reynoldbot
Jupiter
A paper-white mask of evil.
Posts: 790
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Post by reynoldbot on Jun 10, 2008 0:15:12 GMT -4
Do you concede that the spacecraft need not face in the direction that it's traveling?
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Post by JayUtah on Jun 10, 2008 0:44:47 GMT -4
It is possible that the GET 30:28 telecast was sent with the PTC roll stopped, in order to facilitate orienting the high-gain antenna array. However, stopping PTC does not involve changing the spacecraft orientation from its nose-down attitude.
Do you nevertheless concede that a spacecraft need not point its nose in the direction of travel?
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Jun 10, 2008 0:50:28 GMT -4
Spacecraft orientation - I'm not willing to concede on this point, as I see problems with it. sts60 (and Czero) contend that "PTC roll is performed with the longitudinal axis basically perpendicular to the Earth." According to NASA... The Apollo Lunar Module and Command and Service Modules had a PTC of one revolution per minute.er.jsc.nasa.gov/seh/barbeque.htm If the capsule was rotating at 1 rpm, then they wouldn't have been able to film the Earth through the same window for more than 10-20 seconds at a time. But in the 30:28 GET TV transmission, we see the Earth being filmed through the same window for more than 2 minutes. First, the 1 RPM number is incorrect. The PTC rate was, I believe, 3 revolutions per hour. Furthermore, I think we've all come to the consensus opinion that the PTC roll was stopped during the television broadcast so that the high-gain antenna could be kept pointed toward Earth.
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Post by turbonium on Jun 10, 2008 1:07:12 GMT -4
There is another serious problem - there are three windows with a view of "Earth". Two different windows have a view of the "Earth" in this TV transmission... Just like the "Earth" vanishes from view in the first window, only ~ 40 seconds later, we again see the "Earth" being moved around outside the "capsule" through a second window. And a third window (the 9" round window) with a view of the "Earth" is in the subsequent footage... A fake "Earth", being projected outside a capsule that's still here, on the real Earth. I can see no other explanation for it.
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Post by turbonium on Jun 10, 2008 1:20:10 GMT -4
It is possible that the GET 30:28 telecast was sent with the PTC roll stopped, in order to facilitate orienting the high-gain antenna array. However, stopping PTC does not involve changing the spacecraft orientation from its nose-down attitude. Do you nevertheless concede that a spacecraft need not point its nose in the direction of travel? I'm fine with that. But the three different windows with a view of "Earth", and the moving "Earth" - those are my main problems.
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Post by Czero 101 on Jun 10, 2008 1:38:27 GMT -4
Spacecraft orientation - I'm not willing to concede on this point, as I see problems with it. sts60 (and Czero) contend that "PTC roll is performed with the longitudinal axis basically perpendicular to the Earth." According to NASA... The Apollo Lunar Module and Command and Service Modules had a PTC of one revolution per minute.er.jsc.nasa.gov/seh/barbeque.htm If the capsule was rotating at 1 rpm, then they wouldn't have been able to film the Earth through the same window for more than 10-20 seconds at a time. But in the 30:28 GET TV transmission, we see the Earth being filmed through the same window for more than 2 minutes. Yes, your link does give a minimalistic definition of the PTC, however the roll rate is incorrect. The actual roll rate was .3 degrees per second, or 3 rotations per hour. There are a few other more descriptive and accurate resources available that you can easily look through, that explain the maneuver: From the Apollo 11 Flight Plan, page 1-2 " Passive thermal control (PTC) will be conducted during all periods when other activities do not require different attitudes." and from page 1-16 " The translunar and transearth sleep communications mode will be as follows. The CSM x-axis will be placed normal to the ecliptic plane. The CSM will be rolled at a rate of approximately three revolution per hour." Page 1-18 " During PTC the CSM/LM x-axis is pitched up 90° (North) for TLC and down 90° (South) for TEC with the Y-Z axes in the plane of the ecliptic. This change in x-axis pointing is to enable simultaneous viewing of the earth and moon through the side windows while maintaining a favorable high gain antenna position." Page 1-19 " Passive thermal control mode will be initiated after MCC1 or as soon as MCC1 is scrubbed and maintained throughout the mission (except in lunar orbit) until at least three hours before entry except for interruptions for midcourse corrections, communications orientation (maximum interruption of three hours). PTC will not be initiated before approximately 7:00 GET." From the Apollo 11 Mission Report, page 4-3 " The digital autopilot was used to initiate the passive thermal control mode at a positive roll rate of 0.3 deg/sec, with the positive longitudinal axis of the spacecraft pointed toward the ecliptic north pole during translunar coast (the ecliptic south pole was the direction used during transearth coast). After the roll rate was established, thruster firing was prevented by turning off all 16 switches for the service module thrusters. In general, this method was highly successful in that it maintained a satisfactory spacecraft attitude for very long periods of time and allowed the crew to sleep without fear of either entering gimbal lock or encountering unacceptable thermal conditions." Also, in the graqphical representation of the mission timeline in the Mission Report, pages 3-6 to 3-14, you can see that prior to any video communications from the CM, PTC was stopped, then restarted shortly after completion of the video transmissions. Cz
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Post by turbonium on Jun 10, 2008 2:07:43 GMT -4
Yes, your link does give a minimalistic definition of the PTC, however the roll rate is incorrect. The actual roll rate was .3 degrees per second, or 3 rotations per hour. There are a few other more descriptive and accurate resources available that you can easily look through, that explain the maneuver: I assumed a NASA page titled: "SPACE EDUCATORS' HANDBOOK PASSIVE THERMAL CONTROL HOME PAGE" ..would have been an accurate source. Oh well... Can someone address the 3 windows and moving "Earth"?
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Post by JayUtah on Jun 10, 2008 2:24:25 GMT -4
I assumed a NASA page titled: "SPACE EDUCATORS' HANDBOOK PASSIVE THERMAL CONTROL HOME PAGE" ..would have been an accurate source.
I would not have made that assumption. Not everything put out by NASA has been written by a space scientist. There are plenty of operational and technical materials available.
Can someone address the 3 windows and moving "Earth"?
The "moving" Earth has been addressed; your claim that the camera does not move has been met with evidence to the contrary which, to my observation, you have not accounted for.
With the CM in the nose-down position, it is possible for an object in space to be visible from two different windows if the viewer changes position within the cabin.
I dispute that your third photo necessarily shows the sun shining directly through the window. Note that the exposure of the cabin interior suggests that the camera is set for CM interior lighting, which requires opening the aperture considerably. As we've seen, this causes scatter and dispersion effects to saturate the vidicon. This effect requires the sun to shine only on the window, not through it. From any position in the CM, such a window would appear bright if light levels are artificially amplified by wide-open camera apertures.
It is quite possible geometrically for the sun to shine simultaneously on up to three windows: windows 1-3 or 3-5, with the CM in the nose-down attitude.
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Post by Czero 101 on Jun 10, 2008 2:28:46 GMT -4
I assumed a NASA page titled: "SPACE EDUCATORS' HANDBOOK PASSIVE THERMAL CONTROL HOME PAGE" ..would have been an accurate source. Oh well... Interesting that you would put more credence in a document / webpage meant as a resource for those who teach grade school than in the documents and historical records specific to the missions and technology / procedures involved. Oh well.. Cz
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Post by PhantomWolf on Jun 10, 2008 2:45:15 GMT -4
Can someone address the 3 windows and moving "Earth"?The "moving" Earth has been addressed; your claim that the camera does not move has been met with evidence to the contrary which, to my observation, you have not accounted for. With the CM in the nose-down position, it is possible for an object in space to be visible from two different windows if the viewer changes position within the cabin. I dispute that your third photo necessarily shows the sun shining directly through the window. Note that the exposure of the cabin interior suggests that the camera is set for CM interior lighting, which requires opening the aperture considerably. As we've seen, this causes scatter and dispersion effects to saturate the vidicon. This effect requires the sun to shine only on the window, not through it. From any position in the CM, such a window would appear bright if light levels are artificially amplified by wide-open camera apertures. It is quite possible geometrically for the sun to shine simultaneously on up to three windows: windows 1-3 or 3-5, with the CM in the nose-down attitude. For Jay, I think you mean Earth, not Sun. For Turbonium, I suggest you look closer or get your eyes checked, that window is not round. The Earth was only ever imaged though 2 windows, windows that are reasonably close together. The movement is because the camera is moving, not the Earth.
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Post by JayUtah on Jun 10, 2008 3:15:15 GMT -4
Well, I did mean sun; but I should probably clarify. (It is 1 am here.) I don't believe the third photo shows the Earth shining through the window. I'm more inclined to believe it's overexposed dispersion from sunlight.
And yes, it's possible but pointless for the sun to shine on three windows. We're talking about the Earth seen through two, and the sun shining on at least the third.
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Post by Jason Thompson on Jun 10, 2008 4:16:51 GMT -4
Angular size - from my calcs, the Earth could be seen through a 9" diam. window from 130,000 miles away. It's still possible to view Earth from a position several feet away from the window, if the viewer/window/Earth are in proper alignment. Not a certainty, but nonetheless possible - so I'm willing to concede on this point Noted and appreciated.
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Post by Jason Thompson on Jun 10, 2008 4:22:54 GMT -4
There is another serious problem - there are three windows with a view of "Earth". Two different windows have a view of the "Earth" in this TV transmission... Just like the "Earth" vanishes from view in the first window, only ~ 40 seconds later, we again see the "Earth" being moved around outside the "capsule" through a second window. Do you know where the windows are on the command module? Can you see that there can be a line of sight to the Earth from multiple windows? Can you see that this line of sight is even more similar if the Earth is actually thousands of miles away than if it's projected close by? In my old house I could see the Moon through my bathroom window and my bedroom window, and those windows were set in different walls of the house, making an angle of 90 degrees. And a third window (the 9" round window) with a view of the "Earth" is in the subsequent footage... I don't see Earth in that picture. I see a blue glow in the window, which can be caused by light scatter from the Sun shining on the window while out of direct line of sight. OK, it's been a while since I've seen that footage, but isn't it obvious that they're in zero gravity? How do you explain that if they're filming it on Earth?
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Post by Count Zero on Jun 10, 2008 6:05:33 GMT -4
This photo shows one of many angles that allow you to see multiple (in this case, all) windows. Reflexively, from such angles a given object (be it the Earth, Sun or whatever) will be visible from inside the spacecraft through all of the visible windows.
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Post by PhantomWolf on Jun 10, 2008 7:22:33 GMT -4
Well, I did mean sun; but I should probably clarify. (It is 1 am here.) I don't believe the third photo shows the Earth shining through the window. I'm more inclined to believe it's overexposed dispersion from sunlight. And yes, it's possible but pointless for the sun to shine on three windows. We're talking about the Earth seen through two, and the sun shining on at least the third. Time to go for another "I corrected JayUtah" T-Shirt. It is the Earth, though as you say overexposed and likely affected by the coating on the windows as well. I can say this because this shot was taken a seconds previous to the other You can see the spotlight in it to the left of the Earth. The Sun was on the other side of the CSM (we see this later in the footage when they are discussing blocking it out with Buzz's Star Charts.) The Blue light is caused by the Earth backlighting the window (though in all fairness it is sunlight reflected off the Earth.
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