# Calculating orbital heights using known FOV

From: John Locker (john@satcom.freeserve.co.uk)
Date: Mon Oct 25 2004 - 03:02:55 EDT

• Next message: David Brierley: "DMB Obs October 24"

```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

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.

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