CHEEHH@jane.uh.edu (Rikhit Arora) (12/01/89)
This is in response to Phil Jansen's mailing regarding the sequence of SSME
start and SRB ignition and liftoff. The exact number are as follows:
.
.
T-2 minutes, 55 seconds Pressurize liquid oxygen tank for
flight and retract gaseous oxygen
vent hood.
T-1 minute, 57 seconds Pressurize liquid hydrogen tank.
T-31 seconds "Go" from ground computer for
orbiter computers to start the
automatic launch sequence.
T-28 seconds Start SRB hydraulic power units.
T-21 seconds Start SRB gimbal profile test.
T-6.6 seconds Main engine start.
T-3 seconds Main engines at 90 percent thrust.
T-0 SRB ignition, holddown post
release and liftoff.
T+7 seconds Shuttle clears launch tower and
control switches to JSC.
As can be seen, it takes 3.6 sec for the main engines to get to 90% thrust and
3 sec thereafter to go all the way to 104% and the autosequence computers to
verify that the SSME's are delivering the expected thrust. This probably is
the primary reason that the main engines ignite before the SRB's.
--
-------------------------------------------------------------------------------
............. | Rikhit Arora
And, while with silent, lifting mind I've trod | cheehh@uhupvm1.bitnet
The high untrespassed sanctity of space, | cheehh@jane.uh.edu
Put out my hand, and touched the the face of God.| ~~~~~~~~~~~~~~~~~~
-------------------------------------------------------------------------------fisher@devo.dec.com (12/01/89)
> > >T+7 seconds Shuttle clears launch tower and > control switches to JSC. Are you sure about this one? Seems like 7 seconds is more like the tower clear time of a Saturn V. The shuttle is more like a couple seconds! Burns
CHEEHH@jane.uh.edu (Rikhit Arora) (12/02/89)
In article <1730@hiatus.dec.com>, fisher@devo.dec.com writes: >> >> >>T+7 seconds Shuttle clears launch tower and >> control switches to JSC. > Are you sure about this one? Seems like 7 seconds is more like the > tower clear time of a Saturn V. The shuttle is more like a couple seconds! > > Burns Come to think of it, 7 seconds does seem to be too long. But that's the number given in the STS-34 press kit from which I lifted the countdown schedule. Comments anyone?? -- ------------------------------------------------------------------------------- ............. | Rikhit Arora And, while with silent, lifting mind I've trod | cheehh@uhupvm1.bitnet The high untrespassed sanctity of space, | cheehh@jane.uh.edu Put out my hand, and touched the the face of God.| ~~~~~~~~~~~~~~~~~~ -------------------------------------------------------------------------------