[meteorite-list] Slightly OT: UARS decay strategy

From: Marco Langbroek <marco.langbroek_at_meteoritecentral.com>
Date: Wed, 14 Sep 2011 11:38:58 +0200
Message-ID: <4E707632.5040201_at_wanadoo.nl>

Rob Matson wrote:

> 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.

The problem here is, that it would have taken 30+ to 40+ years for UARS to
naturally decay to a suitable altitude for such a burn.

This would have meant they would be obliged to keep the satellite operational
for 40+ years. Apart from questions whether the satellite will not fail before
that time (I am quiet sure it wasn't designed with 40+ years in mind), for a
science satellite that is financially impossible to do.

Why does it need to be kept operational for these 40+ years in this case? The
point is that without active maintenance, the satellite will start to lose
attitude control quickly, pointing wildly to all places as it starts to tumble.
Which means its receiver antennas could no longer point to earth at the moment,
40 years ahead, you want to contact it. But a bigger issue is the fuel in the
tanks. Without active maintenance, the fuel will freeze in the tanks. Once that
happens, it becomes impossible to use the engines for a deorbit boost.

UARS is not the only thing currently coming down by the way. In about a year, a
1.5 tons malfunctioned Japanese spy satellite (IGS 1B) will come down in an
uncontrolled re-entry as well. That sat does still have some fuel onboard,
unlike UARS, which is an added risk.

UARS is a nice bright object easily seen by the naked eye during a pass. Here is
a picture I shot last year:

http://sattrackcam.blogspot.com/2011/09/watch-uars-its-dropping.html

- Marco

-----
Dr Marco (asteroid 183294) Langbroek
Dutch Meteor Society (DMS)

e-mail: dms at marcolangbroek.nl
http://www.dmsweb.org
http://www.marcolangbroek.nl
-----
Received on Wed 14 Sep 2011 05:38:58 AM PDT