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Post by PhantomWolf on Aug 30, 2008 16:43:18 GMT -4
Just on the gif thing, I use AnimationShop, it couldn't be easier. You can either do a layered gif in PaintShopPro and load that in, or just directly select which still pictures you want to animate, order them, and it will load each one into a frame. Then it's just a case of selecting the speed of each frame (or all of them together) testing it and deciding what format to save it as (anything from gif to avi). Takes about 2-3 minutes if that.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Aug 30, 2008 19:14:19 GMT -4
I'm not sure about the equigravisphere definition. I would prefer to make a distinction between (literally) an "equal gravity" surface and the (arbitrary) transition between coordinate systems ("the Moon's sphere of infuence"). Combining the two senses has historically meant confusion by writers and conspiracy theorists alike. I've revised it. How does this sound? The Equigravisphere, or "sphere of influence", is the boundary where the spacecraft trajectory is considered to transition from earth-centered to moon-centered, which NASA defines as being 40,000 statute miles (64,374 kilometers) from the center of the Moon. This arbitrary definition is not to be confused with the commonly held definition of the equigravisphere being all points in space where Earth and lunar gravity are equal, the so-called "neutral point."One thing that has been lost in your transition to the (great) animation is the nice snapshot of the instant where the spacecraft passed the 40000 mile point showing how far off the center-line the trajectory was at the point where they entered the Moon's sphere of influence. For what I'm trying to show, I think the crossing of the equigravisphere is adequately covered in the table and footnote. In the big picture it is a pretty arbitrary and insignificant thing that I don't think warrants any special treatment in the animation.
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Post by George Tirebiter on Aug 31, 2008 0:25:52 GMT -4
I then came across this diagram in one of my books. For a hybrid trajectory, the spacecraft is initially placed on a free return but then switches to a non-free return after a midcourse transfer. The non-free return trajectory takes the spacecraft low over the backside of the Moon, but as you can see, the free return has a pericynthion altitude in the range of 100 to 1,500 nautical miles. My 780 mile figure is almost right down the middle of this range. What I thought was a mistake is near perfect! I like surprises like that. Wow, I've had the same experience in Orbiter. I could never get a low-pericynthion free return trajectory to work. It would look good on paper, but it's much too sensitive to small errors in the TLI burn. But by raising the pericynthion, it became a piece of cake. I thought I was just being sloppy. Thanks for the diagram; it's nice to see that I'm not the only one who couldn't get it to work.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Aug 31, 2008 12:04:15 GMT -4
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Post by LunarOrbit on Aug 31, 2008 21:01:42 GMT -4
I just imagined the scientists at NASA showing a graph exactly like that to a room full of astronauts and Pete Conrad bursting into laughter. Am I the only one who thinks it looks like the profile of a breast? Ok, I'll grow up now. What program are you plotting the trajectories in, Bob? MS Excel?
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Post by Bob B. on Aug 31, 2008 22:54:28 GMT -4
Am I the only one who thinks it looks like the profile of a breast? LOL, I can't believe I didn't notice that until you mentioned it. What program are you plotting the trajectories in, Bob? MS Excel? Yes, I'm using Excel.
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Bob B.
Bob the Excel Guru?
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Post by Bob B. on Sept 1, 2008 1:11:10 GMT -4
Here is another animated simulation: Lunar Hybrid ProfileI went a step further and figured transforming the free return into a non-free return low-pericynthion trajectory. I then added in lunar orbit insertion and a transearth injection maneuvers.
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Post by BertL on Sept 1, 2008 11:55:32 GMT -4
Could you maybe slow down the animation when your object is near the Moon?
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Bob B.
Bob the Excel Guru?
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Post by Bob B. on Sept 1, 2008 14:34:20 GMT -4
I've slowed the whole thing down to a time scale of 1 second = 4 hours.
With this latest simulation, I have now replicated just about every Apollo maneuver. I can say with reasonable confidence that everything in regard to trajectories and propulsion works just as NASA said it should. All HB claims to the contrary are total bunk (like I didn't already know that).
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Post by Ginnie on Sept 1, 2008 16:36:47 GMT -4
I've slowed the whole thing down to a time scale of 1 second = 4 hours. With this latest simulation, I have now replicated just about every Apollo maneuver. I can say with reasonable confidence that everything in regard to trajectories and propulsion works just as NASA said it should. All HB claims to the contrary are total bunk (like I didn't already know that). You've done a great job with those animations Bob.
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Post by Kiwi on Sept 2, 2008 5:36:46 GMT -4
With this latest simulation, I have now replicated just about every Apollo maneuver. Many thanks Bob -- they are fascinating. Perhaps there's one more theoretical trajectory of interest -- one with no moon. Apparently, just after translunar injection the spacecraft were travelling at a little under Earth's escape velocity so I'd assume that if they went nowhere near the moon they would return to Earth, or at least to its general vicinity. Is that the case? Regarding pericynthion: Don't the Apollo 13 crew have the record for being the three people who've travelled farthest from Earth? Apparently this was due to the height at which they passed over the back of the moon.
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Post by gwiz on Sept 2, 2008 9:16:01 GMT -4
Regarding pericynthion: Don't the Apollo 13 crew have the record for being the three people who've travelled farthest from Earth? Apparently this was due to the height at which they passed over the back of the moon. More to do with how far from Earth the moon was in its elliptical orbit at the time of the Apollo 13 mission.
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Bob B.
Bob the Excel Guru?
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Post by Bob B. on Sept 2, 2008 9:28:44 GMT -4
Perhaps there's one more theoretical trajectory of interest -- one with no moon. Apparently, just after translunar injection the spacecraft were travelling at a little under Earth's escape velocity so I'd assume that if they went nowhere near the moon they would return to Earth, or at least to its general vicinity. Is that the case? Yes, the spacecraft was in an elliptical orbit around Earth. If not for the Moon, it would have followed the ellipse and returned to its starting point. It would look like this: www.braeunig.us/apollo/pics/ellipse.gifOf course it might not have returned exactly to its original starting point. I suspect the orbit would have been perturbed some by the Sun. Regarding pericynthion: Don't the Apollo 13 crew have the record for being the three people who've travelled farthest from Earth? I believe this is true, yes. Apparently this was due to the height at which they passed over the back of the moon. This was probably a contributing factor; accompanied by the fact the Moon was near apogee at the time. One of the other missions (don't remember which) also occurred very close to apogee. It is likely Apollo 13 holds the record over the other mission due to its higher pericynthion, but I don't know this for certain. (edit) According to Wikipedia, Apollo 13's closest approach to the Moon was 254.3 kilometers (137.3 nautical miles). This is a higher altitude than a normal mission.
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Post by gwiz on Sept 2, 2008 10:10:00 GMT -4
This was probably a contributing factor; accompanied by the fact the Moon was near apogee at the time. One of the other missions (don't remember which) also occurred very close to apogee. It is likely Apollo 13 holds the record over the other mission due to its higher pericynthion, but I don't know this for certain. Apollo 10 was about 250 km short of the Apollo 13 figure. This is slightly more than the pericynthion difference.
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Bob B.
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Post by Bob B. on Sept 2, 2008 10:20:10 GMT -4
Apollo 10 was about 250 km short of the Apollo 13 figure. This is slightly more than the pericynthion difference. I thought Apollo 10 was the other mission but I wasn't sure. Based on the data, I agree with you -- it looks like Apollo 13 would have had the record even without the higher pericynthion. If Apollo 13 came in at an altitude of 60 nautical miles like normal, it would have still been about 100 km farther than Apollo 10.
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