Author Topic: Question: how did they slow down in space?  (Read 18558 times)

Offline miker

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Question: how did they slow down in space?
« on: November 04, 2016, 06:09:56 PM »

I think they had to slow down three different times while going to the moon.
1. To enter into an orbit around the moon.
2. After detaching from the command module, the lunar module had to slow down in order to fall out of orbit.
3. When the lunar module entered the moon's gravitational field and landed softly.

The only way that I can come up with them slowing down in space is to reverse the module to the EXACT opposite of their flight path and fire the main thruster and travel through their exhaust.
I think their fuel was liquid hydrogen and liquid oxygen which burns at 5500°F. The lunar lander had a skin of aluminum foil which melts at about 1200°F.
What I don't know is how fast temperature and heat dissipate in a vacuum, since they had to travel through it at a high velocity and not melt aluminum.
It reminds me of reverse landing a rocket here on the Earth - which hasn't been done yet.
I would appreciate anyone teaching me how they slowed down in a vacuum, in case there is another way, or that the heat is no problem.


Offline ChrLz

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Re: Question: how did they slow down in space?
« Reply #1 on: November 04, 2016, 06:53:20 PM »
Miker, this is really basic stuff, and perhaps you might want to do a little more work on your own before coming here with what is a request for education on stuff that is:
1. pretty easy to find out
2. at a very basic level of science - ie stuff you should have learned in grade school.

NO, using their own reverse thrust is of course NOT the only way to wash off speed.  You *really* need to learn about how orbits and trajectories work.
However, yes, they turned the craft around to use reverse thrust to assist in the slowdowns.
NO, they would not have traveled through any significant part of the 'exhaust'.
NO, the temperature of a particle of exhaust at the moment it burns has virtually NOTHING to do with the infinitesimally tiny amount of residual heat (hint - temperature and heat are two different things) that might be transferred some time later (after the particle had radiated heat out into cold empty space), and *if* any of the particles hit anything 'delicate'.  Given they are being sprayed BACKWARDS into a vacuum with a velocity added to that of the spacecraft, why would any of them get overtaken by the spacecraft???

Seriously mate - THINK about this stuff.  They are in SPACE, not here on earth, so things are different...

May I suggest you visit Bob Braeunig's excellent site:
http://www.braeunig.us/space/index.htm
and follow the links to the ones about orbital mechanics, Apollo trajectories, etc

Also, do some Wiki-ing before posting more of these requests.. and maybe have a good long look here:
http://jean-fred.com/apollo/poster_high_nasa_apollo.jpg  (Warning, this is a BIG image!!)
 at a schematic of how Apollo worked.  This was done a few years before the actual mission, but it's close enough...

Offline ChrLz

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Re: Question: how did they slow down in space?
« Reply #2 on: November 04, 2016, 07:01:47 PM »
BTW, we have managed to reverse land rockets for a LONG time, and slowing down in space is much easier than a landing.

As for the landings, research the LLTV / LLRV used as a test bed for the Apollo landings, and the several HUNDRED times it landed on Earth, in MUCH more difficult conditions (6x the gravity, atmosphere, wind)....

Here's me at another forum, giving a history lesson to an Apollo denier..
http://www.unexplained-mysteries.com/forum/topic/227095-merged-did-we-land-on-the-moon/?do=findComment&comment=4346865

Miker, please acknowledge the replies you get, and also acknowledge when you get stuff wrong.  That way we will know if you are capable of learning, or have simply decided that you already know 'da troof'.

Offline Gazpar

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Re: Question: how did they slow down in space?
« Reply #3 on: November 04, 2016, 07:19:34 PM »
It reminds me of reverse landing a rocket here on the Earth - which hasn't been done yet.
SpaceX did it.

Offline miker

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Re: Question: how did they slow down in space?
« Reply #4 on: November 04, 2016, 07:32:13 PM »
I'm really confused about all this.
I will take time to check out the links you provided.
Thank you very much.
When a person can't admit they're ever wrong, they are rendered unteachable and can't learn any more. I can admit I'm wrong but I do have to do some learning apparently.
Oh, someone just said a reverse rocket landing has been done, I would really like to see that if someone could post a link.
Thank you

Offline Apollo 957

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Re: Question: how did they slow down in space?
« Reply #5 on: November 04, 2016, 08:11:44 PM »
Oh, someone just said a reverse rocket landing has been done, I would really like to see that if someone could post a link.

Their exact words were "SpaceX did it"

You don't feel inclined to google 'SpaceX landing'?  Nor type that as a search term in YouTube?

We have to do all the work for you?

Offline ChrLz

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Re: Question: how did they slow down in space?
« Reply #6 on: November 04, 2016, 08:28:31 PM »
I'm really confused about all this.
I will take time to check out the links you provided.
Good.  Please come back and report what you have learned, or be specific about anything you do not understand, or that you dispute - you really need to give your reasoning on *why* you dispute something and preferably check your reasoning by researching it first.
Quote
When a person can't admit they're ever wrong, they are rendered unteachable and can't learn any more. I can admit I'm wrong but I do have to do some learning apparently.
Thing is, you have already been given quite a bit of information on the other thread, yet instead of acknowledging that, you posted a new one....  That's not a good sign, but you can rectify it pretty easily - go back to that thread and answer the replies you were given, properly.
Quote
Oh, someone just said a reverse rocket landing has been done, I would really like to see that if someone could post a link.
Thank you
Ever hear that proverb about teaching someone to fish...?  Not only were you given the exact words you could enter at Google, I also gave to a link to the Apollo LLRV and LLTV - those craft did well over SEVEN HUNDRED 'reverse landings' during the testing and development phases for Apollo...  And again, you haven't acknowledged the content of my post properly - do you agree that landing something on the Moon is MUCH easier than here on Earth?  If not, why?

Offline Bob B.

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Re: Question: how did they slow down in space?
« Reply #7 on: November 04, 2016, 10:10:31 PM »
1)  You are correct that they slowed down by using reverse thrust.
2)  The propellant was not liquid hydrogen/liquid oxygen, it was Aerozine 50/nitrogen tetroxide.
3)  The propellant burned at a temperature of about 5500 F in the combustion chamber.  By time it left the nozzle it had expanded and cooled dramatically.
4)  The exhaust was expelled at a velocity of over 3000 m/s relative to the rocket.  So, no, they did not fly through their own exhaust.

Offline Gazpar

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Re: Question: how did they slow down in space?
« Reply #8 on: November 04, 2016, 11:45:55 PM »
Oh, someone just said a reverse rocket landing has been done, I would really like to see that if someone could post a link.

Offline Grashtel

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Re: Question: how did they slow down in space?
« Reply #9 on: November 05, 2016, 01:24:09 AM »
Oh, someone just said a reverse rocket landing has been done, I would really like to see that if someone could post a link.

And a few more:
Blue Origin
DC-X
Bell Rocket Belt
SpaceX Grasshopper

And if you extend it to jet engine powered landings, which mechanically speaking are the same as its still a vehicle being held up by pure thrust, there are even more:
Flyboard air
Jetpack JB-10
Williams Aerial System Platform
Harrier jet
F-35

And lots more examples, those are just he ones that I can easily remember the names of
"Any technology, no matter how primitive, is magic to those who don't understand it." -Florence Ambrose

Offline gwiz

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Re: Question: how did they slow down in space?
« Reply #10 on: November 05, 2016, 06:46:59 AM »
It reminds me of reverse landing a rocket here on the Earth - which hasn't been done yet.
The main difference is the absence of an atmosphere, which means that the exhaust doesn't encounter anything to slow it down once it leaves the nozzle until late in the landing when it touches the ground.  Even then, it spreads into a sheet flowing outwards rather than being reflected back towards the vehicle.  Some of the vehicles mentioned in the post above do have to cope with exhaust being reflected from the ground, but these are the multi-nozzle ones like the Harrier where there is inflowing exhaust in the region between the nozzles which goes upwards because it has nowhere else to go.

Multiple exclamation marks are a sure sign of a diseased mind - Terry Pratchett
...the ascent module ... took off like a rocket - Moon Man

Offline Bob B.

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Re: Question: how did they slow down in space?
« Reply #11 on: November 05, 2016, 01:26:45 PM »

Offline raven

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Re: Question: how did they slow down in space?
« Reply #12 on: November 05, 2016, 02:31:31 PM »
SNECMA Atar Volant, or C.400 P1. Basically a jet engine with a seat.

Offline Allan F

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Re: Question: how did they slow down in space?
« Reply #13 on: November 07, 2016, 11:14:29 AM »
miker - go buy the game "Kerbal Space Program", and play around for a few hours. That will teach you a LOT about rockets and spacetravel.
Well, it is like this: The truth doesn't need insults. Insults are the refuge of a darkened mind, a mind that refuses to open and see. Foul language can't outcompete knowledge. And knowledge is the result of education. Education is the result of the wish to know more, not less.

Offline jfb

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Re: Question: how did they slow down in space?
« Reply #14 on: December 09, 2016, 12:05:45 PM »
I'm really confused about all this.
I will take time to check out the links you provided.
Thank you very much.
When a person can't admit they're ever wrong, they are rendered unteachable and can't learn any more. I can admit I'm wrong but I do have to do some learning apparently.
Oh, someone just said a reverse rocket landing has been done, I would really like to see that if someone could post a link.
Thank you

Supercut of multiple Falcon 9 landings, both on land and at sea. 

As others have pointed out, the CSM would not have been flying through its own exhaust; there's no air or other medium to impede the exhaust flow.  It flies away from the spacecraft at X m/s regardless of the direction the spacecraft is facing.