But therexe2x80x99s a big difference between a successful experiment and an affordably deployable weapon. As part of the earlier effort, several companies produced prototype designs. The weapons they sketched were enormous. One was 72 feet long.

On Wednesday, Defense officials said that advances in technology have brought down the potential size and cost of space-based particle beams.

xe2x80x9cWexe2x80x99ve come a long way in terms of the technology we use today to where a full, all-up system wouldnxe2x80x99t be the size of three of these conference rooms, right? We now believe we can get it down to a package that we can put on as part of a payload to be placed on orbit,xe2x80x9d said a senior defense official. xe2x80x9cPower generation, beam formation, the accelerometer thatxe2x80x99s required to get there and what it takes to neutralize that beam, that capability has been matured and there are technologies that we can use today to miniaturize.xe2x80x9d

Officials, however, stress that the explorative studies do not necessarily mean that the Department will actually deploy a weapon. xe2x80x9cI canxe2x80x99t say that it is going to be at a space and weight requirement thatxe2x80x99s going to actually be feasible, but wexe2x80x99re pushing forward with the prototyping and demo,xe2x80x9d said an official. The exploration, according to the official, xe2x80x9cmeans we need to understand as a Department, the costs and what it would take to go do that. Therexe2x80x99s a lot of folklorexe2x80xa6that says itxe2x80x99s either crazy expensive or that itxe2x80x99s free. It needs to be a definitive study.xe2x80x9d

The push to develop space-based weapons also reflects growing concern about advances in missile technologies from adversarial and so-called xe2x80x9ccompetingxe2x80x9d nations like China, Russia, Iran and North Korea.

xe2x80x9cThe addition of the neutral particle Beam effort will design, develop, and conduct a feasibility demonstration for a space-based Directed Energy Intercept layer. This future system will offer new kill options for the [Ballistic Missile Defense System] and adds another layer of protection for the homeland,xe2x80x9d says an MDA document put out on Tuesday.

Those new options are essential, say defense officials, to hit missiles during their boost phase, as they leave the launch pad and head straight up.

xe2x80x9cThatxe2x80x99s a really hard battle space to go after, right?xe2x80x9d said the senior official. xe2x80x9cItxe2x80x99s a very short timeline, first to even know where it [meaning the missile] is coming fromxe2x80xa6Itxe2x80x99s less than a xc2xa0couple minutes before it leaves the atmosphere. So you have to have a weapon thatxe2x80x99s on station, thatxe2x80x99s not going to be taken out by air batteries and so we have been looking at directed energy applications for that. But you have to scale up power to that megawatt class. Youxe2x80x99ve got to reduce the weight. Youxe2x80x99ve got to have a power source. Itxe2x80x99s a challenge, technically.xe2x80x9d

Itxe2x80x99s also a controversial idea and not popular among arms control proponents. xe2x80x9cThe deployment of interceptors in space would be a disaster for strategic stability. To ensure the credibility of their nuclear deterrents, Russia and China would likely respond by building additional and new types of long-range ballistic missiles as well as missiles that fly on non-ballistic trajectories. Russia and China could also take steps to improve their ability to destroy such U.S. interceptors, thereby greatly increasing the threat to U.S. assets in space,xe2x80x9d said Kingston Reif, who directs disarmament and threat reduction policy at the Arms Control Association.

The U.S. is a signatory to the 1967 Outer Space Treaty, which prohibits placing nuclear weapons in space. Another Defense official made clear that the treaty does not provide an obstacle to the deployment of either lasers or neutral particle beams in orbit. xe2x80x9cThe 1967 Outer Space Treaty says that weapons of mass destruction can not be placed into outer space and then it limits even further specifically military activities on celestial bodies, I think the moon or otherwise. But the treaty does not expressly prohibit activities that are not weapons of mass destruction on outer space.xe2x80x9d

If the Defense Department does deploy weapons in space, the United States would be the first country to do so officially. But defense officials frequently contend that they probably would not be the first to do so in actuality. A February report from the Defense Intelligence Agency suggests that both China and Russia are developing space-based weapons and that they could be in orbit next year.