Space Shuttle - Riding the Booster
Discussion
Simpo - you cynic you.. 
Eric I get that, but this is the bit I am struggling with, when the spacemen/women/frogs or whatever go for a walk outside, there is NO way they are going at 17K mph they would be squished surely, and they are on a lead so they don't float off...
Sooo...why do the boosters fall back down and not go floating off..?
Are they radio controlled / pre-programmed to turn round and re-enter the atmosphere where gravity properly kicks in..?
Eric I get that, but this is the bit I am struggling with, when the spacemen/women/frogs or whatever go for a walk outside, there is NO way they are going at 17K mph they would be squished surely, and they are on a lead so they don't float off...
Sooo...why do the boosters fall back down and not go floating off..?
Are they radio controlled / pre-programmed to turn round and re-enter the atmosphere where gravity properly kicks in..?
When the astronauts go for an EVA they are doing exactly the same speed as the orbiting craft. There is gravity. If the crafts were stationary, they would fall to the earth. They are doing daft mph because the rate at which they fall is the same rate that the earth drops away, (being a sphere/oblique spheroid).
Gaffer said:
Really..? they look so slow when moving round.
I just can't get my head round it.
Think of it as the parabolic vomit comet plane. It is doing relatively daft mph towards the ground and the folks are essentially weightless, (they are free falling). This is what is happening to the astronaut folks, just at a much higher altitude, and at a much greater speed. I just can't get my head round it.
garyhun said:
Do you "feel" you are moving at 500mph when flying in a 747? No atmosphere, no resistance, no feeling of speed.
This, humans don't feel speed, only acceletation.Just standing at the equator would mean you are traveling at 1000mph, and at the poles 0mph. We feel no difference at either.
Edited by 98elise on Tuesday 20th March 07:54
Gaffer said:
Really..? they look so slow when moving round.
I just can't get my head round it.
Imagine firing a bullet at the horizon. gravity will pull it to earth so the flight path is curved.I just can't get my head round it.
Now fire that bullet at 18,000 mph. Gravity will still pull, but the bullets curve is the same as the earths curve.
The bullet keeps "falling". but never enough to get closer to earth.
This is an orbit
Edited by 98elise on Tuesday 20th March 07:51
Gaffer said:
Really..? they look so slow when moving round.
I just can't get my head round it.
People only feel "speed" on earth due to side effects such as wind turbulence, engine noise, tyre noise, wind noise etc.I just can't get my head round it.
When all those "effects" are removed sense of speed disappears completely. As has been said, when you are travelling in an airliner you are moving at 500 mph but inside the cabin everything appears as if it is standing still.
When an astronaut steps outside a spacecraft orbiting the earth, that spacecraft is travelling at 17,500 mph. The astronaut will travel alongside the spacecraft at the same speed. When you think about it, why should he feel any difference? You asked "Wouldn't he be squished?". Why should he be? What is outside the spacecraft to squish him?
During the last three Apollo missions, the Command Module pilots performed spacewalks as the Apollo spacecraft was returning from the moon. They were travelling at about 25,000 mph - the fastest spacewalks ever.
http://www.youtube.com/watch?v=vFwqZ4qAUkE
This is excellent. Slo-mo footage of launch from all kinds of angles, commentated on by guys from Glenn Research Centre. They explain everything thats going on, why it happens etc. Very very good.
This is excellent. Slo-mo footage of launch from all kinds of angles, commentated on by guys from Glenn Research Centre. They explain everything thats going on, why it happens etc. Very very good.
Speed is all relative! Right now, the Earth and everything /everyone on it is whistling through space at several thousand miles per hr when viewed from the refference point of our sun. But i am able to sit here on my sofa typing this post without any effort or sensation of speed whatso ever!
Astronauts must be tethered to their spacecraft due to the lack of means to apply any "reactive" force to enable them to get back towards that craft (EV "jet packs" excluded). Even though both the craft and the astronaut are doing 17,500mph, and without any atmosphere to slow either down (via friction with the air molecules) both objects will continue to travel along the same path.
However if the astronaut was to accidentally push against his craft, his body would accelerate away from the craft (and the craft would accelerate away from him (at a lesser rate, due to it's greater mass). But then, being in "free" space, the astronaut would have nothing on with to push himself back towards the craft. Even a gentle and accidental push would result in the two objects moving apart relentlessly and unstoppably!
Astronauts must be tethered to their spacecraft due to the lack of means to apply any "reactive" force to enable them to get back towards that craft (EV "jet packs" excluded). Even though both the craft and the astronaut are doing 17,500mph, and without any atmosphere to slow either down (via friction with the air molecules) both objects will continue to travel along the same path.
However if the astronaut was to accidentally push against his craft, his body would accelerate away from the craft (and the craft would accelerate away from him (at a lesser rate, due to it's greater mass). But then, being in "free" space, the astronaut would have nothing on with to push himself back towards the craft. Even a gentle and accidental push would result in the two objects moving apart relentlessly and unstoppably!
The tethers the Shuttle astronauts use was based on the tethers used by yachtsmen, I think.
Of course, if for some reason an astronaut did come detached and float away, although he can't get back to the spacecraft, the spacecraft could get to him and haul him in.
NASA tried a Manned Manoeuvering Unit on a a number of occasions between 1966 and 1985 or so. They first had a go at testing it in a Gemini mission but the astronaut, Gene Cernan, had so much trouble getting into the thing that the attempt to use it was abandoned before he was able to detach it from the Gemini spacecraft.
A stripped down version was tested INSIDE Skylab in 1973.
Finally, NASA were able to use it successfully on a number of Shuttle missions in 1984 and 1985 but after the CHallenger accident, it was decided to drop the unit from future mission.
One of the iconic images from the Shuttle era was this shot of Bruce McCandless "flying" the MMU on its first test in 1984.
Of course, if for some reason an astronaut did come detached and float away, although he can't get back to the spacecraft, the spacecraft could get to him and haul him in.
NASA tried a Manned Manoeuvering Unit on a a number of occasions between 1966 and 1985 or so. They first had a go at testing it in a Gemini mission but the astronaut, Gene Cernan, had so much trouble getting into the thing that the attempt to use it was abandoned before he was able to detach it from the Gemini spacecraft.
A stripped down version was tested INSIDE Skylab in 1973.
Finally, NASA were able to use it successfully on a number of Shuttle missions in 1984 and 1985 but after the CHallenger accident, it was decided to drop the unit from future mission.
One of the iconic images from the Shuttle era was this shot of Bruce McCandless "flying" the MMU on its first test in 1984.
The question of speed and what it's relative to lead to fundemental questions, it's an interesting topic.
To help illustrate the gravity/orbit/why don't they fall thing here are a few pics - imagine gravity around the earth being represented by a rubber sheet - not a bad analogy as the closer to the earth you are the more attraction there is etc:
We see how it demonstrates that objects are pulled towards each other, the ball rolled in that picture has had its course altered by the earth-like mass in the middle of the sheet.
So for an orbit, we need to roll a ball at just the right speed so that it rolls around and around the earth (in space there is no friction as there would be with a rubber sheet of course) without dropping into the hole nor escaping from it:
Of course, this is just a flat representation, gravity is 3D and things are a bit more complicated, but in essence that's why satellites/spacecraft and astronauts stay aloft - they aren't unaffected by the earths gravity, it's just that it is a) much weaker at that distance and b) the speed they go means they aren't immediately pulled towards the earth (in simple terms).
To help illustrate the gravity/orbit/why don't they fall thing here are a few pics - imagine gravity around the earth being represented by a rubber sheet - not a bad analogy as the closer to the earth you are the more attraction there is etc:
We see how it demonstrates that objects are pulled towards each other, the ball rolled in that picture has had its course altered by the earth-like mass in the middle of the sheet.
So for an orbit, we need to roll a ball at just the right speed so that it rolls around and around the earth (in space there is no friction as there would be with a rubber sheet of course) without dropping into the hole nor escaping from it:
Of course, this is just a flat representation, gravity is 3D and things are a bit more complicated, but in essence that's why satellites/spacecraft and astronauts stay aloft - they aren't unaffected by the earths gravity, it's just that it is a) much weaker at that distance and b) the speed they go means they aren't immediately pulled towards the earth (in simple terms).
Ascent, bit heavy going but fascinating images also
http://www.youtube.com/watch?v=W2VygftZSCs&fea...
http://www.youtube.com/watch?v=W2VygftZSCs&fea...
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