Ed Kyle wrote:
Allen Thomson wrote:
Ed Kyle wrote:
Today's 9-1-06 Ground Based Midcourse Defense (GMD) test appears to
have succeeded.

I gotta question about the timeline of the test that maybe some of the
readership can help with:

I'm trying to figure out what happened in the GBI/EKV test yesterday
and am having a bit of difficulty with the length of time between
target launch and intercept.

What we have from various report is,

Interceptor speed at burnout said to be 18,000 mph, which is the 8 kps
that I remember from BMDO briefings in 1997.

Target speed said to be upward of 15,000 mph or 6.7 kps which is right
for an ICBM with a range of ~8,000 km, about the range from NK to the
west coast of CONUS. Consistent with that, General Obering said, "But
what we saw today was a very realistic trajectory for the threat, for
the target, and a very realistic trajectory, a very realistic intercept
altitude and intercept speeds for the target enemy -- interceptor
against the target. "

So far so good: We can imagine that the target booster rocket might
have flown into a trajectory (X,Y.Z, Xdot, Ydot, Zdot) emulating that
of an NK ICBM rather than a simple minimum-energy trajectory from
Kodiak.

But then we come to the timeline, and there's where I'm having trouble
figuring out what went on.

Target launch from Kodiak at 10:22 or 10:23

GBI launch from VAFB at 10:39, said to be 16 or 17 minutes after target
launch

Intercept at 10:45 or 10:46, said to be 7 minutes after GBI launch

Let's assume it took three minutes for the STARS to get into the 6.7
kps ICBM trajectory and that it didn't get too far downrange while
doing so. That means that it was at least 7500 km from Kodiak at
intercept.

And, applying similar arithmetic, the EKV could have been no more than
about 3,000 km from VAFB at intercept.

So here's the problem I'm having: there isn't anywhere that satisfies
those two distance conditions. The nearest I can come is a location far
south of VAFB, around 8 N, 117 W, and even that is only 6,300 km from
Kodiak.

Clearly I'm failing to understand something, probably something obvious
(it's happened often enough before). Help!

P.S.: It would help a lot to know the launch azimuth of either or both
of the rockets, particularly the GBI . I've checked the usual NOTAM
sources but haven't found anything -- if any of you have them, please
let me know.

I haven't had time to sit down and do the math, but it seems probable
to me that this intercept could have occurred along a track that would
have been similar to the Athena launch track, visibile at:

"http://spaceflightnow.com/athena/kodiakstar/010919track.html"

News reports said that the intercept occurred a "few hundred" miles
off the California coast, so I doubt that the latitude would have been
much south of 30 N. The intercept altitude might have been pretty
high, playing a role in the timing. ICBMs usually reach higher
apogees than LEO launch vehicles do.

- Ed Kyle

And, the reported velocities might have been burnout velocities, rather

than actual speeds at the time of the intercepts. Or the intercept
might have occurred during descent from apogee, while the target
was accelerating so that it would have spent quite a bit of time
flying a lower speed prior to the intercept. Etc.

- Ed Kyle