RE: KH, Lacrosse orbits

Ted Molczan (molczan@fox.nstn.ca)
Thu, 5 Sep 1996 13:13:47 -0400

Allen Thomson wrote:

>I'm working up an analysis of the USA 86/116 and Lacrosse coverage of 
>southern Iraq for 1-4 September 1996 to see if there's any evidence
>of coordination with the missile strikes there. My latest element
>sets from here and kilroy indicate a striking lack of coverage
>from early morning to early afternoon, with a gap of several hours
>between the strikes and good passes of the satellites for bomb
>damage assessment.

The lack of a Kh in the western (early) plane
hurts in this case. The Lacrosses currently
are about 60 apart, so they are providing reasonably
well spaced coverage.

>Is there any evidence that any of the satellites, particularly USA 86 & 116,
>adjusted their orbits in the past few days to fill in this morning gap?

That would be rather expensive in terms of
propellant, because it would involve a large change in 
plane. There are two ways to effect a change in plane.
The first and most expensive would involve a manoeuvre
to directly change the RAAN, which would be extremely
expensive for any significant change, well outside
the observed capabilities of the either the Kh's or
Lacrosses.

The second, less expensive approach, would be to alter
orbit of one or both spacecraft to change their
relative RAAN precession rate. The disadvantage of
this method is that it will take many weeks or months
to achieve the desired separation.

In the case of the Lacrosses, they already precess at 
different rates, because Lacrosse 1 is in a lower
inclination than Lacrosse 2. It overtakes Lacrosse 2
every 297 days. I believe that a constant RAAN spacing
would have been preferred by NRO, but the shuttle-launched
Lacrosse 1 could not reach the standard 68 deg 
inclination, used later by Lacrosse 2. If there is a
Lacrosse 3, I expect it to match Lacrosse 2's altitude
and inclination, or to establish a different type of
orbit, eventually paired with Lacrosse 4.

Regarding the Kh's, USA 86 has been drifting slowly 
westward since about April, at the rate of about 
1.7 deg/month. It is now about 6 deg west of USA 116.
At its present rate of precession, it would take
25 months to reach the standard western plane, about
49 deg west of USA 116. This could be reduced to say
6 months, at the cost of a fairly expensive manoeuvre,
that would consume a large fraction of the propellant
required to maintain a standard Kh orbit against drag
over its normal lifetime.

The only practical solution to the problem of 
reconnaissance/surveillance gaps is to maintain a 
number of spacecraft in suitably spaced orbital planes.
At a minimum, the NRO needs to quickly replace USA 33, 
the westerly  Kh-11, deorbited in mid-May 1996; and they 
need to launch Lacrosse 3 into a plane 90 deg from 
Lacrosse 2, matching its altitude and inclination, to 
maintain that spacing.

Ted Molczan