TriPoint VertexRSI 7200, Operation And Maintenance Manual

Page: 44 / 266

T HEORY
3 - 3
A ll of these so l ut i ons are generated us i ng the method descr i bed prev i ous l y. The
d i fferences i n the so l ut i ons are due to the t i me span of A ST data used, and the
propagator used. The ST w ill use up to the l ast 1 0 hours of data ava il ab l e, w h il e
the LT (2b and mb) w ill use up to the l ast 7 3 hours of data ava il ab l e.
A ssum i ng that track i ng i s started on a target w i th no stored A ST data, the f i rst ST
so l ut i on w ill be ava il ab l e for use approx i mate l y 9 0 m i nutes after track i ng beg i ns.
The f i rst LT 2b so l ut i on w ill be ava il ab l e 1 8 hours after track i ng beg i ns. The f i rst
LTmb so l ut i on w ill be ava il ab l e 3 5 hours after track i ng beg i ns.
The cho i ce of w h i ch so l ut i on i s used for track i ng i s made by compar i ng, after each
steptrack cyc l e, the peak pos i t i on w i th the pred i cted pos i t i ons from a ll ava il ab l e
mode l s. The so l ut i on w h i ch produces a pos i t i on c l osest to the steptrack peak i s
used.
3.2 O r b i t S ca n
The 7 2 0 0 A C U has a sate lli te l ocat i ng a l gor i thm referred to as O r b i t s ca n . The
purpose of O r b i t s ca n i s to l ocate sate lli tes i n i nc li ned operat i on. Th i s method i s
super i or to other scann i ng methods such as Box Scan, Sp i ra l Scan, or Raster Scan.
Orb i t scan w ill on l y search the most probab l e path of the sate lli te and not w aste
t i me i n empty sky.
The O r b i t s ca n mode i s a user-se l ectab l e opt i on on the O P T track i ng. W hen
correct l y set up, O r b i t s ca n w ill be used w hen no O P T so l ut i ons ex i st, and no s i gna l
i s ava il ab l e at current po i nt i ng or at box center for the des i gnated target.
3.2.1 O r b i t S ca n Th e o r y
Th i s scan method w ill on l y be effect i ve for geosynchronous sate lli tes i n i nc li ned
operat i on. It i s assumed that the sate lli te o w ners are attempt i ng to ho l d nom i na l
l ong i tude and a near c i rcu l ar orb i t.
The 7 2 0 0 A C S creates a set of orb i ta l parameters to p l ace the ascend i ng node at
nom i na l l ong i tude and prov i de the est i mated i nc li nat i on. The resu l t i ng tra j ectory w ill
fo ll o w the most li ke l y path for a sate lli te i n th i s type of operat i on. From the s i te
po i nt of v i e w , th i s produces a f i gure 8 (approx i mate l y) w h i ch i s fo ll o w ed from box
center. The system a l w ays starts by trave li ng north from box center, a ll the w ay
around the f i gure 8 and back to box center (refer to F i gure 3-1). Th i s w ill w ork
correct l y regard l ess of s i te to sate lli te or i entat i on. (Note: F i gure 3-1 sho w s the scan
i n terms of l at i tude/ l ong i tude. The tra j ectory w ill l ook d i fferent i n terms of A Z/EL
based on s i te pos i t i on and sate lli te pos i t i on.)