What was the launch window for a moon shot?

If Apollo 12 had waited an hour or two for the thunderstorm to pass,
how soon after would it have been able to go? The same day, next day,
a month later? How badly would it have messed up the schedule?

In article ,
wrote:

If Apollo 12 had waited an hour or two for the thunderstorm to pass,
how soon after would it have been able to go? The same day, next day,
a month later? How badly would it have messed up the schedule?

It was so long ago, but I think that we had about 1.5 hours launch
window. I do know that a direct ascent trajectory had only about a
3-minute launch window, which is why it was not planned into the
missions.

In article , wrote:
If Apollo 12 had waited an hour or two for the thunderstorm to pass,
how soon after would it have been able to go? The same day, next day,
a month later? How badly would it have messed up the schedule?

An Apollo launch window was usually around three hours long; the Apollo 12
window on 14 Nov 1969 was from 1122 to 1428 EST. Roughly speaking, the
parking orbit had to pass through a predetermined point in space where the
TLI burn would be done. Some delay in launch could be accommodated by
changing the *direction* of launch, so that the parking orbit would still
hit the target point. However, safety and tracking issues permitted only
a limited range of directions from KSC, and that was what usually bounded
the launch window on a particular day. Apollo launches were targeted for
the very beginning of the window, so around three hours were available for
delays before the launch had to be scrubbed for the day.

The day and the choice of TLI point were determined mostly by the Moon's
orbit and rotation, and the requirement that the Sun be low behind the LM
(so shadows would reveal terrain hazards) at landing. The range of
acceptable Sun angles was fairly narrow; sometimes launch windows were
available on two successive days, but in Apollo 12's case, the 14th was
it -- scrub on that day, and you had to wait a month for the Sun to be in
the right place again at that landing site.

(Had more generous margins been available, a desired arrival time could
have been achieved over a range of several launch days, by using faster or
slower trajectories to the Moon. But Apollo simply didn't have that kind
of performance reserve.)

In the early days of Apollo mission planning, there was a concept that if
you missed the window for one site, you could instead go to a site farther
west, which would have the right Sun angle a few days later. This was a
largely theoretical possibility for Apollo 11, whose crew had only barely
enough time for training just for the primary site. But the Apollo 12
crew did train a little bit for a backup site, with a window on 16 Nov.
The backup site unfortunately *didn't* have a Surveyor in it, which
reduced its appeal, and it's an open question whether upper management
would have gone for the backup site or accepted a one-month slip. (Later
Apollos abandoned the backup-site concept entirely.)

It was theoretically possible to recycle for a launch the day after a
scrub, if certain conditions were met, but a two-day recycle was more
comfortable.

If memory serves, Apollo 17 was the only (manned) Apollo that didn't go at
the beginning of the window, and Apollo 16 was the only (manned) Apollo
that didn't go on the originally-selected day (not a scrub -- Charlie Duke
came down with pneumonia during final preparations, and management, having
learned its lesson from Apollo 13, simply postponed the launch a month so
he could recover, rather than rearranging the crew at the last minute).
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. |

On Jun 22, 3:19 pm, wrote:
If Apollo 12 had waited an hour or two for the thunderstorm to pass,
how soon after would it have been able to go? The same day, next day,
a month later? How badly would it have messed up the schedule?

I see that you're still into pretending that we've walked on the moon.

How typically Zion pathetic.
-
"whoever controls the past, controls the future" / George Orwell
-
Brad Guth

On Sat, 23 Jun 2007 05:48:23 GMT, (Henry Spencer)
wrote:

Apollo launches were targeted for
the very beginning of the window, so around three hours were available for
delays before the launch had to be scrubbed for the day.

....Which, as we saw for A17, came in handy. However, where A12 was
concerned, IIRC the weather stayed as ****ty as the stack was launched
in for the rest of the day, and may have been in the same shape the
next two days as well. That's from memory of commentary from one of
the network coverage segments, but a search of NOAA records would no
doubt confirm. With that in mind, waiting three hours wouldn't have
done any good save for leaving SCE to AUX relegated to some dusty old
ops manual :-)

OM
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(Henry Spencer) writes:

Apollo launches were targeted for
the very beginning of the window, so around three hours were available for
delays before the launch had to be scrubbed for the day.

I mean this in the spirit of honest curiosity and not as an
attempt to sound pedantic: are there cases where one would not want
to schedule the initial launch attempt to the beginning of the launch
window?

I don't mean that it would be timed to the first second that
a launch could possibly succeed, but it seems like once you have the
interval when launch will let the mission meet its target then the
desire to allow for last-minute delays pushes you to an attempt as
early in the window as is available. The only complicating factor that
strikes me as obvious is handling logistic problems like clearing time
on tracking stations or scheduling around another rocket's launch from
the same base or something like that. (I imagine Apollo would have a
priority on all rocket launches with the possible exception of an
emergency launch of a spy satellite, but something like a Mars probe
could be directed to wait till the next day.)

Am I overlooking the even more obvious?

--
Joseph Nebus
------------------------------------------------------------------------------

On 26 Jun 2007 16:17:15 -0400, in a place far, far away,
(Joseph Nebus) made the phosphor on my monitor glow
in such a way as to indicate that:

(Henry Spencer) writes:

Apollo launches were targeted for
the very beginning of the window, so around three hours were available for
delays before the launch had to be scrubbed for the day.

I mean this in the spirit of honest curiosity and not as an
attempt to sound pedantic: are there cases where one would not want
to schedule the initial launch attempt to the beginning of the launch
window?

You generally get more performance margin if you launch in the middle.
For an ISS launch, if you launch too early, or too late, you can't get
there, so if you launch right at the beginning of the window, you're
right on the edge of being able to do so, and may require all of your
flight propellant reserves on a three-sigma day (I'm sure that Jorge
will correct me if I'm wrong).

So you have to trade that off against the possibility that you'll get
weathered out or something that prevents you from launching later.

In article ,
h (Rand Simberg) wrote:

On 26 Jun 2007 16:17:15 -0400, in a place far, far away,
(Joseph Nebus) made the phosphor on my monitor glow
in such a way as to indicate that:

(Henry Spencer) writes:

Apollo launches were targeted for
the very beginning of the window, so around three hours were available for
delays before the launch had to be scrubbed for the day.

I mean this in the spirit of honest curiosity and not as an
attempt to sound pedantic: are there cases where one would not want
to schedule the initial launch attempt to the beginning of the launch
window?

You generally get more performance margin if you launch in the middle.
For an ISS launch, if you launch too early, or too late, you can't get
there, so if you launch right at the beginning of the window, you're
right on the edge of being able to do so, and may require all of your
flight propellant reserves on a three-sigma day (I'm sure that Jorge
will correct me if I'm wrong).

So you have to trade that off against the possibility that you'll get
weathered out or something that prevents you from launching later.

In the case of Apollo, it wasn't so much a performance problem as it was
a restriction due to range safety, which limited the launch azimuth to
72 deg to 108 deg. The launch window started when the launch plane
coincided with the 72 deg. launch azimuth and ended at 108 deg.

You certainly do want to launch at the first opportunity, since there
were something like 3 million separate parts in a Saturn V/Apollo system.

Rand Simberg wrote:
On 26 Jun 2007 16:17:15 -0400, in a place far, far away,
(Joseph Nebus) made the phosphor on my monitor glow
in such a way as to indicate that:

(Henry Spencer) writes:

Apollo launches were targeted for
the very beginning of the window, so around three hours were available for
delays before the launch had to be scrubbed for the day.
I mean this in the spirit of honest curiosity and not as an
attempt to sound pedantic: are there cases where one would not want
to schedule the initial launch attempt to the beginning of the launch
window?

You generally get more performance margin if you launch in the middle.
For an ISS launch, if you launch too early, or too late, you can't get
there, so if you launch right at the beginning of the window, you're
right on the edge of being able to do so, and may require all of your
flight propellant reserves on a three-sigma day (I'm sure that Jorge
will correct me if I'm wrong).

Generally correct - though IIRC the three-sigma reserves are stacked
such that even if you launch at the edge of the window, you can
generally "buy back" a lot of the reserves as you go along.

At the beginning of the Shuttle/Mir program, launch was targeted for the
opening of the window since it was a tight window by historical shuttle
standards and managers wanted maximum flexibility to handle small slips.
As the ISS program matured they started targeting for the in-plane time
in the middle of the window to maximize performance.

So you have to trade that off against the possibility that you'll get
weathered out or something that prevents you from launching later.

For the Apollo case, they weren't doing a rendezvous in LEO so that
planar issue wasn't there, but you had the variable azimuth thing to
deal with for the TLI window. In that case I'd think that the optimal
performance would be at 90 azimuth. I think they always went for the
beginning of the window (72, as Orval pointed out) but had the program
continued further and their confidence in their ability to launch within
the window increased, I think they might have started shooting for 90 to
wring a bit more performance out of the system.

It will be interesting to see how these tradeoffs play out for an
EOR/LOR system like Ares. The Ares V may have a variable azimuth
targeting scheme, but once it launches, the Ares I will have a fixed
azimuth to shoot for.

On Jun 23, 4:26 am, Orval Fairbairn wrote:
I do know that a direct ascent trajectory had only about a
3-minute launch window, which is why it was not planned into the
missions.

Presumably the launch to parking orbit was more down to a desire to
check out the spacecraft before committing to the Moon? If there was a
major fault (e.g. an air leak somewhere which couldn't be fixed, or
multiple fuel cell failure) then they could rapidly return to Earth
from the parking orbit, whereas if they launched on a direct ascent to
the Moon they'd take quite a while to get back even with a direct
abort using the SPS.

Mark