launch windows

I saw on the CBS News page that the launch window for STS-115 extends
from Aug 27th to Sept. 7th. However if Atlantis doesn't fly then,
there are two launch days in October (23rd and 24th I think) and one in
December - the 23rd -and that's it!
I know basically why they have restricted launch windows, because of
the lighting conditions and the limited ISS rendezvous windows anyhow,
but this webpage said the reason for the limited time is because of
temperature restrictions on the ISS... anyone able to explain that to
me?
Also, they (media, and NASA) said a few weeks ago that STS-116
Discovery was hopeful for the December launch window, however with only
one possible day that doesn't seem very worthwhile to even consider
it..more than likely it'll be pushed into next year - obviously
slipping downstream flights as well..

wrote in news:1154991978.129111.291310
@i3g2000cwc.googlegroups.com:

I saw on the CBS News page that the launch window for STS-115 extends
from Aug 27th to Sept. 7th. However if Atlantis doesn't fly then,
there are two launch days in October (23rd and 24th I think) and one in
December - the 23rd -and that's it!
I know basically why they have restricted launch windows, because of
the lighting conditions and the limited ISS rendezvous windows anyhow,
but this webpage said the reason for the limited time is because of
temperature restrictions on the ISS... anyone able to explain that to
me?

Sure. How detailed an explanation you want? :-)

The temperature restrictions are expressed with respect to a parameter
called "solar beta angle". That's the angle between the ISS orbit plane
and the line-of-sight to the sun. This varies throughout the year due to
the Earth's axial tilt with respect to its orbit around the sun (called
the "obliquity of the ecliptic", about 23.4 degrees), and the Earth's
equatorial bulge, which causes the ISS orbit plane to shift westward
about five degrees per day.

Beta angle affects both solar power generation and thermal control. At
higher beta angles, ISS spends less time in the Earth's shadow, and must
fly different attitudes to keep its solar arrays facing the sun and its
radiators edge-on away from the sun. At beta angles above 70 degrees,
there is no orbital night at all. The maximum beta angle is 75 degrees,
the sum of the ISS orbit inclination (51.6 degrees) and the obliquity of
the ecliptic.

Throw a docked orbiter into the mix and you have a third constraint,
shuttle thermal control. The attitude of the orbiter/ISS stack must be
chosen to satisfy ISS power/thermal constraints and shuttle thermal
constraints. It turns out that at beta angles larger than 60 degrees,
there is no attitude that satisfies all three. So the shuttle program has
a launch window cutout when the beta angle will exceed 60 degrees at any
time during docked ops.

These cutouts occur around the solstices, because that's the time of year
when the sun's declination is farthest north (summer) or south (winter)
and so the odds are greatest that the sum of the sun's declination and
the orbit inclination will exceed 60 degrees. The summer cutout affects
night launches and the winter cutout affects day launches. The shuttle
return-to-flight restriction on night launches has effectively mooted the
summer beta cutout, but the combination of the night launch restriction
and the winter beta cutout makes winter launch opportunities few and far-
between.

The 60 degree limit on beta angle during docked ops is a certification
limit. The station program is looking at expanding certification to relax
the limit. This will not be complete any time soon.

Also, they (media, and NASA) said a few weeks ago that STS-116
Discovery was hopeful for the December launch window, however with only
one possible day that doesn't seem very worthwhile to even consider
it..more than likely it'll be pushed into next year - obviously
slipping downstream flights as well..

Different story there. :-) The night launch restrictions are only in
effect until the shuttle program has two consecutive flights with foam
shedding within allowable limits. STS-121 was the first, so if STS-115
flies clean, STS-116 will be able to launch at night, which greatly
expands the launch window.

--
JRF

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check "Organization" (I am not assimilated) and
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Jorge R. Frank wrote:
wrote in news:1154991978.129111.291310
@i3g2000cwc.googlegroups.com:


SNIP

Also, they (media, and NASA) said a few weeks ago that STS-116
Discovery was hopeful for the December launch window, however with
only one possible day that doesn't seem very worthwhile to even
consider it..more than likely it'll be pushed into next year -
obviously slipping downstream flights as well..

Different story there. :-) The night launch restrictions are only in
effect until the shuttle program has two consecutive flights with foam
shedding within allowable limits. STS-121 was the first, so if STS-115
flies clean, STS-116 will be able to launch at night, which greatly
expands the launch window.

Will they be examining the orbiter's heat sheild with the OBSS on every
flight from now on? Will they flip the shuttle during docking with ISS for
the ISS crew to take pics? Or will these time-consuming and complex
procedures be scrapped alongside the night launch restrictions?

Xizor

"Xizor" wrote in
:

Jorge R. Frank wrote:
wrote in news:1154991978.129111.291310
@i3g2000cwc.googlegroups.com:


SNIP

Also, they (media, and NASA) said a few weeks ago that STS-116
Discovery was hopeful for the December launch window, however with
only one possible day that doesn't seem very worthwhile to even
consider it..more than likely it'll be pushed into next year -
obviously slipping downstream flights as well..

Different story there. :-) The night launch restrictions are only in
effect until the shuttle program has two consecutive flights with
foam shedding within allowable limits. STS-121 was the first, so if
STS-115 flies clean, STS-116 will be able to launch at night, which
greatly expands the launch window.

Will they be examining the orbiter's heat sheild with the OBSS on
every flight from now on?

The early (flight day 2) inspections are planned to continue. It is
possible that if NASA gains confidence in the wing leading-edge sensor
system to detect impacts, that the early inspection will be reduced to
"focused inspections" of suspect areas rather than a complete survey.

The late (just prior to undocking) inspections will be performed on the
next few flights but are still being evaluated for the remainder of the
program. They reduce risks due to orbital debris, but also increase risk by
crowding the crew timeline, increasing crew fatigue and the likelihood of
crew error.

Will they flip the shuttle during docking
with ISS for the ISS crew to take pics? Or will these time-consuming
and complex procedures be scrapped alongside the night launch
restrictions?

The Rbar Pitch Maneuver only consumes eighteen minutes and about eighty
pounds of propellant, so it will likely continue.

--
JRF

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

"Jorge R. Frank" wrote in message
...
Sure. How detailed an explanation you want? :-)

The temperature restrictions are expressed with respect to a parameter
called "solar beta angle". That's the angle between the ISS orbit plane
and the line-of-sight to the sun. This varies throughout the year due to
the Earth's axial tilt with respect to its orbit around the sun (called
the "obliquity of the ecliptic", about 23.4 degrees), and the Earth's
equatorial bulge, which causes the ISS orbit plane to shift westward
about five degrees per day.

Beta angle affects both solar power generation and thermal control. At
higher beta angles, ISS spends less time in the Earth's shadow, and must
fly different attitudes to keep its solar arrays facing the sun and its
radiators edge-on away from the sun. At beta angles above 70 degrees,
there is no orbital night at all. The maximum beta angle is 75 degrees,
the sum of the ISS orbit inclination (51.6 degrees) and the obliquity of
the ecliptic.

Throw a docked orbiter into the mix and you have a third constraint,
shuttle thermal control. The attitude of the orbiter/ISS stack must be
chosen to satisfy ISS power/thermal constraints and shuttle thermal
constraints. It turns out that at beta angles larger than 60 degrees,
there is no attitude that satisfies all three. So the shuttle program has
a launch window cutout when the beta angle will exceed 60 degrees at any
time during docked ops.

These cutouts occur around the solstices, because that's the time of year
when the sun's declination is farthest north (summer) or south (winter)
and so the odds are greatest that the sum of the sun's declination and
the orbit inclination will exceed 60 degrees. The summer cutout affects
night launches and the winter cutout affects day launches. The shuttle
return-to-flight restriction on night launches has effectively mooted the
summer beta cutout, but the combination of the night launch restriction
and the winter beta cutout makes winter launch opportunities few and far-
between.

The 60 degree limit on beta angle during docked ops is a certification
limit. The station program is looking at expanding certification to relax
the limit. This will not be complete any time soon.


O.K Jorge, I am humbled by your knowledge. I have to ask one thing. Did you
type that all out on the fly? or copy and paste it from somewhere. I didn't
understand any of it, although, oddly enough. It made sense.

"Doctor Bombay" wrote in
:

O.K Jorge, I am humbled by your knowledge. I have to ask one thing.
Did you type that all out on the fly? or copy and paste it from
somewhere. I didn't understand any of it, although, oddly enough. It
made sense.

Typed on the fly, but it's not as impressive as it sounds since I've
answered the question before (perhaps enough to justify calling it a FAQ)
so it's largely a "mental cut-and-paste" from my previous posts.


--
JRF

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

Jorge R. Frank wrote:

The 60 degree limit on beta angle during docked ops is a certification
limit. The station program is looking at expanding certification to relax
the limit. This will not be complete any time soon.

Doesn't the beta angle cutout restriction go away entirely after STS-115
installs the alpha joint, allowing the beta joint to act as a beta joint
and not an alpha joint?

Mike

Michael Kent wrote in
:

Jorge R. Frank wrote:

The 60 degree limit on beta angle during docked ops is a
certification limit. The station program is looking at expanding
certification to relax the limit. This will not be complete any time
soon.

Doesn't the beta angle cutout restriction go away entirely after
STS-115 installs the alpha joint, allowing the beta joint to act as a
beta joint and not an alpha joint?

Unfortunately, no. The annoying XPOP attitude does go away, but the mated
beta restriction remains.


--
JRF

Reply-to address spam-proofed - to reply by E-mail,
check "Organization" (I am not assimilated) and
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