Milstar and Centaur

Philip Chien (kc4yer@amsat.org)
Sun, 2 May 1999 01:00:53 -0400

Well that was weird.  It's been a very busy week for me, including some
rather unique opportunities.

I heard the Titan IV-Centaur launch, but didn't see anything due to the
clouds.  By early afternoon it was quite clear that something was wrong.
What was unexpected was how open the managers were at the failure press
conference.

The Milstar (USA 143) and Centaur are in a 400 x 2700 nautical mile orbit.
(sorry 'bout the weird antique units).  Unfortunately the inclination and
Arg. Perigee weren't given.  OIG lists them as "NO ELEMENTS AVAILABLE".
Unless the solar arrays somehow opened up the satellite is almost certainly
dead by now.

Closed up for launch the satellite is a rough rectangular shape about 15 x
15 x 50 ft. and covered with orange-ish Kapton.  If all of the apendages
are deployed then it will look like a giant "X" extending 51 ft on the long
axis of the spacecraft body and 116 ft. across the solar arrays.  The
earlier Milstar have been spotted in geosync and at low altitude these will
be a *very* impressive objects.

The Centaur stage is 14 ft. in diameter and 29 ft. long.  Check out the
Florida Today web pages for this mission for line art of Milstar and
Centaur from the press handouts.

The Centaur had enough propellants for about 600 seconds of burns with a
nominal Delta-V of 2,400 meters per second.

The normal Titan IV-Centaur profile calls for the core vehicle to raise the
upper stage and satellite almost to orbital velocity.  The Centaur performs
a small burn to place itself and the payload in to a 94 x 104 nautical mile
parking orbit.  Half an orbit away it performs the Perigee burn and after
the stack reaches geosync altitude a third burn is performed to circularize
the orbit at geo altitude and cancel the inclination.  The Titan IV core
stage remains on a ballistic trajectory and does not achieve orbit.

According to Brig. General Starbuck as far as is known the Titan IV core
vehicle (strap-on solids + 2 stages) functioned properly.  It's believed
that the problems occurred during the first Centaur burn.

If the burns occurred at the wrong times, durations, or directions (or some
combination) then it may explain the rather low final altitude achieved.

There is certainly a good possibility that not all of the propellant was
expended when the Milstar was deployed at 3 pm local (about 4 hours before
it should have deployed).  Normally after spacecraft separation the Centaur
stage performs a backaway maneuever to avoid any potential recontact,
exhausts its propellants, and shuts down.  If the problems were serious
enough to prevent the safing sequence from occuring then there's a
potential for a rather impressive explosion on the Centaur.  I don't know
if there's a 'burst disk' to prevent over-pressurization from happening.

There is plenty of data since the NASA TDRS satellites were used to track
the Centaur and return telemetry.  But it will take time to sift through
all of it.  The question is whether or not the Air Force will continue to
be as open with providing information.

In any case the Milstar and Centaur will certainly be very interesting
visual objects, even at medium latitudes.  Centaurs are extremely
interesting objects to view, and there are only a handful of them at low
altitudes in roughly circular orbits (Centaur 2, HEAO, SAX).  This
particular Centaur is 14' in diameter in comparison with the 10' diameter
ones used with Atlases.

Currently no elements are available from OIG for either object so this
looks like an excellent opportunity for the amateur observers to find these
objects and amateur orbital mechanics community to derive the orbit.  I
would be especially interested in looking at any element sets for search
orbits.


Philip Chien, KC4YER
Earth News
world (in)famous writer, science fiction fan, ham radio operator,
all-around nice guy, etc.