2
$\begingroup$

Wright, a physicist and technical arms control specialist, said the launch appears to show North Korea can "go considerably farther" than previous efforts. He believes this missile on a standard trajectory would have a range of 10,400 kilometers (close to 6,500 miles) before accounting for the rotation of the Earth, which extends the range of missiles fired from west to east. However, Wright said it's still unclear if North Korea reduced the payload on this new test to get a longer range than the test on July 4.

https://www.cnbc.com/2017/07/28/half-the-continental-us-within-range-of-latest-north-korean-missile.html

Earth rotates West to East... Shouldn’t the article read Missiles fired East to West extends the range?

Maybe the tangential velocity adds to the eastward trajectory (while it would subtract from the westward trajectory) having a greater net affect than the actual angular displacement of rotation?

R/ Projection Plane

$\endgroup$
1
$\begingroup$

No. We launch rockets from Florida eastward not just because of the ocean for a possible failed launch. A missile gets a substantial velocity kick due to earth rotating in an eastward direction. The article is stated correctly. You are right that earth rotates west to east. It's this rotation that adds to a missile launch. The speed of a point on the earth surface, at the equator, moves at around 350 m/sec. The speed decreases as latitude increases. This adds to the down range velocity of the missile.

$\endgroup$
4
  • 1
    $\begingroup$ Yes, but that velocity kick only helps for putting objects in orbit. It's the relative velocity that'll affect the distance the rocket moves from A to B on Earth. Only if the rocket also moves away from the equator in latitude in its trajectory will the Earth's rotation matter because the speed at which the surface of the earth is rotating decreases as one goes away from the equator in latitude. $\endgroup$
    – WAH
    Jul 31 '17 at 18:54
  • $\begingroup$ Yes of course. I should have stated the 350 m/sec was at the equator. But going into orbit or landing down range is really just a function of burn out velocity for a given launch angle. $\endgroup$
    – Natsfan
    Aug 1 '17 at 0:21
  • $\begingroup$ @Wah -- Throw a ball and it's temporarily in orbit. That the orbit happens to be one that intersects the surface of the Earth is immaterial, at least for the brief moment between when you throw it and when it hits the ground. Throw the ball to the east and it will remain aloft a tiny bit longer than if you throw it to the west. This effect isn't so small when the thing throwing the ball (or ICBM) is a rocket engine. $\endgroup$ Aug 1 '17 at 3:27
  • $\begingroup$ @Wah, yes I agree. A launch out of North Korea to CONUS fits your requirement very well. $\endgroup$
    – Natsfan
    Aug 1 '17 at 4:11

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.