Launch windows when launching to GEO?

Tonight, an Atlas 5 is going to launch an Inmarsat satellite. The launch
window opens at 2142 UTC and closes 15 minutes later.

-why? Why is there a launch window when launching to GEO? Couldn't a
satellite destined for GEO be launched at any time?

/steen

On Thu, 10 Mar 2005, Steen wrote:

Tonight, an Atlas 5 is going to launch an Inmarsat satellite. The launch
window opens at 2142 UTC and closes 15 minutes later.

-why? Why is there a launch window when launching to GEO? Couldn't a
satellite destined for GEO be launched at any time?

Perhaps they are exploiting some aspect of lunar/solar tidal angle for a
minimum energy transfer?

Actually, It does seem awfully peculiar. You would think that the energy
for launch from a particular spot to a particular Geosynchronous orbit
would be very nearly constant.

Gene P.

--
Alcore Nilth - The Mad Alchemist of Gevbeck

Steen wrote:

Tonight, an Atlas 5 is going to launch an Inmarsat
satellite. The launch window opens at 2142 UTC and
closes 15 minutes later.

-why?

Why is there a launch window when launching to
GEO? Couldn't a satellite destined for GEO be
launched at any time?

Purely speculating:

1) Even aiming at a spot moving in lockstep with
regard to your launch site, there are still Sun and
Moon tidal forces that can help or hurt you.

2) Even more prosaicly, it could be something as
simple as "how much big, expensive, heavily
committed ground support equipment" they could, or
did, afford themselves to schedule beyond their
ideal launch time; a communications antenna
sufficient to communicate with the launch vehicle
(not payload) minimal capacity radio system for
final precise orbit tuning might be one such
resource that needs scheduling well in advance and
that will be in use by others shortly after nominal
usage time by the launch team.

Being able to launch "at any time" isn't equivalent
to being able to "tie up launch resources for any
conceivable length of time".

FWIW

xanthian.

"Steen" wrote in news:42304a2f$0$181
:

Tonight, an Atlas 5 is going to launch an Inmarsat satellite. The launch
window opens at 2142 UTC and closes 15 minutes later.

-why? Why is there a launch window when launching to GEO? Couldn't a
satellite destined for GEO be launched at any time?

My take on this is that it's going to a supersynchronous transfer
orbit with a very high apogee that may be affected by things like
the Moon's gravity. Seems like we've had a discussion on this
before...

The launch was, of course, scrubbed; they may try again on Friday.

--Damon

-why? Why is there a launch window when launching to GEO? Couldn't a
satellite destined for GEO be launched at any time?

I suppose in principle, the answer is yes. However, moving in longitude
takes time, because the satellite is drifted slowed towards its assigned
orbital slot - and INMARSAT might not want to wait weeks or months for
the thing to arrive at its designated space. Just speculation, though.

Jan

Steen wrote:
Tonight, an Atlas 5 is going to launch an Inmarsat satellite. The launch
window opens at 2142 UTC and closes 15 minutes later.

-why? Why is there a launch window when launching to GEO? Couldn't a
satellite destined for GEO be launched at any time?

/steen


In principle yes, but as you want to be in sunlight when executing
critical spacecraft operations, using for instance simple sun sensors,
the mission planning calls for a certain launch window

--
th

Damon Hill wrote in
31:

"Steen" wrote in news:42304a2f$0$181
:

Tonight, an Atlas 5 is going to launch an Inmarsat satellite. The
launch window opens at 2142 UTC and closes 15 minutes later.

-why? Why is there a launch window when launching to GEO? Couldn't a
satellite destined for GEO be launched at any time?

My take on this is that it's going to a supersynchronous transfer
orbit with a very high apogee that may be affected by things like
the Moon's gravity. Seems like we've had a discussion on this
before...

The launch was, of course, scrubbed; they may try again on Friday.

--Damon


Does anybody know why a super-synchronous transfer orbit? Looking at the
diagrams, it didn't look like the most efficient way of getting to GEO in
the end.

orbital plane changes require less propellant.


"Tom Kent" wrote in message
. 30.42...
Damon Hill wrote in
31:

"Steen" wrote in news:42304a2f$0$181
:

Tonight, an Atlas 5 is going to launch an Inmarsat satellite. The
launch window opens at 2142 UTC and closes 15 minutes later.

-why? Why is there a launch window when launching to GEO? Couldn't a
satellite destined for GEO be launched at any time?

My take on this is that it's going to a supersynchronous transfer
orbit with a very high apogee that may be affected by things like
the Moon's gravity. Seems like we've had a discussion on this
before...

The launch was, of course, scrubbed; they may try again on Friday.

--Damon


Does anybody know why a super-synchronous transfer orbit? Looking at the
diagrams, it didn't look like the most efficient way of getting to GEO in
the end.

Tom Kent wrote:

Does anybody know why a super-synchronous transfer orbit? Looking at
the
diagrams, it didn't look like the most efficient way of getting to
GEO in
the end.

The supersynchronous transfer orbit approach actually
decreases the delta-v requirements for putting a payload
into GEO. This is because orbit plane changes are more
efficiently performed at the lower velocity of the
supersynchronous apogee.

The 400-series Atlas V Centaur can only perform two-burns,
so it cannot do insertion burns at transfer orbit apogee.
(500-series Atlas V Centaurs do have a three-burn option.)
The Atlas V-431 model had a lot of excess payload capability
for this flight. Supersynchronous provided a way to use
the excess capability. Another, even more efficient option
might have been to perform an extended-coast profile to
inject the payload into a higher perigee/GSO apogee
transfer orbit (as was done during the AV-003 mission).

- Ed Kyle

wrote in news:1111079751.762331.8400
@o13g2000cwo.googlegroups.com:

Tom Kent wrote:

Does anybody know why a super-synchronous transfer orbit? Looking at
the
diagrams, it didn't look like the most efficient way of getting to
GEO in
the end.

The supersynchronous transfer orbit approach actually
decreases the delta-v requirements for putting a payload
into GEO. This is because orbit plane changes are more
efficiently performed at the lower velocity of the
supersynchronous apogee.

That makes sense.



The 400-series Atlas V Centaur can only perform two-burns,
so it cannot do insertion burns at transfer orbit apogee.
(500-series Atlas V Centaurs do have a three-burn option.)

So in the three burn circumstance, any third burn would be a
cirrcularization burn? If that was the case, then it would be doing the
part of the satellite in Henry's parell post. In that case (without case
of doing the inclination transfer) you'd just want to go to a typical GTO,
because you WOULD burn the tanks dry?



- Ed Kyle



Tom Kent