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Steerable solid rocket possible?

Posted by: Ekkehard Augustin - Thu Jul 06, 2006 10:56 am
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Steerable solid rocket possible? 
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Post Steerable solid rocket possible?   Posted on: Thu Jul 06, 2006 10:56 am
Regarding solid rockets I read under Wikipedia that the flight profile is soemthing like imaged in the internal shape/profile of the solid propellant.

This appears to me as if the rocket is programmed that way irreversibly.

Now solid propellant is said to be rubber in principle under Wikipedia. Because of this I have the question if there might be a way the internal shape/profile of the rubber can be modified.

The question come to me because I know rubber as something that is reshapable.

What about it?



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Post    Posted on: Thu Jul 06, 2006 2:00 pm
We already have steerable solid rockets. The space shuttle solid rockets are steered with movable nozzles.


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Post    Posted on: Thu Jul 06, 2006 2:12 pm
To steer a rocket even includes to change or modify the thrust if wanted. According to the explanantion under Wikipedia this is not possible at existing rockets.



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Post    Posted on: Thu Jul 06, 2006 4:47 pm
Most solid rockets have a hollow space at the center, and burn outwards to the casing. (core burning). A few burn from the bottom up.

The hollow space can have different horixontal profiles, from a simple circle to a many pointed star, and further. The shape determines the rate of burning over time. Thus the rocket can be 'pre-programmed' to increase or decrease thrust at different times.

The hollow space can also have varying vertical profiles for even more complicated control.

Another way to control a solid is to pump a fluid from the top, that either increases or decreases the rate of burning. The ultimate evolution of this technique is the Hybrid rocket, where the fluid flow is essential.


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Post    Posted on: Thu Jul 06, 2006 5:01 pm
Ekkehard Augustin wrote:
To steer a rocket even includes to change or modify the thrust if wanted. According to the explanantion under Wikipedia this is not possible at existing rockets.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


jet vanes for steering


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Post    Posted on: Fri Jul 07, 2006 6:54 am
Hello, WannabeSpaceCadet,

what you said is what I read under Wikipedia - but all of it is programmed prior to launch.

But what about possibilities to change the profile(s) of the core during flight because of winds and the like? It might be required to increase of reduce the thrusts away from what has been pre-programmed. Since the solid propellant is rubber or rubber-like deformations of the profile(s) might be possible - but is it really? And if no what all prevents that?



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Post Re: Steerable solid rocket possible?   Posted on: Fri Jul 07, 2006 2:36 pm
Ekkehard Augustin wrote:
...
This appears to me as if the rocket is programmed that way irreversibly.

Now solid propellant is said to be rubber in principle under Wikipedia. Because of this I have the question if there might be a way the internal shape/profile of the rubber can be modified. ...


Try to reshape a structure that's burning away! It might be feasible (say to constrict it) in theory but I've never heard of any application. Anyway, in order to influence the thrust by shaping the rubber you'd need to modify the burn rate, by changing e.g. the aspect ratio of your inverse-star-shaped propellant segments. It would be much easier just to change the nozzle characteristics, or inject a fluid that modifies the burn rate.

On the other hand, as pointed out before, you can use a steerable nozzle, and thrust control. The former is easy and common, the latter hard and uncommon for solids.

Type "thrust modulation solid propellant" (without quotes) in Google and you'll find the four most promising concepts on the first results page. You can use a restricting nozzle (allowing thrust control within certain limits, but you have to take care what happens inside because you're not influencing the burn rate), or go to something like a solid-propellant ramjet, where the air flux intensifies the burn rate and effectivity, though it burns even without air. On the whole, there are only a few companies or research outfits who've given much consideration to it, mostly for missiles.

Regards
Max

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