Apollo Mission: Why 3 Astronauts? Why not two?

[Nibb31]

There's an inherent problem with that approach. Should the lander fail to dock with the automated CSM, all astronauts would either be killed or stranded on the moon, and likely to exhaust their life support system while waiting for a rescue mission. If one stayed in the CSM, he would be able to return to Earth, albeit alone.

If the LM failed to dock, the plan was to transfer to the CSM by EVA. This required that the Command Module Pilot would depressurize the CSM, open the hatch, and maintain position with the LM.

Just about every event during the mission had at least one or two contingency modes. Just about the only thing that didn't was if the LM ascent engine failed. And that was the event for which a presidential speech prepared.

[Shuttle]

Just about the only thing that didn't was if the LM ascent engine failed. And that was the event for which a presidential speech prepared.

Why didn't they install two ascent engines?

[KASASpace]

Why didn't they install two ascent engines?

Weight.

Just about every event during the mission had at least one or two contingency modes. Just about the only thing that didn't was if the LM ascent engine failed. And that was the event for which a presidential speech prepared.

Lucky thing they had that pen on Apollo 11.

[Nibb31]

Why didn't they install two ascent engines?

Weight. The engine weigned 82 Kgs and the LM had to be as light as possible. It was so shaved down that its skin was as thin as aluminium foil in some places.

Instead of adding a redundant engine, they decided to make it as reliable as possible by using gravity-fed hypergolics and limiting the number of moving parts to a couple of valves.

[Nibb31]

Lucky thing they had that pen on Apollo 11.

You've really got to stop rehashing that pen thing. It was just a circuit breaker switch that broke off, nothing life-threatening and hardly a "stranded on the Moon" situation.

There were a dozen contingency plans for such a situation, including rerouting the circuit through another switch or fixing it with any of the tools they had on board. They simply used a felt-tip pen to move the switch because it was at hand and it was the obvious thing to do.

[Brotoro]

When the 3-man Apollo capsule was originally designed, it was expected that all three of the astronauts AND the Apollo capsule would land on the Moon (using some Earth-Orbit Rendezvous or direct ascent mission profile). So they envisioned having three guys on the Moon to do the work and help each other.

When they switched over to Lunar Orbit Rendezvous mission profile, they had to leave one guy in orbit to man the CSM/SM to increase the chances of a successful rendezvous. And so the LM was designed to carry just the other two down to the Moon (although I recall seeing some LOR concepts that had two single-man landers in place of the two-man LM).

[Javster]

When the 3-man Apollo capsule was originally designed, it was expected that all three of the astronauts AND the Apollo capsule would land on the Moon (using some Earth-Orbit Rendezvous or direct ascent mission profile). So they envisioned having three guys on the Moon to do the work and help each other.

When they switched over to Lunar Orbit Rendezvous mission profile, they had to leave one guy in orbit to man the CSM/SM to increase the chances of a successful rendezvous. And so the LM was designed to carry just the other two down to the Moon (although I recall seeing some LOR concepts that had two single-man landers in place of the two-man LM).

So if the CSM started spinning, the CMP could bring it back under control?

[Nibb31]

So if the CSM started spinning, the CMP could bring it back under control?

Among other things, yes. Having a crew member aboard the CSM allowed all sorts of contingency modes that simply weren't possible if they had left it on orbit unmanned.

For example, the CMP could have performed the rendez vous if the LM failed to reach the proper altitude. Or he could have actively done the docking if the LM's tracking radar had failed or if, for some reason, the LM's manoeuvring systems didn't work. Or he could have prepared an EVA if the LM failed to dock. He could also relay communications between the LM and Houston.

The CMP's role was essential. It really was a no brainer.

[KASASpace]

You've really got to stop rehashing that pen thing. It was just a circuit breaker switch that broke off, nothing life-threatening and hardly a "stranded on the Moon" situation.

There were a dozen contingency plans for such a situation, including rerouting the circuit through another switch or fixing it with any of the tools they had on board. They simply used a felt-tip pen to move the switch because it was at hand and it was the obvious thing to do.

Any exact sources for those contingency plans? I've read up a lot about Apollo, and it was even stressed by many of the ground crew and even some of the crew that actually flew to the moon. Seriously, do some reading.

[Moar Boosters]

Why didn't they install two ascent engines?

There were plans for a contingency system that was to be taken on cancelled longer lunar missions. The thought being that the longer the spacecraft is left idle, the greater the chance of the engine failing to ignite.

It was the most kerbal spacecraft ever designed. Just a couple of seats on top of some fuel tanks and engines. No life support, and no guidance computer. They sat on it in their spacesuits, and piloted their way into orbit manually.

http://en.wikipedia.org/wiki/Lunar_Escape_Systems

[Nibb31]

Any exact sources for those contingency plans? I've read up a lot about Apollo, and it was even stressed by many of the ground crew and even some of the crew that actually flew to the moon. Seriously, do some reading.

I have, and so can you. You could start by the actual voice recorder transcript of the event here. Aldrin reports the problem at 04 06 56 28. Later, the problem seems to be solved at 05 03 20 43. Liftoff happens nominally 1 hour later at 05 04 21 54. There doesn't seem to be any other reference to the engine arm circuit breaker problem, so judging by the transcript and the 3 or 4 lines dedicated to the matter, without making a big deal out of it, he just stuck a pen into the hole when he was supposed to close the breaker a few hours before liftoff. His only concern was that he couldn't reopen the circuit breaker if necessary, but there was no reason to do so and Houston didn't seem too concerned.

I found this tidbit here.

In his book, Men from Earth Buzz elaborates, "We discovered during a long checklist recitation that the ascent engine's arming circuit breaker was broken off on the panel. The little plastic pin (or knob) simply wasn't there. This circuit would send electrical power to the engine that would lift us off the moon...We looked around for something to punch in this circuit breaker. Luckily, a felt-tipped pen fit into the slot."

And also this:

I'll have to go and dig out my copy of Tom Kelly's book, but I remember in it he remarked that they discovered the broken breaker before the moonwalk, and the LM team were horrified at the suggestion by Buzz that he could jam a pen in there. While the walk was in progress, they designed a work around using redundant wiring and switchgear to bypass the broken switch, and that this was how the problem was solved. He painted it as a vindication of the decision to include multiple wiring circuits in the LM control system.

So there seems to be some confusion about whether the circuit breaker was fixed by rewiring or by inserting a pen.

There are some other quotes here.

* Buzz Aldrin, lunar module pilot, Apollo 11: As I got down on the floor to sleep [the night before], I could see the broken head of a circuit breaker. It was the engine-arm circuit breaker--the one that's got to be in to get electricity to turn the ascent engine on. Since it was on my side, obviously I would have to take the blame for my backpack knocking against things clumsily and breaking it off.

* Hal Loden, lunar module control officer (CONTROL), Black Team, Mission Control: That circuit breaker allowed the lunar guidance system to start the engine automatically--but there was another way to start the engine. We had redundancy. They would have had to hit a pushbutton manually at T minus zero.

* Aldrin: It looked as though there was enough left to push [the breaker] in. When the time came, I just said I was going to push it in with a pen.

You can see what the panels looked like here. Look for the LMP Circuit Breaker Panels. Like the rest of the LM, these panels had apparent screws so that they could be dismantled and fixed if necessary. It would have been easy to replace the broken circuit breaker if necessary. The LM had all sorts of backup systems and redundancies. I can assure you that neither NASA nor the astronauts were stupid enough to die stranded on the Moon because of a dumb switch.

Edited April 29, 2014 by Nibb31

[shynung]

I can assure you that neither NASA nor the astronauts were stupid enough to die stranded on the Moon because of a dumb switch.

I suppose it makes sense for both NASA and the Soviet Space Program to not lose any astronauts on their respective moon landing missions; otherwise, it would have been a big blow to their national ego, considering the era the programs were run in. The Soviets ensure this by designing a multi-engine lander, while NASA did the same by using an ultra-reliable lander engine.

[Red Iron Crown]

The amazing thing to me is that the LM ascent engine was untested before launch, due to the corrosiveness of the propellants. I know it was as mechanically simple as possible (two moving parts, IIRC), but that would have made me nervous.

[KASASpace]

I have, and so can you. You could start by the actual voice recorder transcript of the event here. Aldrin reports the problem at 04 06 56 28. Later, the problem seems to be solved at 05 03 20 43. Liftoff happens nominally 1 hour later at 05 04 21 54. There doesn't seem to be any other reference to the engine arm circuit breaker problem, so judging by the transcript and the 3 or 4 lines dedicated to the matter, without making a big deal out of it, he just stuck a pen into the hole when he was supposed to close the breaker a few hours before liftoff. His only concern was that he couldn't reopen the circuit breaker if necessary, but there was no reason to do so and Houston didn't seem too concerned.

I found this tidbit here.

That wasn't as much a problem with the circuit as it was with the actual handle. No physical way to tell the computer to fire the engine, the engine won't fire.

And I was referring to them putting stress on the event after landing on the moon, when they were on Earth.

When I said do some reading I meant do some reading and point me to some sources on contingency plans for a broken handle.

[Javster]

I suppose it makes sense for both NASA and the Soviet Space Program to not lose any astronauts on their respective moon landing missions; otherwise, it would have been a big blow to their national ego, considering the era the programs were run in. The Soviets ensure this by designing a multi-engine lander, while NASA did the same by using an ultra-reliable lander engine.

I think you got them swapped around. AFAIK the LK dropped the landing legs and empty fuel tanks and used the same engine.

[sgt_flyer]

I think you got them swapped around. AFAIK the LK dropped the landing legs and empty fuel tanks and used the same engine.

actually, he's right in fact.

the LK had a backup engine with two exhausts on each side of the main engine. the backup engine was fired simultaneously with the main, and shut down once the main central engine was able to get to full thrust.

for the LEM, each engine (the descent and ascent ones) had no redundancy.

the soviets engineers did that because they could not reach the imposed very high reliability for a single engine design asked by the bureaucracy.

(mainly because soviets used turbopump fed engine instead of pressure fed engines - heck, they even put SRB's inside the engine to be able to spin the engine pumps to max speed extremely fast in case an abort was needed - AKA, if they would have needed more than 25s of firing to land - they would not have enough DV to make it back)

Edited April 29, 2014 by sgt_flyer

[Nibb31]

It wasn't a handle. It was a circuit breaker. And it had nothing to do with the computer. Do you even know what a circuit breaker is?

The engine could be fired manually by pressing a big yellow START button. The circuit could also have been rerouted and the switch could have been repaired.

The pen didn't save their lives. Their lives were never at risk. It saved them a bit of repair work or manual burn, that's all.

[KASASpace]

It wasn't a handle. It was a circuit breaker. And it had nothing to do with the computer. Do you even know what a circuit breaker is?

The engine could be fired manually by pressing a big yellow START button. The circuit could also have been rerouted and the switch could have been repaired.

The pen didn't save their lives. Their lives were never at risk. It saved them a bit of repair work or manual burn, that's all.

Did I read somewhere where the ascent circuit breaker pull handle was broken off accidentally by the portable life support system (PLSS) of one of the astronauts during egress on the Apollo 11 EVA?

That was from what you yourself referenced.

I know what a circuit breaker is.

Sure, it has little to do with a computer, specifically the AGC, but it does have some thing to do with it.

If they had taken too long to repair the breaker, or if the START button had taken some sort of damage (so much happened it was mighty possible).

Maybe if they could have used the DSKY..........

[Nibb31]

That was from what you yourself referenced.

Did you bother to read the rest of the thread?

A circuit breaker doesn't have a «handle». It has a push-pull button. The button broke off leaving a hole.

You keep on moving goalposts here, and using words that you clearly don't understand (use the DSKY ? Seriously?). You claimed that without their pen, they would have been stranded on the Moon. You were wrong. Which seems to be a bit of a pattern here.

Edited April 29, 2014 by Nibb31

[KASASpace]

Did you bother to read the rest of the thread?

A circuit breaker doesn't have a «handle». It has a push-pull button. The button broke off leaving a hole.

You keep on moving goalposts here, and using words that you clearly don't understand (use the DSKY ? Seriously?). You claimed that without their pen, they would have been stranded on the Moon. You were wrong. Which seems to be a bit of a pattern here.

I never claimed that they would have died without it. I said lucky they had because they managed to get a quick solution easily.

(Do YOU even know what the DSKY is? It's the interface between the crew and the computer. It could have been used to start up the engine, but I wouldn't know. I don't have all the programs in it memorized.)

[Drunkrobot]

Most components on the Lunar Module had a back-up spare, including the pilot. Even if the Commander had no complications during the landing or launching sequence, the Lunar Module Pilot fed him critical information so that he didn't have to check his instruments as much, taking some of the pressure off him and letting him make a smoother landing.

And no, the Lunar Module Pilot didn't actually pilot the Lunar Module.

[Xavven]

Thank you everyone for your well-informed responses. This prompted me to do some reading on the role of a flight engineer, and I also read about the LESS -- holy cow! NASA designed what amounts to a command seat ascent vehicle! I guess I can't be too critical of some certain Eve return landers I've seen lately LOL!

Anyway, I started to think about some of the flight sims I play (DCS A-10C Warthog specifically) and how task saturation can quickly overwhelm you in a single-seat aircraft, but computers have come a long way in helping with that. In fact, I read that flight engineer positions started declining as computers became more powerful and lighter. When malfunctions occur, the computer can even compensate on its own to varying extents. What do you all think of the prospect of single-person landers today, aided by advances in computing? Does anyone know what mission profile China is working on?

[shynung]

And no, the Lunar Module Pilot didn't actually pilot the Lunar Module.

What did he do, then? Read out the instrumentation?

[Red Iron Crown]

Anyway, I started to think about some of the flight sims I play (DCS A-10C Warthog specifically) and how task saturation can quickly overwhelm you in a single-seat aircraft, but computers have come a long way in helping with that. In fact, I read that flight engineer positions started declining as computers became more powerful and lighter. When malfunctions occur, the computer can even compensate on its own to varying extents. What do you all think of the prospect of single-person landers today, aided by advances in computing? Does anyone know what mission profile China is working on?

I think a second person is not necessary for pilot workload reduction, the lander could easily be made to land without pilot interaction. The buddy system is still a good idea, though. Not just for the scenarios we have thought of, but also the ones we haven't. Just being able to inspect the back of a spacesuit could be critical.

[KASASpace]

And, you only have to remember half of the entire LM. Makes the mental workload easier. Plus, I wouldn't want to be lost and alone on the moon.