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Post by ka9q on Feb 3, 2012 1:31:32 GMT -4
I know this means you need to get the timing pretty exact and any delays in launch would create further delays, but why would have it meant not getting to the moon by the end of the decade? It has to do with the relative positioning of the launch site and the moon. To do a direct injection from KSC into a lunar trajectory, the injection point (where the upper stage shuts down) has to be at the antipode of the moon's position at arrival. That's a latitude equal to the negative of the moon's declination. I really should check the references first, but here's my understanding from memory. KSC is at about 28.5 deg north. You have some control over launch azimuth, but physical and range safety limits still mean that the moon's declination would definitely have to be negative (in the earth's southern hemisphere) at arrival. Add to that the constraint that you want a landing site on the near side in early solar morning, and the relative orientation of the moon's orbital plane to the earth's rotational axis could mean no launch windows for months or maybe years at a time. But with a parking orbit, relatively small changes in the exact time of TLI could put the latitude of the injection point anywhere within the extremes of the parking orbit, thus accomodating a wide range of lunar declinations and allowing launch windows every day for several days each month to any given lunar destination. Again, that's from memory and I may have gotten it wrong. BTW, some form of parking orbit (or coast phase) is practically standard practice in any launch beyond LEO (including earth escape) that you'll see on NASA TV. This explains the popularity of pressure fed hypergolic upper stages because they are very easily restarted; just close the propellant valves and open them again at the right time. Sometimes they'll do a third burn at apogee after spacecraft separation to cause the spent stage to re-enter on the next perigee instead of becoming another piece of space junk. But restarts are much trickier with a big cryogenic stage like the S-IVB. Several things have to happen in sequence and at the right times, such as repressurizing the propellant tanks, restarting the turbopumps (how?) and re-igniting the propellants quickly enough to avoid a "hard start" that could damage the combustion chamber or nozzle. Many large rocket engines use hypergolic cartridges or small solid rocket engines for these tasks, making it difficult to do them more than once. Another way is to just separate the burns into separate stages. I have wondered if the designers of the Saturn V considered making the S-II larger so that it could achieve parking orbit, allowing the first and only firing of the S-IVB to occur at TLI.
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Post by ka9q on Feb 3, 2012 1:21:45 GMT -4
Bob, I haven't checked your math but overall it looks right assuming the 1 MeV electrons aren't so energetic as to ever pass completely through the body.
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Post by ka9q on Feb 3, 2012 1:18:26 GMT -4
I cannot find a single photo taken from the surface of the moon during the Apollo 11 moon walk with a landmark identiying the site as unique. Generic nothing if you ask me. Perhaps I'd rather not ask you. I'd rather look at the pictures myself. And when I compare the 16mm movie of the Apollo 11 landing with new photography of the site from LRO, guess what? Every tiny crater, boulder, depression, hill, what have you, is a perfect match! Mind you, in the last minute or two before landing these features were far too small to have been seen from lunar orbit with the technology of the 1960s. Not until the development of the modern CCD imaging technology now carried in LRO could objects this small be seen from orbit, and in fact they still look better in the Apollo 11 film. And the Apollo 11 landing film ends with blowing dust at the precise spot where LRO now sees the descent stage parked on the lunar surface. So there's simply no escaping the fact that the Apollo 11 landing movie was indeed made by a spacecraft landing on the moon in that location. A spacecraft that looked just like the Apollo LM, which was designed to carry humans. So is it that hard to accept that humans were in fact flying it when it landed? And let's not forget that there were five more landings, each making their own landing films that also match the LRO imagery, and some occurring in lunar locations much less "boring" than the Apollo 11 site is to you.
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Post by ka9q on Feb 3, 2012 1:02:53 GMT -4
What is to say that the Apollo 8 and 10 images are not courtesy of unmanned probes. That seems quite possible to me. Not at all. First of all, every Apollo mission, including every lunar mission, returned pictures of the earth, and earlier in this thread you will see our own member threadworm present an exhaustive comparison of Apollo earth photography with contemporary weather information showing that their earth pictures were taken at the correct dates and times. This knocks down your hypothesis (wild unfounded speculation, actually) that they were all taken ahead of time. Secondly, in 1968 and 1969, the only technology available for returning extremely high quality images of the moon (especially high quality color) was to photograph it on large format photographic film (e.g., 70mm or larger) and to physically return that film to earth for processing. High quality electronic CCD imagers like those used on today's LRO (and the computers needed to handle them) would not be available for several more decades. And if you were to allege (without evidence, of course) that CCDs were available then to the secret parts of government, then why did classified spy satellites like the now-declassified KH-9 still use, as late as 1986, physical film return, a far more expensive, slow and clumsy method? The only system the United States has ever had for returning significant amounts of material from the moon or its vicinity is the Apollo spacecraft. Although the Lunar Orbiter satellites of the 1960s did use (black and white) film, it was not physically returned to earth; it was processed on board and electronically scanned, creating artifacts that are very conspicuous -- yet absent from the Apollo pictures. So if you are to claim that Apollo's high quality pictures of the moon (which match those now being returned by LRO, by the way) were taken by unmanned spacecraft, you must show not only which spacecraft and launches performed this task but you must also show how they physically returned their film to earth. I think you'll have great difficulty doing this.
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Post by ka9q on Feb 3, 2012 0:42:17 GMT -4
I checked every one of the OP's references cited in his long posts on page nine of this thread. Every one of them checked out. Each author did make reference to the astronauts not knowing where they were. Not much else to understand. The OP is correct here. Those are the authors' statements. Clear statements. I'd say that both the original poster and you (in the unlikely event you're distinct) still share some common problems and misunderstandings. You don't seem to understand that accuracy is fundamentally a quantitative notion, i.e., specified with numbers, and that measurement accuracies often improve with time as complementary meaurement methods are combined, systemic errors are found and corrected, and random measurement "noise" is averaged out through repetitive data-taking. You must understand that measurements are almost always relative, and they can often be made far more accurately in relation to some things than to others. When a measurement is said to be "not good enough", that is always with respect to some specific use. It does not mean that no one has any idea at all. It may still be perfectly good enough for some other use that isn't nearly as critical. This is why Michael Collins never located the landed Eagle. He needed a very accurate estimate of Eagle's landed position relative to the moon itself, and he never got it in time. There may not even be a well defined limit on what constitutes an "good" measurement if you've got enough time to make use of a poor one. That's why it took over a week for the Lick Observatory to make its first successful laser contact with the Apollo 11 LRRR. But when it came to linking the LM back up with the CSM, what mattered was not the positions of the spacecraft relative to the moon, but their positions relative to each other. And that's where the rendezvous radar on the LM and the VHF ranging system on the CSM excelled. That's what they were designed to do, that's why they were built, and that's why the Eagle was able to find its way back to Columbia in just a few hours. Even these systems only had to be good enough to get them within visual range of each other, at which time the crew could do the rest.
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Post by ka9q on Feb 2, 2012 8:05:07 GMT -4
I have the original (non-GPS) mount with my LX200. Because of this, it's a bit of a pain to align (you basically do the equivalent of an Apollo 'P52' but from scratch) but once it's aligned it seems pretty stable.
I see that it's now possible to just stop sidereal tracking, point the scope at one fixed point on the sky, snap a long series of CCD images and then have software assemble them into a wide panorama as the stars move through your field of view. Wow.
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Post by ka9q on Feb 2, 2012 7:59:40 GMT -4
I blame the Internet. Some people are so stupid they think if they are smart enough to operate a browser then they are smart enough to understand all the information displayed on that browser. They go well beyond that -- they think they're smart enough to have proved wrong any information on that browser they don't happen to like for various ideological reasons.
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Post by ka9q on Feb 1, 2012 5:29:26 GMT -4
Page 16 of this PDF of the "Apollo 11 Preliminary Science Report"seems to give the information desired, I think. Yes, it does: 1.25 deg. Thanks! Here's why I ask. Two of the six LM ascent stages that lifted off the moon were abandoned in lunar orbit rather than being intentionally deorbited onto the moon to provide seismic signals: Apollos 11 and 16. 11 probably because no one had thought of it yet, or perhaps because the engineers wanted to conduct a stress test to see what happened when the consumables (mainly cooling water) ran out. This later became useful during the Apollo 13 emergency. 16's Orion was left in orbit because a procedural mistake deprived the ground of the attitude control needed to do the deorbit maneuver. Because lunar orbits are unstable, both LMs eventually struck the surface but we don't know where. But I'm wondering if it may now be possible to discover their craters. LRO has now mapped most of the moon at high resolution, and it has shown us what an LM ascent stage impact crater looks like (about 10m in diameter, slightly elongated because of the low angle of impact). With GRAIL's forthcoming improvements in the moon's gravity model it may even be possible to project the last known state vectors forward to estimate the impact points. But even without those estimates, it could be done with a lot of eyeballing of the LRO pictures to look for the characteristic craters, perhaps confirming that those craters are not present in the LO images of the same area. The impacts could have occurred anywhere in a latitude band defined by the inclination of their lunar orbits, and since A11 has the lower inclination this band would be much smaller and easier to search by eye than that for A16.
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Post by ka9q on Feb 1, 2012 4:46:05 GMT -4
Wow, that is stunning. Maybe it's time to dust off my 8" LX200 and shop for a CCD imager. Last I looked you could easily spend several times the price of your scope on the imager...and they were so small...
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Post by ka9q on Jan 31, 2012 14:50:38 GMT -4
Hey, does anybody know the inclinations of the lunar orbits used during each Apollo mission? This is surprisingly hard to find, as it's not in Apollo by the Numbers. I'm looking for the lunar orbit inclinations of the CSMs for each mission when the LMs were jettisoned, specifically for Apollos 11 and 16, the two missions that abandoned their LMs in lunar orbit.
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Post by ka9q on Jan 31, 2012 14:48:43 GMT -4
Yes, it was drilled into us by our physics teachers that if the units weren't right, the numbers were totally meaningless.
BTW, dimensionally all radiation exposures have units of energy per mass. The SI unit of radiation exposure is the Gray (Gy), equal to one joule per kilogram, released by energetic particles as they deposit their energy in a target. 1 Gy = 100 rad, because 1 rad = 100 ergs (energy) / gram.
Corresponding units of Sieverts (Sv) and Rontgen Equivalent Man (REM), with 1 Sv = 100 REM, have the same units of energy per unit mass but scaled with a dimensionless effectiveness factor that depends on the type of radiation. For photons (X-rays and gamma rays) 1 Sv = 1 Gy, but for particles like neutrons, protons and electrons the damage is greater so each Gray of absorbed dose results in more than one Sievert of damage.
Knowing this, and knowing the energies and numbers of your incoming particles and how much of their energy they deposit in each type of material (shielding and the people behind it) you can compute radiation exposures for yourself. It takes a lot of particles to accumulate even 1 Gy because the amount of energy carried by even a highly energetic particle (e.g, 100 MeV) is a tiny fraction of a joule, and that joule is divided by the entire mass of the body.
This is something I think the HBs don't get because they seem to think of each charged particle as something like a bullet, able to kill all by itself if it gets through your shielding. Bullets move vastly slower than most charged particles, but they are even vastly more massive so they carry more than enough energy in each one to kill you. Basically, it's energy that kills though the amount required to do so varies a lot depending on how it's delivered.
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Post by ka9q on Jan 31, 2012 4:58:27 GMT -4
Oh Jay, you know they'll go for the rover tracks. They always go for the rover tracks. Yes! Of course! There aren't any rover tracks in the Apollo 11, 12 and 14 pictures. Obvious fakes! ;-)
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Post by ka9q on Jan 31, 2012 2:30:42 GMT -4
I guess I wasn't the only one to look up at the moon while humans were there and wonder why I was surprised that it didn't look any different.
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Post by ka9q on Jan 31, 2012 2:15:13 GMT -4
Vincent - Here is the Earth orbital parameters for all of the Apollo missions. Yes, note how all the lunar missions before Apollo 15 used 100 nautical mile parking orbits, while Apollos 15-17 used 90 nautical mile orbits. BTW, I've never particularly liked the practice of describing orbits by their apogees and perigees because of the ambiguities associated with the earth not being quite spherical. Are the altitudes given with respect to an elliptical earth or a spherical one? And if it's elliptical, do the figures actually reflect the closest and furthest distances to the earth's surface, or are they the distances to the surface when the satellite reaches geometric perigee and apogee, i.e., closest and furthest approach to the center of the earth? It's much more precise to describe an orbit by either its classical Keplerian orbital elements (with eccentricity plus either mean motion or semi-major axis describing the size and shape of the orbit in space) or by its state vector, a 3-dimensional position vector plus a 3-dimensional velocity vector.
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Post by ka9q on Jan 31, 2012 2:08:15 GMT -4
The Apollo parking orbits were all quite low to maximize efficiency. It would have been even more efficient to launch directly into a lunar trajectory, but the launch windows would have been extremely limited. So much so that they wouldn't have made it to the moon by the end of the decade. So early on in the planning for Apollo a parking orbit was chosen that would let them choose the time and place of the TLI burn somewhat separately from the launch time. This in turn was a major driver in the design of the Saturn V's S-IVB stage that had to burn once for earth orbit injection and then restart a few hours later for TLI. Making a large rocket engine restartable when it burns non-hypergolic fuels and uses a turbopump to get them into the engine is decidedly non-trivial.
The J-class Apollo missions (15-17) used even lower parking orbits - less than 100 nautical miles - to increase the Saturn V's throw weight to the moon. These would have been very short lived orbits had they stayed in them more than 1-2 orbits before TLI.
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