[thedoc (OP)]

Arun asked the Naked Scientists:

How the did astronauts return from the Moon? How did the spacecraft launch back from the Moon to Earth?

What do you think?

[evan_au]

How did the spacecraft launch back from the Moon to Earth?

Rockets.

In more detail:

• The Moon has far less surface gravity than the Earth, so it takes a much smaller rocket than launch from Earth.
  
• The Earth's gravity is stronger than the Moon's gravity, so you don't have to go far from the Moon before the Earth's attraction dominates, and you "fall" towards the Earth.
  
• The Moon has no air, so the rocket thrust isn't wasted pushing aside air.
  
• They didn't take all the fuel, air and living space for the return journey down to the Moon's surface. They left it in orbit (with an astronaut to look after it).
  
• They didn't take all the empty fuel tanks, tools, experiments or the lunar rover back from the Moon - they are still there.
  
• One of the experiments (a laser ranging experiment) is still use, and is used to measure precise distances to the Moon.
   

See: http://en.wikipedia.org/wiki/Apollo_Lunar_Module#Ascent_stage

[thedoc (OP)]

We discussed this question on our  show
Kat Arney put this question to Cambridge astronomer Matt Middleton...

Matt: - When the Apollo missions went to the moon. which is probably still regarded as mankind’s greatest achievement, they went in a multistage vehicle. They started off in a Saturn 5 rocket - the most powerful rocket known to man - and that comprised of something called the command and service module, which included as part of it, a lunar module, and that lunar module was the thing that went down to the surface of the moon. The command and service module, or CSM, would orbit round the moon, they dumped off the lunar module with Neil and Buzz because, obviously, we were on first name terms, and they landed on the moon and then we all know what happened next…
Kat - They did the moon thing…
Matt - They did the moon thing, unless you are a conspiracy nut, you know…
Kat - They definitely did the moon thing…
Matt - They definitely did the moon thing, yes.
Kat - So how did they get them back off the from there?
Matt - Well. The beautiful gold foil thing that we all know and love which is the iconic image of people being on the moon. That’s actually two parts. So in total it’s called the descent module or descent stage, and that landed and then they got back inside and the top bit blasted off. So, the descent stage was actually used as a launch pad and then you have the ascent stage which fired propellant, and the actual propellant is hypergolic. So, what basically happens is you have these two chemicals and as soon as they combine, instantly “boom” blast off. And so this thing took them back up to the command and service module and then the left lunar orbit. What’s important to stress is, because the moon is so much smaller, they didn’t need to have a Saturn 5 rocket plus they weren't taking all that kit with them…
Chris - Because the gravity’s lower?
Matt - It is lower. The escape velocity is five times smaller on the moon than it is on the earth.
Margarita - So the descent module is still on the moon?
Matt - It is - yes, yes.
Chris - There’s a whole lot of litter that we’ve left up there - isn’t there?
Matt - We have left a terrible amount of litter.
Margarita - You know there is something now being developed called “space archaeology.” I think that’s a prime…
Matt - Oh really! Is that where you’re going next?
Chris - The fact that there are nice artifacts up there…
Margarita - There are so many objects now orbiting the earth that the people are seriously talking about starting space archeology…
Matt - Oh yes…
Chris - There’s a lovely headline isn’t there “footprints that no wind has ever blown away” and they are there on the moon’s surface from those first space walks.
Matt - They also left really cool stuff up there. There’s a reflecting thing so you can actually fire a laser and work out the distance to the moon.
Chris - Yes the laser goes every day - doesn’t it? We know the moon is moving 2 cms away from the earth every year owing to the fact that the time it takes the light to get there and come back is stretching out.
Matt - Yes, and I think that’s fantastic. It’s still a legacy that I think we can all be proud of as humans.
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