Was it really necessary for the Lunar Module to have 2 stages?Did the Apollo lunar module descent stage have a role as a sort of service module?How was reserve fuel calculated for the Apollo missions?Could the Apollo LM abort mode be engaged after touchdown? What would have happened if it was?Is true that Armstrong was not designated as first to walk on the moon?Where is the first Lunar soil sample currently located?Could a single crew member fly the Apollo LM?How might the Lunar X Prize contestant spacecraft have navigated their descent from orbit, to landing?Could the Apollo LM abort mode be engaged after touchdown? What would have happened if it was?Did the combined Command and Service Module and Lunar Module perform another 180° turn after transposition, docking and extraction?How did the Lunar Module dock with the rest of Apollo 11 and what is the “CSM”?Was there a technical reason why Apollo 10 didn't land on the moon?How long is the Apollo Lunar Module extraction window?Was there fuel consumption budgeting for Apollo 11 Lunar module?

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Was it really necessary for the Lunar Module to have 2 stages?


Did the Apollo lunar module descent stage have a role as a sort of service module?How was reserve fuel calculated for the Apollo missions?Could the Apollo LM abort mode be engaged after touchdown? What would have happened if it was?Is true that Armstrong was not designated as first to walk on the moon?Where is the first Lunar soil sample currently located?Could a single crew member fly the Apollo LM?How might the Lunar X Prize contestant spacecraft have navigated their descent from orbit, to landing?Could the Apollo LM abort mode be engaged after touchdown? What would have happened if it was?Did the combined Command and Service Module and Lunar Module perform another 180° turn after transposition, docking and extraction?How did the Lunar Module dock with the rest of Apollo 11 and what is the “CSM”?Was there a technical reason why Apollo 10 didn't land on the moon?How long is the Apollo Lunar Module extraction window?Was there fuel consumption budgeting for Apollo 11 Lunar module?













4












$begingroup$


We all know the 2 stages LM design used by Grumman was intended to discard the mass of the landing gear (+ other components) at the moment of launching off the Moon surface to reach back the Service module. But was it really necessarily for the LM to have two stages? The reason I wonder is that, when Armstrong landed, there was fuel left for about 25 seconds - however, this was actually 25 s before aborting the landing, not before running out of fuel. After these 25 seconds of burning fuel, the complete LM still had enough fuel to ascend with both of its stages right back to the Service module. In other words, the LM was designed to be able to take off from the Moon surface with BOTH stages, even right after touching the surface, in case something would have gone wrong. Then, why did it use two stages? It surely added complexity, weight and a second engine.










share|improve this question









New contributor




Mathias is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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$endgroup$







  • 2




    $begingroup$
    Do you have a reference for the ascent stage having enough fuel to return to orbit? Every source I have seen talks about the criticality of the ascent stage working because there were no other options. including sub optimal performance choices for better reliability and design of this en.wikipedia.org/wiki/Lunar_escape_systems. AFAIK the abort at 25 seconds involved firing the separation bolts and dumping the descent stage.
    $endgroup$
    – GremlinWranger
    13 hours ago






  • 1




    $begingroup$
    related ahttps://space.stackexchange.com/questions/2493/how-was-reserve-fuel-calculated-for-the-apollo-missions/30208#30208. Looks like descent module was designed to land with about 1.8% of the fuel it started out with.
    $endgroup$
    – GremlinWranger
    13 hours ago










  • $begingroup$
    There are a few documentaries on Youtube that include interviews with astronauts and engineers. It is mentioned that the remaining fuel was simply a measure of the safe point where the mission would have been aborted if the surface wasn't touched at that point. So aborting the landing would have meant going back to the service module with the LM in its complete configuration. An example, in the middle of this page it is mentioned the fact that the remaining fuel was the limit for abort landing moment space.com/26593-apollo-11-moon-landing-scariest-moments.html (a great page btw)
    $endgroup$
    – Mathias
    13 hours ago










  • $begingroup$
    See this previous question for clarity about LEM abort modes. space.stackexchange.com/questions/21686 There’s more than one, but none of them get back to orbit on descent stage engine only
    $endgroup$
    – Bob Jacobsen
    12 hours ago






  • 3




    $begingroup$
    "So aborting the landing would have meant going back to the service module with the LM in its complete configuration." -- why do you think that?
    $endgroup$
    – Russell Borogove
    12 hours ago















4












$begingroup$


We all know the 2 stages LM design used by Grumman was intended to discard the mass of the landing gear (+ other components) at the moment of launching off the Moon surface to reach back the Service module. But was it really necessarily for the LM to have two stages? The reason I wonder is that, when Armstrong landed, there was fuel left for about 25 seconds - however, this was actually 25 s before aborting the landing, not before running out of fuel. After these 25 seconds of burning fuel, the complete LM still had enough fuel to ascend with both of its stages right back to the Service module. In other words, the LM was designed to be able to take off from the Moon surface with BOTH stages, even right after touching the surface, in case something would have gone wrong. Then, why did it use two stages? It surely added complexity, weight and a second engine.










share|improve this question









New contributor




Mathias is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$







  • 2




    $begingroup$
    Do you have a reference for the ascent stage having enough fuel to return to orbit? Every source I have seen talks about the criticality of the ascent stage working because there were no other options. including sub optimal performance choices for better reliability and design of this en.wikipedia.org/wiki/Lunar_escape_systems. AFAIK the abort at 25 seconds involved firing the separation bolts and dumping the descent stage.
    $endgroup$
    – GremlinWranger
    13 hours ago






  • 1




    $begingroup$
    related ahttps://space.stackexchange.com/questions/2493/how-was-reserve-fuel-calculated-for-the-apollo-missions/30208#30208. Looks like descent module was designed to land with about 1.8% of the fuel it started out with.
    $endgroup$
    – GremlinWranger
    13 hours ago










  • $begingroup$
    There are a few documentaries on Youtube that include interviews with astronauts and engineers. It is mentioned that the remaining fuel was simply a measure of the safe point where the mission would have been aborted if the surface wasn't touched at that point. So aborting the landing would have meant going back to the service module with the LM in its complete configuration. An example, in the middle of this page it is mentioned the fact that the remaining fuel was the limit for abort landing moment space.com/26593-apollo-11-moon-landing-scariest-moments.html (a great page btw)
    $endgroup$
    – Mathias
    13 hours ago










  • $begingroup$
    See this previous question for clarity about LEM abort modes. space.stackexchange.com/questions/21686 There’s more than one, but none of them get back to orbit on descent stage engine only
    $endgroup$
    – Bob Jacobsen
    12 hours ago






  • 3




    $begingroup$
    "So aborting the landing would have meant going back to the service module with the LM in its complete configuration." -- why do you think that?
    $endgroup$
    – Russell Borogove
    12 hours ago













4












4








4





$begingroup$


We all know the 2 stages LM design used by Grumman was intended to discard the mass of the landing gear (+ other components) at the moment of launching off the Moon surface to reach back the Service module. But was it really necessarily for the LM to have two stages? The reason I wonder is that, when Armstrong landed, there was fuel left for about 25 seconds - however, this was actually 25 s before aborting the landing, not before running out of fuel. After these 25 seconds of burning fuel, the complete LM still had enough fuel to ascend with both of its stages right back to the Service module. In other words, the LM was designed to be able to take off from the Moon surface with BOTH stages, even right after touching the surface, in case something would have gone wrong. Then, why did it use two stages? It surely added complexity, weight and a second engine.










share|improve this question









New contributor




Mathias is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







$endgroup$




We all know the 2 stages LM design used by Grumman was intended to discard the mass of the landing gear (+ other components) at the moment of launching off the Moon surface to reach back the Service module. But was it really necessarily for the LM to have two stages? The reason I wonder is that, when Armstrong landed, there was fuel left for about 25 seconds - however, this was actually 25 s before aborting the landing, not before running out of fuel. After these 25 seconds of burning fuel, the complete LM still had enough fuel to ascend with both of its stages right back to the Service module. In other words, the LM was designed to be able to take off from the Moon surface with BOTH stages, even right after touching the surface, in case something would have gone wrong. Then, why did it use two stages? It surely added complexity, weight and a second engine.







apollo-program lunar-landing lunar-module






share|improve this question









New contributor




Mathias is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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share|improve this question









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Mathias is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
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share|improve this question




share|improve this question








edited 9 mins ago









Dr Sheldon

4,93011650




4,93011650






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asked 13 hours ago









MathiasMathias

211




211




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New contributor





Mathias is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






Mathias is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







  • 2




    $begingroup$
    Do you have a reference for the ascent stage having enough fuel to return to orbit? Every source I have seen talks about the criticality of the ascent stage working because there were no other options. including sub optimal performance choices for better reliability and design of this en.wikipedia.org/wiki/Lunar_escape_systems. AFAIK the abort at 25 seconds involved firing the separation bolts and dumping the descent stage.
    $endgroup$
    – GremlinWranger
    13 hours ago






  • 1




    $begingroup$
    related ahttps://space.stackexchange.com/questions/2493/how-was-reserve-fuel-calculated-for-the-apollo-missions/30208#30208. Looks like descent module was designed to land with about 1.8% of the fuel it started out with.
    $endgroup$
    – GremlinWranger
    13 hours ago










  • $begingroup$
    There are a few documentaries on Youtube that include interviews with astronauts and engineers. It is mentioned that the remaining fuel was simply a measure of the safe point where the mission would have been aborted if the surface wasn't touched at that point. So aborting the landing would have meant going back to the service module with the LM in its complete configuration. An example, in the middle of this page it is mentioned the fact that the remaining fuel was the limit for abort landing moment space.com/26593-apollo-11-moon-landing-scariest-moments.html (a great page btw)
    $endgroup$
    – Mathias
    13 hours ago










  • $begingroup$
    See this previous question for clarity about LEM abort modes. space.stackexchange.com/questions/21686 There’s more than one, but none of them get back to orbit on descent stage engine only
    $endgroup$
    – Bob Jacobsen
    12 hours ago






  • 3




    $begingroup$
    "So aborting the landing would have meant going back to the service module with the LM in its complete configuration." -- why do you think that?
    $endgroup$
    – Russell Borogove
    12 hours ago












  • 2




    $begingroup$
    Do you have a reference for the ascent stage having enough fuel to return to orbit? Every source I have seen talks about the criticality of the ascent stage working because there were no other options. including sub optimal performance choices for better reliability and design of this en.wikipedia.org/wiki/Lunar_escape_systems. AFAIK the abort at 25 seconds involved firing the separation bolts and dumping the descent stage.
    $endgroup$
    – GremlinWranger
    13 hours ago






  • 1




    $begingroup$
    related ahttps://space.stackexchange.com/questions/2493/how-was-reserve-fuel-calculated-for-the-apollo-missions/30208#30208. Looks like descent module was designed to land with about 1.8% of the fuel it started out with.
    $endgroup$
    – GremlinWranger
    13 hours ago










  • $begingroup$
    There are a few documentaries on Youtube that include interviews with astronauts and engineers. It is mentioned that the remaining fuel was simply a measure of the safe point where the mission would have been aborted if the surface wasn't touched at that point. So aborting the landing would have meant going back to the service module with the LM in its complete configuration. An example, in the middle of this page it is mentioned the fact that the remaining fuel was the limit for abort landing moment space.com/26593-apollo-11-moon-landing-scariest-moments.html (a great page btw)
    $endgroup$
    – Mathias
    13 hours ago










  • $begingroup$
    See this previous question for clarity about LEM abort modes. space.stackexchange.com/questions/21686 There’s more than one, but none of them get back to orbit on descent stage engine only
    $endgroup$
    – Bob Jacobsen
    12 hours ago






  • 3




    $begingroup$
    "So aborting the landing would have meant going back to the service module with the LM in its complete configuration." -- why do you think that?
    $endgroup$
    – Russell Borogove
    12 hours ago







2




2




$begingroup$
Do you have a reference for the ascent stage having enough fuel to return to orbit? Every source I have seen talks about the criticality of the ascent stage working because there were no other options. including sub optimal performance choices for better reliability and design of this en.wikipedia.org/wiki/Lunar_escape_systems. AFAIK the abort at 25 seconds involved firing the separation bolts and dumping the descent stage.
$endgroup$
– GremlinWranger
13 hours ago




$begingroup$
Do you have a reference for the ascent stage having enough fuel to return to orbit? Every source I have seen talks about the criticality of the ascent stage working because there were no other options. including sub optimal performance choices for better reliability and design of this en.wikipedia.org/wiki/Lunar_escape_systems. AFAIK the abort at 25 seconds involved firing the separation bolts and dumping the descent stage.
$endgroup$
– GremlinWranger
13 hours ago




1




1




$begingroup$
related ahttps://space.stackexchange.com/questions/2493/how-was-reserve-fuel-calculated-for-the-apollo-missions/30208#30208. Looks like descent module was designed to land with about 1.8% of the fuel it started out with.
$endgroup$
– GremlinWranger
13 hours ago




$begingroup$
related ahttps://space.stackexchange.com/questions/2493/how-was-reserve-fuel-calculated-for-the-apollo-missions/30208#30208. Looks like descent module was designed to land with about 1.8% of the fuel it started out with.
$endgroup$
– GremlinWranger
13 hours ago












$begingroup$
There are a few documentaries on Youtube that include interviews with astronauts and engineers. It is mentioned that the remaining fuel was simply a measure of the safe point where the mission would have been aborted if the surface wasn't touched at that point. So aborting the landing would have meant going back to the service module with the LM in its complete configuration. An example, in the middle of this page it is mentioned the fact that the remaining fuel was the limit for abort landing moment space.com/26593-apollo-11-moon-landing-scariest-moments.html (a great page btw)
$endgroup$
– Mathias
13 hours ago




$begingroup$
There are a few documentaries on Youtube that include interviews with astronauts and engineers. It is mentioned that the remaining fuel was simply a measure of the safe point where the mission would have been aborted if the surface wasn't touched at that point. So aborting the landing would have meant going back to the service module with the LM in its complete configuration. An example, in the middle of this page it is mentioned the fact that the remaining fuel was the limit for abort landing moment space.com/26593-apollo-11-moon-landing-scariest-moments.html (a great page btw)
$endgroup$
– Mathias
13 hours ago












$begingroup$
See this previous question for clarity about LEM abort modes. space.stackexchange.com/questions/21686 There’s more than one, but none of them get back to orbit on descent stage engine only
$endgroup$
– Bob Jacobsen
12 hours ago




$begingroup$
See this previous question for clarity about LEM abort modes. space.stackexchange.com/questions/21686 There’s more than one, but none of them get back to orbit on descent stage engine only
$endgroup$
– Bob Jacobsen
12 hours ago




3




3




$begingroup$
"So aborting the landing would have meant going back to the service module with the LM in its complete configuration." -- why do you think that?
$endgroup$
– Russell Borogove
12 hours ago




$begingroup$
"So aborting the landing would have meant going back to the service module with the LM in its complete configuration." -- why do you think that?
$endgroup$
– Russell Borogove
12 hours ago










2 Answers
2






active

oldest

votes


















15












$begingroup$


After these 25 second would have ended, the LM still had enough fuel to ascend with both of its stages right back to the Service module. In other words, the LM was designed to be able to take off from the Moon surface with BOTH stages, even right after touching the surface, in case something would have gone wrong. Then, why using two stages which surely added complexity, weight and a second engine?




Your assumption is not correct. Aborting from the "bingo" (low fuel) call would have required the ascent stage to be used. The stages can be separated, and the ascent engine fired, while in flight; this was demonstrated on Apollo 9 and Apollo 10.



Because there would be a brief delay between staging and the ascent stage coming up to full thrust, the safest way to abort in this case would be to take the descent stage to full thrust to gain altitude and vertical speed, then stage and activate the ascent stage engine once the descent stage fuel was exhausted.



The ascent from lunar surface to rendezvous orbit took about 7 minutes on the ascent stage; there was nowhere near enough fuel in the descent stage to do that.






share|improve this answer











$endgroup$












  • $begingroup$
    Thanks, I've now read a little about the Abort Stage sequence which describes this procedure, with the descent stage being jettisoned near the Moon surface, then ascent stage would ignite while in flight (surely very challenging) and ascent back. Very interesting. The Apollo 10 did just that - only from much high above Moon's surface. Also interesting there was a 'dead man's zone' at low altitude where this procedure would have not been possible - so there were only land or crash alternatives at such altitude. Very interesting, if someone has links with this procedure please share.
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    In comparison, it seems the Russian lunar module, the LK, used a single engine/fuel tanks configuration for descent and ascent, while still leaving on the Moon surface the landing gear assembly. Basically, it was a single stage module design. Perhaps a simpler design, compared with the LM who had dual engines/tanks and systems, one for each of the two stages. en.wikipedia.org/wiki/LK_(spacecraft)
    $endgroup$
    – Mathias
    5 hours ago











  • $begingroup$
    @Mathias: The LK design requires the ascent to carry all the batteries, oxygen and water tanks, propellant tankage needed only for descent, etc. This is OK for short lunar stays, but it wouldn't scale well to the 3-day stays of the later Apollo flights. Being able to leave behind equipment needed to support the surface stay was a huge advantage for the two-stage LM. (Note that LK did have two engines -- one was a pure redundant backup.)
    $endgroup$
    – Russell Borogove
    1 hour ago


















6












$begingroup$

Early conceptual designs suggested that two stages would save weight. Another issue came up that made a single-stage lander unreliable.



Pressurizing the fuel and oxidizer tanks of the lunar module was a considerable engineering challenge. Because of the temperature changes that happen during launch and Earth orbit, the tanks were kept unpressurized until right before they were needed. At that time, the astronauts would fire some explosive valves (i.e. you can open them but never close them again) which would release a small amount of supercritical helium to pressurize the tanks.



Development and testing of the LM pressurization system took 6 years and had a lot of problems. The fuel froze, so they added a heat exchanger. A test article exploded, so they had to change the alloy used in the heat exchanger. The pressure regulator cracked. You were supposed to be able to raise or lower the thrust of the descent engine; the pressurization system wasn't compatible with that, so there was another re-design. Another heat exchanger was added. The descent engine shut down prematurely on Apollo 5. It was under-pressured on Apollo 9. When Apollo 11 dumped their excess descent fuel, the fuel lines froze and over-pressurized.



Suffice to say, once you've popped the valves on the LM pressurization system, you have a few hours to use the engine before it becomes unreliable. This was enough time to land on the moon, but not reliable enough to last several days on the moon. A one-stage craft is just too risky. Instead, the ascent stage had its own fuel and pressurization system. (Apollo 13 took the risk of reusing the descent engine, and was lucky.)



The Soviets designed a manned lunar lander, the LK. To save weight, it would have had a single engine for descent and ascent. However, it still would have left some parts behind on the moon.



Soviet LK






share|improve this answer









$endgroup$








  • 1




    $begingroup$
    These are many interesting technical details. We don't have much information on the LM design and testing challenges, but I'm sure there was some unprecedented engineering efforts put into this space ship. On the risk factor, you are suggesting that one of the reasons for a two stages LM was reducing the risk of failure (increasing reliability). From an engineering point of view, I feel that adding complementary instead of redundancy systems, actually increases the odds of system and consequently mission failure. Of course, only my suppositions.
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    Also worth adding that the Russian lunar module (acronym-ed NK) was initially designed to carry only one astronaut, at 1/3 the LM total weight. Several NK were built, there are 5 still existing. There are several very interesting design/concept differences between the NK and the LM, on the Wiki page at the bottom en.wikipedia.org/wiki/LK_(spacecraft)
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    Didn't one of the early LM flights have problems with high supercritical helium pressure before launch? I thought that was Apollo 9, but Wikipedia doesn't seem to mention that at all. It does mention a similar issue on Apollo 13, though, but I'm pretty sure that's not what I have in mind.
    $endgroup$
    – a CVn
    6 hours ago










  • $begingroup$
    @aCVn Apollo 11 had a problem with helium pressure immediately after landing on the moon, perhaps that is what you are remembering? hq.nasa.gov/alsj/a11/a11iceclog.html
    $endgroup$
    – Organic Marble
    2 hours ago










  • $begingroup$
    Note that LK actually had two engines; one was a pure redundant backup, which would not be used at all in a nominal flight.
    $endgroup$
    – Russell Borogove
    1 hour ago











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2 Answers
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2 Answers
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active

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active

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15












$begingroup$


After these 25 second would have ended, the LM still had enough fuel to ascend with both of its stages right back to the Service module. In other words, the LM was designed to be able to take off from the Moon surface with BOTH stages, even right after touching the surface, in case something would have gone wrong. Then, why using two stages which surely added complexity, weight and a second engine?




Your assumption is not correct. Aborting from the "bingo" (low fuel) call would have required the ascent stage to be used. The stages can be separated, and the ascent engine fired, while in flight; this was demonstrated on Apollo 9 and Apollo 10.



Because there would be a brief delay between staging and the ascent stage coming up to full thrust, the safest way to abort in this case would be to take the descent stage to full thrust to gain altitude and vertical speed, then stage and activate the ascent stage engine once the descent stage fuel was exhausted.



The ascent from lunar surface to rendezvous orbit took about 7 minutes on the ascent stage; there was nowhere near enough fuel in the descent stage to do that.






share|improve this answer











$endgroup$












  • $begingroup$
    Thanks, I've now read a little about the Abort Stage sequence which describes this procedure, with the descent stage being jettisoned near the Moon surface, then ascent stage would ignite while in flight (surely very challenging) and ascent back. Very interesting. The Apollo 10 did just that - only from much high above Moon's surface. Also interesting there was a 'dead man's zone' at low altitude where this procedure would have not been possible - so there were only land or crash alternatives at such altitude. Very interesting, if someone has links with this procedure please share.
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    In comparison, it seems the Russian lunar module, the LK, used a single engine/fuel tanks configuration for descent and ascent, while still leaving on the Moon surface the landing gear assembly. Basically, it was a single stage module design. Perhaps a simpler design, compared with the LM who had dual engines/tanks and systems, one for each of the two stages. en.wikipedia.org/wiki/LK_(spacecraft)
    $endgroup$
    – Mathias
    5 hours ago











  • $begingroup$
    @Mathias: The LK design requires the ascent to carry all the batteries, oxygen and water tanks, propellant tankage needed only for descent, etc. This is OK for short lunar stays, but it wouldn't scale well to the 3-day stays of the later Apollo flights. Being able to leave behind equipment needed to support the surface stay was a huge advantage for the two-stage LM. (Note that LK did have two engines -- one was a pure redundant backup.)
    $endgroup$
    – Russell Borogove
    1 hour ago















15












$begingroup$


After these 25 second would have ended, the LM still had enough fuel to ascend with both of its stages right back to the Service module. In other words, the LM was designed to be able to take off from the Moon surface with BOTH stages, even right after touching the surface, in case something would have gone wrong. Then, why using two stages which surely added complexity, weight and a second engine?




Your assumption is not correct. Aborting from the "bingo" (low fuel) call would have required the ascent stage to be used. The stages can be separated, and the ascent engine fired, while in flight; this was demonstrated on Apollo 9 and Apollo 10.



Because there would be a brief delay between staging and the ascent stage coming up to full thrust, the safest way to abort in this case would be to take the descent stage to full thrust to gain altitude and vertical speed, then stage and activate the ascent stage engine once the descent stage fuel was exhausted.



The ascent from lunar surface to rendezvous orbit took about 7 minutes on the ascent stage; there was nowhere near enough fuel in the descent stage to do that.






share|improve this answer











$endgroup$












  • $begingroup$
    Thanks, I've now read a little about the Abort Stage sequence which describes this procedure, with the descent stage being jettisoned near the Moon surface, then ascent stage would ignite while in flight (surely very challenging) and ascent back. Very interesting. The Apollo 10 did just that - only from much high above Moon's surface. Also interesting there was a 'dead man's zone' at low altitude where this procedure would have not been possible - so there were only land or crash alternatives at such altitude. Very interesting, if someone has links with this procedure please share.
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    In comparison, it seems the Russian lunar module, the LK, used a single engine/fuel tanks configuration for descent and ascent, while still leaving on the Moon surface the landing gear assembly. Basically, it was a single stage module design. Perhaps a simpler design, compared with the LM who had dual engines/tanks and systems, one for each of the two stages. en.wikipedia.org/wiki/LK_(spacecraft)
    $endgroup$
    – Mathias
    5 hours ago











  • $begingroup$
    @Mathias: The LK design requires the ascent to carry all the batteries, oxygen and water tanks, propellant tankage needed only for descent, etc. This is OK for short lunar stays, but it wouldn't scale well to the 3-day stays of the later Apollo flights. Being able to leave behind equipment needed to support the surface stay was a huge advantage for the two-stage LM. (Note that LK did have two engines -- one was a pure redundant backup.)
    $endgroup$
    – Russell Borogove
    1 hour ago













15












15








15





$begingroup$


After these 25 second would have ended, the LM still had enough fuel to ascend with both of its stages right back to the Service module. In other words, the LM was designed to be able to take off from the Moon surface with BOTH stages, even right after touching the surface, in case something would have gone wrong. Then, why using two stages which surely added complexity, weight and a second engine?




Your assumption is not correct. Aborting from the "bingo" (low fuel) call would have required the ascent stage to be used. The stages can be separated, and the ascent engine fired, while in flight; this was demonstrated on Apollo 9 and Apollo 10.



Because there would be a brief delay between staging and the ascent stage coming up to full thrust, the safest way to abort in this case would be to take the descent stage to full thrust to gain altitude and vertical speed, then stage and activate the ascent stage engine once the descent stage fuel was exhausted.



The ascent from lunar surface to rendezvous orbit took about 7 minutes on the ascent stage; there was nowhere near enough fuel in the descent stage to do that.






share|improve this answer











$endgroup$




After these 25 second would have ended, the LM still had enough fuel to ascend with both of its stages right back to the Service module. In other words, the LM was designed to be able to take off from the Moon surface with BOTH stages, even right after touching the surface, in case something would have gone wrong. Then, why using two stages which surely added complexity, weight and a second engine?




Your assumption is not correct. Aborting from the "bingo" (low fuel) call would have required the ascent stage to be used. The stages can be separated, and the ascent engine fired, while in flight; this was demonstrated on Apollo 9 and Apollo 10.



Because there would be a brief delay between staging and the ascent stage coming up to full thrust, the safest way to abort in this case would be to take the descent stage to full thrust to gain altitude and vertical speed, then stage and activate the ascent stage engine once the descent stage fuel was exhausted.



The ascent from lunar surface to rendezvous orbit took about 7 minutes on the ascent stage; there was nowhere near enough fuel in the descent stage to do that.







share|improve this answer














share|improve this answer



share|improve this answer








edited 11 hours ago

























answered 12 hours ago









Russell BorogoveRussell Borogove

90.6k3302388




90.6k3302388











  • $begingroup$
    Thanks, I've now read a little about the Abort Stage sequence which describes this procedure, with the descent stage being jettisoned near the Moon surface, then ascent stage would ignite while in flight (surely very challenging) and ascent back. Very interesting. The Apollo 10 did just that - only from much high above Moon's surface. Also interesting there was a 'dead man's zone' at low altitude where this procedure would have not been possible - so there were only land or crash alternatives at such altitude. Very interesting, if someone has links with this procedure please share.
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    In comparison, it seems the Russian lunar module, the LK, used a single engine/fuel tanks configuration for descent and ascent, while still leaving on the Moon surface the landing gear assembly. Basically, it was a single stage module design. Perhaps a simpler design, compared with the LM who had dual engines/tanks and systems, one for each of the two stages. en.wikipedia.org/wiki/LK_(spacecraft)
    $endgroup$
    – Mathias
    5 hours ago











  • $begingroup$
    @Mathias: The LK design requires the ascent to carry all the batteries, oxygen and water tanks, propellant tankage needed only for descent, etc. This is OK for short lunar stays, but it wouldn't scale well to the 3-day stays of the later Apollo flights. Being able to leave behind equipment needed to support the surface stay was a huge advantage for the two-stage LM. (Note that LK did have two engines -- one was a pure redundant backup.)
    $endgroup$
    – Russell Borogove
    1 hour ago
















  • $begingroup$
    Thanks, I've now read a little about the Abort Stage sequence which describes this procedure, with the descent stage being jettisoned near the Moon surface, then ascent stage would ignite while in flight (surely very challenging) and ascent back. Very interesting. The Apollo 10 did just that - only from much high above Moon's surface. Also interesting there was a 'dead man's zone' at low altitude where this procedure would have not been possible - so there were only land or crash alternatives at such altitude. Very interesting, if someone has links with this procedure please share.
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    In comparison, it seems the Russian lunar module, the LK, used a single engine/fuel tanks configuration for descent and ascent, while still leaving on the Moon surface the landing gear assembly. Basically, it was a single stage module design. Perhaps a simpler design, compared with the LM who had dual engines/tanks and systems, one for each of the two stages. en.wikipedia.org/wiki/LK_(spacecraft)
    $endgroup$
    – Mathias
    5 hours ago











  • $begingroup$
    @Mathias: The LK design requires the ascent to carry all the batteries, oxygen and water tanks, propellant tankage needed only for descent, etc. This is OK for short lunar stays, but it wouldn't scale well to the 3-day stays of the later Apollo flights. Being able to leave behind equipment needed to support the surface stay was a huge advantage for the two-stage LM. (Note that LK did have two engines -- one was a pure redundant backup.)
    $endgroup$
    – Russell Borogove
    1 hour ago















$begingroup$
Thanks, I've now read a little about the Abort Stage sequence which describes this procedure, with the descent stage being jettisoned near the Moon surface, then ascent stage would ignite while in flight (surely very challenging) and ascent back. Very interesting. The Apollo 10 did just that - only from much high above Moon's surface. Also interesting there was a 'dead man's zone' at low altitude where this procedure would have not been possible - so there were only land or crash alternatives at such altitude. Very interesting, if someone has links with this procedure please share.
$endgroup$
– Mathias
6 hours ago




$begingroup$
Thanks, I've now read a little about the Abort Stage sequence which describes this procedure, with the descent stage being jettisoned near the Moon surface, then ascent stage would ignite while in flight (surely very challenging) and ascent back. Very interesting. The Apollo 10 did just that - only from much high above Moon's surface. Also interesting there was a 'dead man's zone' at low altitude where this procedure would have not been possible - so there were only land or crash alternatives at such altitude. Very interesting, if someone has links with this procedure please share.
$endgroup$
– Mathias
6 hours ago












$begingroup$
In comparison, it seems the Russian lunar module, the LK, used a single engine/fuel tanks configuration for descent and ascent, while still leaving on the Moon surface the landing gear assembly. Basically, it was a single stage module design. Perhaps a simpler design, compared with the LM who had dual engines/tanks and systems, one for each of the two stages. en.wikipedia.org/wiki/LK_(spacecraft)
$endgroup$
– Mathias
5 hours ago





$begingroup$
In comparison, it seems the Russian lunar module, the LK, used a single engine/fuel tanks configuration for descent and ascent, while still leaving on the Moon surface the landing gear assembly. Basically, it was a single stage module design. Perhaps a simpler design, compared with the LM who had dual engines/tanks and systems, one for each of the two stages. en.wikipedia.org/wiki/LK_(spacecraft)
$endgroup$
– Mathias
5 hours ago













$begingroup$
@Mathias: The LK design requires the ascent to carry all the batteries, oxygen and water tanks, propellant tankage needed only for descent, etc. This is OK for short lunar stays, but it wouldn't scale well to the 3-day stays of the later Apollo flights. Being able to leave behind equipment needed to support the surface stay was a huge advantage for the two-stage LM. (Note that LK did have two engines -- one was a pure redundant backup.)
$endgroup$
– Russell Borogove
1 hour ago




$begingroup$
@Mathias: The LK design requires the ascent to carry all the batteries, oxygen and water tanks, propellant tankage needed only for descent, etc. This is OK for short lunar stays, but it wouldn't scale well to the 3-day stays of the later Apollo flights. Being able to leave behind equipment needed to support the surface stay was a huge advantage for the two-stage LM. (Note that LK did have two engines -- one was a pure redundant backup.)
$endgroup$
– Russell Borogove
1 hour ago











6












$begingroup$

Early conceptual designs suggested that two stages would save weight. Another issue came up that made a single-stage lander unreliable.



Pressurizing the fuel and oxidizer tanks of the lunar module was a considerable engineering challenge. Because of the temperature changes that happen during launch and Earth orbit, the tanks were kept unpressurized until right before they were needed. At that time, the astronauts would fire some explosive valves (i.e. you can open them but never close them again) which would release a small amount of supercritical helium to pressurize the tanks.



Development and testing of the LM pressurization system took 6 years and had a lot of problems. The fuel froze, so they added a heat exchanger. A test article exploded, so they had to change the alloy used in the heat exchanger. The pressure regulator cracked. You were supposed to be able to raise or lower the thrust of the descent engine; the pressurization system wasn't compatible with that, so there was another re-design. Another heat exchanger was added. The descent engine shut down prematurely on Apollo 5. It was under-pressured on Apollo 9. When Apollo 11 dumped their excess descent fuel, the fuel lines froze and over-pressurized.



Suffice to say, once you've popped the valves on the LM pressurization system, you have a few hours to use the engine before it becomes unreliable. This was enough time to land on the moon, but not reliable enough to last several days on the moon. A one-stage craft is just too risky. Instead, the ascent stage had its own fuel and pressurization system. (Apollo 13 took the risk of reusing the descent engine, and was lucky.)



The Soviets designed a manned lunar lander, the LK. To save weight, it would have had a single engine for descent and ascent. However, it still would have left some parts behind on the moon.



Soviet LK






share|improve this answer









$endgroup$








  • 1




    $begingroup$
    These are many interesting technical details. We don't have much information on the LM design and testing challenges, but I'm sure there was some unprecedented engineering efforts put into this space ship. On the risk factor, you are suggesting that one of the reasons for a two stages LM was reducing the risk of failure (increasing reliability). From an engineering point of view, I feel that adding complementary instead of redundancy systems, actually increases the odds of system and consequently mission failure. Of course, only my suppositions.
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    Also worth adding that the Russian lunar module (acronym-ed NK) was initially designed to carry only one astronaut, at 1/3 the LM total weight. Several NK were built, there are 5 still existing. There are several very interesting design/concept differences between the NK and the LM, on the Wiki page at the bottom en.wikipedia.org/wiki/LK_(spacecraft)
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    Didn't one of the early LM flights have problems with high supercritical helium pressure before launch? I thought that was Apollo 9, but Wikipedia doesn't seem to mention that at all. It does mention a similar issue on Apollo 13, though, but I'm pretty sure that's not what I have in mind.
    $endgroup$
    – a CVn
    6 hours ago










  • $begingroup$
    @aCVn Apollo 11 had a problem with helium pressure immediately after landing on the moon, perhaps that is what you are remembering? hq.nasa.gov/alsj/a11/a11iceclog.html
    $endgroup$
    – Organic Marble
    2 hours ago










  • $begingroup$
    Note that LK actually had two engines; one was a pure redundant backup, which would not be used at all in a nominal flight.
    $endgroup$
    – Russell Borogove
    1 hour ago















6












$begingroup$

Early conceptual designs suggested that two stages would save weight. Another issue came up that made a single-stage lander unreliable.



Pressurizing the fuel and oxidizer tanks of the lunar module was a considerable engineering challenge. Because of the temperature changes that happen during launch and Earth orbit, the tanks were kept unpressurized until right before they were needed. At that time, the astronauts would fire some explosive valves (i.e. you can open them but never close them again) which would release a small amount of supercritical helium to pressurize the tanks.



Development and testing of the LM pressurization system took 6 years and had a lot of problems. The fuel froze, so they added a heat exchanger. A test article exploded, so they had to change the alloy used in the heat exchanger. The pressure regulator cracked. You were supposed to be able to raise or lower the thrust of the descent engine; the pressurization system wasn't compatible with that, so there was another re-design. Another heat exchanger was added. The descent engine shut down prematurely on Apollo 5. It was under-pressured on Apollo 9. When Apollo 11 dumped their excess descent fuel, the fuel lines froze and over-pressurized.



Suffice to say, once you've popped the valves on the LM pressurization system, you have a few hours to use the engine before it becomes unreliable. This was enough time to land on the moon, but not reliable enough to last several days on the moon. A one-stage craft is just too risky. Instead, the ascent stage had its own fuel and pressurization system. (Apollo 13 took the risk of reusing the descent engine, and was lucky.)



The Soviets designed a manned lunar lander, the LK. To save weight, it would have had a single engine for descent and ascent. However, it still would have left some parts behind on the moon.



Soviet LK






share|improve this answer









$endgroup$








  • 1




    $begingroup$
    These are many interesting technical details. We don't have much information on the LM design and testing challenges, but I'm sure there was some unprecedented engineering efforts put into this space ship. On the risk factor, you are suggesting that one of the reasons for a two stages LM was reducing the risk of failure (increasing reliability). From an engineering point of view, I feel that adding complementary instead of redundancy systems, actually increases the odds of system and consequently mission failure. Of course, only my suppositions.
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    Also worth adding that the Russian lunar module (acronym-ed NK) was initially designed to carry only one astronaut, at 1/3 the LM total weight. Several NK were built, there are 5 still existing. There are several very interesting design/concept differences between the NK and the LM, on the Wiki page at the bottom en.wikipedia.org/wiki/LK_(spacecraft)
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    Didn't one of the early LM flights have problems with high supercritical helium pressure before launch? I thought that was Apollo 9, but Wikipedia doesn't seem to mention that at all. It does mention a similar issue on Apollo 13, though, but I'm pretty sure that's not what I have in mind.
    $endgroup$
    – a CVn
    6 hours ago










  • $begingroup$
    @aCVn Apollo 11 had a problem with helium pressure immediately after landing on the moon, perhaps that is what you are remembering? hq.nasa.gov/alsj/a11/a11iceclog.html
    $endgroup$
    – Organic Marble
    2 hours ago










  • $begingroup$
    Note that LK actually had two engines; one was a pure redundant backup, which would not be used at all in a nominal flight.
    $endgroup$
    – Russell Borogove
    1 hour ago













6












6








6





$begingroup$

Early conceptual designs suggested that two stages would save weight. Another issue came up that made a single-stage lander unreliable.



Pressurizing the fuel and oxidizer tanks of the lunar module was a considerable engineering challenge. Because of the temperature changes that happen during launch and Earth orbit, the tanks were kept unpressurized until right before they were needed. At that time, the astronauts would fire some explosive valves (i.e. you can open them but never close them again) which would release a small amount of supercritical helium to pressurize the tanks.



Development and testing of the LM pressurization system took 6 years and had a lot of problems. The fuel froze, so they added a heat exchanger. A test article exploded, so they had to change the alloy used in the heat exchanger. The pressure regulator cracked. You were supposed to be able to raise or lower the thrust of the descent engine; the pressurization system wasn't compatible with that, so there was another re-design. Another heat exchanger was added. The descent engine shut down prematurely on Apollo 5. It was under-pressured on Apollo 9. When Apollo 11 dumped their excess descent fuel, the fuel lines froze and over-pressurized.



Suffice to say, once you've popped the valves on the LM pressurization system, you have a few hours to use the engine before it becomes unreliable. This was enough time to land on the moon, but not reliable enough to last several days on the moon. A one-stage craft is just too risky. Instead, the ascent stage had its own fuel and pressurization system. (Apollo 13 took the risk of reusing the descent engine, and was lucky.)



The Soviets designed a manned lunar lander, the LK. To save weight, it would have had a single engine for descent and ascent. However, it still would have left some parts behind on the moon.



Soviet LK






share|improve this answer









$endgroup$



Early conceptual designs suggested that two stages would save weight. Another issue came up that made a single-stage lander unreliable.



Pressurizing the fuel and oxidizer tanks of the lunar module was a considerable engineering challenge. Because of the temperature changes that happen during launch and Earth orbit, the tanks were kept unpressurized until right before they were needed. At that time, the astronauts would fire some explosive valves (i.e. you can open them but never close them again) which would release a small amount of supercritical helium to pressurize the tanks.



Development and testing of the LM pressurization system took 6 years and had a lot of problems. The fuel froze, so they added a heat exchanger. A test article exploded, so they had to change the alloy used in the heat exchanger. The pressure regulator cracked. You were supposed to be able to raise or lower the thrust of the descent engine; the pressurization system wasn't compatible with that, so there was another re-design. Another heat exchanger was added. The descent engine shut down prematurely on Apollo 5. It was under-pressured on Apollo 9. When Apollo 11 dumped their excess descent fuel, the fuel lines froze and over-pressurized.



Suffice to say, once you've popped the valves on the LM pressurization system, you have a few hours to use the engine before it becomes unreliable. This was enough time to land on the moon, but not reliable enough to last several days on the moon. A one-stage craft is just too risky. Instead, the ascent stage had its own fuel and pressurization system. (Apollo 13 took the risk of reusing the descent engine, and was lucky.)



The Soviets designed a manned lunar lander, the LK. To save weight, it would have had a single engine for descent and ascent. However, it still would have left some parts behind on the moon.



Soviet LK







share|improve this answer












share|improve this answer



share|improve this answer










answered 8 hours ago









Dr SheldonDr Sheldon

4,93011650




4,93011650







  • 1




    $begingroup$
    These are many interesting technical details. We don't have much information on the LM design and testing challenges, but I'm sure there was some unprecedented engineering efforts put into this space ship. On the risk factor, you are suggesting that one of the reasons for a two stages LM was reducing the risk of failure (increasing reliability). From an engineering point of view, I feel that adding complementary instead of redundancy systems, actually increases the odds of system and consequently mission failure. Of course, only my suppositions.
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    Also worth adding that the Russian lunar module (acronym-ed NK) was initially designed to carry only one astronaut, at 1/3 the LM total weight. Several NK were built, there are 5 still existing. There are several very interesting design/concept differences between the NK and the LM, on the Wiki page at the bottom en.wikipedia.org/wiki/LK_(spacecraft)
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    Didn't one of the early LM flights have problems with high supercritical helium pressure before launch? I thought that was Apollo 9, but Wikipedia doesn't seem to mention that at all. It does mention a similar issue on Apollo 13, though, but I'm pretty sure that's not what I have in mind.
    $endgroup$
    – a CVn
    6 hours ago










  • $begingroup$
    @aCVn Apollo 11 had a problem with helium pressure immediately after landing on the moon, perhaps that is what you are remembering? hq.nasa.gov/alsj/a11/a11iceclog.html
    $endgroup$
    – Organic Marble
    2 hours ago










  • $begingroup$
    Note that LK actually had two engines; one was a pure redundant backup, which would not be used at all in a nominal flight.
    $endgroup$
    – Russell Borogove
    1 hour ago












  • 1




    $begingroup$
    These are many interesting technical details. We don't have much information on the LM design and testing challenges, but I'm sure there was some unprecedented engineering efforts put into this space ship. On the risk factor, you are suggesting that one of the reasons for a two stages LM was reducing the risk of failure (increasing reliability). From an engineering point of view, I feel that adding complementary instead of redundancy systems, actually increases the odds of system and consequently mission failure. Of course, only my suppositions.
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    Also worth adding that the Russian lunar module (acronym-ed NK) was initially designed to carry only one astronaut, at 1/3 the LM total weight. Several NK were built, there are 5 still existing. There are several very interesting design/concept differences between the NK and the LM, on the Wiki page at the bottom en.wikipedia.org/wiki/LK_(spacecraft)
    $endgroup$
    – Mathias
    6 hours ago










  • $begingroup$
    Didn't one of the early LM flights have problems with high supercritical helium pressure before launch? I thought that was Apollo 9, but Wikipedia doesn't seem to mention that at all. It does mention a similar issue on Apollo 13, though, but I'm pretty sure that's not what I have in mind.
    $endgroup$
    – a CVn
    6 hours ago










  • $begingroup$
    @aCVn Apollo 11 had a problem with helium pressure immediately after landing on the moon, perhaps that is what you are remembering? hq.nasa.gov/alsj/a11/a11iceclog.html
    $endgroup$
    – Organic Marble
    2 hours ago










  • $begingroup$
    Note that LK actually had two engines; one was a pure redundant backup, which would not be used at all in a nominal flight.
    $endgroup$
    – Russell Borogove
    1 hour ago







1




1




$begingroup$
These are many interesting technical details. We don't have much information on the LM design and testing challenges, but I'm sure there was some unprecedented engineering efforts put into this space ship. On the risk factor, you are suggesting that one of the reasons for a two stages LM was reducing the risk of failure (increasing reliability). From an engineering point of view, I feel that adding complementary instead of redundancy systems, actually increases the odds of system and consequently mission failure. Of course, only my suppositions.
$endgroup$
– Mathias
6 hours ago




$begingroup$
These are many interesting technical details. We don't have much information on the LM design and testing challenges, but I'm sure there was some unprecedented engineering efforts put into this space ship. On the risk factor, you are suggesting that one of the reasons for a two stages LM was reducing the risk of failure (increasing reliability). From an engineering point of view, I feel that adding complementary instead of redundancy systems, actually increases the odds of system and consequently mission failure. Of course, only my suppositions.
$endgroup$
– Mathias
6 hours ago












$begingroup$
Also worth adding that the Russian lunar module (acronym-ed NK) was initially designed to carry only one astronaut, at 1/3 the LM total weight. Several NK were built, there are 5 still existing. There are several very interesting design/concept differences between the NK and the LM, on the Wiki page at the bottom en.wikipedia.org/wiki/LK_(spacecraft)
$endgroup$
– Mathias
6 hours ago




$begingroup$
Also worth adding that the Russian lunar module (acronym-ed NK) was initially designed to carry only one astronaut, at 1/3 the LM total weight. Several NK were built, there are 5 still existing. There are several very interesting design/concept differences between the NK and the LM, on the Wiki page at the bottom en.wikipedia.org/wiki/LK_(spacecraft)
$endgroup$
– Mathias
6 hours ago












$begingroup$
Didn't one of the early LM flights have problems with high supercritical helium pressure before launch? I thought that was Apollo 9, but Wikipedia doesn't seem to mention that at all. It does mention a similar issue on Apollo 13, though, but I'm pretty sure that's not what I have in mind.
$endgroup$
– a CVn
6 hours ago




$begingroup$
Didn't one of the early LM flights have problems with high supercritical helium pressure before launch? I thought that was Apollo 9, but Wikipedia doesn't seem to mention that at all. It does mention a similar issue on Apollo 13, though, but I'm pretty sure that's not what I have in mind.
$endgroup$
– a CVn
6 hours ago












$begingroup$
@aCVn Apollo 11 had a problem with helium pressure immediately after landing on the moon, perhaps that is what you are remembering? hq.nasa.gov/alsj/a11/a11iceclog.html
$endgroup$
– Organic Marble
2 hours ago




$begingroup$
@aCVn Apollo 11 had a problem with helium pressure immediately after landing on the moon, perhaps that is what you are remembering? hq.nasa.gov/alsj/a11/a11iceclog.html
$endgroup$
– Organic Marble
2 hours ago












$begingroup$
Note that LK actually had two engines; one was a pure redundant backup, which would not be used at all in a nominal flight.
$endgroup$
– Russell Borogove
1 hour ago




$begingroup$
Note that LK actually had two engines; one was a pure redundant backup, which would not be used at all in a nominal flight.
$endgroup$
– Russell Borogove
1 hour ago










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