[meteorite-list] Slightly OT: UARS decay strategy

From: Matson, Robert D. <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Mon, 12 Sep 2011 10:03:29 -0700
Message-ID: <9180F6B27399C541B10663E21C8BDE9202B889C3_at_0461-its-exmb09.us.saic.com>

Hi Jim,

Doug has already provided most of the answer to your question. The
bottom line
is that for objects in low earth orbit, it is far less expensive
fuel-wise to
force early reentry than it is to move the satellite to a (MUCH) higher
orbit
that won't decay for hundreds or thousands of years. UARS did not have
sufficient fuel remaining to achieve anything useful in terms of raising
its
orbit, so they made the smarter decision to expedite its reentry by
lowering
the orbit.

A third alternative would have been to let the orbit naturally decay to
a
lower altitude before doing that burn. The advantage of this approach is
that once the orbit is very low (as it is now), that final burn can push
perigee so low that reentry is guaranteed half an orbit after the burn.
This allows spacecraft controllers to choose the reentry location
judiciously (e.g. over the South Pacific Ocean). By burning years early
as
they did, they sacrificed the ability to choose the reentry location.

In essence, they balanced two risks: the risk of death, injury or
property
damage on the ground associated with an uncontrolled reentry vs. the
increased risk of collision between UARS and another satellite or piece
of space debris during the added years or decades that it would have
taken UARS to naturally decay to its current altitude. --Rob
Received on Mon 12 Sep 2011 01:03:29 PM PDT