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From: PIERRE Marguerite <marguerite.pierre@cea.fr>
Subject: Bug in XMM visibility tool?
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Date: Wed, 16 Sep 2009 17:01:10 +0200
Subject: Bug in XMM visibility tool?
From: PIERRE Marguerite <marguerite.pierre@cea.fr>
To: <xmmhelp@sciops.esa.int>
Dear Colleagues

I am using the XMM visibility tool,
http://xmm2.esac.esa.int/external/xmm_sched/vischeck/
to check the visibility of a target over several years

131.2500    -4.2500


When I set AO9, it's OK

When I set date range = 01 May 2011 to 01 May 2012, it says in the output
page: 
        Start Orbit    End Orbit    Start Date    End Date
        2086    2210    01 May 2011    01 May 2012
Which is wrong since a year = 183 orbits

When I set date range = 01 May 2012 to 01 May 2013, it says in the output
page:
    Start Orbit    End Orbit    Start Date    End Date
    2210    2210    01 May 2012    01 May 2013
 Which is completely wrong

It seems thus, that there is a problem in the orbit computation for AOs
>AO9.
Could you please check this? Thanks.

Marguerite Pierre


Reply 1

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From: Rosario Gonzalez Riestra <xmmhelp@sciops.esa.int>
To: marguerite.pierre@cea.fr
Subject: Re: Bug in XMM visibility tool? (PR#42088)
Date: Wed Sep 16 16:46:10 2009
Dear Dr. Pierre,

Thanks for letting us know about the anomalous behaviour of the AO9 Visibility
Checker.

I am afraid that the current version of the visibility checker only covers the
revolution range 1750-2150 (see
http://xmm2.esac.esa.int/external/xmm_sched/vischeck/howto.shtml).

The tool uses a DataBase of Observable Bins (DBOB) that is valid only for this
period. The visibility of each bin is then assessed against viewing constraints
with respect to the Earth, Sun and Moon, that require an accurate estimation of
the spacecraft orbital parameters. Going beyond the current dates may result in
wrong visibility predictions.

Having said that, taking into account only the Sun constraint (neither the Earth
nor the Moon) the visibility of a target is roughly the same from one year to
the next.

Sorry for the inconveniences,

Rosario Gonzalez-Riestra
XMM-SOC User Support Group









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