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The DIY Danes planning to launch a man into space

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

#21

Post by Gravityloss »

ColinWright wrote: post #15
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.

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…

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 you must launch to an inclined orbit from there) which is about 0.4 km/s. So you need a 20x change. (Coincidentally reciprocal of 5%.)

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

#22

Post by ColinWright »

Gravityloss wrote: post #21
ColinWright wrote: post #15

Earlier quoted context omitted.

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…

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. Maybe I'm just the wrong audience.

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

#23

Post by barking »

jacquesm wrote: post #20
barking wrote: post #16

Earlier quoted context omitted.

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).

That's a very interesting link, the diagram of the earth moon system explains it quite well, I think. I just googled and found this article that reports the same effect between the earth and the sun http://www.newscientist.com/article/dn17228-why-is-the-earth...

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

#24

Post by lutusp »

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…

The easy way to solve this class of problem is to compute two quantities -- one, the object's energy at rest on earth's surface, and two, the object's energy when it gets into orbit.

The first is mostly gravitational potential energy (GPE), the second is a mixture of GPE and kinetic energy (KE). They're both easy to compute.

Finally, to figure out how much energy is required to go from the launch pad to orbit, simply subtract one energy number from the other, remembering that the total energy is the sum of KE and GPE.

A complicating factor is the fact that a rocket's mass decreases as it ascends (as the fuel is burned), but this isn't a deal-breaker -- all one needs to do is profile the ascent, the increase in velocity alongside the decrease in mass, using a numerical integral. That's not difficult at all (and it has to be a numerical integral).

More here: http://arachnoid.com/gravitation_equations/orbital_mechanics...

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

#25

Post by kalms »

Imagenuity wrote: post #3

It's great to see people hacking away at space travel. Not everything needs to be done on a NASA scale. The hard part will be the rocket engine, access to rocket fuel and launch facilities where you can launch without risking homes and lives. Denmark is in a poor location for launches: too far north, surrounded by populated countries, and their likely launch direction would go over Russia. You need a heat shield if y…

They always launch from the Baltic sea, and test the engines in and around Copenhagen.

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

#26

Post by jlgreco »

6ren wrote: post #18
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.

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.

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

Here is am image of the moon, taken from orbit around it, a mere 28.4 miles above the surface: http://neverworld.net/lunar/lo2_h162_3a-m.jpg

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

#27

Post by jlgreco »

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…

Tidal forces between the Earth and its Moon in fact result in the Moon (very slowly) getting further and further away from the earth.

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

#28

Post by jacquesm »

jlgreco wrote: post #27
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…

Tidal forces between the Earth and its Moon in fact result in the Moon (very slowly) getting further and further away from the earth.

Yep. The actual experimental verification of this makes for very interesting reading.

see: http://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment

and lots of links referenced from there.

Amazing precision, I still find it quite incredible that such a distance could be reliably measured to such precision and that meaningful conclusions could be drawn from those measurements.

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

#29

Post by jlgreco »

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.

> 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://en.wikipedia.org/wiki/Centrifugal_force_(rotating_ref...)

I think the best way to get an intuitive understanding of how orbit works is with Newton's cannonball thought experiment, and perhaps playing around with a simulation of it.

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

#30

Post by c10n »

For anyone not following the project, here is a small status of where they are (please note that I'm just lurking - any errors below are mine):

Founded in 2008, as an open source and non-profit project. Currently about 40 people involved on a volunteer basis. The support organisation has about 800 paying members.

The first major success was the flight of the HEAT 1X Tycho Brahe, a 6 meter 65 cm Ø rocket and launch vehicle, which was test fired over the Baltic sea on 3rd June 2011 and was aborted at an altitude of 2.8 km.

The HEAT 1X Tycho Brahe was passively stable and propelled by a Polyurethane fuel with LOX oxidizer.

After this, the focus shifted towards liquid propelled rockets (75% alcohol LOX) and currently the TM65 engine has been tested numerous times and is due for a launch next summer. In the most recent version the rocket is fed by a H2O2 driven Turbo pump and can provide around 65 kN of thrust. http://www.copenhagensuborbitals.com/tm65.php http://en.wikipedia.org/wiki/TM65

In parallel, work has been done on a number of other sub projects

- the launch vehicle Tycho Deep Space II (http://en.wikipedia.org/wiki/Copenhagen_Suborbitals#Tycho_De...) - the Launch Escape System (LES) - the space suit (http://www.youtube.com/watch?v=fcZOsdoCjqU) - active stability system tested on the Sapphire rocket (http://www.copenhagensuborbitals.com/sapphire.php) which was successfully launched to a height of more than 8 km on June 23, 2013 (http://www.youtube.com/watch?v=kcF5xNrb3HA&feature=c4-overvi...).

Also, the plans for the next version of the rocket (the HEAT 1600) which might use either a cluster of TM65s or a single engine. http://www.wired.com/wiredscience/2013/05/heat-1600-concept-...

A manned launch is 3–5 years away

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