ET Ascent Heating from SRBs

Hello All,

The SRB cams from STS-121 clearly showed how "charred" the aft dome of
the ET gets from the SRB exhaust during first stage ascent. Does anyone
know the specific details of how hot the ET gets as a result of the SRB
exhaust? Also, a follow up question: what effect does this heating
have on the LH2 in the tank (in other words, does the ET insulation
provide adequate protection from the SRBs to keep the hydrogen mostly
liquid, or has a lot of it become gaseous by SRB sep?)

Thanks!

-Craig

I seem to recall, the last time this question came up, folk suggested that
the blackening was just a deposit, and although there is undoubtedly heating
there, its well within design limits.

Anyone like to put the figures on this, and exactly what is the deposit from
a solid, Aluminium oxide??

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Craig Cocca" wrote in message
oups.com...
Hello All,

The SRB cams from STS-121 clearly showed how "charred" the aft dome of
the ET gets from the SRB exhaust during first stage ascent. Does anyone
know the specific details of how hot the ET gets as a result of the SRB
exhaust? Also, a follow up question: what effect does this heating
have on the LH2 in the tank (in other words, does the ET insulation
provide adequate protection from the SRBs to keep the hydrogen mostly
liquid, or has a lot of it become gaseous by SRB sep?)

Thanks!

-Craig

"Craig Cocca" wrote in news:1154640451.721829.204200
@p79g2000cwp.googlegroups.com:

The SRB cams from STS-121 clearly showed how "charred" the aft dome of
the ET gets from the SRB exhaust during first stage ascent. Does anyone
know the specific details of how hot the ET gets as a result of the SRB
exhaust? Also, a follow up question: what effect does this heating
have on the LH2 in the tank (in other words, does the ET insulation
provide adequate protection from the SRBs to keep the hydrogen mostly
liquid, or has a lot of it become gaseous by SRB sep?)

Charring should be from radiant heating and exhaust gas recirculation.
There should NOT be any LH2 boiling in that area; bubbles would be ingested
in the engine propellant line with potentially disastrous results in
the high pressure fuel turbopumps and downstream from there.

--Damon

Damon Hill wrote:
"Craig Cocca" wrote in news:1154640451.721829.204200
@p79g2000cwp.googlegroups.com:


The SRB cams from STS-121 clearly showed how "charred" the aft dome of
the ET gets from the SRB exhaust during first stage ascent. Does anyone
know the specific details of how hot the ET gets as a result of the SRB
exhaust? Also, a follow up question: what effect does this heating
have on the LH2 in the tank (in other words, does the ET insulation
provide adequate protection from the SRBs to keep the hydrogen mostly
liquid, or has a lot of it become gaseous by SRB sep?)


Charring should be from radiant heating and exhaust gas recirculation.
There should NOT be any LH2 boiling in that area; bubbles would be ingested
in the engine propellant line with potentially disastrous results in
the high pressure fuel turbopumps and downstream from there.

--Damon
There is considerable work done to ensure that the LH2 remains subcooled
and retain quality so that the turbo pump suction does not cause the
LH2 to form bubbles. It is a very delicate balance between the amount of
insulation, the amount of pressurization of the LH2 and required
strength of the tank to ensure that the last amount of LH2 does not
cavitate in the turbo pumps. If I recall correctly, there are 2000lbs of
unused LH2 in the ET at MECO due to lack of quality. Trying to figure
out the temperature of that last gulp of LH2 is incredibly difficult due
to prelaunch heating, circulation of LH2, and ascent heating with
decreasing liquid level during flight. Consideration of non normal
flight conditions such as an engine out make this a real nightmare to
analyze for all conditions!

Maybe I'm being a bit thick here...Nothing new there then... but, is there
no way to test the quality of the fuel long before it gets to the
turbopumps?

I've often wondered how the starting and stopping of engines can be so safe
considering the speed of the pumps etc.

Brian

--
Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
Email:
__________________________________________________ __________________________________________________ __________


"Ghost Rider" wrote in message
...
Damon Hill wrote:
"Craig Cocca" wrote in
news:1154640451.721829.204200
@p79g2000cwp.googlegroups.com:

The SRB cams from STS-121 clearly showed how "charred" the aft dome of
the ET gets from the SRB exhaust during first stage ascent. Does anyone
know the specific details of how hot the ET gets as a result of the SRB
exhaust? Also, a follow up question: what effect does this heating
have on the LH2 in the tank (in other words, does the ET insulation
provide adequate protection from the SRBs to keep the hydrogen mostly
liquid, or has a lot of it become gaseous by SRB sep?)


Charring should be from radiant heating and exhaust gas recirculation.
There should NOT be any LH2 boiling in that area; bubbles would be
ingested
in the engine propellant line with potentially disastrous results in the
high pressure fuel turbopumps and downstream from there.

--Damon
There is considerable work done to ensure that the LH2 remains subcooled
and retain quality so that the turbo pump suction does not cause the LH2
to form bubbles. It is a very delicate balance between the amount of
insulation, the amount of pressurization of the LH2 and required strength
of the tank to ensure that the last amount of LH2 does not cavitate in the
turbo pumps. If I recall correctly, there are 2000lbs of unused LH2 in the
ET at MECO due to lack of quality. Trying to figure out the temperature of
that last gulp of LH2 is incredibly difficult due to prelaunch heating,
circulation of LH2, and ascent heating with decreasing liquid level during
flight. Consideration of non normal flight conditions such as an engine
out make this a real nightmare to analyze for all conditions!

Brian Gaff wrote:

Maybe I'm being a bit thick here...Nothing new there then... but, is there
no way to test the quality of the fuel long before it gets to the
turbopumps?

I've often wondered how the starting and stopping of engines can be so safe
considering the speed of the pumps etc.

Brian


There are low level sensors (so the tank isn't run dry) and some
temperature sensor in the bottom of the tank. The difficulty is that the
LH2 becomes stratified with typically warm fluid at the top and colder
at the bottom once the tank is locked up (pressurized - vent valve
closed). Heat absobed through the walls tends to make the LH2 adjacent
to the vertically oriented walls rise due to buoyancy efects. It goes to
the top and a central core area tends to fall the other direction. The
ullage gas used to pressurize the tank and shove the LH2 out is hot and
adds heat too. (You have to replace the volume of the used LH2)So the
last bit of propellant (BTW, the propulsion people never call LH2
'fuel')is a 'hot' layer and difficult to predict.

The term 'quality' is used to describe how much the LH2 is subcooled.
When the ET is filled the Lh2 vent valve is opened and hydrogen boils
off. It is at a saturated condition - liq and gas at 1 atmosphere and 1
temperature about -423F. Once the ET is pressurized, the only way to
make the LH2 boil is to add heat or locally cause a reduction in the
static pressure. Ascent heating on the aft dome and walls and the
suction/flow of the turbo pumps does just those two things. The aft dome
is more sensitive to heating since it is almost alway wet during the
draining of the tank and adds temperature the propellant right down to
MECO.