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Post by thetart on Aug 23, 2010 8:46:11 GMT -4
Does anybody know where I can get info on how the LM seperated on takeoff? I always wondered how the two parts of the LM were seperated and how the system was developed and tested.
Thanks,
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Post by echnaton on Aug 23, 2010 9:42:12 GMT -4
The LM sections were mechanically connected by "explosive bolts" that fired to separate the halves. All the wires and supply lines for water and other consumables ran through a single channel and were severed by a explosively charged guillotine. You can find more than you ever wanted to know in Scott Sulivian's great book Virtual LM.
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Post by Jason Thompson on Aug 23, 2010 9:49:04 GMT -4
It was, incidentally, a lack of such an explosively powered guillotine system that prevented a number of Vostok and Voskhod re-entry capsules from properly separating from their instrument modules, causing a spin on re-entry that persisted until the umbilical burned through. Fortunately their design was a spherical re-entry module covered all over in ablative heat shield material. Had such a failure occurred on Mercury, Gemini or Apollo the results could have been disastrous.
Explosive bolts are a common method used to separate rocket stages and spacecraft modules.
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Post by thetart on Aug 23, 2010 10:19:12 GMT -4
Thanx for the book Reference. I'll get that on order.
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Post by banjomd on Aug 23, 2010 11:00:54 GMT -4
From Moon Lander: Thomas Kelly. Smithsonian Institution Press 2001 (p69) "...detonator cartridges...were components required to effect ascent/descent stage separation during launch from the Moon's surface: explosive nuts and bolts that secured the stages together, and the umbilical cutter and circuit interruptor that severed and inerted the interstage umbilical wire and tubing bundle." Of interest: Kelly states that, since the functioning of the devices was critical, both nuts and bolts were severed, dual igniters were used and dual cutter blades were used to sever the bundles.
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Post by echnaton on Aug 23, 2010 11:01:02 GMT -4
Check out the drawing on Eric Hartwell's site. They are large JPG files but contain a wealth of info on LM design.
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Post by ka9q on Aug 24, 2010 11:03:30 GMT -4
For things like electrical cables, relays were first opened to isolate the stages so that the blades wouldn't cause nasty short circuits. Those descent stage batteries still had a fair bit of juice in them.
The one I don't fully understand is the interstage coupling from the descent oxygen tanks. I don't see any isolation valves, only a "quick disconnect" directly in the high pressure oxygen line. Did it really seal when the LM lifted off, or did high pressure O2 just blow out the top of the descent stage? Might help explain some of that blowing mylar...
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Post by echnaton on Aug 24, 2010 13:48:35 GMT -4
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Post by echnaton on Aug 24, 2010 14:37:20 GMT -4
One paragraph in that describes a procedure where a sample from each batch of pyrotechnics flown on a mission was test fired at KSC prior to launch. The test was done to assure that there had been no degradation of the pyrotechnics over time. Reading through the numerous examples of this type of system documentation that are available should erase all reasonable doubt of a hoax.
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Post by echnaton on Aug 25, 2010 9:39:55 GMT -4
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Post by ka9q on Aug 25, 2010 14:22:57 GMT -4
One paragraph in that describes a procedure where a sample from each batch of pyrotechnics flown on a mission was test fired at KSC prior to launch. There was also great concern about possible miswiring of the firing circuits. This is something I'd be concerned about given that you can't fully test them in advance. To reduce the chances of miswiring, each initiator (electrical detonator) had a connector that could be uniquely keyed so that it would only mate with the proper cable connector. It was possible to install an unkeyed initiator that would fit any connector, but special authorization was required. I have wondered how much of the inherent risk associated with each mission was due to the fact that all of its hardware was flying for the first and only time. After a few missions you tend to find and fix the design bugs, but you still have to worry about QC flaws such as miswired connectors. The CM was the only part of the Apollo/Saturn stack to return to earth, and while it was a tiny fraction of the total mass it still contained a significant share of the complexity. I've always wondered how hard it would have been to reuse the CM. Later crews would get the benefit of a flight-tested module, although there would also be wearout issues to consider.
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Post by randombloke on Aug 25, 2010 14:29:51 GMT -4
Hmm. Talking of separations and umbilicals; where were the umbilicals between the SM and CM exactly? Surely not in the re-entry shield?
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Bob B.
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Post by Bob B. on Aug 25, 2010 14:48:05 GMT -4
Hmm. Talking of separations and umbilicals; where were the umbilicals between the SM and CM exactly? Surely not in the re-entry shield? They came through the wall and were covered by a fairing. You can see the umbilical cover very clearly in the following photo (near bottom of photo spanning the CM-SM interface). NASA Image AS15-88-11963
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Post by echnaton on Aug 25, 2010 15:27:38 GMT -4
Hmm. Talking of separations and umbilicals; where were the umbilicals between the SM and CM exactly? Surely not in the re-entry shield? They came through the wall and were covered by a fairing. You can see the umbilical cover very clearly in the following photo (near bottom of photo spanning the CM-SM interface). Looking somewhat charred form the RCS thruster, I think.
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Post by randombloke on Aug 25, 2010 15:29:19 GMT -4
I see. I also see that someone managed to put them directly in the "line of fire" of one of the RCS thrusters...is that thermal discolouration on the fairing?
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