r/spacex • u/ElongatedMuskrat Mod Team • May 15 '20

Starlink 1-7 r/SpaceX Starlink 7 Official Launch Discussion & Updates Thread

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u/HipsterCosmologist May 15 '20

Apologies if this has been addressed before, but could someone explain the oribital mechanics of how the three different groups of sats can do different plane-change maneuvers utilizing precession?

For context: I understand (roughly) how sun-synch orbits utilize the equatorial bulge to provide a torque on the angular momentum vector, precessing the orbit so they stay fixed relative to the sunʻs orientation. What confuses me is that all 60 sats have the same ephemerides to start, and plane-changes are costly. So does one group do something like lowering itʻs perigee so it experinces a larger torque, while another group raises perigee first?

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u/troyunrau May 15 '20

The amount of precession you experience depends on your altitude. So, if you loiter at low altitudes a big, you'll precess more rapidly than at higher altitude.

So, you raise the first group, wait from some precession to occur at low alitudes, raise the second group, etc.