Author Topic: Debate with hunchbacked on facebook  (Read 10572 times)

Offline benparry

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Debate with hunchbacked on facebook
« on: June 15, 2018, 02:42:19 PM »
Hi all

After wrongly thinking Pascal had retired from Facebook he is back and debating me in a group. Although he wasn't the original poster he has had some thoughts. I think the answer is simple do you guys have any thoughts

Offline onebigmonkey

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Re: Debate with hunchbacked on facebook
« Reply #1 on: June 15, 2018, 02:50:07 PM »
Simple is the word. The moon does rotate, and the image is a composite. Earth is not in the original - in fact I'm not even sure it's from Apollo 11!

Offline molesworth

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Re: Debate with hunchbacked on facebook
« Reply #2 on: June 15, 2018, 02:55:30 PM »
Hi all

After wrongly thinking Pascal had retired from Facebook he is back and debating me in a group. Although he wasn't the original poster he has had some thoughts. I think the answer is simple do you guys have any thoughts
Only one question - does he actually think that's a genuine photograph?
Days spent at sea are not deducted from one's allotted span - Phoenician proverb

Offline benparry

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Re: Debate with hunchbacked on facebook
« Reply #3 on: June 15, 2018, 03:01:22 PM »
Tbh I don't know but can I just ask 1 question. Obviously the big moon with writing is not real but even if it was is the simple fact that we can sometimes see the moon high in the sky and sometimes low explain why the earth could be low on the horizon.

Offline benparry

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Re: Debate with hunchbacked on facebook
« Reply #4 on: June 15, 2018, 03:08:47 PM »
This is a copy and paste from another comment he has just made in the same post to try to push the hoax in another way

Mark Ferguson Now, if you want a precise example, I have laughed when I have looked at the logical command interface of the lateral thrusters; each pitch or roll command activates two vertical thrusters directly opposed to each other, so pushing in opposite directions, which means that they cancel their mutual effects (and I remind you they were not throttleable); how could this work?
Moreover, the engineers had added some fun, by uselessly complicating the way that the commands were sent to the interface; intead of directly applying the commands to the interface, they were modulating a high frequency carrier with these commands, sending the modulated carrier into a wire, and demodulating the carrier to extract the commands at the other end of the wire; but you only do that when you send commands through air, like for a drone, not when you send the commands through a wire; this useless complication was a hint given by the NASA engineers that this interface was a farce.

Any ideas it's way over my head

Offline molesworth

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Re: Debate with hunchbacked on facebook
« Reply #5 on: June 15, 2018, 04:23:56 PM »
This is a copy and paste from another comment he has just made in the same post to try to push the hoax in another way

Mark Ferguson Now, if you want a precise example, I have laughed when I have looked at the logical command interface of the lateral thrusters; each pitch or roll command activates two vertical thrusters directly opposed to each other, so pushing in opposite directions, which means that they cancel their mutual effects (and I remind you they were not throttleable); how could this work?
Moreover, the engineers had added some fun, by uselessly complicating the way that the commands were sent to the interface; intead of directly applying the commands to the interface, they were modulating a high frequency carrier with these commands, sending the modulated carrier into a wire, and demodulating the carrier to extract the commands at the other end of the wire; but you only do that when you send commands through air, like for a drone, not when you send the commands through a wire; this useless complication was a hint given by the NASA engineers that this interface was a farce.

Any ideas it's way over my head
I'm sure people with more in-depth knowledge than myself can give you more detail, but I'd consider a couple of points :
  • Why does he think the RCS thrusters would be counteracting each other?  The "quads" each have four nozzles, facing in different directions, and when e.g. the upward facing one on one side is firing, the downward facing one on the opposite side fires, to provide a rotational force round the centre of gravity (or close to it).
  • There are many reasons why using modulated signals is preferable to straight DC coupling, such as electrically noisy environments or lack of a common stable reference, although I'd have to do a bit of research to find out why it was used in Apollo.  There are many types of system where a DC connection just wouldn't be possible.
I suspect too little research and too much "assuming" on his part, without considering the design constraints for the systems.
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Offline benparry

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Re: Debate with hunchbacked on facebook
« Reply #6 on: June 15, 2018, 04:36:21 PM »
isn't that pascals way lol

thanks for that molesworth

Offline Jason Thompson

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Re: Debate with hunchbacked on facebook
« Reply #7 on: June 15, 2018, 05:29:12 PM »
Hi all

After wrongly thinking Pascal had retired from Facebook he is back and debating me in a group. Although he wasn't the original poster he has had some thoughts. I think the answer is simple do you guys have any thoughts

Yes, he needs to show where that photo came from. It's a composite picture. The astronaut on the ladder is Buzz Aldrin, and the picture is AS11-40-5868. The Earth has been added later by extending the image past the left margin, and at first glance this was done by pasting a low res version of the Apollo 8 Earthrise image on.

On Apollo 11 the astronauts did actually take pictures of Earth, and it was above their heads just as it should be. AS11-40-5923, for example.
"There's this idea that everyone's opinion is equally valid. My arse! Bloke who was a professor of dentistry for forty years does NOT have a debate with some eejit who removes his teeth with string and a door!"  - Dara O'Briain

Offline Jason Thompson

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Re: Debate with hunchbacked on facebook
« Reply #8 on: June 15, 2018, 05:33:43 PM »
Tbh I don't know but can I just ask 1 question. Obviously the big moon with writing is not real but even if it was is the simple fact that we can sometimes see the moon high in the sky and sometimes low explain why the earth could be low on the horizon.

No. We see the Moon at varying elevations because of the interrelationship between the ecliptic plane, the lunar orbital plane and the rotational axis of the Earth. It's essentially the same reason we have seasons, with the Sun high in the sky in summer and low in winter, but with the added complexity of the lunar orbital plane thrown in. The Moon always shows the ame face towards Earth, however, so there is very little variation in the elevation of the Earth as seen from any point on the lunar surface. If you stand on a site at the centre of the side of the moon facing us, you will always see the Earth more or less overhead, and if you are near the limb as seen from Earth you will always see Earth low on the horizon.
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Offline Jason Thompson

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Re: Debate with hunchbacked on facebook
« Reply #9 on: June 15, 2018, 05:40:27 PM »
As for the pitch and roll issue...

Quote
Mark Ferguson Now, if you want a precise example, I have laughed when I have looked at the logical command interface of the lateral thrusters; each pitch or roll command activates two vertical thrusters directly opposed to each other, so pushing in opposite directions, which means that they cancel their mutual effects (and I remind you they were not throttleable); how could this work?

He needs to do some basic geometry. The two thrusters are not directly opposite, they are separated by the spacecraft. If you fire one on one side of the spacecraft in one direction and fire the opposite in the other direction you will induce a rotational force around the centre of the axis connecting them. Rocket engines are only directly opposed is they thrust on exactly the same axis.

How does this idiot think a catherine wheel firework works? The simplest of these consist of two rockets firing in opposite directions at each end of a connecting arm. The only reason they have a pin through the centre to be mounted is so they don't fly off uncontrollably, because they're not perfectly aligned and perfectly balanced in terms of thrust. Even if you don't mount them the forces from those rockets will still cause it to spin.
"There's this idea that everyone's opinion is equally valid. My arse! Bloke who was a professor of dentistry for forty years does NOT have a debate with some eejit who removes his teeth with string and a door!"  - Dara O'Briain

Offline Abaddon

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Re: Debate with hunchbacked on facebook
« Reply #10 on: June 15, 2018, 05:44:30 PM »
Hi all

After wrongly thinking Pascal had retired from Facebook he is back and debating me in a group. Although he wasn't the original poster he has had some thoughts. I think the answer is simple do you guys have any thoughts
Simple. Take your phone at arms length selfie style. See your own image. Standing in place, circle in place with phone at arms length filming all the while.

Now explain why your phone has NOT ROTATED AT ALL.

Job done.


Offline benparry

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Re: Debate with hunchbacked on facebook
« Reply #11 on: June 15, 2018, 06:18:13 PM »
ah ok thanks Jason. yes the firework example is a good one. sorry abaddon I don't quite follow your point

Offline JayUtah

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Re: Debate with hunchbacked on facebook
« Reply #12 on: June 15, 2018, 06:40:07 PM »
He needs to do some basic geometry. The two thrusters are not directly opposite, they are separated by the spacecraft.

Wow, and how.  That's basic spacecraft dynamic control.  In the real world RCS thrusters are never optimally placed, so we always design according to a generalized free-body method.  Even though the quads are ostensibly placed to give "pure" pitch, yaw, and roll moments, that is never actually achieved in practice.  So any "pure" maneuver in the cardinal axes always requires multiple firings from RCS jets you wouldn't think are appropriate to that.  One of the hardest things to do in manual spaceflight is "nulling" or trimming after a burn, to take down the residual unwanted rotations in odd axes.

Fun fact:  the reference axes for the LM RCS were not an orthonormal basis like you'd expect.  It was biased for forward motion, to optimize the control solution for landing.  There's a great paper out of MIT's Draper lab that explains and justifies this, and it has a good introduction to basic dynamic control theory.  The generalized free-body method is explained in full in Sidi's book, which is still the standard reference.

As for modulated signals, that's almost a no-brainer.  You often get the carrier for free from the power supplies, and a passive band-pass filter can be made for a few bucks using a home electronics kit.  Not only is it much, much safer in the space environment, where you can have transient electrical and magnetic interference and short circuits, but it also lets you multiplex different control signals on the same wire.  That way you have to run only one wire out to the RCS from the controller, and then split the different signals out at the remote site.  It saves mass and electricity.
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Offline Allan F

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Re: Debate with hunchbacked on facebook
« Reply #13 on: June 15, 2018, 06:41:27 PM »
No, the RCS wasn't throttleable, but could be fired in very short bursts, down to 1/100th of a second. They provided both pitch, yaw and roll, and also lateral movement.
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Offline JayUtah

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Re: Debate with hunchbacked on facebook
« Reply #14 on: June 15, 2018, 06:47:14 PM »
No, the RCS wasn't throttleable, but could be fired in very short bursts, down to 1/100th of a second. They provided both pitch, yaw and roll, and also lateral movement.

A.k.a. "pulse mode" in the relevant literature.  If you do a 0.01-second pulse with several idle pulses (say, 4) following, then another power pulse etc., it's effectively the same as throttling to 20 percent rated thrust.  Slightly more, because the effect of the ignition transient will be more pronounced.

Obviously the same RCS had to serve the fully loaded and docked LM and the ascending stage after landing, which is roughly a tenth the mass.
"Facts are stubborn things." --John Adams