SETI AstroAlert: Solar Disturbance Affects Geosynchronous Satellites


Larry Klaes (lklaes@bbn.com)
Fri, 30 Jul 1999 20:51:39 -0400


>From: "Cary Oler"<oler@dns.uleth.ca>
>Subject: AstroAlert: Solar Disturbance Affects Geosynchronous Satellites
>To: sun-earth@skypub.com
>Date: Fri, 30 Jul 1999 18:11:07 -0600 (MDT)
>X-Mailer: ELM [version 2.4 PL24]
>Sender: owner-sun-earth@skypub.com
>
> ------------------------------------
> | |
> Magnetopause | A s t r o A l e r t | 30 July 1999
> Crossing Alert | |
> ---------------- Sun-Earth Alert ----------------
>
>
> On 30 July 1999, a disturbance in the solar wind was observed that had a
>dramatic effect on the Earth's magnetosphere. It began near 10:00 UTC (6 am
>EDT) during a time when the solar wind velocity was fluctuating between 350
>to 400 kilometers per second (km/sec, or near 844,000 miles per hour). During
>the next 11 hours (by 21:00 UTC), the solar wind increased in velocity to a
>respectable 650 km/sec (or near 1.4 million miles per hour).
>
> At 19:48 UTC, a sudden high-density transient imbedded within this high
>velocity solar wind flow impacted the Earth's magnetosphere. This caused the
>sunward side of the Earth's magnetosphere to become compressed and drove the
>magnetopause (the boundary between the more chaotic conditions in the
>magnetosheath region and the relatively calm conditions inside the
>magnetopause) inside geosynchronous orbit.
>
> Numerous satellites near the sunward side of the magnetosphere
>experienced fairly significant crossings through the magnetopause and into
>the magnetosheath region. The GOES-8 and GOES-10 spacecraft, for example,
>spent a little over an hour inside the magnetosheath region between 19:50 and
>21:00 UTC. This is significant for geosynchronous satellites, which can
>suffer from the more turbulent magnetic field conditions and the more direct
>onslaught of the solar wind. For example, the rapidly fluctuating and near
>oppositely-directed magnetic fields that exist in the magnetosheath region
>can result in incorrect torques being applied to maintain spacecraft
>orientation. This can result in mispointings and in severe cases even loss of
>satellite control. In addition, the adverse conditions in the magnetosheath
>can result in the degradation of satellite solar cells, which can affect the
>overall health and longevity of satellites.
>
> Geosynchronous satellite magnetopause crossings are relatively rare, but
>become increasingly common during the maximum phase of the solar cycle when
>high velocity and high density transients in the solar wind (some from large
>coronal mass ejections) impact the Earth more frequently.
>
> Today's crossing event is the first since 16 April 1999. It was also
>more serious and was of longer duration than the April event.
>
> For more information concerning this event, including plots of the
>observed activity, please visit: http://solar.uleth.ca/astroalert.html
>
>
>** End of AstroAlert **
>



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