RE: KH, Lacrosse orbits

Ted Molczan (
Sun, 8 Sep 1996 01:36:14 -0400

Allen Thomson wrote:

>   I find myself at a loss to understand the KH-11/8, USA 86,=20
>and USA 116 story.  Presumably 11/8 was nonfunctional as an imager but=20
>could still be commanded to perform a deorbit maneuver -- or at least =

The 11/8 situation seems pretty straightforward to me. It operated=20
in the standard western KH plane for a record 7.5 years, then was=20
deorbited, like each of its predecessors.

> USA 86 is drifting as if it has lost propulsive capability,=20
>but I'm not sure that idea is confirmed by the details of its orbital=20
>history and would like to get others' views on that.  In addition, if =
>were dead in orbit, you might expect it to tumble at some rate and show =

>brightness variations: is that happening?  USA 116 seems to be healthy, =

>but the mispositioning of USA 86 detracts greatly from the utility of=20
>the constellation, as witness the poor coverage of Desert Strike.

The USA 86 and 116 story is less straightforward than that of USA 33.
USA 116 was launched into nearly the same plane as USA 86 in Dec'95, =
apparently as its replacement. Then and now, this seemed to me to be
rather early, given that USA 86 had been barely 3 years in orbit,
while KH-11-6, 11-7 and 11-8 had remained in their standard orbits=20
4 years, 4.5 years and 7.5 years, respectively.

If USA 86 was unusable, I believe it would have been de-orbited prior=20
to USA 116's launch, or shortly afterward, assuming its propulsion and =
command/control systems were operable. As the following discussion will
show, they were in fact operable as of the spring of this year.

My analysis indicates that USA 86 remained in nearly its standard orbit=20
after USA 116 was launched, until the spring of 1996, when it raised=20
its perigee to more than 400 km, and lowered its inclination slightly.
The magnitude of this manoeuvre was more than sufficient to have =
a de-orbit, had that been deemed necessary. That it was not deemed=20
necessary strongly suggests that the spacecraft is at least partially=20
usable. The characteristics of USA 86's new orbit further support this =
USA 86's orbit changed from the standard sun-synchronous, 4 day =
repeating groundtrack - to a quasi-sun-synchronous, 2 day repeating =
The change to a 2 day repeating groundtrack seems to be related to the
de-orbiting of USA 33, which occurred not long afterward. I suspect this
because with the standard 2 satellite constellation, the eastern =
repeats the groundtrack of the western satellite 2 days later, providing
a measure of repeat coverage. With the demise of USA 33, 2 day coverage
would have been lost, so USA 86 seems to be providing it.

Changing its orbit to quasi-sun-synchronous, causes USA 86's plane to=20
drift - in this case 1.7 deg/month west. The westward drift appears =
designed to provide a small degree of ground track diversity relative to =
USA 116,=20
which remains in the standard eastern KH orbit and plane. It will be=20
interesting to see whether or not it eventually re-established a =
orbit, and where that will be relative to the two standard planes.

USA 86's new orbit appears to offer the additional advantage of a great
reduction the rate of decay - the saving in orbital maintenance
propellant somewhat offsetting the costly perigee raising and =
decreasing manoeuvre. Of course, if the spacecraft is not completely
healthy, as seems likely, given its early replacement, then perhaps
frequent manoeuvres are undesirable.

>   All in all, the US imaging spysat situation seems to be something=20
>of a mess  -- is there another plausible but less gloomy =

While it is possible that both Kh's and both Lacrosse's are nearly
fully operational, it seems improbable. USA 86 must have some kind
of serious problem, otherwise it would not have been replaced. Lacrosse =
is nearly 8 years old, so it may well have been shut down by now.=20
Lacrosse 2 is 5.5 years old, so it too is getting old. So the system
may well be something of a mess.

There is a Titan 4 scheduled for launch in December, from Vandenberg
AFB, which I suspect will be a replacement for USA 33. It could easily
be a new Lacrosse. Either one would be a good first step toward=20
rebuilding and rejuvenating the system.

Ted Molczan