Orbital Characteristics of Megha-Tropiques
T.Ravindra BabuM.S.Jayashree
G.Raju
ISRO Satellite CentreBangalore
Payloads
Microwave Analysis and Detection of Rain and Atmospheric Structures (MADRAS)
A microwave instrument for retrieval of water vapour vertical profiles (SAPHIR)
A radiometer devoted to the measurement of Outgoing radiative fluxes at the top of atmosphere (SCARAB)
Keplerian Elements
X,Y,Z – Earth Centred Inertial Coordinate System N – Ascending node, point of intersection between Equatorial and orbital planes, when spacecraft is North bound P – Perigee point S – Spacecraft i - inclination of orbit - Right Ascension of Ascending node - Argument of perigee - True anomaly, related to Eccentric Anomaly (E). E and Mean anomaly(M) are related through Kepler’s equation
i
P
N XY
Z
S
Repeat Cycle
Non-sun synchronous orbit
Ground track repetitivity
Prograde orbit (inclination, i < 90)
Repeat cycle as function of nodal days
Repeat Cycle – options
Altitude ProfileOrbit options for 7-day cycle
500600700800900
1000110012001300
88 93 98 103
No. of orbits in 7-day cycle
Orb
it A
ltit
ud
e (k
m)
Repeat Cycle - options
Revolutions per dayOrbit options for 7-day cycle
12.5
13
13.5
14
14.5
15
15.5
88 90 92 94 96 98 100 102 104
No. of revoultions in 7-day cyle
No
. o
f re
volu
tio
ns
per
day
Repeat Cycle – Chosen orbit
No. of nodal days in the cycle : 7
No. of revolutions per cycle : 97
Nodal period of the orbit : 6116.4 sec
No. of revolutions per day : 14.13
Rate of Right Ascension of node : - 6.01 deg/day
Apsidal rotation rate (frozen perigee): 0 deg/day
Sun-aspect Angle
vXrh
r v
xY
Z
Sun-aspect angle
Sun AnglesSun Aspect Angle variation
Sun Angles
Radio visibilities in one cycle
Ground Trace
Frozen orbit analysis
Eclipse Duration
Eclipse Duration for one cycle of sun aspect angle
282930313233343536
0 100 200 300 400 500 600 700 800
Revolution Number
Ecl
ipse
du
rati
on
(m
in)
Local Time
Descending Node local time of 12:00
N
Local Time change
Local time variation at equator in one cycle of sun-aspect angle
0
6
12
18
24
0 100 200 300 400 500 600 700 800
Revolution number
Lo
cal
tim
e (h
ou
rs)
Ground Track Velocity
Ground Track Velocity
6.096.095
6.16.1056.11
6.1156.12
6.1256.13
0 1000 2000 3000 4000 5000 6000 7000
Time since asc node crossing(sec)
Gro
un
d T
rack
ve
loci
ty(k
m/s
ec)
Ground track azimuth
Heading angle
60
70
80
90
100
110
120
2400 3400 4400 5400 6400 7400 8400 9400 10400
Time in sec since nearest eq. crossing
Hea
din
g a
ng
le (
deg
)
Earth coverage