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Apollo CM engine.
My 1st and lasting impression of the CM engine bell is it was to big.
I do know about the bell size as it relates to use in a vacuum, my question is why the engine needed the thrust it had? Seems to me, in all maneuvers, the same impulse would occur with say 1/2 the thrust and 2x the thrust time. Which maneuver (engine firing) needed the supplied CM engine thrust? Ken |
#2
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Apollo CM engine.
In article , says...
My 1st and lasting impression of the CM engine bell is it was to big. I do know about the bell size as it relates to use in a vacuum, my question is why the engine needed the thrust it had? Seems to me, in all maneuvers, the same impulse would occur with say 1/2 the thrust and 2x the thrust time. Which maneuver (engine firing) needed the supplied CM engine thrust? LOI burn? LOI burn was the "big burn" which needed to be done by the SM. LOI burn for Apollo 12 was already nearly 6 minutes long. Doubling that to 12 minutes would have done what? It's been 20+ years since my orbital mechanics class, but my recollection is that, with all other variables being equal, a burn like this becomes *less* efficient (in terms of fuel burned) the longer the burn takes. Since this burn took "33,500 pounds of propellant or about 60 percent - 61 percent of the propellant carried", making the burn less efficient doesn't sound like a good idea. But I'll have to leave "the math" to someone who has a better handle on orbital mechanics and has the time to set this problem up in a proper simulator. I remember that in 1991, we wrote our own simulation programs in Fortran 77 using a math library to do the numerical integration. Gee, that was fun... :-P Here is my source: http://history.nasa.gov/ap12fj/10day4_loi.htm The quote below comes right after 081:52:16 Public Affairs Office - "This is Apollo Control at 81 hours, 53 minutes. The spacecraft now traveling at a speed of 4,726 feet per second and about 4,000 nautical miles from the lunar surface. We have the preliminary figures on the Lunar Orbit Insertion maneuver, the first of two maneuvers to place the spacecraft in a more or less circular orbit about the Moon. The ignition for LOI-1 ignition time will be 83 hours, 25 minutes, 19 seconds. A burn duration will be 5 minutes, 58 seconds, and we'll subtract about 2,880 feet per second from the spacecraft velocity with that maneuver. In performing that 5 minute, 58 second burn, the Service Propulsion System engine will consume about 33,500 pounds of propellant or about 60 percent - 61 percent of the propellant carried. The spacecraft currently weighs 96,076 pounds. We estimate after the Lunar Orbit Insertion maneuver, the weight will be about 62,491 pounds - the difference in weight, of course, being accounted for in the propellant consumed in the burn..." Jeff -- "the perennial claim that hypersonic airbreathing propulsion would magically make space launch cheaper is nonsense -- LOX is much cheaper than advanced airbreathing engines, and so are the tanks to put it in and the extra thrust to carry it." - Henry Spencer |
#3
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Apollo CM engine.
Ken S. Tucker wrote:
Which maneuver (engine firing) needed the supplied CM engine thrust? The one it was originally intended to fulfil - lifting off from the surface of the moon. When that requirement went away the higher thrust was still useful for various aborts during launch after tower jettison. Jim Davis |
#4
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Apollo CM engine.
On Mon, 8 Oct 2012 18:34:22 +0000 (UTC), Jim Davis
wrote: Ken S. Tucker wrote: Which maneuver (engine firing) needed the supplied CM engine thrust? The one it was originally intended to fulfil - lifting off from the surface of the moon. That is what I read too. It was overengineered by about a factor of 2 when the direct ascent method was the plan. |
#5
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Apollo CM engine.
Jeff Findley wrote:
In article , says... My 1st and lasting impression of the CM engine bell is it was to big. I do know about the bell size as it relates to use in a vacuum, my question is why the engine needed the thrust it had? Seems to me, in all maneuvers, the same impulse would occur with say 1/2 the thrust and 2x the thrust time. Which maneuver (engine firing) needed the supplied CM engine thrust? LOI burn? LOI burn was the "big burn" which needed to be done by the SM. LOI burn for Apollo 12 was already nearly 6 minutes long. Doubling that to 12 minutes would have done what? It's been 20+ years since my orbital mechanics class, but my recollection is that, with all other variables being equal, a burn like this becomes *less* efficient (in terms of fuel burned) the longer the burn takes. Since this burn took "33,500 pounds of propellant or about 60 percent - 61 percent of the propellant carried", making the burn less efficient doesn't sound like a good idea. But I'll have to leave "the math" to someone who has a better handle on orbital mechanics and has the time to set this problem up in a proper simulator. I remember that in 1991, we wrote our own simulation programs in Fortran 77 using a math library to do the numerical integration. Gee, that was fun... :-P Here is my source: http://history.nasa.gov/ap12fj/10day4_loi.htm The quote below comes right after 081:52:16 Public Affairs Office - "This is Apollo Control at 81 hours, 53 minutes. The spacecraft now traveling at a speed of 4,726 feet per second and about 4,000 nautical miles from the lunar surface. We have the preliminary figures on the Lunar Orbit Insertion maneuver, the first of two maneuvers to place the spacecraft in a more or less circular orbit about the Moon. The ignition for LOI-1 ignition time will be 83 hours, 25 minutes, 19 seconds. A burn duration will be 5 minutes, 58 seconds, and we'll subtract about 2,880 feet per second from the spacecraft velocity with that maneuver. In performing that 5 minute, 58 second burn, the Service Propulsion System engine will consume about 33,500 pounds of propellant or about 60 percent - 61 percent of the propellant carried. The spacecraft currently weighs 96,076 pounds. We estimate after the Lunar Orbit Insertion maneuver, the weight will be about 62,491 pounds - the difference in weight, of course, being accounted for in the propellant consumed in the burn..." Jeff Interesting Jeff, Wiki on the CSM agrees with Jim Davis, but I think you're also right, in that, the LOI would need a longer burning and a bit more propellant using a smaller engine that wouldn't make the hassle of changing motors worth it. Wonder if you're same argument is better justified by the A13 trans Earth burn with the LM attached. Thanks all. Ken |
#6
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Apollo SM engine [was Apollo CM engine.]
Note subject correction.
"Ken S. Tucker" writes: [...] Interesting Jeff, Wiki on the CSM agrees with Jim Davis, but I think you're also right, in that, the LOI would need a longer burning and a bit more propellant using a smaller engine that wouldn't make the hassle of changing motors worth it. Wonder if you're same argument is better justified by the A13 trans Earth burn with the LM attached. That burn was performed by the LM descent engine, since the SM engine (the entire SM actually) was not available. |
#8
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Apollo SM engine [was Apollo CM engine.]
Chris Jones wrote:
Note subject correction. "Ken S. Tucker" writes: [...] Interesting Jeff, Wiki on the CSM agrees with Jim Davis, but I think you're also right, in that, the LOI would need a longer burning and a bit more propellant using a smaller engine that wouldn't make the hassle of changing motors worth it. Wonder if you're same argument is better justified by the A13 trans Earth burn with the LM attached. That burn was performed by the LM descent engine, since the SM engine (the entire SM actually) was not available. Yes, the LM descent engine, thrust ~10K#, compared to the ~20K# the CSM had. Ken |
#9
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Apollo CM engine.
On Monday, October 8, 2012 1:34:27 PM UTC-5, Jim Davis wrote:
Ken S. Tucker wrote: Which maneuver (engine firing) needed the supplied CM engine thrust? The one it was originally intended to fulfil - lifting off from the surface of the moon. ....Correct. By the time LOR had won out, the SM part of the CSM stack had been pretty much locked into place. To have redesigned it as extensively as switching to, say, a set of smaller engines would have required significantly more $$$ than NASA could afford even with the "Go Fever" funding at the time. ....One thing I can't recall seeing any posts on over the years is whether or not anyone's taken a good draftsman's look at the final design of the SM to see if any hardpoints for mounting the landing gear. With regards as to whether they retained once DA and EOR were dropped, and/or where they were situated and intended to be mounted on the SM. Another little space history mystery that needs to be resolved one day. [thinks] ....Hmm. "Space History Mysteries". Wonder if I can sell that to the Inbred...er, I mean Hitler...oh, no wait, that's the *History* Channel, right? OM |
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