Provocations of the sort we saw last night will only further isolate them, as we stand by our allies, strengthen our own missile defence and lead the world in taking firm action in response to these threats.

BBC: State of the Union: Obama pledges to reignite economy

"Provocations of the sort we saw last night will only isolate them further as we stand by our allies, strengthen our own missile defence and lead the world in taking firm action in response to these threats, " he said.

BBC: Obama: Nuclear test 'isolates North Korea further'

China's concern was that the American missile defence system would lead to increasing use of space for military purposes and fuel an arms race.

ECONOMIST: China admits shooting down a satellite

Others say keeping Gates could delay the change that Obama promised during his campaign, because it could lead to potential policy conflicts over missile defense funding and a speedy Iraq pullout.

CNN: Obama rolls out national security team

Some supporters of nuclear disarmament describe our current approach to nuclear strategy as a failure of imagination that one day could lead to unprecedented catastrophe (proponents of missile defense often say the same thing).

FORBES: Nuclear Weapons: How Few Is Too Few?

If Europe is included in a missile defense system, it could lead to a renewal of the Western Alliance.

CENTERFORSECURITYPOLICY: Center For Security Policy

Its space and communications division, based in Seal Beach, California, is the lead contractor working on America's national missile-defence system, as well as the provider of the future combat system that is part of the integrated battlespace system for the army.

ECONOMIST: America's defence companies are turning dual-purpose

At that point, much of the action in missile defense shifted to the Air Force, which was the lead service for military uses of space.

FORBES: Missile Defense Becomes A Navy Mission