01-Dec-17 – North Korea’s Low Orbit ICBM

Question 1:

…’The only thing Iran has done was loft a satellite into low earth orbit at 300 miles altitude and the neocons freak that this is a cover for an ICBM program, uh-no. That doesn’t get you much…

Question 2:

Iran is propelling the rocket up to an altitude of 300 miles, so even if you double it to guesstimate the horizontal range, that’s only 600 miles…
…They are pushing satellites into orbit but that doesn’t allow them to test warhead reentry technology.
…Other than the general connection to rocketry, is there anything unique to launching satellites that makes it ICBM specific…’

I understand your desire to keep some here from deflecting this ‘rocket’ issue onto Iran…and that is commendable…

However…your complete lack of any technical knowledge about space flight does not help the discussion…

For one thing…putting a spacecraft into orbit is a Very Big Deal…
Once a spacecraft is in low earth orbit…it flies around the earth about once every 90 minutes…
That means it could hit anywhere on earth within 90 minutes…
Your second comment about the altitude reached has absolutely nothing to do with orbit…
In a nutshell…it’s not about altitude…it’s all about speed…
Here is a simple primer in physics that even high-school students should know…and surely do in countries like North Korea…
Question…how does a satellite in orbit…i.e. flying around the earth…stay there…?
It is explained by two forces pulling in opposite directions being in equilibrium…as per Newton’s Third Law…
In the case of a satellite the force pulling it to the earth is the acceleration of earth’s gravity…which is 9.8 meters per second squared…[32.2 ft/s^2]
Obviously if there is no equal and opposite force to counter earth’s gravitational pull…the satellite will come down instead of staying in orbit…
That equal and opposite force is the centrifugal force acting on the satellite…
We all know what centrifugal force is…remember the spinning a water bucket around demonstration…or the hammer throw in Olympics…where that guy spins a heavy ball on the end of a chain around and then releases it…
Well…that satellite flying around earth at Very High Speed is exactly like that ball…
The chain is like the force of gravity holding it in an ‘orbit’ as the guy spins around…
While he’s holding on to it the two forces are in equilibrium…but at some point the centrifugal force overcomes his ability to hold on…and off she goes…
With a spacecraft in orbit we want to achieve just the right speed in order to keep the centrifugal force in equilibrium with the earth’s gravitational pull…
It is a simple calculation of basic algebra…

Centrifugal force = mass x velocity squared / radius…
The gravitational pull on the vehicle = mass x g
where g is the acceleration of gravity…i.e. 9.8 m/s^2…
since the two are in equilibrium we get…
m x V^2 / r = mass x 9.8 m/s
where m is mass of the vehicle…r is earth’s radius…and V is velocity of the vehicle…
since the mass of the vehicle is the same value…it cancels out on both sides of the equation and we are left with…
V^2 / r = 9.8
We can now solve for the velocity of the vehicle by rearranging that equation…
i.e….V = sqrt(r x 9.8)
the radius of the earth is roughly 6,000 km [or six million meters]
So now we find the velocity required to reach orbit…
V = sqrt( 6,000,000 x 9.8) = 7,668 m/s…or 7.67 km/s…

that’s 17,153 mph…
Why is this a big deal…?
…because it has to do with the capability of the rocket propulsion to reach that Speed…
We recall from the early days of the space race that the Russians launched the first satellite Sputnik 1 in 1957…
The US launched its first satellite in 1958…Explorer 1…but we note that its mass was less than one fifth that of sputnik…[14 kg vs 84 kg]…
…which means the Russian rocket was more than five times as powerful…
Then in 1961…the Russians launched the first man into ORBIT…on the Vostok 1…
Then just weeks later…the US launched its first man into space…But Not Orbit…
Alan Shepard’s Mercury Redstone 3 Rocket was able to achieve a maximum speed of only 5,134 mph…
…which is less than one-third the Velocity needed to reach ORBIT…
We also note the launch mass of the MR3 vehicle was less than half that of the Vostok…
It wasn’t until a year later, 1962, that John Glenn became the first US man in Orbit…on the Mercury Atlas 6 rocket…
We note again that the mass of the MA6 vehicle was only 1,300 kg…barely a quarter that of the 4,700 kg Vostok 1…
those two cardinal parameters…ie Orbital Velocity…and Payload…speak directly to the rocket capability…
It was crystal clear that the Russians had a big lead in rocket engine technology…
The fact that the Iranians can put a vehicle in orbit…no matter its mass…also speaks to an advanced rocket capability…ie being able to reach Orbital Velocity…
The North Koreans are in a different league now…this is an impressive rocket and there can be little doubt that it has intercontinental range…
Incidentally ICBMs aren’t designed to reach orbital velocity…there is a tradeoff between payload and maximum velocity…i.e….cut down the payload and you get more velocity…which is what the US did in the early years to try to keep up…
A Typical ICBM will only need to reach as little as 4 to 5 km/s…but modern Russian and US typically go to over 6 km/s…
They do not enter orbit because there is a prohibition on weapons in orbit that everyone has signed…but the US considers that it is within the law if it launches a weapon that does not make one full orbit…
Of course the Russians can play that game too… https://en.wikipedia.org/wiki/Fractional_Orbital_Bombardment_System
B brought to light some good technical points here including the details on the rocket engine turbo-pump…which is the heart of the machine…
Their progress has been incredible. I didn’t get a good view of this new rocket, but their previous liquid fuel rockets burned extremely cleanly. After initial launch there was virtually no smoke at all. Even stranger is the precision that they achieved with the guidance systems; the things went exactly where they wanted them to go. This is all very mystifying.

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