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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

#11

Post by eksith »

gnerd wrote: post #8
eksith wrote: post #2

I wish these guys the best of luck and hope they get to do it quickly and safely. If anything, our drive for beating someone else into space for political or economic reasons has really poisoned the well, so to speak. Maybe it does take the crazy pioneers to get up to the Black Sky... just because it's there.

> If anything, our drive for beating someone else into space for political or economic reasons has really poisoned the well, so to speak. I assume you are American. If so, I may be fuzzy on the historical facts, but didn't the Russians beat you guys into space?

Yep. Which is why we took enormous risks and end up losing 3 astronauts in Apollo 1, which wasn't even a proper spaceflight, on our way to beat them to the Moon.

Russians lost 4 cosmonauts as well on 2 separate missions.

Like I said. Poisoned well.

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

#12

Post by jacquesm »

barking wrote: post #10
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.

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.

It's actually a very gradual spiraling inward. This is because the momentum imparted initially is slowly dissipated (by impacts & interaction with the gravitational field of the sun), an extremely small factor.

The question is whether the sun will go nova before or after we (or our sterilized remains) finally arrive :)

That's not the only effect, all of this is counteracted by the decrease in mass of the sun and the tidal interaction between the sun and its planets (which slows down the rotation of the sun), both of these should push the earth outward from the sun.

I'm not sure how it all works out (whether it is a net positive or a net negative) but it can't be much or we'd have drifted out of the zone where life is sustainable long ago.

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

#13

Post by jonmrodriguez »

barking wrote: post #10
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.

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.

Yes, I think you're correct

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

#14

Post by [deleted] »

eksith wrote: post #11
gnerd wrote: post #8

Earlier quoted context omitted.

> If anything, our drive for beating someone else into space for political or economic reasons has really poisoned the well, so to speak. I assume you are American. If so, I may be fuzzy on the historical facts, but didn't the Russians beat you guys into space?

Yep. Which is why we took enormous risks and end up losing 3 astronauts in Apollo 1, which wasn't even a proper spaceflight, on our way to beat them to the Moon. Russians lost 4 cosmonauts as well on 2 separate missions. Like I said. Poisoned well.

[deleted]

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

#15

Post by ColinWright »

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.

Extremely simple sums tells you orbital kinetic energy is about 10 times gravitational potential energy.

Orbital velocity is about 8 km/s [0], so KE/kg is 1/2 v^2 which is about 32 * 10^6. At 320 km altitude the PE/kg is about g.h = 10.320.1000 = 32 * 10^5.

So getting up to the right height is about one tenth of the energy needed.

[0] You can compute this using Pythagoras and the fact that the Earth's radius is about 6.4 * 10^6 meters.

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

#16

Post by barking »

jacquesm wrote: post #12
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.

It's actually a very gradual spiraling inward. This is because the momentum imparted initially is slowly dissipated (by impacts & interaction with the gravitational field of the sun), an extremely small factor. The question is whether the sun will go nova before or after we (or our sterilized remains) finally arrive :) That's not the only effect, all of this is counteracted by the decrease in mass of the sun and the…

Thanks. I can understand the mass of the sun having an effect but why would the speed of rotation of the sun have an effect on earth's orbit?

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

#17

Post by barking »

jonmrodriguez wrote: post #13
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.

Yes, I think you're correct

Yay me!

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

#18

Post by 6ren »

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.

Another way to visualize this is if you had a perfectly flat planet with no atmosphere, you could orbit at head height.

You could sort of do this on the moon, but mountains.

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

#19

Post by [deleted] »

jacquesm wrote: post #12
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.

It's actually a very gradual spiraling inward. This is because the momentum imparted initially is slowly dissipated (by impacts & interaction with the gravitational field of the sun), an extremely small factor. The question is whether the sun will go nova before or after we (or our sterilized remains) finally arrive :) That's not the only effect, all of this is counteracted by the decrease in mass of the sun and the…

[deleted]

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

#20

Post by jacquesm »

barking wrote: post #16
jacquesm wrote: post #12

Earlier quoted context omitted.

It's actually a very gradual spiraling inward. This is because the momentum imparted initially is slowly dissipated (by impacts & interaction with the gravitational field of the sun), an extremely small factor. The question is whether the sun will go nova before or after we (or our sterilized remains) finally arrive :) That's not the only effect, all of this is counteracted by the decrease in mass of the sun and the…

Thanks. I can understand the mass of the sun having an effect but why would the speed of rotation of the sun have an effect on earth's orbit?

I think that's this effect:

http://en.wikipedia.org/wiki/Tidal_acceleration

Speaking about the rotation of a gaseous body is a bit tricky anyway, not all parts of the sun rotate equally fast. (inside/outside, equatorial/polar).

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