Space Forum / Shuttle / April 2008

On Mar 31, 9:17 am, "max...@mission51l.com" <max...@mission51l.com>
wrote:

Idiot, you have two threads going on this

On Mar 30, 12:00 am, charliexmur...@yahoo.com wrote:

On Mar 31, 7:39 am, charliexmur...@yahoo.com wrote:

I agree that there is no question that MMH does break down to hydrogen
gas and anhydrous ammonia in an irridium catalyst bed.  This generate
a tremendous amount of heat and essentially ammonia/hydrogen steam. I
am not sure what happens to that lone methyl group (ionic form), are
you? Does it add a charged "natural gas" ion to the exhaust? That
would add one additional flammable gas to the exhaust.

I have seen a lot more liftoffs than landings on TV but I have never
seen the phenomenon you mention. This may be in part because it is
obscured by the OMS pod viewed from the side. It should be visible
from the south and several pad cameras used by NASA PAO. Anyway, I
would appreciate it if you could point me to a few launch videos where
it can be readily seen.

Thanks.

Dave

On Mar 31, 12:16 pm, "max...@mission51l.com" <max...@mission51l.com>
wrote:

There was no hydrazine leak.  Only GN2.

There is no "situation" and nothing out of the ordinary.

If you could read NasaSpaceflight L2, you would see that there was no
issue.  In the same L2, you can see videos of flames from other
landings and even on launches.  But since you are an idiot, liar, and
generally no good, you were banned from NasaSpaceflight

On Mar 31, 9:16 am, "max...@mission51l.com" <max...@mission51l.com>
wrote:

You are correct.  There is no hypergolic oxidizer (nitrogen tetroxide)
in use for the APUs.

I did some research on this issue because I found it interesting and I
have been wondering if what happened on STS 123 was nominal or near
nominal or did something unexpected happen. This is not the only place
that has discussed this issue and I do wonder why after 123 missions,
with about 20% of them ending at night how so many people could be
surprised at what they saw including myself.

With that in mind, the APUs' monomethyl hydrazine flows or is injected
(not sure which) over an irridium bed or some similar catalyst. This
causes an exothermic reaction releasing a tremendous amount of heat,
about 1470 degrees Fahrenheit or more depending on the catalyst. The
catalyst is not consumed in any manner so it saves a lot of weight on
the spacecraft as no oxidizer is needed.  What is neat is that you get
a very good yield for the small volume of the monomethyl hydrazine
used.

The reaction generates nitrogen gas which does not further react with
the other products. The reaction also generates hydrogen gas in H2
form and ammonia gas. I don't know what happens to the methyl group
but if unchanged, it would be a fuel too. Both ammonia and hydrogen
are good fuels but in this instance I believe these superheated high
pressure gases drive the APU turbines. Someone please correct me if I
am wrong. They can not burn as a normal fuel would because there is no
oxidizer generated during the catalyzation of the monomethyl hydrazine
and of course there is no flame source. The first oxidizer the ammonia
and hydrogen contacts is the oxygen in the atmosphere as it is vented
from the APU exhaust port.

Hydrogen gas will autoignite at 930 degrees Fahrenheit and anhydrous
ammonia will autoignite at about 1200 degrees Fahrenheit. These
temperatures are both below the temperature of the initial catalytic
reaction. Theoretically at least, a flame source might not be
necessary to cause ignition of either fuel as it leaves the exhaust
port. There may be some atmospheric cooling variations during reentry
and final approach that cause cooling of the APU compartments and
associated exhaust plumbing that lowers the temperatures of the fuels
in the exhaust lines enough to prevent autoignition in some or most
cases.

I just do not know enough about the air flow/pressure equalization
process of the orbiter during entry or lift-off for that matter, to
discuss the variables. Anyway, if the temperatures of the fuels are
still at or above their respective autoignition temperatures they will
ignite without a flame source, otherwise, a flame source would be
necessary and yes John static electricity could spark a fire under the
right conditions.

My questions then are, what is the nominal temperature of the ammonia
and hydrogen exhaust gases at the APU exhaust port and does this vary
in some manner? Would an overheated APU make a difference? Somewhere
in the answers to these questions you should find your answers John.

Dave