From my understanding, 'SDI' was not actually feasible as originally envisioned in the 1980s, because of technological limitations of the time. Did the military continue spending on the program as a political tool, or was it vastly less influential then popularly assumed?
I have read various things on this, so I decided to actually dig up some numbers, just to see what I could find for myself.
The current US Missile Defense Agency, which is the successor of the SDI program, lists its funding numbers here. SDI was the name of the program from 1984-1993, but it's the same program today (it just got a new name).
I played around with that data, and a few other datasets, in Excel, and came up with these charts:
Adjusted spending on missile defense in constant USD 2009 dollars
Spending on missile defense as percentage of defense R&D spending
Spending on missile defense as percentage of total defense budget
By "spending" here I am using the total Congressional appropriation passed. Actual spending may vary a bit from that but I figured that was going to give us a baseline to deal with. My DOD/defense figures come from GPO.
What to make of that? It's kind of impressive by itself that over 1% of the entire defense budget (which is massive) has been spend on missile defense over the years, and still is — literally one penny of every dollar (if not more) spent on defense has gone towards missile defense research since 1986. Pretty impressive given that the technical feasibility is still pretty uncertain (it depends what you think is the goal — the mission has shrunk from "be able to defend against a full, sophisticated, massive Soviet attack" to "be able to have theatre-range defense against a state like Iran or North Korea, which will only be able to field a handful of missiles"; the latter is potentially doable, the former is a much harder thing to imagine pulling off).
The spending as percentage of GDP doesn't tell you too much except give you a way to contextualize the relative amounts — you can see the big dip in emphasis during the immediate post-Cold War, and the resurgence to Reagan-era levels when Bush came back into the Presidency. No huge surprise there, other than the fact that there is nothing very dramatic when Obama took over (the adjusted expenditures have been gradually decreasing, but it's not very dramatic).
The real kicker graph is on missile defense as a percentage of the total DOD R&D budget. During the SDI period it hovered at around 8-11% of the defense budget, with little change over the 1990s, and then quite a jump from 2001 onward (hovering more around 12%, as high as 16%).
Did these expenditures take away from other defense programs? Well, let's take a look at how DOD R&D funding went by itself over that period. Here's an ugly little graph I made of DOD funding on research and development. Blue is in constant 2009 USD (billions), red is unadjusted.
The graphs tell a somewhat complicated story in my eyes. You can see that military R&D had already boomed in the early Reagan years, but was on a decreasing slide. During the period of SDIO (1985-1993), the amount of R&D was dramatically decreasing. Which is to say, SDI consistently took about 10% of a constantly shrinking budget. Which does lead one to think that it must have been edging out other programs that might have been on the table, though the fact that the R&D budget was unusually large during that time also has to be taken into account.
In the Bush years, the R&D budget was booming again, and MDA was taking up a rather large percentage of it. In that case, it's harder to say it was taking away from other programs — it seems like they were just tacking it on to an already increased set of expenditures. Today military R&D is dropping back again.
So, anyway, that's all very interesting. Does it really answer your question about the motivations? Not really. My impression is that the military and the national laboratories do believe that missile defense is in fact technically feasible, but again it depends on your definition of feasibility (what your goals for the program is). The people who say it is unfeasible are generally outsiders to the system (but not exclusively). The program's goals and technological means have changed numerous times over its existence, however, and that perhaps says something about the persistence of this budget. At various times, "ballistic missile defense" has meant nuclear-tipped interceptor rockets, nuclear-driven X-ray laser satellites, chemical laser satellites, kinetic-interceptor satellites, kinetic-interceptor ground-based missiles, kinetic-interceptor ship-based missiles, chemical laser carrying airplanes, and probably a few I am forgetting. Its goals have changed, as I noted, from being able to be a totalizing ballistic missile "shield," to something much more limited (being able to shoot down one or two land-based missiles). The general goal of "ballistic missile defense" has been remarkably constant perhaps because they are politically and militarily appealing (and because faith in true deterrence often wavers), and that has perhaps allowed it to wiggle out of failure problems better than many other programs.
Anyway, the above is somewhat speculative, but I thought it made for an interesting food-for-thought on a blizzardy Saturday morning. There is a large literature on the Star Wars program, but much of it in my mind is pretty biased. Most of the people who write about it have been convinced by the anti-SDI advocates that it is technically impossible, but the evidence for that can be slimmer than is acknowledged (this is not to say that aspects of it have not been overhyped, to be sure). Many of those who write about it are also pretty committed against Reagan and the other pro-MDA people (Bush, Edward Teller, etc.). It makes for a hard situation, to sort out the reality from the exaggeration.
