DPRK Missle Launch, physics of

[diogenesNY]

I have been watching the news coverage of North Korea's latest test launch of a ballistic missile. One piece that I read noted that the recent launch had a significant range increase over the last launch: 2300 miles vs. 1700 miles.

The article in question is here:

http://www.dailymail.co.uk/news/article-4886026/North-Korea-fires-missile-Japan.html

In addition, the article had a nice graphic that illustrated the paths and landing points of the two most recent missiles. The illustration also drew radial circles centered on the launch point, and whose radius bisected the landing point, in order to illustrate the ranges of the missiles and some of the potential targets that such a missile could hit. One of the main points of the illustration was to show that Guam was now within the range of their current missiles.

Now, I am aware of the advantages of launching a rocket that is intended for orbit from as close to the equator as possible and in an easterly direction. These launches, however, were semi-orbital ballistic shots. Further noting that these were both is a mostly easterly direction (over Japan).

This got me to wondering...

My superficial (and largely intuitive) analysis would lead me to conclude that for a launch of this type (notwithstanding the vicissitudes of the weather) that aiming to the east or west would yield pretty much the same performance characteristics, in terms of range, etc. The more the missile was aimed to the north or south, however, I suspect, would bring in a much more complicated calculation to determine range, ultimate direction, landing point, etc. Beyond that, my knowledge (guessing? assumptions? intuition?) on the topic is pretty much exhausted. While this offers no particular comfort, I did note that Guam was 2114 miles SSE of Pyongyang.

While the diagram in the article was a fairly simple, illustrative info-graphic, I did get to pondering over the question of what specific effects a more North/South launch would have on the flight path, etc, and which principles would dominate and otherwise come into play that were not so applicable in an E/W launch... or whether for that matter I am simply barking up the wrong tree.

diogenesNY

 

[Bandersnatch]

My superficial (and largely intuitive) analysis would lead me to conclude that for a launch of this type (notwithstanding the vicissitudes of the weather) that aiming to the east or west would yield pretty much the same performance characteristics, in terms of range, etc. The more the missile was aimed to the north or south, however, I suspect, would bring in a much more complicated calculation to determine range, ultimate direction, landing point, etc. Beyond that, my knowledge (guessing? assumptions? intuition?) on the topic is pretty much exhausted. While this offers no particular comfort, I did note that Guam was 2114 miles SSE of Pyongyang.

Your intuition is on target.
This can be understood by viewing the missile in an inertial frame. In this frame, the launch velocity is the velocity imparted by the rocket engine plus the eastward rotation of the Earth at a given latitude.
This makes the missile have greater velocity if launched eastwards. However, in an inertial frame, the Earth is rotating under the missile in flight, so that the target point moves eastwards as well. This means that the extra eastward velocity is 'used up' to make up for the extra distance to the target (and vice versa if launched westwards).

When launched at an azimuth other than 90/270 degrees, the target will move underneath the missile less or more, depending on relative latitudes, while the missile retains the Earth's rotational velocity component of the launch site, regardless of how far N or S it travels. This will cause deflection eastwards towards the poles and westwards towards the equator, as seen from the surface, with associated range extension in those directions (and conversely, range reduction to the west towards the poles and to the east towards the equator).
Which is of course nothing else than the Coriolis force if viewed in the rotating frame.