In 18 months, if things go according to plan, an old Pershing 1A missile will roar off a launch pad somewhere in the Western desert -- and then be struck by the beam of a powerful laser. The purpose of this Strategic Defense Initiative experiment, says an SDI official, will be to test the laser's ability to track targets. Critics claim the real motive is publicity.
But whatever the reason behind the test, it demonstrates that SDI is on the verge of a new phase.
Three years ago Saturday, President Reagan's ``star wars'' speech launched SDI on its way. After all that time and billions of dollars, a number of key points have emerged in recent months:
The design of a possible defense against ballistic missiles is taking shape, with certain weapon technologies now clear front-runners.
A large, and growing, slice of SDI funds is being spent on nuclear research.
US allies are falling in line behind the SDI effort, though not all with enthusiasm.
It is still far from certain whether SDI technologies would ever be able to tie together in a working defense against incoming nuclear warheads. The problems involved are vast, ranging from construction of computers more complex than any ever built to accounting for what the Soviets might deploy in retaliation.
According to SDI officials, however, in coming months major parts of their program begin to move out of the lab and into the testing field. ``This year our research is moving more from the technology development into major experiments,'' said SDI's chief, Lt. Gen. James Abrahamson, in March 5 Senate testimony.
The Pershing shoot is one such experiment in the offing. Others include tests of the Terminal Defense Tier, a system of radars and missiles that would be the last bastion against incoming warheads, and the Boost Surveillance System, a space-based missile-launch detector.
SDI researchers have also begun to winnow out the weapons applicable to missile defense.
Three years ago artists' concepts of SDI included all manner of things: lasers both on the ground and in space, exotic particle-beam weapons, ``railguns'' that shoot projectiles at incredible speed, interceptor rockets, etc., etc. Today the diagrams can be much simpler.
Two technologies are leading the research pack. The first is the fast, chemical-powered rocket, which is now in the engineering development stage. McDonnell Douglas Astronautics has won a contract for the rocket's booster; Lockheed is working on its reentry vehicle.
The second favorite is the ``free electron'' type of laser, which would be based on the ground and shoot its beam off mirrors in space. ``The potential for large, effective ground-based laser systems is very real,'' said General Abrahamson March 5.
The ``excimer'' type of laser appears to have fallen out of the race. SDI work continues on particle-beam weapons and railguns.
Quietly, so does work on the X-ray laser, which is powered by a nuclear explosion. The administration continues to downplay the X-ray laser's possible role, and insists SDI is a nonnuclear program. But some say it is being increasingly nuclearized.
President Reagan's fiscal 1987 budget proposes an 85 percent increase in Department of Energy SDI research funds, most of which go for the X-ray laser. With such a rise, the X-ray laser would account for 25 percent of all US spending on directed-energy weapons, estimates the newsletter SDI Monitor.
Proponents of the nuclear-powered weapon say it could be popped up by rocket during a missile attack. Critics say it wouldn't get high enough fast enough for use in strategic defense.
``They're spending this money and nobody's figured out a mission for it,'' claims John Pike, an SDI analyst with the Federation of American Scientists.
SDI officials complain that the shake-out of prospective weapon systems was in part necessitated by cuts made by Congress in its budget requests during the last two years. SDI funds have been marching steadily upward, but they haven't gone up as fast as the Pentagon would like.
``We have been forced to reduce the effort on certain major technologies, such as space-based lasers, prematurely,'' Abrahamson said.
For fiscal 1987, Reagan is requesting $4.8 billion for SDI, up from $2.7 billion in 1986. Funds for directed energy weapons would increase 91 percent, to $1.6 billion; funds for kinetic-energy weapons, such as rockets and railguns, would go up 68 percent, to $1 billion.
One nontechnological area where SDI officials say they have made real progress is in relations with allies. The British have signed a government-to-government agreement governing their involvement in SDI research. Germany is expected to sign a similar pact soon.
Privately, however, a high administration official admits that the Germans are dragging their heels on the issue, trying to get the prospective agreement downgraded, perhaps to a simple exchange of letters.
Abrahamson recently went on a promotional tour of Israel, where defense firms are reportedly very interested in SDI work. Japan is also exploring the possibility of SDI contracts. A 50-person Japanese delegation is slated to make a late-March US visit for briefings from SDI officials and US contractors.