STS-72 collision avoidance.

Philip Chien (
Fri, 12 Jan 1996 16:51:09 -0400

Neil Clifford <> said:
>Interesting to note the burn carried out to avoid the defunct USAF
>satellite nicknamed 'Misty'. Judging from the clues on NASA TV this was
>USA 103 (23097/94026A) whose Titan IV may have been seen venting over
>Europe (3rd May 1994) (see any recent Molczan tle file).

no.  MSTI-2 was launched on a Scout ELV from Vandenberg.  Its Intl ID 1994
28A  Norad #23101 and unclassified TLES are in Molczan's files.  The Titan
was launched from CCAFS.

The burn was a .4 foot per second posigrade burn which changed the
conjunction distance from .8 nautical miles to 5.2 nmi.  Typically a burn
like this is performed an orbit or two in advance.  The Mission Elapsed
Time for the burn was 21 hours 57 minutes.

There have been several burns within the shuttle program for conjunction
avoidance (no actual predicted collisions, but the accuracy of the tracking
network results in NASA taking a conservative approach by defining the size
of the safety zone box around the shuttle).  The upper stages of a couple
of COSMOS launches come to mind.

But is this the first time the shuttle made an avoidance for an actual
satellite (as opposed to an upper stage or debris)?

And does the fact that the shuttle is in an elliptical orbit increase the
probability of encounters?  I'd suspect yes because most operational
satellites are in fairly circular orbits, along with their associated
debris.  So if you're in a circular orbit you're following the rest of the
pack, but in an elliptical orbit you're going to go through the orbits of a
bunch of circularly orbiting bodies.

Philip Chien, Earth News - space writer and consultant  PCHIEN@IDS.NET
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