How did the lunar landers re-launch ?

[UM-Bot]

How did the landers manage to launch back in to space when the Moon has no oxygen ?

 

[Peter B]

Yeah, good summary of the chemistry of rocket fuels (some strange computer graphics of rockets, though). And frankly, what kid with a fascination for things going kaboom wouldn't be interested in rocket fuel? :-)

For me the amazing thing about the LM Ascent Engine was just how simple it was. You opened a valve for each of the propellant and oxidiser tanks, and the (toxic and corrosive) liquids flowed down pipes under gravity into the combustion chamber where they just mixed and went kaboom explosively enough to launch the LM Ascent Stage. No pumps, no throttle, no steering (by that engine, that is), not as energetic as other fuel/oxidiser combinations. But very simple and very reliable.

[ChrLzs]

I still firmly believe that for its time, Apollo was the most brilliant engineering project *ever*.  Born out of a completely re-invigorated NASA as they rebuilt their management systems after the tragic (and avoidable) fire of Apollo 1, the inventiveness and problem solving was far ahead of anything before or after.

Reaching and returning from the Moon was/is Humankind's greatest ever engineering/technical achievement, imo..

Edited December 1, 2017 by ChrLzs

[Derek Willis]

5 hours ago, ChrLzs said:

I still firmly believe that for its time, Apollo was the most brilliant engineering project *ever*.  Born out of a completely re-invigorated NASA as they rebuilt their management systems after the tragic (and avoidable) fire of Apollo 1, the inventiveness and problem solving was far ahead of anything before or after.

Reaching and returning from the Moon was/is Humankind's greatest ever engineering/technical achievement, imo..

In my opinion also. What I find disappointing is that the Apollo missions were almost half a century ago. How come nothing has bettered the achievement in all that time? I also wonder if young people see the Apollo missions as the greatest ever engineering/technical achievement? People of our age witnessed the event, but for my kids the Apollo missions were something taught in history lessons. Perhaps some people see the internet as the greatest ever technical/engineering achievement? It will be interesting to see how the Apollo missions are viewed at the time of the half-century point. I have a feeling that the engineering/technical achievement - and not least the courage of the astronauts who flew on the missions - will be overshadowed by the societal aspects. Yes, it was only white men who went to the moon. That is how it was back then. Times have changed, and that is great. But it will be a pity if an event that for a moment at least brought the world together is remembered for the way society was fifty years ago and not for what Apollo really was - humanity taking on a challenge and succeeding.

[Derek Willis]

18 hours ago, Peter B said:

Yeah, good summary of the chemistry of rocket fuels (some strange computer graphics of rockets, though). And frankly, what kid with a fascination for things going kaboom wouldn't be interested in rocket fuel? :-)

For me the amazing thing about the LM Ascent Engine was just how simple it was. You opened a valve for each of the propellant and oxidiser tanks, and the (toxic and corrosive) liquids flowed down pipes under gravity into the combustion chamber where they just mixed and went kaboom explosively enough to launch the LM Ascent Stage. No pumps, no throttle, no steering (by that engine, that is), not as energetic as other fuel/oxidiser combinations. But very simple and very reliable.

On a technical point, the propellants flowed due to being pressurized by a tank of helium. 

[Peter B]

22 hours ago, Derek Willis said:

On a technical point, the propellants flowed due to being pressurized by a tank of helium. 

Sorry, you're quite right. I stand corrected.

In fact, now that I think about it...of course: for stability reasons the propellant tanks were set very low on the LM Ascent Stage - so low they were below the engine. So, yes, they needed pressure from the gaseous helium to force the propellants into the engine - not gravity.

Nevertheless, it was an amazingly simple and reliable engine.

[Derek Willis]

1 hour ago, Peter B said:

Sorry, you're quite right. I stand corrected.

In fact, now that I think about it...of course: for stability reasons the propellant tanks were set very low on the LM Ascent Stage - so low they were below the engine. So, yes, they needed pressure from the gaseous helium to force the propellants into the engine - not gravity.

Nevertheless, it was an amazingly simple and reliable engine.

Gravity has nothing to do with it. In a rocket engine the propellants have to enter the combustion chamber at a pressure higher than the chamber pressure. So in big engines pumps are used, and in little engines a pressure-feed system is used. The trajectory of a rocket (or Lunar Module ascent stage) heading for orbit requires that as quickly as possible the rocket tilts over so that it flies increasingly parallel with the surface. Hence gravity is acting increasingly perpendicular to the direction of flight. And or course, when in orbit or flying to/from the Moon, a spaceship is in zero-g.  

But you are right regarding the simplicity and reliability of the ascent stage engine. In fact, this was the only component that really worried the astronauts. If the descent stage engine didn't ignite, then that meant the mission was aborted but the astronauts would have survived. But if the ascent stage engine didn't ignite, then the astronauts would have been marooned. At one point the astronauts asked if handles could be fitted so they could manually operate the valves in case the actuator failed. However, the engineers had total confidence in the engine, and they were right. In fact, there were no significant failures in any of the Lunar Modules. Added to the fact that the Lunar Module Aquarius saved the lives of the Apollo 13 crew, I'd say the Lunar Module is the best space ship ever designed!

As an aside, the re-ignition of the Service Module engine to propel the Service/Command module out of lunar orbit and back to Earth was also critical. During Apollo 8 - the first time this was done - when the Service Module engine ignited right on schedule, Frank Borman said: "You beauty! You absolute beauty!".