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How high can a rocket go?

Posted by: roygrif - Tue Oct 12, 2004 2:07 am
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How high can a rocket go? 
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Post How high can a rocket go?   Posted on: Tue Oct 12, 2004 2:07 am
Before re-entry heat shielding is needed?

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Post    Posted on: Tue Oct 12, 2004 5:20 am
Very recently - last week if I remember right - I posted a new topic concerning improvement prizes.

Your question might be answered by such a prize because improvements might be possible to increase the altitude reachable without needing a heat shield for reentry.

This improvement can reduce the investment costs of the vehicles and cause easier development.



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Post    Posted on: Tue Oct 12, 2004 9:30 am
If you carry enough fuel, you could of course fly without heatsheilding at all - all deceleration/ done by engines rather that atmosperic friction. Armadillo will probably reenter like that.

James


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Post Re: How high can a rocket go?   Posted on: Tue Oct 12, 2004 10:13 am
roygrif wrote:
Before re-entry heat shielding is needed?

If I understand things correctly, I believe that SS1 flies with some sort of ablative heat shielding (?) ... so the answer to your question is either (or both) of the following ...

i) not very high
ii) it depends on what your rocket is made of

That's not much help I guess. Sorry.

DKH

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Post    Posted on: Tue Oct 12, 2004 10:27 am
Does the heating depend on the angel of reentry? Is there less heating if this angel isn't 90° but somewhere between 90° and 0° (excluded)?

If yes then this factor effects the altitude asked for too.

The thicker regions of the atmosphere at a given velocity might cause more heating than the thinner regions I suppose. At angels near to 0° the thicker regions are reached later than at angels near to 90°.

If I'm right the competitors for altitude could choose wider trajectories to prevent heating partially.



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Post    Posted on: Tue Oct 12, 2004 12:28 pm
I actually believe the amount of heating is dependant on the speed of re-entry. The friction due to atmospheric drag will always be the same... the question is how quickly does the heat need to be dissipated. Do this experiment... drag your hand across a carpet VERY slowly... now do it again but this time VERY fast. What is the difference? The first time the heat building up from the friction had a chance to dissipate, the second time the heat built up so fast it had nowhere to go.

The problem is re-entry from an orbit.... first off you're going pretty fast to start with... second problem, if you don't hit the atmosphere at a high enough angle you're going to skip out of the atmosphere like a rock skipping along the surface of the water.


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Post    Posted on: Tue Oct 12, 2004 12:46 pm
Allright but the thickness or density of the air has an effect on the heating.

The heated parts of the Space Shuttle don't begin to glow at the first touch to the atmosphere and they don't begin to glow immediatly after the first touch - the glowing begins in regions a little bit deeper in the atmosphere which is a little bit denser there.

In your example the paper always has identical thickness - if you choose thinner paper it might be possible that you choose it a little bit too thin. Then it might be hurt instead of heating my hand even if I move my hand faster.

The problem at reentry isn't the heating itself but the degree of temperature the heating is causing.

At angles of reentry near to 0° more than to 90° it may be possible to remain longer times at the first touch to the atmosphere to use the drag there to decelerate. This can be kept while sinking deeper.

Perhaps those regions where the Space Shuttle begins to glow are reached by a velocity less than the Shuttle's velocity. Then the heating in that regions will be reduced too.

The danger that the near-0°-angle will push the vehicle back into space may be handled by providing equipments the pilot can change the angle. The minimum angle will - and has to- be calculated before the first flight.

This results in a spiral landing course around our planet instead of the 8000 km landing distance of the Space Shuttle.



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Post    Posted on: Tue Oct 12, 2004 12:49 pm
Funny, I thought the original poster was talking about sub-orbital launches ... asking about "how high" was a big clue. You guys have completely hijacked this thread :lol:

Ekkehard is, unlike me, a real gentleman but he can go *spwanggggg* off on a tangent pretty quickly. Ya hafta watch out for that.

DKH

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Post    Posted on: Tue Oct 12, 2004 1:23 pm
A few moments ago I too realized what has happened by my post and that I have answered.

To correct this - I thought of a spacecraft going up to high apogee but at "suborbital" velocity. So it wouldn't be an orbital flight. But the "suborbital" trajectory will be much wider than that of SS1 at its winning flights. It would be widened to a degree providing entry at a "suborbital" velocity by a course that is approximately a tangent to the atmosphere - "approximately" but not exactly because it has to go into the atmosphere slightly.

The course could be widened by using rockets after reaching the apogee.



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Post    Posted on: Tue Oct 12, 2004 2:39 pm
This post is really about heat-shielding ... no, really it is.

First of all, I would like to say sorry ... FOR THIS LINK !!! But even though I would like to, I wont, because it wasn't my fault.

Second of all, I would like to add ... B'WHAAHAHAHAHAHAHAHAhahahaaaaa ... (cough) ... erm, yeah.

DKH

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Post    Posted on: Tue Oct 12, 2004 3:07 pm
Well, yes, you guys have strayed off topic somewhat. However, this is a good thing. Basically, there doesn't appear to be an answer yet to my initial question.

Let me pose another question, at what height is a low earth orbit achieved?

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Post    Posted on: Tue Oct 12, 2004 3:32 pm
Well ... if you are asking for a definition rather than an absolute ...

Encyclopedia of Astrobiology, Astronomy and Spaceflight wrote:
Definitions vary. According to some, LEO includes orbits having apogees (high points) and perigees (low points) between about 100 km and 1,500 km. Others extend that range up to 2,000 or 3,000 km. In some cases, the distinction between LEO and MEO (medium Earth orbit) is dropped and LEO is considered to be any orbit below geosynchronous altitude. The majority of all satellites, as well as the Space Shuttle and International Space Station, operate from LEO.

Would you like any pizza with that?

DKH

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Post    Posted on: Tue Oct 12, 2004 3:49 pm
Dr_Keith_H wrote:
Well ... if you are asking for a definition rather than an absolute ...

Encyclopedia of Astrobiology, Astronomy and Spaceflight wrote:
Definitions vary. According to some, LEO includes orbits having apogees (high points) and perigees (low points) between about 100 km and 1,500 km. Others extend that range up to 2,000 or 3,000 km. In some cases, the distinction between LEO and MEO (medium Earth orbit) is dropped and LEO is considered to be any orbit below geosynchronous altitude. The majority of all satellites, as well as the Space Shuttle and International Space Station, operate from LEO.

Would you like any pizza with that?

DKH

Yes, pineapple and anchovy please. 8)

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Post    Posted on: Wed Oct 13, 2004 6:16 pm
To get this particular thread back on track :) there are a few things you need to consider about re-entry.

All re-entry involves heating, no matter what height it is from, and the amount of heating is proportional to the height (double the height and you will, generally, double the amount of heating).

At this point you need to define heat shielding. If you consider it to be anything which is on the rocket solely for the purpose of protecting it from heat, then I'm afraid the answer is not very high.

You can even buy model rocket kits that come with heat shielding, and these will typically only go about 50,000 feet. In this case though, it's because of the fact that they go supersonic as they go up, and it is breaking the sound barrier that would melt the materials they are normally made from.

There are two ways you can try and reduce the heat on a specific point on an aircraft.
1. Large surface area. This is one of the motives behind SS1's feathered re-entry, as the large surface area helps spread the heating over a larger area, as well as creating more drag so that the heating can be spread over a longer period of time.
2. Fine angle of attack. This basically means that you decend through the atmosphere more slowly, and give the heat/energy more time to dissipate, to try and reduce the maximum heat.

A standard rocket, because of it's small surface area and the fact they normally come back to Earth in much the same way they leave it (ie, in a straight line), is probably going to need heat shielding long before a winged craft.

There is no real set answer to your question, since it depends upon so many other things, but I hope this goes part way to answering it :)

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Post    Posted on: Thu Oct 14, 2004 5:35 am
Hello, Sev,

so I had in mind the second way obviously.

Are there possibilties to combine the two ways to achieve further reductions of the problem?



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