How to Fly a Spaceship to the Space Station.

Galileo disagrees...

Nils R Grotnes

You're probably right that my understanding of orbital mechanics is a little off. I decided to do a little reading and I've been looking at the equations here: <a href="http://en.wikipedia.org/wiki/Circular_orbit" rel="nofollow noopener" target="_blank">http://en.wikipedia.org/wiki/Circular_orbit</a> If I understand them correctly, as the radius increases, velocity decreases and orbital period increases. That seems to explain why the ISS is taking longer to travel around the earth, but it doesn't explain why it's travelling faster. Maybe it has to do with the difference in mass between the Soyuz and the ISS? That's the only other variable in those equations. A larger mass would require a higher velocity.

I would disagree with you Paul;what the Astronaut said made sense, although it was a bit confusingly put. One way to look at it through the simplified equation (V^2)/r=9.81m/s^2, which shows that as the radius of orbit increases, the linear velocity of the orbiter increases. Another perspective is that in order to increase the radius of circular orbit the ship must fire a rocket (twice) with the force of this acting in the same direction as the velocity of the ship. The first burn increases kinetic energy, then this is "traded" for gravitational potential energy as the rocket orbits to it's slowest, farthest out point, and then the kinetic energy is increased once again until the orbit is circular. The confusing part is that while increasing the radius of orbit leads to a higher linear velocity, it leads to a longer orbital period. Sorry if I've misunderstood your perspective on this. I found the video fascinating, and I can tell you did too, so cheers!

You have understand geometry correctly, but misunderstand orbital mechanics. Bodies simply can not orbit at whatever velocity they like.

Paul and Anna Spooner

If both are orbiting at the same speed (1 "lap" every 90 minutes) than the one with the larger orbit would be travelling faster because it needs to go farther. Just because they're orbiting the same body doesn't necessarily mean one is faster than the other. In this case, they said that Soyuz is travelling around 17,000 m/h and orbits in 86 minutes, and the IIS is travelling around 17,500 m/h and orbits in 90 minutes.

Your numbers must be off. If both orbits are circular around the same body, then the smaller one will have the higher velocity.

Paul and Anna Spooner

I think he said it correctly... Soyuz is moving slower at about 17,000 miles per hour and the ISS is moving at about 17,500 m/h. But, because Soyuz is closer to the earth, the distance it needs to travel to go around once is smaller than that of the ISS, so it gets around it faster.... Soyuz is moving slower but orbiting faster.

Awesome video! Just one problem though. At 7:34, the visual annotations mention that Soyuz is moving slower, but orbiting faster. But in actuality, the Soyuz is both moving and orbiting faster, and the ISS is both moving and orbiting slower. Then at 9:02 you make the same mistake, only in the voice-over.

Paul and Anna Spooner

Wait...I thought the closer you are to the planet, the faster you had to move to keep missing it. You're saying the velocity of the Soyuz is SLOWER than the velocity of the ISS? I fully understand that the Soyuz is orbiting Earth more quickly and 'catching up' to the ISS.

Jeff Dzado

So, Destin - he mentioned that, after they turn the Soyuz around to dock with the ISS, they hit the breaks; is that what the blue handle in front of Scott Kelly, between his knees, is the hand break? :-) Awesome video man - can't wait till you're broadcasting from ISS - get'em dude, get'em

The things you do are just damn cool Destin!

Incredible video. That animation really turned out great. I loved that you interviewed Scott Kelly while sitting in a Soyuz capsule. Touches like that really help me get into your videos. Thanks again.