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The DIY Danes planning to launch a man into space

theguardian.com

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Re: The DIY Danes planning to launch a man into space

#31

Post by tocomment »

jonmrodriguez wrote: post #7
jholman wrote: post #4

This is awesome, and nothing in this comment is meant to take away from that awesome, only to contextualize it. Getting above the Karman Line (100km above sea level) and getting into orbit are dramatically different problems. In case the name "Copenhagen Suborbitals" didn't make it clear, they're shooting for the former. For an amusingly-illustrated take on this, see the recent http://what-if.xkcd.com/58/ As another…

http://what-if.xkcd.com/58/ This xkcd explains this really well. At orbital height, Earth's gravity's pull is still a full 90% of what we experience on the surface. Orbiting objects "dodge" this fall by going really fucking fast . I think I saw a comparison once that it takes about 15~20X more energy to attain orbit speed as it does to attain orbital height.

Along this line of thinking I was wondering how much energy it would take to reach the height of one of the lagrangian points? And once we get there would it be possible to stay there and resist the pull of earth?

If so that would be cheap space access right there.

Re: The DIY Danes planning to launch a man into space

#32

Post by barking »

jlgreco wrote: post #29
barking wrote: post #10

Earlier quoted context omitted.

So is this centrifugal force counteracting gravity? So then gravity would be like your hand's grip preventing the bucket from flying away when you swing a bucket of water? If this is the case then I think I'd understand the way planets don't fall into the sun better. The way I've heard it described before as something like 'forever falling into the sun' confusing.

> So is this centrifugal force counteracting gravity? I think that is probably a relatively reasonable way of considering it, but to be clear, centrifugal force isn't actually something that exists. It wouldn't be drawn in a free body diagram unless the diagram was drawn with a non-inertial reference frame, but even then it is only drawn so that equations meant for inertial reference frames will still work. ( http://…

Thanks I looked it up on wikipedia and they have a nice simulation there.

http://en.wikipedia.org/wiki/Newton%27s_cannonball

I didn't understand the elliptical orbit at first and was writing a supplementary question here but as i did so the following explanation occurred to me.

As it spirals outward it's no longer travelling at right angles to the force of gravity so now gravity exerts some force parallel and opposite to its direction of travel and starts to slow it down.

It slows down at a rate greater than the required orbital speed does and eventually it's travelling at less than orbital speed and starts to travelling closer to earth again and now gravity starts to act to increase its speed because the ball is again not travelling perpendicular to the force of gravity but this time gravity's pull increases its speed.

Now the ball's speed increases faster than the required orbital speed does until it exceeds orbital speed again.

And so ad infinatum!

Re: The DIY Danes planning to launch a man into space

#33

Post by tocomment »

tocomment wrote: post #31
jonmrodriguez wrote: post #7

Earlier quoted context omitted.

http://what-if.xkcd.com/58/ This xkcd explains this really well. At orbital height, Earth's gravity's pull is still a full 90% of what we experience on the surface. Orbiting objects "dodge" this fall by going really fucking fast . I think I saw a comparison once that it takes about 15~20X more energy to attain orbit speed as it does to attain orbital height.

Along this line of thinking I was wondering how much energy it would take to reach the height of one of the lagrangian points? And once we get there would it be possible to stay there and resist the pull of earth? If so that would be cheap space access right there.

Seriously a downvote? Why not explain why it's wrong?

Re: The DIY Danes planning to launch a man into space

#36

Post by metageek »

tocomment wrote: post #33
tocomment wrote: post #31

Earlier quoted context omitted.

Along this line of thinking I was wondering how much energy it would take to reach the height of one of the lagrangian points? And once we get there would it be possible to stay there and resist the pull of earth? If so that would be cheap space access right there.

Seriously a downvote? Why not explain why it's wrong?

IIRC, it takes just as much energy to reach L4 (or L5) as to reach the Moon--they're in the same orbit.

If you've got settlers on the Moon, or beyond the Earth-Moon system, L4 is probably a good place to build a commercial and industrial outpost; but, for your only space installation, something lower down is much cheaper.

Re: The DIY Danes planning to launch a man into space

#37

Post by tocomment »

metageek wrote: post #36
tocomment wrote: post #33

Earlier quoted context omitted.

Seriously a downvote? Why not explain why it's wrong?

IIRC, it takes just as much energy to reach L4 (or L5) as to reach the Moon--they're in the same orbit. If you've got settlers on the Moon, or beyond the Earth-Moon system, L4 is probably a good place to build a commercial and industrial outpost; but, for your only space installation, something lower down is much cheaper.

I'm talking about earth sun Lagrange points. Those wouldn't be orbiting the moon.

Re: The DIY Danes planning to launch a man into space

#38

Post by bencollier49 »

rhengles wrote: post #35
bencollier49 wrote: post #6

I immediately thought "Kerbal Space Program". This is extremely cool.

This reminded me of the 2006 film The Astronaut Farmer with Billy Bob Thornton.

I hadn't heard of that film at all! Will be watching it at some point in the future, it sounds like fun.

Re: The DIY Danes planning to launch a man into space

#39

Post by Gravityloss »

ColinWright wrote: post #22
Gravityloss wrote: post #21

Earlier quoted context omitted.

One can also look at it this way, though it does not explain the energies' relation to each other: The total gravitational potential energy you start from, from Earth's surface, is far from zero, as you are already at over 6000 km height. The 300 km height is a small blip on top of that. A 5 % change. The velocity you start with is only the spinning of the earth (lower velocity closer to poles, vector sum too because…

But that's really misleading, as the energy involved in increases in velocity go as a square, whereas increases in height are linear. In fact, if you go to 600 km height then you double the PE change, but don't much change the KE requirement. I'm not sure your comment would really help someone who doesn't already know what's going on, but I'd appreciate replies from people who are trying to understand more about this…

Yeah, you're right.
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