Geosynchronous Satellites

[Bushranger]

A very basic question...How do geosynchronous satellites maintain their position in regard to the earth's continuous seasonal shift?  For instance, if a geosynchronous communication satellite (my HughesNet Network Provider for instance) is positioned above the equator, how does it maintain its alignment despite the seasonal tilting of the earth between the Tropics of Cancer and Capricorn?  The alignment of my receiver dish and the satellite, I have been told is critical, so how does it compensate for seasonal changes in the earth's position relative to the satellite? It seems that the satellite would need to, at the minimum, rotate to maintain alignment...likely using thrusters.  If they use thrusters, that would mean that eventually, the thrusters would run out of fuel/compressed gas, etc.

Edited October 31, 2017 by Bushranger
duplicate posting

[rangerx]

The Clark Belt satellites are lined up along the earth's equator, not the sun's. Occasionally they need to be re-positioned, but for decaying orbits due to drag.

[Bushranger]

56 minutes ago, rangerx said:

The Clark Belt satellites are lined up along the earth's equator, not the sun's. Occasionally they need to be re-positioned, but for decaying orbits due to drag.

I still do not understand.  If the satellites are lined up with the earth's equator do they follow the seasonal tilting of the earth, and why would they follow the earth's tilt?  Gravity?  It seems counterintuitive to me that gravity could pull them along with the seasonal tilting.

Edited October 31, 2017 by Bushranger
addendum

[Janus]

11 minutes ago, Bushranger said:

I still do not understand.  If the satellites are lined up with the earth's equator do they follow the seasonal tilting of the earth, and why would they follow the earth's tilt?  Gravity?

The Earth's tilt remains constant. (This is why the North pole remains relatively fixed in the sky.)  The seasonal changes are due to the  fact that the Earth orbits the Sun.

Look at the following diagrams. The slanted line is the Earth showing its axial tilt, and the "O" is the Sun.

Summer in the Northern Hemisphere:

/................O................

Winter in the Northern Hemisphere:

.................O.............../

The Earth has moved to the other side of the Sun. Its tilt has not changed direction, but now the Northern hemisphere is tilted away from the Sun instead of towards it.

Anything orbiting the Earth would have the same orientation to the Earth in both cases.

Edited November 1, 2017 by Janus

[rangerx]

29 minutes ago, Janus said:

The Earth's tilt remains constant. (This is why the North pole remains relatively fixed in the sky.)  The seasonal changes are due to the  fact that the Earth orbits the Sun.

Look at the following diagrams. The slanted line is the Earth showing its axial tilt, and the "O" is the Sun.

Summer in the Northern Hemisphere:

/................O................

Winter in the Northern Hemisphere:

.................O.............../

The Earth has moved to the other side of the Sun. Its tilt has not changed direction, but now the Northern hemisphere is tilted away from the Sun instead of towards it.

Anything orbiting the Earth would have the same orientation to the Earth in both cases.

Precisely.

The OP would be correct in their thinking if the satellite footprint was directed at the sun, instead of the earth. However, in that event, the Clarke belt would be eclipsed by the earth on the winter solstice.

[Bushranger]

Thanks, guys...now I understand.

[HB of CJ]

Yep, the geostationary satellites respond to the average center of mass of the planet.  During seasonal shifts the planet just rotates North to South or moves up or down in relationship to the equator but as far as the satellite is concerned everything stays almost the same.  They do carry lots of reaction mass to make subtle orientation corrections. 

The heaviest part of the satellite is closest to earth creating a slight tidal effect so the thing does not tumble and the same part of the satellite remains oriented towards our planet. Seems the Earth is not quite round.  Also there are areas of the planet that have different mass than the rest thus the force of gravity is slightly different than average

Over time this counts up and becomes a big concern.  The geostationary satellite can only be so big.  Expensive to put them there.  Eventually the satellite will run low then run out of thruster gas.  Also most, (all) are powered by PV panels.  Keeping them aligned well enough to provide sufficient power is also a big problem.  Over time stuff wears out.

Our own sun also tries to knock the satellites around.  Solar wind.  Hard radiation takes its toll.  Temperature swings from daylight to nighttime.  What is the average lifespan of a modern geostationary satellite today as compared to the very early days?  All of the above makes it amazing our stuff stays functional for so long.  Much progress indeed.