T HEORY
3 - 2
3.1.2 O
r
b
i
t D
e
t
e
r
m
i
n
a
t
i
on
A n orb
i
ta
l
e
l
ement set
i
s composed by mak
i
ng an
i
n
i
t
i
a
l
guess of the orb
i
t and then
generat
i
ng pos
i
t
i
ons from th
i
s guess, us
i
ng the propagators descr
i
bed prev
i
ous
l
y.
These pos
i
t
i
ons are compared w
i
th the pos
i
t
i
ons gathered by A ST. The d
i
fferences
bet w een A ST data and propagator-generated data are used to determ
i
ne a
correct
i
on to the orb
i
t. The process
i
s repeated unt
il
the RMS error bet w een the
A ST data and the propagator-generated data
i
s m
i
n
i
m
i
zed. The a
l
gor
i
thm used to
perform th
i
s
i
s referred to as the so
l
ver.
The orb
i
t must be per
i
od
i
ca
ll
y re-so
l
ved
i
n order to rema
i
n accurate. Theoret
i
ca
ll
y,
i
f a
ll
of the forces act
i
ng upon the spacecraft are kno w n at any t
i
me, the orb
i
ta
l
e
l
ement set can be pred
i
cted forw ard to any des
i
red t
i
me. Ho w ever, a
ll
of the
forces are not kno w n at a
ll
t
i
mes. The
l
argest unkno w n force comes from the
stat
i
on-keep
i
ng maneuvers performed
i
n order to keep the spacecraft
i
n the des
i
red
orb
i
t. Stat
i
on-keep
i
ng
i
s on
l
y performed per
i
od
i
ca
ll
y (typ
i
ca
ll
y once every fe w
days). If the orb
i
t
i
s determ
i
ned from data after a maneuver has taken p
l
ace, then
stat
i
on-keep
i
ng has no effect on the va
li
d
i
ty of the orb
i
t so
l
ut
i
on unt
il
a ne w
stat
i
on-keep
i
ng maneuver
i
s performed.
The t w o-body propagator does not take
i
nto account any forces except those
generated by the Earth’s grav
i
ty, and even then, on
l
y a s
i
mp
li
f
i
ed mode
l
i
s used. A
pos
i
t
i
on pred
i
ct
i
on from a t w o-body propagator has an error that gro w s w
i
th t
i
me
due to the om
i
ss
i
on of these forces
i
n the orb
i
t determ
i
nat
i
on.
Ne
i
ther propagator can account for vary
i
ng effects on the ground. The pr
i
mary
ground errors affect
i
ng the system are:
W
i
nd
l
oad
i
ng of the antenna.
Therma
l
d
i
stort
i
on of the antenna, caused by non-un
i
form so
l
ar heat
i
ng.
Both of these factors affect the data co
ll
ected by A ST. Ho w ever,
O
P
T
i
s ab
l
e to
separate ground errors from the orb
i
ta
l
so
l
ut
i
on by tak
i
ng advantage of the fact that
the spacecraft’s mot
i
on must fo
ll
o w Ne w ton’s
l
a w s. Th
i
s
i
nformat
i
on
i
s reta
i
ned
as t w o error terms, one per ax
i
s. These error terms are used to correct future
pos
i
t
i
on pred
i
ct
i
ons.
3.1.2.1 Sho
r
t-t
e
r
m
a
nd
L
ong-t
e
r
m O
P
T So
l
ut
i
ons
O
P
T
generates three d
i
st
i
nct types of orb
i
ta
l
so
l
ut
i
ons:
Short-term so
l
ut
i
on us
i
ng t w o-body propagator (ST)
Long-term so
l
ut
i
on us
i
ng t w o-body propagator (LT 2b)
Long-term so
l
ut
i
on us
i
ng mu
l
t
i
body propagator (LTmb)
Содержание VertexRSI 7200
Страница 15: ...INTRODUCTION 1 4 THIS PA GE INTENTIONALLY LEFT BLANK...
Страница 21: ...O VERVIEW 2 6 Figure 2 3 7200 A CU Functional Block Diagram...
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Страница 46: ...THEORY 3 5...
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Страница 259: ...VENDOR DA T A H 1 APPENDIX H VENDOR DATA This appendix contains the Sumitomo NTAC 2000 O M manual for the inverters...
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