Reflective surfaces on the booster body aren’t really of issue; with a weapon of this energy level any reflective coating would be vaporized virtually instantly. (Never mind the difficulty of applying this perfectly reflective coating to a modern composite rocket motor body, which is typically covered with a layer of cork to insulate it.) The much more significant issue is, as Chronos alludes to, is thermal blooming in the atmosphere; specifically, when pumping that amount of energy through the air, even at wavelengths that are normally transparent in air, even a small fraction of a percent absorbed will cause the air to roll and become turbulent, resulting in a more opaque media, which then absorbs more energy, ad nauseam. Pundits then like to throw out terms like “adaptive optics”, but regardless of what you do, the atmosphere is still going to boil turbulently.
Another problem is the sheer power required; not only do you need a lot of energy, but you need it delivered through the system very, very rapidly. This means banks of supercapacitors; not a very portable thing. The current SDI-derived directed energy system, the Air-Borne Laser (ABL) is basically capable of one shot at high power, or a few at lower (essentially system test) power. ABL was downgraded to a ‘demonstrator’ program about three years ago because of the technical problems and lack of clear direction to clear hurdles. One suggestion back in the really crazy days of SDI was an x-ray or gamma ray spaced based laser platform that would be powered by an exploding nuclear bomb; in essence, x-rays or gammas from the explosion would be shunted into a lasing cavity (using electrons and reflective fields rather than optical mirrors) which would fire a few quick shots before being destroyed. Not only was this in violation of the Outer Space Treaty, it also offends good sense that tells us that detonating nuclear weapons in orbit is likely to have severe problems for everyone, including widespread EMP effects and creating new Van Allen belts as a navigation hazard for satellites and spacecraft.
mlees makes a very astute observation about what threshold of effectiveness the overall system would have to achieve in order to be considered successful in an operational context. When you set aside all of the viewgraphs and color charts, the fact is that there was no realistic analysis of the SDI directed energy proposals that demonstrated any measure of near-term technical feasibility of either the technology or the system. Although we have higher energy lasers today, the essential problems still remain.
In short, no, directed energy SDI is not feasible, now or within the foreseeable future. Other defensive methods (ground based missile interception, “Brilliant Pebbles” type space-based intercepts, et cetera) have some measure of technical feasibility, but still fall short of offering the promise of a complete defensive shield. The current focus in ABM is against a very restricted party (typically referred to as a “rogue nation”) launching a limited number of weapons (<10) of limited countermeasure or evasive capability. Systems which are devoted to theater-level defense (Patriot Advanced Capability 2 and 3, the USN Standard Missile 2 and 3, THAAD) are more viable, albeit not typically against strategic-class weapons.
I’m not sure why Dex bounced your question; it seems like a perfectly legitimate question for Cecil or the SDSAB to address; although politically contentious, it has an easily referenced technical answer.
Stranger
