RE: Information on VAFB Titan IV launch

Ted Molczan (
Wed, 16 Jul 1997 07:00:18 -0400

Vladimir Agapov wrote about the now delayed VAFB Titan IV

>Name:           TITAN IVA/NUS, A-18/K-18/NUS
>Launch agency:  4 SPACE LAUNCH SQUADRON
>Launch azimut:  153.0000 DEG
>Launch window:  16 JUL 97 0529Z TO 16 JUL 97 0859Z

At VAFB's latitude of 34.7 deg N, the launch azimuth would produce the following orbital inclination:

inc = acos(sin(AZ) * cos(lat))

    = acos(sin(153) * cos(34.7))

    = 68 deg

This is the inclination of Lacrosse 2, which, combined with
the lack of an upper stage, and the earlier de-orbiting of
Lacrosse 1, all but confirms that this will be Lacrosse 3.

Assuming that it is desired to build a constellation
with Lacrosse 2, here are some possibilities. First,
note that Lacrosse 2's orbital plane will be over the
launch site, south-bound, at about 03:57 UTC. This
means that the launch window would place Lacrosse 3
east of Lacrosse 2 (91017A). Here are some interesting
possible spacings within the launch window from 05:29
to 08:59 UTC, on 16 Jul 97:

Launch    Deg East
 UTC     of 91017A

07:56       60
07:14       49.4
06:56       45
05:56       30
05:35       24.7

My favourite is 07:14, which yields a 49.4 deg spacing. 
This may seem like an odd-ball value; however, it 
duplicates the philosophy of the Keyholes, by spacing
the planes by the amount of Earth's rotation through
two Lacrosse orbital revolutions, including precession
due to Earth's oblateness. This spacing affords a large
number of repeated ground-tracks within a 2 satellite
constellation, over short periods of time. I believe
that Keyhole would benefit more from this, since it
suffers from cloud-cover problems. However, both systems
might benefit from repeat coverage for the purpose of
near-real-time detection of changes, such as motion of 

All of the other spacings imply constellations of more
than two spacecraft. My guess is that in these times 
of reduced threat and deficit-fighting, they will live
with two satellites.

For each day of launch delay, the above times would
be 15 minutes earlier. Also, there is several minutes
"slop" in those times, since I have not taken the time 
to account for the time taken to achieve orbit. That
can wait until we get closer to launch. Based on the early history of the orbit of Lacrosse 2 and its rocket, it will be
fairly easy to construct accurate, predictive search elements.

Ted Molczan