I see news reports saying that the North Korean test rocket traveled 400 KM while attaining 1000 KM altitude. I find it difficult to believe a ballistic missile went 2.5 times higher than the ISS orbit and only traveled 400 KM across the earth. If it did attain 1000 KM altitude it would orbit unless it had controlled reentry. Am I correct? What would be the expected result of a rocket making 1000 KM altitude?

Question

I see news reports saying that the North Korean test rocket traveled 400 KM while attaining 1000 KM altitude. I find it difficult to believe a ballistic missile went 2.5 times higher than the ISS orbit and only traveled 400 KM across the earth. If it did attain 1000 KM altitude it would orbit unless it had controlled reentry.  Am I correct? What would be the expected result of a rocket making 1000 KM altitude?

mrnood · Answer

I am not sure about the figures you quote but 

it is not true to say that it would enter orbit.

You can project an item vertically upwards as far as you like, and it will return to earth under gravity.

The key thing for entering orbit is the 'tangential velocity' i.e. how fast it is travelling AROUND the earth.

If you watch a launch of a rocket to orbit you will see that it very early on 'rolls' to start accelerating 'downrange' as well as 'up'

4simon · Answer

Thanks, that makes sense.

mrnood · Answer

BTW - that is also the reason why most launch sites are located near the equator - the earth already has a tangential velocity of about 1000 mph on the equator, so less energy is requirted to launch from there