I Spotted Something NASA Missed

[Stub Mandrel]

I spotted something NASA missed in all their plans - I 've been listening to 'Apollo 11 in real time' and when  Neil and Buzz returned after the moonwalk, they removed the PLSS antennae from their suits as planned and stow them - these are what they used to communicate with each other and CAPCOM from the surface. Then fifteen anxious minutes for Houston until they realise why they can't contact the astronauts, as they haven't yet been able to activate the LMs comms.

[JOC]

I watched the same documentary as the rest of you the other week and have a couple of questions/observations.

1.  That tricky bit of the manoeuvre when they had to get the lunar module bit to disconnect and turn-around in space and re-connect the right way around to approach the moon.  Why didn't they just build it that way round to begin with and give the astronauts swivel chairs if they needed to see where they were going?

2.  My son was interested in how they might have calculated the distance to the moon prior to anything first being landed on it in terms of them knowing how much fuel would be needed to get there either during the landing mission or even before with the test approaches etc.  I assume that some sort of triangulation or radar bounced signal might have been used, but I wasn't sure.  Can anyone help?

[barkis]

At a point during de orbit descent. Transmit return signals from the surface would 
be used to equate  the decreasing distance, and thereby incorporate the fuel  
reserves required to execute a safe landing. Mind you, as we know
the margin of safety turned out to be very Hairy 😯.
I'm only surmising this is possibly how it was done, I don't know for certain.
Ron.

 

Edited July 22, 2019 by barkis

[Gina]

It was an enormous risk landing on the moon - the ground could have been metres deep in dust where they landed.  I didn't see any mention of finding out what the surface was like before they landed.  As it was Neil Armstrong had to choose a new landing site from that predicted due to lots of steep craters.  That mission was so very close to disaster!!  The technology just barely worked with a couple of worrying moments.

[saac]

Re question 2 JOC the fuel load requirement inst really determined by distance  - remember Newton 1 means they coast to the moon with the engines off.  The main fuel load requirement comes from the escape of Earth orbit (Lunar insertion) , retardation to moon orbit and then landing and escape from the moon orbit (Earth insertion) , and finally retardation to achieve Earth orbit & decent. These calculations are then essentially one of energy (speed or rather impulse) and not distance.

Jim   

 

Edited July 22, 2019 by saac

[Gfamily]

13 minutes ago, JOC said:

I watched the same documentary as the rest of you the other week and have a couple of questions/observations.

1.  That tricky bit of the manoeuvre when they had to get the lunar module bit to disconnect and turn-around in space and re-connect the right way around to approach the moon.  Why didn't they just build it that way round to begin with and give the astronauts swivel chairs if they needed to see where they were going?

2.  My son was interested in how they might have calculated the distance to the moon prior to anything first being landed on it in terms of them knowing how much fuel would be needed to get there either during the landing mission or even before with the test approaches etc.  I assume that some sort of triangulation or radar bounced signal might have been used, but I wasn't sure.  Can anyone help?

The distance to the moon can be measured fairly straightforwardly by trigonometry from the earth's surface, even without radar techniques.

As for the configuration of the CSM and the stowed LM: the CM was the pointed end of the Saturn V rocket, so had to be at the top. The LM, being as wide as it is, couldn't have been mounted higher up, and couldn't have been entered from the other end of the CM as the SM was in the way.

[saac]

3 minutes ago, Gina said:

It was an enormous risk landing on the moon - the ground could have been metres deep in dust where they landed.  I didn't see any mention of finding out what the surface was like before they landed.  As it was Neil Armstrong had to choose a new landing site from that predicted due to lots of steep craters.  That mission was so very close to disaster!!  The technology just barely worked with a couple of worrying moments.

I believe they had a notion that a successful landing was in order of 50:50.  They really did not expect it to work first time - quite remarkable and a testament to "the right stuff".  I wonder how prepared we are to accept that level of risk with our modern plans for revisiting the moon and beyond. I really do wonder how we would cope with failure.  The  generation that brought as the moon landing was a little more battle hardened. 

Jim 

[Gina]

Yes indeed.  We were in the middle of the "Cold War" and the moonshot was political.  The need to prove to the Russians that the West had the ability to launch and accurately deploy nuclear weapons if needed.  Hence risk-taking was stepped up a couple of notches.  Not sure why this needed a manned lunar landing though.

Edited July 22, 2019 by Gina

[saac]

23 minutes ago, Gina said:

 Not sure why this needed a manned lunar landing though.

Purely political Gina. But aren't you glad they did.  

Jim 

[Gina]

I certainly am!!  And watching the moonwalk live as it happened was a wonderful birthday present I thought.  Those were some exceptionally brave men!  The whole mission was quite remarkable and unforgettable.

[Stub Mandrel]

1 hour ago, JOC said:

1.  That tricky bit of the manoeuvre when they had to get the lunar module bit to disconnect and turn-around in space and re-connect the right way around to approach the moon.  Why didn't they just build it that way round to begin with and give the astronauts swivel chairs if they needed to see where they were going?

With every ounce being trimmed and very limited space swivel chairs would not have been practical - also because of the heat shield it's only practical to have windows in the conical end of  the Command Module.

Most importantly, however, the astronauts needed to be right on top of the Saturn V at launch so the escape rocket would be able to pull the command module free in an emergency, leaving empty service module and lunar module to their fate. In fact, they didn't have a view at all until after the escape rocket with its cone covering the command module jettisoned around stage 2 separation.

Another consideration is that the complex mechanism and critical seals for the docking mechanism could easily have been damaged by the extreme acceleration and vibration of launch if the two parts were connected from the start.

[Stub Mandrel]

1 hour ago, Gfamily said:

The distance to the moon can be measured fairly straightforwardly by trigonometry from the earth's surface, even without radar techniques.

The moon is about 30 earth-diameters away, much closer than we tend to think!

 

[Stub Mandrel]

1 hour ago, Gina said:

It was an enormous risk landing on the moon - the ground could have been metres deep in dust where they landed. 

Possibly, but the surveyor landings gave them a fair degree of confidence that they wouldn't simply sink into a sea of dust - they also had abort points within seconds and minutes of landing, if necessary.