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I What causes the deceleration of a satellite? Space dust?

  1. Mar 22, 2017 #1
    After talking to a coworker, I looked into the wikipedia article on "Gravity of Earth". I found that the Earth's gravity is not uniform, which makes sense (never thought about it). I have always wondered why satellites de-orbit over time. Someone told me that there is enough space dust to slow down a artificial satellite and they need to speed back up to maintain altitude.

    My real question is do the variations in the Earth's gravity slow down a satellite's orbit?
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  3. Mar 22, 2017 #2


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    It's not variations in the Earth's gravity, it's just that there is a very small, but non-zero amount of gas from the atmosphere at the altitudes that low-orbit satellites orbit at. This gas gradually slows down anything orbiting very close to the Earth, including satellites and the ISS.

    Satellites higher up in orbit, geostationary satellites for example, generally need to use fuel to correct for gravitational disturbances from other bodies that disrupt their orbits over time.
  4. Mar 22, 2017 #3
    Thanks! Good to know for when I start building satellites soon ;-)
  5. Mar 22, 2017 #4


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    While the atmospheric drag is the larger component, there are effects due to gravitational anomalies. For example, the 2011 Japan quake actually shifted the orbits of satellites as discussed here - Japan megaquake shifted gravity satellite orbits.
  6. Mar 22, 2017 #5


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    For an unanticipated example of the use of station-keeping fuel, see https://en.wikipedia.org/wiki/TDRS-1. The bird did not initially make it to geostationary orbit and had to burn station keeping fuel over a period of months before finally arriving on station.

    As I recall from a briefing at the time, one of the key orbital perterbations normally requiring the use of station-keeping fuel is due to the influence of the moon -- it tends to pull craft out of purely equatorial orbits.
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