Major US Launches this Week: • SUN FL Falcon9 / Starlink • TUE CA Falcon9 / Starlink • WED FL Falcon9 / Starlink • FRI FL Falcon9 / Starlink (500th launch/landing of an orbital-class rocket) • SAT CA Falcon9 / Starlink ______ Updated: 6 SEP / 1430 (all times US Eastern) Last week Engineering Fun:
Entry Burn.
Why not just do a landing burn only?
Because aft-end aerodynamic heating is an engineering nightmare.
Heating and Drag ~ (air density)x(speed squared) for a given orientation (attitude).
In the upper atmosphere, air density ≈ 0, so heating and drag are small.
Upon entering the middle/lower atmosphere, density becomes more and more significant.
Also, speed has been increasing due to gravity free-fall after reaching ballistic apex.
The entry burn quickly slows the booster’s falling speed before aero heating becomes damaging.
The booster then slows aerodynamically as air density increases and drag > weight.
It’s fun to replay the vid around entry burn and watch the speed numbers.
Sometimes, you can see the speed increase for a few seconds after entry-burn shutdown,
until air density increases enough for drag to start slowing the fall.
Yeah, pretty sure that’s how it works, without a slide rule and tables of data.
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• SAT CA 
