Ahhhhhh Crud! Launch Clock liftoff question.

"John" wrote in
ups.com:

0236 GMT (9:36 p.m. EST Thurs.)

SCRUB. Tonight's liftoff has been scrubbed due to low clouds over the
launch site


I saw they stopped the clock at five minutes. So lets say they are in the
last thirty seconds of the launch window and they get a break. Do they
take time off the clock, and go? If they restarted the clock at five
minutes they would be out of the launch window after five minutes, or is
the five correlated with the end of the end of the launch window?

Bart wrote:
I saw they stopped the clock at five minutes. So lets say they are in the
last thirty seconds of the launch window and they get a break. Do they
take time off the clock, and go?

No. It means there's five minutes of 'stuff' left to do before they can
launch, no matter when they decide to restart the countdown.

I believe they can stop the clock any time prior to 30-odd seconds when
the launch sequencer takes over and restart from there, but the later
in the count they wait the less time they can hold for (e.g. once the
APUs are running there are only a few minutes of excess fuel available
for a hold).

From what I remember of the couple of ISS launches I was at, they
always had a planned hold at five minutes to give them time to deal
with any unexpected problems before they had to make a definite
decision as to whether to launch during the launch window. The non-ISS
launches didn't do that unless they had problems to sort out.

Mark

On 8 Dec 2006 09:05:48 -0800, in a place far, far away,
" made the phosphor on my
monitor glow in such a way as to indicate that:


From what I remember of the couple of ISS launches I was at, they
always had a planned hold at five minutes to give them time to deal
with any unexpected problems before they had to make a definite
decision as to whether to launch during the launch window. The non-ISS
launches didn't do that unless they had problems to sort out.

It's not just ISS launches. Hubble will have a window as well.

" wrote in
oups.com:

Bart wrote:
I saw they stopped the clock at five minutes. So lets say they are in
the last thirty seconds of the launch window and they get a break. Do
they take time off the clock, and go?

No. It means there's five minutes of 'stuff' left to do before they can
launch, no matter when they decide to restart the countdown.

I believe they can stop the clock any time prior to 30-odd seconds when
the launch sequencer takes over and restart from there, but the later
in the count they wait the less time they can hold for (e.g. once the
APUs are running there are only a few minutes of excess fuel available
for a hold).

From what I remember of the couple of ISS launches I was at, they
always had a planned hold at five minutes to give them time to deal
with any unexpected problems before they had to make a definite
decision as to whether to launch during the launch window. The non-ISS
launches didn't do that unless they had problems to sort out.

Mark



You missed what I was asking or I didn't ask clearly. I know what
determines the window.

Let's say there is five minutes on the launch clock and only two minutes
left in the launch window, obviously they can't restart the clock because
after five minutes time they would be three minutes out of the window.

So I'm guessing the way it works: lets say there is a five minute launch
window and five minutes on the clock. Once you get into the launch
window, but the clock hasn't restarted there won't be a launch that day
because starting and running the clock down the window would have passed.

I thought it was strange last night when they were talking 30 seconds of
window left but there were five minutes on the clock, and that's what made
me think about the above. Time on the clock dictates if a launch can occur
in the window.

Bart wrote:
So I'm guessing the way it works: lets say there is a five minute launch
window and five minutes on the clock. Once you get into the launch
window, but the clock hasn't restarted there won't be a launch that day
because starting and running the clock down the window would have passed.

I *think* the way it works is, when they say there's 30 seconds left in
the launch window while they are holding at 5:00, there is really 5:30
left in the window and 30 seconds left for them to restart the
countdown.

Lee Jay

Bart wrote:
I saw they stopped the clock at five minutes. So lets say they are in the
last thirty seconds of the launch window and they get a break. Do they
take time off the clock, and go? If they restarted the clock at five
minutes they would be out of the launch window after five minutes, or is
the five correlated with the end of the end of the launch window?



They cannot just skip the last 5 minutes and just press the big red button
to go "now". When they entered the hold at T-5, all operations still
needing to be done were also put on hold. Those 5 minutes are filled with
many procedures that are executed to start things up one my one.

So, when they declared the launch window had been exceeded, it meant that
if they were to resume countdown at that point, the launch would occur
outside the launch window.


They had said that the hold at T-5 would be a maximum of 4.5 minutes. And
once the hold went beyond 4.5 minutes, the had to srub with or without
weather reports.

"Lee Jay" wrote in
ups.com:

Bart wrote:
So I'm guessing the way it works: lets say there is a five minute
launch window and five minutes on the clock. Once you get into the
launch window, but the clock hasn't restarted there won't be a launch
that day because starting and running the clock down the window would
have passed.

I *think* the way it works is, when they say there's 30 seconds left in
the launch window while they are holding at 5:00, there is really 5:30
left in the window and 30 seconds left for them to restart the
countdown.

Lee Jay


Exactly.

So when they scrubbed the launch, the launch site was still in the
window(ISS orbital plane), they just didn't have enough time to do
five minutes worth things and still launch within the window.

bart

"Lee Jay" wrote in
ups.com:

Bart wrote:
So I'm guessing the way it works: lets say there is a five minute
launch window and five minutes on the clock. Once you get into the
launch window, but the clock hasn't restarted there won't be a launch
that day because starting and running the clock down the window would
have passed.

I *think* the way it works is, when they say there's 30 seconds left
in the launch window while they are holding at 5:00, there is really
5:30 left in the window and 30 seconds left for them to restart the
countdown.

You are correct.
--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
think one step ahead of IBM.

Bart wrote:
So when they scrubbed the launch, the launch site was still in the
window(ISS orbital plane), they just didn't have enough time to do
five minutes worth things and still launch within the window.


It doesn't matter if the they are inside or outside a window when they
decide on a go/nogo. What matters is whether such a decision would get the
count to 0 (shuttle ignites its SRBs) within the launch window.

From T-9 down to 0, all tasks are extremely regimented. You cannot
compress the last 5 minutes into 3 or 2 minutes just because you were
"late" in resuming the coundown.

It is a pretty easy decision: if the countdown is to terminate after the
close of the window, it is pointless to continue the countdown since the
decision to scrub is automatic.

One could argue that perhaps NASA has some comfort margins in the
definition of the launch window and that some launch manager might decide
that the shuttle still has enough performance to launch 30 seconds late.
Would the launch computers allow for the manager/director to lengthen the
launch window during a T-5 hold ?


Also, if they had managed to push the clouds away during the T-5 hold and
the shuttle had launched within 1 second of the close of the window, how is
the addditional delta V achieved ?

Do the SSMEs expand fuel early on to travel in a different direction to
catch up with the orbital plane and then correct course to accelerate in
that plane ? Or do they launch in the "wrong" plane normally, with
additional OMS burns done later on to correct it ?

If they catch up with the orbital plane by using SSMEs, is there some
buffer fuel that allows them to do so and still have MECO happen at the
right altitude/energy ? Or is the shuttle left at lower altitude/energy,
and compensation is done with longer OMS burns ?

On Fri, 08 Dec 2006 10:47:09 -0800, Lee Jay wrote:
Bart wrote:
So I'm guessing the way it works: lets say there is a five minute launch
window and five minutes on the clock. Once you get into the launch
window, but the clock hasn't restarted there won't be a launch that day
because starting and running the clock down the window would have passed.

I *think* the way it works is, when they say there's 30 seconds left in
the launch window while they are holding at 5:00, there is really 5:30
left in the window and 30 seconds left for them to restart the
countdown.

The wording confused me as well. They could have phrased things a bit
better to avoid confusion.