I always remember it as the opposite of what I think is typically called the granny knot. In the case of the square knot, it's just right over left, then left over right.
Have you taken a look at Iran's targeting capabilities and the assets they were able to destroy? More importantly, have you considered who facilitated those targeting capabilities?
Wow. I was not expecting that topic when I clicked on the link you provided.
When I went through such a selection process years ago, we took all sorts of tests before and even after the selection process. Towards the end, the head instructor told us they don't really have a good way to measure who will make it through. What he did tell us though is that top physical fitness test scores were not indicative that a candidate will make it to the end.
Is there a PDF version or instructions for building your thesis? I'd like to read it.
> There were engineering questions around how to purify uranium and how to actually construct the weapon etc. But the phenomenon was known.
FWIW, constructing a weapon with highly enriched uranium is, relatively, simple. At the time, the choice was made to use a gun-type weapon that shot a projectile of highly enriched uranium into a a "target" of highly enriched uranium. The scientists were so sure it would work that the design didn't necessitate a live test. This was "little boy", which was eventually dropped on Hiroshima.
Fat Man utilized plutonium which required an implosion to compress the fissile material that would set off the chain reaction. This is a much more complex undertaking, but it's much more efficient. Namely, you need much less fissile material, and more of that fissile material is able to participate in the chain reaction. This design is what allows for nuclear tipped missiles. The same principles can be applied to a U-235 based weapon as well.
The implosion based design is super interesting to read about. One memorable aspect is that the designers realized that applying a tamper of uranium (U-238) around the fissile material allows for significant improvement in yield. The chain reaction is exponential, so the few extra nanoseconds that the uranium keeps the fissile material together leads to significant increase in yield.
The Royal United Services Institute (RUSI) has an updated tally on defensive and offensive munition expenditures. It's likely not 100% accurate due to the sensitive nature of those figures.
> 11,294 munitions in the first 16 days of the conflict, at a cost of approximately $26 billion.
Author here. The $75M is specifically for Ground Based Interceptors (GBIs). This is the U.S.'s ICBM mid-course interceptor. There are other interceptor types in the current U.S. arsenal:
Patriot PAC-3 (~$4M): Nations burnt through 600-800 in the first few days of Operation Epic Fury. There are reports that they're being used for drone defense.
SM-3 (~$10-30M): Ship-launched
SM-6 (~$4-5M): Ship-launched
THAAD (~$12-15M): Terminal phase, high altitude
GBI (~$75M): intended for interception of ICBMs (reported as the hardest type of missile to intercept)
Each type of interceptor is optimal for certain type of threats, which is yet another constraint on the optimization problem.
The recently announced "Golden Dome" project intends to get around this issue by putting a vast constellation of satellites into orbit. Each satellite would likely need a serious source of power in order to use its laser. Assuming that's just an engineering problem, then the issue becomes coverage. That is, depending on the adversary's capabilities, you'd need an absolutely massive constellation in orbit [0].
> For ICBMs, one idea was to use orbital, nuclear powered lasers to hit the missile on the boost phase.
Author here. Thank you for your insight.
I took some time to read about the recently proposed "Golden Dome" defense system, and what you laid out seems to be the end goal [0]. It's difficult to tell how realistic this actually is. The size of the constellation of satellites needed seems prohibitive, to say the least.
That's also great for letting the compiler unlock auto-vectorization opportunities without delving into the world of manual SIMD.
Even storing something simple such as an array of complex numbers as a structure of arrays (SoA) rather than an array of structures (AoS) can unlock a lot of optimizations. For example, less permutes/shuffles and more arithmetic instructions.
Depending on how many fields you actually need when you iterate over the data, you prevent cache pollution as well.
GitHub: https://github.com/smu160