Discover and read the best of Twitter Threads about #hotbird13f
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THREAD: 1/ We got lots of good questions today on why #FalconHeavy was needed for #USSF44 instead of Falcon 9. You can actually see the reason (yay maths!!!) by comparing the Hotbird 13F & USSF-44 stage separation velocities. 
2/ This is the center booster's shutdown velocity (2nd stage starting velocity) for USSF-44: ~14,270 km/h. That's 51% of low Earth orbit velocity. Now, compare that to the geostationary transfer orbit (GTO) mission of #Hotbird13F just a few weeks prior...
3/ On that GTO mission, the #Falcon9 booster (while still recovered) got the 2nd stage to a starting velocity of ~8,210 km/h. That 2nd stage had quite a lot more work to do (more deltaV needed) to haul the payload into the parking orbit before burning for GTO than USSF-44's did.
