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