# Why is the Orbital Velocity after SECO of Crew Dragon with 27K km/h lower than of ISS?

Crew Dragon after SECO: Orbital Vfelocity at 27,000km/h at 200km altitude (roughly 9-10min after liftoff). ISS Orbital Velocity at ca. 28,000 km/h at 400km altitude.iss_altitude,iss speed

However from the equation $$v = \sqrt{\frac{GM}r}$$, I expect Crew Dragon to actually rotate faster than the ISS around earth?! What is wrong with my thinking?

• sources for you figures? Most likely a non-circular orbit, with further orbital rendezvous manoeuvrers to follow.
– user20636
Dec 24, 2020 at 10:10
• 1) If your source was the video, that might still be ground speed relative to the rotating Earth's surface, after all, it starts at zero, not 465 $\sin(lat)$ m/s right? 2) The vis-viva equation is $$v=\sqrt{GM \left(\frac{2}{r}-\frac{1}{a} \right)}$$ which works for elliptical orbits (and I think hyperbolic ones as well if you are careful). Your equation is for circular. Use the complete equation and solve for $a$ and you may discover that Crew Dragon was in an elliptical orbit that will carry it to or past the ISS' altitude. It's just a guess
– uhoh
Dec 24, 2020 at 10:21
• Min/Max apogee 197km/202km (source: Commentator Crew Demo in Livestream Youtube Video) that orbit is elliptical, but always roughly 200km below ISS. Dec 24, 2020 at 10:22
• Possible duplicate of 2nd stage speed - with respect to what? (SpaceX webcast of Orbcomm OG2 deployment). The answer makes it clear that @uhoh is correct: The velocities are Earth-centered Earth-fixed rather than Earth-centered inertial. Dec 24, 2020 at 16:03
• @DavidHammen thanks for finding that, this sounded familliar. Wow five years ago already!
– uhoh
Dec 24, 2020 at 17:25