermal input to a vertical surface was essentially the same as during their first EVA. The lunar surface, being essentially horizontal, reached an equilibrium temperature according to the sine of the sun's elevation so it was warmer during the second EVA.
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