I watched the latest SpaceX launch of Intelsat 35e on 05 July 2017 carried by their Falcon 9 rocket into geostationary orbit, and noticed some confusing telemetry data.
Telemetry just before the second burn was as follows:
Velocity: 26503 km/hr Altitude: 248 km
Using the vis-viva equation, I calculated the semi-major axis (a) of this low Earth orbit and found a = 6017.6 km
This means that the semi-major axis of this orbit is SMALLER than the radius of the Earth (R = 6371 km), and therefore, will have a perigee that is BENEATH the Earth's surface....i.e. the orbit is sub-orbital. If the 2nd stage were to continue in this orbit (and not perform the second burn to get it into higher orbit) then doesn't this mean the 2nd stage would crash back into the Earth?
Given that the 2nd stage sat in this sub-orbital low Earth orbit for only about 20 minutes before performing the second burn, it wasn't an issue.
But my question is this: Is parking a 2nd stage in a sub-orbital low Earth orbit safe, even if it is eventually going to get boosted to a higher altitude orbit? Is this routine or common?
Thank you very much! I appreciate it!