Earth Orbits

Orbits are complicated, because they involve both position and velocity in three spatial dimensions and time. Simple two-body "Kepler" orbits relate the position and velocity at one time to the position and velocity at other times. In reality, orbits are also complicated by drag, light pressure, and gravitational perturbations by other bodies, and in the extreme by relativistic effects. For this discussion, we will not consider the complications, so that we get closed-form algebraic solutions. Of course, in real life, we will need to include all the complications in our calculations of orbital properties. Thinsats are deployed in closely packed orbital families. One central orbit, perfectly circular and in the orbital plane, with a sidereal period of 14393 seconds and a radius of 12789 kilometers, surrounded by slightly inclined and slightly elliptical orbits that fill a toroidal region around that central orbit. By carefully assigning orbital parameters, this region can be filled with densely packed orbits and objects in them.

Describing Earth Orbits

Orbits are ellipses in a plane which also contains the center of the mass that defines the orbit.

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Earth Orbit Parameters

system

status

number

planes

#/plane

perigee

apogee

inclination

period

uplink GHz

downlink GHz

Space Station

in use

1

1

1

6727

6736

51.6

5480

x

x

Iridium

in use

66

6

11

7158

7158

86.4

6027

Ka band

Ka band

Teledesic

bankrupt

288

12

24

7778

7778

98.2

6827

28.6-29.2

18.9-19.3

Globalstar

in use

48

x

x

7792

7792

52

6845

x

x

m288 core

empty

0

1

0

12789

12789

0

14393

x

x

m288 outer

empty

0

many

0

12739

12839

2.24

14393

x

x

O3b

planned

12?

1

12

14441

14441

0

17271

x

x

Molniya

in use

3?

3?

1

7885

45683

63.4

43082

x

x

GPS

in use

31

6?

-

26600

26600

55

43082

x

x

GEO

in use

361

1

-

42164

42164

0 to 14.3

86164

-

-

Moon

natural

1

1

1

364397

406731

5.14

2360592

x

x

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M orbits

orbit

passes

radius

radius

altitude

sidereal

max

45N max

45N azim

45N

visible

rads

/ day

km

RE

km

per secs

latitd

elevation

degrees

ping ms

fraction

/sec

m120

12

7639

1.2

1261

6645

33.5

-10.2

---

---

---

2e-4

m160

9

9099

1.4

2721

8638

45.6

0.6

22.5

43

0.04

6e-3

m240

6

11540

1.8

5162

12338

56.5

12.4

97.1

56

0.21

8e-3

m288

5

12789

2.0

6411

14393

60.1

16.5

109.9

63

0.25

2e-3

m360

4

14441

2.3

8063

17271

63.8

20.6

121.1

73

0.29

2e-3

m480

3

16756

2.6

10378

21585

67.7

24.8

131.5

87

0.32

2e-3

m720

2

20295

3.2

13917

28774

71.7

29.1

141.4

110

0.35

2e-2

m1440

1

26586

4.2

20208

43141

76.1

33.5

151.4

150

0.39

1e-2

GEO

0

42164

6.6

42164

86164

81.3

38.2

162.4

253

0.43

5e-4

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Light Pressure Modified Orbits

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References

Wikipedia : Orbit

Wikipedia : Orbital Elements

Wikipedia : Two Line element description (with SGP4 fortran)

Ellipse Geometry Review (pdf)

OrbitSoftware

Notes on GPS satellite orbits

SaVi satellite constellation visualization

Encyclopedia Astronautica

Description of NORAD 2 line elements

NORAD Space Tracking Information requires account.

Celestrak

Real Time Satellite Tracking

NASA 3D Realtime Satellite Tracker (Java)

Geosynchronous Satellites

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EarthOrbits (last edited 2014-05-30 20:53:59 by KeithLofstrom)