Ed Huntress wrote on 8/24/2017 8:04 PM:
On Thu, 24 Aug 2017 19:44:42 -0400, EBsoZZ?? ?????? ? ??????? ??TeRcSC
wrote:

Ed Huntress wrote on 8/24/2017 6:42 PM:
If you're interested in this story, it may be in print somewhere, but
it's also in this podcast that you can listen to online, with no
add-on apps:

https://www.nytimes.com/2017/08/24/p...s-ukraine.html

Hint: They didn't do it themselves.



It is very easy to make a rocket. The difficult part is the flight
control unit that keeps the rocket flying straight and narrow instead of
going in random directions after liftoff and crashing back to earth near
the launchpad.

A modern smartphone has all the sensors required to let the rocket
correct its course and guide itself to its destination.

All you need to do is write an App and send the output to an interface
to control the power of each of the three nozzles (a rocket as no wings
or rudder, so a minimum of three nozzles would be needed to make the
rocket go in any direction you want it to).

North Korea makes smartphones:
http://www.telegraph.co.uk/news/worldnews/asia/northkorea/10238617/Kim-Jong-un-visits-North-Korean-smartphone-factory.html

Download this Android App (Sensors Multitool) to read the sensors:
https://play.google.com/store/apps/details?id=com.wered.sensorsmultitool&hl=en

This "Sensors Multitool" App can read all the sensors in your Android
smartphone (everything you need to guide a missile to its destination):

GPS
Rotation Vector
Linear Acceleration
Gravity
Gyroscope
Accelerometer
Magnetic
Pressure
Orientation

The story is about the engines. N. Korea couldn't get a mid-range
rocket to fire reliably. All of a sudden, they're building ICBMs that
work.

The analysts recently realized why. The engines are Cold-War-Era
Russian -- possibly made in the old Russian heavy-engine factory in
the Ukraine.



As I said, it is very easy to make a rocket. North Korea's Hwasong
rocket is using liquid hydrogen and oxygen. You can tell from the clean
exhaust:
https://d3i6fh83elv35t.cloudfront.net/newshour/wp-content/uploads/2017/01/RTX2OB9Q.jpg

A rocket propels itself according to the theory of "Conservation of
Momentum". It throws the mass out at high speed (the burning fuel) and
the rockets accelerates in the opposite direction. The hydrogen and
oxygen can by obtained by simple electrolysis of water. The gas valves
and brass tubing can be bought in hardware store. Even the Palestinians
can lob rockets at Israel (they just don't know how to control the
flight path so their rockets zigzag wildly in the air).