Re: Bum elements?

Alan Pickup (
Tue, 10 Nov 1998 21:34:18 +0000

It was probably just unfortunate that the molczan.tle file included
elsets for TRMM and Cosmos 2347 issued as (or shortly after) both
objects were boosted into slightly higher/longer-period orbits. In both
cases, the drag terms were at their most negative and appeared to take a
day or two to revert to their normal positive values. In fact, I suspect
that the boosts were short-lived events and the prolonged negative drag
terms are an artefact of the tle-generation algorithm.

When Rob predicted from the negative-drag elsets, he obtained
predictions which were too late (ie the objects came earlier than

TRMM is being manoeuvred frequently but over the past 10 days has kept
within +-20 seconds of a zero drag orbit with a mean motion of 15.743
revs/day. Though Cosmos 2347 may be manoeuvred quite often by small
amounts, it has stayed within +-3 seconds of predictions given by a
zero-drag 15.520 revs/day orbit over a similar period.

Elsets for both objects are included in my select.tle file, available
from my WWW page below.

 Alan Pickup | COSPAR 2707:   55d53m48.7s N   3d11m51.2s W   156m asl
 Edinburgh   | Home:    +44 (0)131 477 9144
 Scotland    | SatEvo page: