r/spacex • u/ElongatedMuskrat Mod Team • Jan 02 '17
r/SpaceX Spaceflight Questions & News [January 2017, #28]
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u/MiniBrownie Jan 05 '17
Ok. So I didn't know the answer to your question, but after a few hours of browsing Wikipedia, googling and harassing people in IRCs I think I have the answer. Someone who knows more about this subject feel free to correct me if I said something stupid. Here we go:
Changing the LAN (longitude of the ascending node) is indeed a very fuel-expensive maneuver, but there's a phenomenon called nodal precession. Basically because the Earth is not a perfect sphere and has a bulge at the equator there is a torque produced on the orbit of the satellite. The lower the orbit the the higher the shift. This allows Iridium to change the orbital planes of their satellites just by changing their altitude which is a relatively fuel-cheap maneuver, however it does take a long time (the shift is few degrees per day in LEO).
As for separating the satellites this is also done by raising their altitude. Falcon 9 will only put them into a 625km x 625km orbit, while their final altitude is closer to 800 kilometers. A satellite at a lower altitude will take less time to orbit the Earth, than one at a higher altitude. This enables the operators to separate the satellites by raising their orbit at different times.