Bob B.
Bob the Excel Guru?
Posts: 3,072
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Perigee
Aug 16, 2011 21:54:20 GMT -4
Post by Bob B. on Aug 16, 2011 21:54:20 GMT -4
… when NASA talks dramatically about the CM "skipping" back into space, never to returnI’ve never liked that language. If the spacecraft was in an Earth orbit when it entered the atmosphere, it’s certainly going to remain in Earth orbit after leaving the atmosphere. In fact, the vehicle will have a lower apogee after passing through atmosphere because it has lost energy. The vehicle will return on its next perigee passage. It should be noted that passing a spacecraft through the thin upper atmosphere of a planet to lower the apoapsis has actually been done on purpose – it’s called aerobraking. The spacecraft typically makes many passes through the atmosphere at an altitude high enough that it just skims through and passes back out into space, but low enough that drag slows in down a little bit each passage. During each passage the apoapsis is lowered by a small amount. Once the apoapsis is lowered to the desired altitude, a burn is performed at apoapsis to raise the periapsis above the planet’s atmosphere.
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Perigee
Aug 16, 2011 22:31:25 GMT -4
Post by coelacanth on Aug 16, 2011 22:31:25 GMT -4
You won't get a penny from the U.S. government until you learn to spell "check" and "program." They should have covered that in the CIA orientation. You misspelled "misspell"!
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Perigee
Aug 16, 2011 22:44:41 GMT -4
Post by ka9q on Aug 16, 2011 22:44:41 GMT -4
I know that TLI gave Apollo an eccentricity of about 0.97, which is a highly elliptical earth orbit but not an escape trajectory. That would be an eccentricity >= 1. But I don't know if the same was true for the return trajectory after TEI.
Trajectories that eccentric tend to be highly affected by solar and/or lunar perturbations, so even if they don't achieve escape velocity right away that could change. The early lunar flights sent the spent S-IVBs around the trailing side of the moon, which perturbed them right out of earth orbit and into an independent orbit around the sun. So even if the CM somehow missed capture and remained in a highly elliptical earth orbit, perturbations or some future encounter with the moon might eventually eject it into orbit around the sun or cause it to hit the earth. I think Andrew Chaikin found a simulation showing that, had Apollo 13 not been able to get back on a free return trajectory, it would have eventually hit the earth some months later.
The Apollo 12 S-IVB slingshot wasn't done quite right so it remained in a highly eccentric earth orbit for some time before finally being ejected into interplanetary space. It seems to be generally agreed that it was temporarily recaptured into earth orbit and discovered in 2002 as object J002E3, then ejected again a few years later.
BTW, it bugs me when people say that Apollo was when man first left earth orbit. No one has yet left earth orbit in the sense that I think of it since the moon also orbits the earth. (Now just wait for some HB to quote me out of context!)
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Perigee
Aug 17, 2011 1:03:51 GMT -4
Post by Bob B. on Aug 17, 2011 1:03:51 GMT -4
I know that TLI gave Apollo an eccentricity of about 0.97, which is a highly elliptical earth orbit but not an escape trajectory. That would be an eccentricity >= 1. But I don't know if the same was true for the return trajectory after TEI. The transearth trajectories where elliptical orbits, though they were more eccentric than the translunar trajectories. The median eccentricity was about 0.985. The apogees of the transearth orbits varied, but the median was about twice lunar distance. That far out I imagine the grip on Earth is fairly weak and the spacecraft would be very susceptible to perturbations. But the spacecraft would go out that far only if it missed the atmosphere entirely. Any passage through the atmosphere would slow the spacecraft down and lower the apogee. It would take only a -40 m/s change in velocity to lower the apogee by half and reduce the eccentricity to 0.97. That's not much of a velocity change. It would take a pretty egregious guidance error to come in so shallow as to not produce a significant delta-v during the perigee passage.
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Perigee
Aug 17, 2011 2:01:52 GMT -4
Post by ka9q on Aug 17, 2011 2:01:52 GMT -4
You're right, and it would be known long before actual entry so there'd be plenty of time to correct it unless they were to completely lose propulsion.
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Perigee
Aug 17, 2011 2:09:28 GMT -4
Post by ka9q on Aug 17, 2011 2:09:28 GMT -4
It would take a pretty egregious guidance error to come in so shallow as to not produce a significant delta-v during the perigee passage. As A11 CMP, Michael Collins would have known this as well as anyone, but he still breathed a sigh of relief when their entry velocity dropped below that required to guarantee earth capture...
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Perigee
Aug 17, 2011 19:48:37 GMT -4
Post by lukepemberton on Aug 17, 2011 19:48:37 GMT -4
They simply worked differently than we do. In my opinion these guys used their brains more. I agree. They also did hard physical yards too. As a physicist I am always amazed by the early pioneers of modern particle physics. My lecturer for 2nd year nuclear physics was describing his doctoral research (proton interactions) and the times he spent patiently sat on top of a bubble chamber recording events and then doing the hard computations. Nowadays, the data would be captured digitally and processed using computers. Luckily there are still enough practitioners of those old methods around to tell us when our computers get the wrong answersYes, rubbish in rubbish out. A perennial bug bear of mine when I ask a modeler to run a simulation and he gives me an answer that I know does not make sense. I do wonder about the current generation, but then I am probably getting old. It irks me that young graduates run models and do not think about the outputs and what they mean. They see a number and think 'the model said so, it must be right.' My impression was that Apollo was considered high enough priority that it could legitimately use leading-edge military assets.Oh to have been part of it. I was still a babe in arms when Apollo 14 was making its flight, and probably just out of nappies by the time Apollo 17 left the moon. I cannot possibly imagine what it would have been like to work on the Apollo. The culture that had to be instilled to achieve the final goal. It amazes me that they did it in the time available. It was more than a technical achievement - it was a lesson in project management (most of the time). As you note, the hoax community on YouTube seems to be a hotbed of anti-government sentiment.If there is an acceptable face of the moon hoax theory it was Kaysing. While he lied and told untruths that are hard to forgive, I think he grew up in a hotbed of political distrust during the Cold War. I don't see him as a villain par se. He seemed like a kindly old man who wanted to tell tall tales. Having spent some time at YouTube, my experience is that the HB is very much tied in with distrust of government and just about every conspiracy that is doing the rounds. I tend to look at the positives and how it shows that small community, cozy at their walled gardens, to be perceived by the outside world. For my way of thinking, if I can see that positive light, then I can accept they are probably not doing their cause any favours. In an odd sort of way, I think that he-who-shall-not-be-named is actually betraying Kaysing. For example, while Kaysing tried to sue Lovell (a cheap trick), I think he was generally content with having his voice heard and did not act with the vitriol that the YT community show. Regardless of your moral views on the military, from an engineering perspective they have a very good track record of handling high-risk technologies.Thankfully. Yes, unavoidably so. The civilian space program occasionally served as cover for covert missions, although we know of only one such instance in Apollo (Project Chapel Bell).A Google search on Chapel Bell brings up seismic experiments. I am aware of such experiments, but not that they were called Chapel Bell. What was Chapel Bell? It's no accident that after the LM team perfected chemical milling, that technique was used on the F-14 produced by the same team at the same company.An example of a technique or process that has been used elsewhere. The sad part is while the HB community are anti-NASA, they forget their daily lives are touched by the legacy of Apollo and the exploitation of NASA research. It is this that drives me to despair more than anything. I am afraid that the Internet generation are taking a grip, and their attitudes are symptomatic of our throw away society. Children are growing up fast in a consumer world without time to pause, and their expectations as adults are high. There are those that have their expectations dashed, and fall into less productive ventures such as conspiracism, often for their five minutes of fame. I think we have seen an examples of consumer society in the UK with recent looting. I feel that conspiracism is another way that younger people express themselves, and are probably those that fell along the wayside at some academic level. He-who-shall-not-be-named clearly has an interest in space and science, but did not make the grade. I have reached the conclusion that the hoax theory is his way of achieving recognition as an expert. For them the battle is political, so they assume our defense of NASA is just as politically motivated as their attack on it. Defense, what is that word? ;D This is why they fail. I do not defend NASA or Apollo. I defend the people that made it possible, and find their denigration a loathsome act. Apollo could have been a deep sea voyage to the bottom of the Pacific Ocean, setting up under water stations to observe deep ocean life. The fact it was a moon landing achieved by the work of NASA and their contractors has no bearing on my feelings towards the HB community. In their fantasy world they're the top-notch sleuths who cracked the Apollo conspiracy.Or, as discussed, they are disenchanted and feel their lot is a rotten lot. They are angry with their lack of achievement, and use the hoax as a platform to gain peer recognition. A prime example is Ralph Rene. I think he was just an insecure man who didn't make the grade. His alternative theories were a reaction to his own failings, and he took on the academic world. I certainly think he was paranoid, but whether he had paranoid tendencies from the beginning, or he became paranoid through his continued activities, I could not possibly say. Maybe this is simplistic, but we are all descended from primates and our psychology and behaviour still has echoes from that time. Within his world, he-who-shall-not-be-named is top of the tree. His reaction toward you and others is the young chimp making an attack on the alpha male. He just doesn't learn that he will always get slapped down. His recent behaviour is telling, and it shows his angry disdain for those on the higher branches. He'll get slapped down again, and come back for more. It can be quite entertaining when couched in those terms. I fear it's only going to be a matter of time before they style someone as a villain to the point where he takes legal action.I don't understand what there is to fear. I hope someone does take legal action for defamation. I'd like to see a few individuals account for their behaviour, especially those that cry defamation, slander and libel and have no sense of what actually constitutes those acts. But then those prepared to commit perjury and fraud probably don't care much for the law.
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Perigee
Aug 18, 2011 6:59:55 GMT -4
Post by gwiz on Aug 18, 2011 6:59:55 GMT -4
A Google search on Chapel Bell brings up seismic experiments. I am aware of such experiments, but not that they were called Chapel Bell. What was Chapel Bell? Chapel Bell was an over-the-horizon radar system. The Saturn V was simply used as an unusual test target for the radar. It's been discussed on BAUT.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Perigee
Aug 18, 2011 12:06:24 GMT -4
Post by Bob B. on Aug 18, 2011 12:06:24 GMT -4
I want to find out at what height the command module stopped accelerating. Also, I want to find out the final (maximum) velocity of the command module, when it did stop accelerating. I set up a simulation to see if I could get a better answer to your question. I used the standard atmosphere and and drag and lift coefficients from the following document: ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20080014105_2008013652.pdfDelightfully, I get a maximum velocity of 36,277 ft/s (11,057.2 m/s) -- precisely the number reported by NASA. This maximum occurs 31.3 seconds after entry interface and at an altitude of 87.4 kilometers. The true anomaly at this point is -10.01 degrees.
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Perigee
Aug 18, 2011 15:14:36 GMT -4
Post by Count Zero on Aug 18, 2011 15:14:36 GMT -4
It should be noted that passing a spacecraft through the thin upper atmosphere of a planet to lower the apoapsis has actually been done on purpose – it’s called aerobraking... ...which is not to be confused with lithobraking, which was perfected on NASA's Genesis probe, when it returned to Earth in 2004.
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Perigee
Aug 18, 2011 16:07:02 GMT -4
Post by JayUtah on Aug 18, 2011 16:07:02 GMT -4
...at an altitude of 87.4 kilometers. Or about 30,000 feet higher than what I was able to glean from the control laws and the recollection of the controllers.
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Perigee
Aug 18, 2011 16:09:37 GMT -4
Post by JayUtah on Aug 18, 2011 16:09:37 GMT -4
... lithobraking, which was perfected on NASA's Genesis probe, when it returned to Earth in 2004. Caused, appropriately enough, by the failure to install the ELS circuitry such that the 0.05 g interface trigger accelerometer was aligned with the spacecraft axis of travel. Hence the flight control system never switched to atmospheric flight mode. The moral: don't assign an electrical engineer to approve mechanical plans.
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Bob B.
Bob the Excel Guru?
Posts: 3,072
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Perigee
Aug 18, 2011 19:42:07 GMT -4
Post by Bob B. on Aug 18, 2011 19:42:07 GMT -4
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Perigee
Aug 18, 2011 20:51:45 GMT -4
Post by PhantomWolf on Aug 18, 2011 20:51:45 GMT -4
It should be noted that passing a spacecraft through the thin upper atmosphere of a planet to lower the apoapsis has actually been done on purpose – it’s called aerobraking... ...which is not to be confused with lithobraking, which was perfected on NASA's Genesis probe, when it returned to Earth in 2004. Still too soon
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Perigee
Aug 23, 2011 11:55:41 GMT -4
Post by pleasedebunkme on Aug 23, 2011 11:55:41 GMT -4
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