THE cold war may be fading away, but the United States is pressing forward with plans for modernization of its nuclear arsenal. An earth-penetrating warhead and a new nuclear depth bomb are among the weapons now under development by US government scientists. Concepts under evaluation include maneuvering reentry vehicles, and the Hypervelocity Glide Vehicle, a winged nuclear missile that could evade defenses while plunging toward targets at supersonic speed.
Defense officials admit that the world security structure is in a great deal of flux. But the Soviets still possess a formidable nuclear arsenal, and the US modernization program should continue until such time as ``we have a better chance to evaluate the direction this new future world will take us,'' said Robert Barker, assistant to the Secretary of Defense for Atomic Energy, in secret Congressional testimony recently made public.
Dr. Barker's comments were made at a closed hearing of a House Appropriations panel. The transcript of this annual hearing, declassified and published in a 500-plus page book, is among the most detailed accounts of US nuclear weapons activities available, and is avidly scoured by experts outside government for hints about what is happening in this mysterious, closed world.
According to the transcript, the current US stockpile of warheads ``has decreased by about 10 percent since 1985.'' References to exact numbers are deleted, though estimates place the US arsenal at some 12,000 nuclear weapons.
Production this year apparently promises to be disappointing. ``Due to a combination of program slips and funding constraints'' fewer warheads than anticipated will roll off production lines, according to the transcript.
Disruptions caused by safety problems at aging Department of Energy production plants were undoubtedly a major factor here. But production may have increased, even if it did not meet projected goals. In previous declassified documents, defense officials let slip the fact that warhead deliveries were supposed to go up 27 percent in 1990, largely due to the beginning of production of the Trident 2 missile's W88 warhead. And W88 deliveries have begun, according to this year's transcript.
New warheads are needed not just for new delivery vehicles such as the Trident 2, but to replace older bombs and missiles which may not have the safety features of modern designs, according to defense officials. The oldest single weapon still in the stockpile is a B-28 bomb which was produced in 1958. Overall, the Department of Energy is planning to retire five of the current 25 types of US nuclear weapons over the next three years.
To further enhance safety, DOE this year is requesting $19.7 million for purchase of 12 additional security trailers. Some US nuclear weapons are currently shipped around the country by air, and DOE wants to eliminate this practice by 1993.
``This change will reduce the risk of plutonium dispersal in the event of a transportation accident,'' according to a supporting document supplied by the Energy Department to Congress.
As for US nuclear modernization plans, the LOBFA, the Low Observable Bomb for Aircraft, otherwise known as the Stealth bomb, has met its demise. Several years ago, Air Force officials requested that DOE study such a weapon, thinking they might need it for Stealth aircraft. Apparently, the Air Force now has no interest in the project and ``LOBFA has been dropped from the budget,'' according to John Tuck, acting assistant secretary of energy for defense programs.
But an earth-penetrator warhead (EPW) for attacking underground targets is proceeding toward deployment. This long-standing project has been split into two efforts: an interim EPW, likely a strengthened version of an existing weapon, and a strategic or long-term EPW for more deeply buried targets. ``Little is being done'' on the long-term project, but the Air Force has already instructed the contractor for the interim EPW to begin work.
Weapons now being studied for their feasibility include the maneuvering reentry vehicle, high power microwaves, and the hypervelocity glide vehicle.
The glide vehicle seems to be a project the Pentagon is serious about. Warhead studies are complete, and contractors are studying how to construct its airframe.
Directed energy weapons, however, appear to be fading from favor. The nuclear-powered X-ray laser was once hailed as a potential breakthrough Star Wars weapon for strategic defense, but for 1991 the Energy Department is requesting about 10 percent less money for this and related projects.
Nuclear-directed energy weapon research has ``been scaled back consistent with overall priorities,'' according to DOE testimony.