Ballistic Missile Defence (BMD) Missiles Unviable for Australia

Running parallel to the threat of North Korean missiles to the US Guam territory issue is a sporadic, ill-informed Australian domestic debate on the viability of any Australian ballistic missile defences (BMD).

Isolated current and former Australian politicians (Abbott and Rudd respectively) advocate BMD for Australia against the North Korean threat. The Australian Government insists that Australian BMD is  technically ineffective and would be hugely expensive. 

I agree. This particularly applies to such scenarios as North Korean, Chinese or Russian ICBM nuclear warhead reentry vehicles descending on the terminal phase of their flight toward major Australian cities and military/intelligence sites. See Diagram-Map 1. below.

Diagram-Map 1. Guam already in range. NK is steadily developing ICBM to hit any targets in Australia. Darwin may already be in range. (Map courtesy The Daily Telegraph)
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In view of physical realities and cost Australia doesn't have THAAD or Patriot missiles. One of Australia's AWDs (Air Warfare Destroyers) (HMAS Hobart) has AEGIS. Hobart is about to be commissioned and two more are being completed. None have BMD capable SM-3 missiles and might not have.

Australia best anti-missile missile hope is the US Ground-Based Midcourse Defense (GMD) system - and that's a poor system. 

US Ground-Based Midcourse Defense (GMD)

The US Ground-Based Midcourse Defense (GMD) BMD system goes back to Reagan era SDI "Star Wars" years and is nowhere near ready after more than US$41 Billion spent. GMD:

-  has a high failure rate, that is, a low success rate in shootdown-friendly tests,

-  would be ineffective against most enemy submarines firing nuclear tipped ballistic and cruise
   missiles from most launch positions at Australia, and
-  probably needs decades more development
-  again is extremely expensive making it perhaps of low marginal utility compared to a sovereign
   Australian nuclear deterrent

Unlike the US Australia has no overpolar (over Alaska) interceptor "chokepoint" see Diagram-Map 2 below which would increase the US chances of interception. Australia's geography, with more than 10 dispersed large cities and 10+ dispersed military/intelligence bases, would need 20+ interceptor batteries (perhaps talking 100 x GMD missiles - see below).

Diagram-Map 2.  includes the US$multi-billion giant radars deployed forward for interception of enemy ballistic missiles at their midcourse overflight "chokepoint" over Alaska. Australia has no such chokepoint but instead would need to construct 20+ interceptor batteries - a system probably more expensive than the ineffective US system. (Diagram-Map courtesy http://www.analisidifesa.it/2017/06/la-nuova-guerra-fredda-si-combatte-a-suon-di-missili/ ).

Patriot, THAAD or SM-3s located in Northeast Asia have the greatest chance of shooting down North Korean ICBMs in the early boost-phase. Australia could only send one or two AEGIS Air Warfare Destroyers, future armed with SM-3, across the world, to Northeast Asia, in the unlikely event of North Korea launching something. Australia's US, Japanese and South Korean allies are better situated for action in Northeast Asia.

The best deterrent against North Korea (like all enemy nuclear armed states) is nuclear weapons. Australia lacks its own nuclear weapons. Australia, like SK and Japan, therefore relies on their US ally's nuclear weapon deterrent.

Pete