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N-Prize Lower Stage

Shaving grams off reusable casings
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Modern rebuildable high power rocket motors are powerful, they can be the same formula as the Shuttles SRBs, but the reusable casings are heavy. The idea is a redesign to reduce weight and add the possibility of thrust vector control. Per the link the reusable casings usually weigh about the same as the propellant they are surrounding and to have any hope of reaching space, every gram must be saved and drag must be reduced wherever possible.

Rebuildable cases need to perform 3 functions, contain the pressure of the burning fuel, contain the heat from the burning fuel and provide the appropriate nozzle for directing thrust. Present cases do this with an aluminum outer tube with internal threads at each end and two O-ringed end caps, one is just a plug and the other has the nozzle.

Replace the aluminum tube with radial wrapped carbon fiber (thickness based calculated hoop stress * safety factor) with only the outer layer being a single layer of longitudinal fibers spaced out leaving ten longitudinal grooves between the runs. The ends on the carbon would be slotted with a convex slice which will be explained later. The end caps are replaced with cylindrical aluminum tubes with a semi-spherical ends. The basic idea is an aluminum can with the top cut off and then bottom pushed out to be semispherical. Each of the end caps are capped by a ceramic “bobbin” with one spherical side to match the end cap. One bobbin will have a solid center and the other will have hollow center with a SS cylinder inserted to support radial compression on the bobbin. On the nozzle end (the side with the hollow bobbin) a hole is drilled in the aluminum end cap which is the same size as the hole in the bobbin. This needs to be large enough for both the nozzle and to allow slight nozzle deflection. On the inside of the nozzle end cap goes quarter semi-spherical Teflon washer and a ceramic nozzle with a quarter semi-spherical base. A ceramic cap with a small spring is C-cliped around the nozzle to keep the nozzle assembly in contact with the aluminum end cap, but will still allow slight radial sliding deflections. Cover exposed aluminum surfaces with a thin ceramic insulator sheets (McMaster 93615K14). Create an aluminum tube and ceramic insulator spacer to go between the two end caps.

Now assemble the motor by stacking the motor grains inside the end cap and then another ceramic sheet and aluminum cap the ends so that the aluminum and ceramic butt against each other and slide the carbon fiber tube around the assembly. Take a Kevlar thread that has loops spliced onto each of its ends and thread around the assembly by wrapping first the bobbin then pass along the longitudinal gaps to the other bobbin. If this works, it should use the aluminum as a gas envelope, the ceramic as the thermal barrier, the carbon fiber as the hoop stress support and the Kevlar as the longitudinal stress support. Small piezoelectric actuators could be added to slightly deflect the nozzle for steering.

MisterQED, Mar 31 2008

Reloadable motors http://www.apogeero...h_Reload_Motors.asp
[MisterQED, Mar 31 2008]

[link]






       Sounds like a good plan for a lightweight rocket stage. Can you build it for £999.99?
wagster, Mar 31 2008
  

       Well the key is reusability and saving weight. If you can reuse all the parts then all you pay for is fuel. I figure you can't out science NASA, so you have to try to do stuff that they can't due to scale such as complete carbon fiber assemblies which actually aren't all that expensive if you buy them in common sizes. The big problems that need to be solved is guidance which seems to be a subject that no one in model rocketry has tackled.
MisterQED, Mar 31 2008
  

       Guidance is a small problem, I think.   

       The carbon fibre manufacture is bigger.   

       computers are now cheap.   

       Long live sentience!
Zimmy, Apr 01 2008
  

       //big problems that need to be solved is guidance which seems to be a subject that no one in model rocketry has tackled.//
I think model rocketeers are not /allowed/ to solve the problem, lest they get paid a visit by the men in trenchcoats.
coprocephalous, Apr 01 2008
  

       Yes, "guidance" seems taboo, but "atitude control" seems to be a topic of at least minimal discussion. I wonder how much of the legalities you could dodge by launching from international waters or a small country. My guess is it would just delay the arrest, but it doesn't matter, I'm really only pursuing this as a thought experiment. We need to go back to space.
MisterQED, Apr 01 2008
  

       //Long live sentience!//   

       Absolutely - and vive le brain!
wagster, Apr 01 2008
  

       Blimey! I leave this place alone for a few days, and when I get back you've all got the pointy scissors out and Kevlar all over the floor.   

       Sounds like an excellent plan to me. I'd disagree about the "can't out-science NASA" - they are handicapped by a sophisticated infrastructure and a huge budget.
MaxwellBuchanan, Apr 04 2008
  

       Reloadable motor casings are intentionally built to be robust. They are quite often called upon to take severe treatment.   

       Degrees of success on a high power launch:
>Everything recovered successfully - celebrate!
>Parachute tangled and hard landing, a few dings - still celebrate
>No parachute, crushed the airframe; fin can, altimeter and motor recovered OK - still a good flight
>Turf shot, altimeter's gone, motor case OK - ouch, commiseration
>Total loss, motor whanged - you'd go get drunk, but can't afford it.
lurch, Apr 04 2008
  
      
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