RE: Upcoming T-4
Ted Molczan (molczan@fox.nstn.ca)
Wed, 4 Dec 1996 15:58:05 -0500
John Pike wrote:
>According to usually reliable sources, the next Titan-4 launch from
>Vandenberg is anticipated on 18 December, with a window between 8:30 AM and
>11:00 AM PST.
The above equals 16:30 to 19:00 UTC on 18 Dec 96.
My guess remains that they are going to replace the eastern
Keyhole imaging reconsat, which requires a launch near
18:00 UTC.
Before I get into talking about alternatives, it may be worth
a reminder that what we are loosely calling a "launch window" is more
like a "launch period" - a larger period of time surrounding the
real launch window. The last two LEO Titan 4 launches from
VAFB involved very narrow launch windows, perhaps +/- 15 minutes,
within announced launch periods, 2.5 h to 4 h in duration.
Specifically, the replacement western Keyhole launched on 5 Dec 95
at 21:18 UTC, had an announced launch period of 20:00 to 22:30 UTC.
NOSS 2-3 launched on 12 May 96 at 21:32 UTC, had an announced
launch period of 19:00 to 23:00 UTC.
So for the upcoming launch, the announced launch period is not
reason in itself to believe that the intended launch window is not a
much shorter period centred on 18:00 UTC. Moreover, it is pretty
common knowledge that the operators of the Keyhole satellites prefer
to operate with the standard 2 satellite constellation, with both
sats in their respective standard orbital plane. The eastern Keyhole
slot has been vacant since mid-May'96, and historically the favourite
launch season has been Oct-Dec, so I am betting on a Keyhole launch
at 18:00 UTC.
Of course, the above is just experienced speculation, so I have
considered possible Lacrosse or NOSS replacements/additions.
Both Lacrosses are fairly old, 8 and 6 years respectively, so one or
both may be in need of replacement. If they are dead or on life-support,
then there would be no orbital plane constraints for a Lacrosse 3,
so the launch could be any time within the announced period. So if the
launch time is radically different than 18:00 UTC, then Lacrosse 3
becomes a good candidate.
Coincidentally, Lacrosse 1's orbital plane would permit a direct
replacement to be launched into the same orbit with a liftoff at about
17:07 UTC, which is within the launch period. However, I doubt that it
would be placed in the same orbit as Lacrosse 1, because its orbital
inclination of 57 deg was almost certainly a compromise, to enable a
shuttle-launch from Cape Canaveral. Lacrosse 2, launched from VAFB on
a Titan 4, is in a 68 deg orbit, which I assume to be the standard
orbit. So Lacrosse 1's orbit is unlikely to influence the upcoming
launch. However, if Lacrosse 2 is still operational, and expected to
operate for say 2 or 3 more years, then Lacrosse 3's RAAN might well be
positioned some distance away from Lacrosse 2's RAAN, to provide for
more even coverage throughout the day.
A 90 deg RAAN would appear to be the most logical choice, but that
would require Lacrosse 3 to be launched at either 00:38 UTC, or
12:36 UTC, both of which are outside the launch period. The situation
is no better for 45 deg, 60 deg, 120 deg or 135 deg spacings.
A 180 deg spacing would fall near the end of the launch period, at
about 18:35 UTC, but I see nothing useful in having two LEO sats in the
same plane, but traveling in opposite directions.
So there are no strong Lacrosse indications in the launch period.
Now let us consider NOSS. Some time ago, John Pike expressed the belief
that there will be no more NOSS 2 launches, but just in case the U.S. Navy
is of a different opinion ... The only direct replacement opportunity
involves NOSS 2-3, but since that constellation is only 7 months old, I
believe we can safely rule that out. So all that remain are augmentation
possibilities, but the existing spacings make it difficult to guess where
a fourth NOSS 2 would be placed.
NOSS 2-1 and 2-2 were placed 120 deg apart (or 240 deg on the other side
of the equator), so I assumed that NOSS 2-3's plane would have bisected
their planes. But both the failed NOSS 2-3 launch of Aug'93, and the
successful May'96 NOSS 2-3 launch were aimed at splitting the 240 deg
separation into about a 90 and 150 deg separation. NOSS 2-2 and 2-3 are
95 deg apart, and I have no idea how another NOSS 2 should be spaced
relative to them. A 47.5 deg bisection would require a launch outside the
announced launch period. NOSS 2-1 is rather old, so I doubt they would be
building a constellation around it now. I have no idea where another
NOSS 2 should go, and since there are no reasonable replacement opportunities,
I am inclined to rule out a NOSS launch.
Of course there is always a chance that it will turn out to be a NOTA, but
I am predicting a Keyhole at about 18:00 UTC.
Clear skies!
Ted