Last week I was playing around with a couple of videos taken earlier in the year , showing objects moving "near" to the geo belt. George Roberts very kindly pointed out that an object moving with a differential speed ( compared to a geosat ) of about 450 km /hour would likely be in an orbit a little over 3000 km "below" the geos....and also supplied me with the mathematical data to do my own calculations. As I am going through a "senior moment " or two in the maths dept , I decided to see if I could find a web based orbit calculator ....and here it is http://liftoff.msfc.nasa.gov/academy/rocket_sci/orbmech/vel_calc.html As I targetted a known satellite , in drift mode , W3A , I have a reference to work to. TLEs for W3A during drift show it 50 km or so below the arc. By applying a grid to my video images , which have a FOV of 30 arc minutes , I can calculate the movement to within a few km/hour. W3A exhibits a differential speed of 15 km hour. Using the orbit calculator , I see that reducing the orbit by a 100 km results in a differential in the region of 25-30 km /hour. This ties in nicely with my visual obs of W3a in drift. The other two drifters have a differential speed of 450 km/hour .....putting them at a height of around 32,500 km , just as George suggested. All three objects move from west to east. As most geos are put into graveyard at around 150-200 km "above" the arc , I have two options with the lower birds . They could be one and the same , seen a few weeks apart , or they could be separate satellites , at an obital height of 32,500 km , with a period of about 21.18 hours. If the latter , can anyone suggest what they might be ? Many thanks , John. ------------------------------------------------------------------------- Subscribe/Unsubscribe info, Frequently Asked Questions, SeeSat-L archive: http://www.satobs.org/seesat/seesatindex.html
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