Month: July 2025

Fun & Curios

Stuff That’s Hard to Do (27 JUL – 2 AUG)

DougM 
Major Launches this Week:

- TUE AUS Eris-1 / Maiden Flight (didn't go far) 
• TUE FL Falcon9 / Starlink (Stg1's 26th mission) 
• THU CA Falcon9 / Starlink (classic Vandenfog SFB launch)
  (new graphic shows ballistic trajectory in blue 
   approaching target in white as Stg2 burns)
▶︎ FRI FL Falcon9 / Crew Dragon RTLS landing
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Updated: 2 AUG / 1200 (all times US Eastern)
Last week

Docking with ISS:

Engineering Fun:

Ever notice that Stg1 rocket plumes grow visibly wider and wider between maxQ and staging?
Sure, it’s pretty, but all that exhaust inertia that isn’t flung off directly aft is just inefficiency.

Nozzle exit pressure is a function of the bell’s expansion ratio,
so it’s essentially constant for a given engine;
but atmospheric pressure drops with altitude.

Stg1 engine bells are optimized for 1-atm exit pressure for maximum thrust at liftoff,
so they lose efficiency as they climb, due to more exhaust going sideways.
Stg2 vacuum engines, however, have larger engine bells for the highest practical expansion ratio
to get the exit pressure near zero in a vacuum, so there’s less sideways loss and more efficiency.

(I’ll stop there. Anything more requires a sliderule.)

Fun & Curios

Stuff That’s Hard to Do (20-26 JUL)

DougM 
Major US Launches this Week:

★ TUE FL Falcon9 / O3b mPower (nice vids)
★ WED CA Falcon9 / Tracers (RTLS @SLC-4W, me ol' stompin' grounds)
(cool vids of satellite deployments: two @ T+54m, T+1h35m, T+1h39m, four @ T+1h43m)
• SAT FL Falcon9 / Starlink 
• SUN CA Falcon9 / Starlink 
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Updated: 27 JUL / 0030 (times US Eastern)
Last week

Engineering Fun:

If you pay attention to the gauges on the lower RH and LH corners during Tuesday’s launch, you’ll see some interesting basic physics play out.

Acceleration goes from about 1.4g at launch to almost 4g at separation, due to the nearly constant thrust of the nine engines having less-and-less mass to push around as propellant is expended (F=ma or a=F/m so a~1/m) and less aero drag after maxQ.
When the single Stg2 engine lights, acceleration is even higher. Sure, the single Stg2 engine is optimized for vacuum operation, so it has a slightly higher thrust than any of the nine individual Stg1 engines; but the actual difference in acceleration is due to tossing-away all that Stg1 mass (see: rocket staging).

Next Episodes: Throttling back near maxQ, number of engines used, plus Stg1 return speed/altitude as gravity and drag have their way.

Homework Assignment: Watch the Stg1 speed and altitude gauges a few times and see if you can figure out what’s going on after separation.
(Yeah, I knowww… engineers get to do this all the time!)

Rocket PrOn: