[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: AO40: status



>Hummh...  You are thinking in terms of a liquid I think.  I am thinking in
>terms of a gas (I assume that all of the liquids instantly vaporize to a
>gas in the vacuum at the point of the leak (near the center of the
>spacecraft).  At that point, the gas is not in contact with the spacecraft
>and so it does not take away any angular momentum as it finds its way out
>of the bird through whatever holes it finds.

Just a second. What is the key property of a gas that distinguishes it
from a liquid? It expands to fill, i.e., contact, its container! If a
gas did not contact the spacecraft or impart momentum, then how would
the kick motor work??

It doesn't matter what physical state the propellant is in, gas, liquid
or solid. If its mass moves radially inward or outward in the spinning
spacecraft, the spin rate will change.

>Kind of like the fly flying around the cockpit of Lindberg's plane.  Does
>it add to the weight of his plane or not?

Sure it does. The fly, being heavier than air, must flap its wings to
stay in the air. This results in a downward motion of air that pushes
on the cockpit floor. The only time the fly doesn't add to the weight
of the plane is when it stops flapping its wings and falls
ballistically.  Of course, that only lasts until it hits the floor,
imparting all of the momentum it would have imparted indirectly by
flapping its wings during the fall time.

>But I guess it does take a finite period of time for any molecule of gas
>to get through the compartments and out, and by that time it has picked up
>the angular momentum of that compartment (no matter how small)...

Bingo.

>So then it must have all escaped near the center..

Only if the spinup was caused by simple mass movement. If external
energy were added to this mass before it was ejected, then it could
have exited almost anywhere as long as there was a moment arm between
the exit point and the spin axis. I see two possible sources for this
extra energy: helium pressure, either in the helium tank or in the
ullage spaces of the propellant tanks, and the energy that would be
released by the reaction of MMH and N2O4. Energy could also be
released by MMH alone if it were heated (reportedly to 400C) or if it
encountered a catalyst that decomposed it.

Phil

----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home