Solid vs. liquid rocket motors

"Alan Erskine" wrote in message
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"F/32 Eurydice" wrote in message
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Am I correct that solid rocket motors are always running at full
thrust, because they have no valves to control the fuel flow, so you
can't throttle them up and down?

As Fred eluded to, picture drawings of a circle and a star - the star has
much more surface area. A star-shaped solid propellant segment (grain)
will have much greater thrust than one shaped like a circle.

Star shaped hollow core designs actually have more thrust at the beginning
of the burn and less at the end of the burn as the star shape slowly changes
to a more circular shape over the course of the burn. By carefully chosing
the shape of the hollow core, you can actually tailor the thrust versus time
profile of the solid rocket motor.

Jeff
--
"Take heart amid the deepening gloom
that your dog is finally getting enough cheese" - Deteriorata - National
Lampoon

On Apr 24, 6:17*pm, "Alan Erskine" wrote:
"F/32 Eurydice" wrote in message

...



Am I correct that solid rocket motors are always running at full
thrust, because they have no valves to control the fuel flow, so you
can't throttle them up and down?

As Fred eluded to, picture drawings of a circle and a star - the star has
much more surface area. *A star-shaped solid propellant segment (grain) will
have much greater thrust than one shaped like a circle.

The most interesting part of October Sky was where Hickam described
how his nitrate/sugar mix was burning irregularly, because of
granulation in the fuel. His solution was to melt the mix into a
homogeneous goop and pour it into the rocket before it hardened, which
then worked fine.

But I suppose you wouldn't need that if the granules already have a
stoichiometric mix of fuel and oxidizer.

On 5/8/2010 4:21 AM, F/32 Eurydice wrote:

The most interesting part of October Sky was where Hickam described
how his nitrate/sugar mix was burning irregularly, because of
granulation in the fuel. His solution was to melt the mix into a
homogeneous goop and pour it into the rocket before it hardened, which
then worked fine.

That's exactly how you do it by the way.
The stuff is called "Carmel Candy" because of its brown color when melted.
The thing that makes its production tricky is that it won't melt right
till it reaches 400 F., and its ignition temperature is 600 F.
That sounds pretty safe until you realize that all it takes is for the
smallest fraction of it to reach 600 F. for the whole works to go up.
I used to bake it up in the oven, but in retrospect it would be a lot
safer to melt it in a container that was immersed in hot oil so that you
could monitor the temperature with more accuracy.
If nothing else, cleaning up the pot and stirring spoon that are used to
make it is a piece of cake, as you simply ignite them and let the goo
burn off.
I was going to try and figure out a way to make it that didn't involve
heating, by dissolving the ingredients in something that could be dried
out of the finished fuel grain by air exposure, like alcohol or acetone,
but lost interest in it before it got that far along.
My favorite part in the movie was when he was was talking to von Braun
about his work on Project Vanguard...without realizing that that would
be the perfect way to **** him off. :-)

Pat