Sunday, 28 September 2014

Observing HEO objects

Friday evening I missed the LEO window because of a dinner. When back home near midnight, conditions were dynamic: intermittent clear skies and roving cloud fields.

A HEO (Highly Elliptical Orbit) object called "Unknown 051230" (2005-864A) was well-placed near the zenith, in Cepheus. I targetted it using the 2.8/180mm Zeiss Sonnar MC lens, snapping pictures during clear spells. It shows up well, as a tiny but clear trail (indicated by the arrow in the image):

click image to enlarge

This object is one which our analysts cannot link to any particular launch - hence the designation "Unknown". It is being tracked by us for quite a couple of years now (since Greg Roberts discovered it on 30 December 2005). It could be either a (defunct) payload, or an old rocket booster.

At the time of my observations it was at an altitude of 36650 km, close to its apogee, situated over the Arctic circle roughly above Iceland:

orbital position of Unknown 051230 at the time of observation
click image to enlarge

Nadir view from orbital position of Unknown 051230 at the time of observation
click image to enlarge

Highly Elliptical Orbits (also called a Molniya orbit) typically have an orbital inclination near 63.4 degrees, an apogee near 36000 km, and perigee at only a few hundred km altitude, usually over Antarctica.

63.4 degree orbital inclination of Unknown 051230
click image to enlarge

The ~63.4 degree inclination with these orbital parameters ensures that the perigee is stable, i.e. always stays over the southern hemisphere.

An object in this orbit has a period of 0.5 day, so it makes 2 revolutions per day. Its residence time in perigee over the southern hemisphere is only brief: most of the time it is at high altitude over the northern hemisphere, allowing many hours of  continued presence above that area (see image above).

Objects in these orbits are therefore typically used to provide communications at high Northern latitudes, or for SIGINT and infra-red surveillance.

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