North Korea’s decision to test fire seven ballistic missiles, in violation of its solemn vow not to do so, underscores the unpredictable, highly dangerous nature of the global ballistic missile threat. Although the largest of those missiles, a Taepodong 2, failed shortly after ignition, it had the potential to deliver a nuclear warhead to parts of the United States. This situation highlights yet again the need for an effective national missile defense.

Crazy states such as North Korea and Ahmadinejad’s Iran cannot be allowed to employ nuclear weapons and ballistic missiles to threaten the United States, its friends and global interests. If these threats cannot be negotiated away, then they must be neutralized. The most effective way to accomplish this goal is with a robust national missile defense.

Unfortunately, what is likely to be the most successful effort to target and track warheads, the Space Tracking and Surveillance System (STSS), has encountered stiff opposition in the House. System proponents need to rally to its defense.

The growing ballistic missile threat is why the Bush administration, with strong, bipartisan congressional support, moved aggressively to field an initial generation of missile defenses. The National Missile Defense site at Fort Greeley, Alaska, is operational with some 20 ground-based interceptors. This defense can be supplemented, in some instances, by U.S. Navy Aegis cruisers armed with the new Block 3 Standard missile and, in a few years, the U.S. Army’s Terminal High Altitude Area Defense (THAAD) theater missile defense system.

Each of these systems requires sensors to track a missile in flight, discriminate the missile warhead from surrounding debris or decoys, and guide the interceptor to its target. Without adequate sensors, the interceptors are useless. With the appropriate sensors, located in the right places, the effectiveness of the interceptors is multiplied because they can intercept a missile earlier in its flight trajectory and more easily find the actual warhead.

Currently, all interceptors that could defend the U.S. homeland depend on ground-based or ship-borne radar for missile tracking, discrimination and guidance. Radar must wait until the missile or warhead is above the Earth’s horizon before they can begin to operate. For many interceptors, their effectiveness is limited by their dependence on radar . Moreover, unless the radar is deployed in the right place, looking in the right direction and operational at the time a ballistic missile is launched, the defense is effectively blind.

To address this problem, the Missile Defense Agency is developing the STSS. An operational constellation of STSS satellites (the Block 12 variant) will provide uninterruptible global coverage; there would be no surprise missile launches.

Based in space, the STSS constellation will provide earlier and more accurate tracking and discrimination of missile threats than can be achieved by radar alone. Its electro-optical and infrared sensors will reduce the chance that a ground-based interceptor might miss intercepting an incoming warhead.

When it comes to defending the U.S. homeland, STSS is more than merely another sensor system. It very well may make the difference between a successful intercept of a warhead bound for a U.S. city and the deaths of countless Americans. This is because of the advantages that having sensors in space provide to a missile defense.

With STSS, the range at which a ground-based interceptor, Standard missile or THAAD can engage an incoming warhead is greatly increased, in some cases it is more than doubled. This allows the defense to take multiple shots at a target, if needed.

It is a little known fact that the current radar system in Alaska will not allow the ground-based interceptor to protect all of the Hawaiian Islands. With the STSS, the ground-based interceptors could defend Alaska, Hawaii and the lower 48 states as well as support operations by Aegis and THAAD. The STSS’ sensors make it much less likely that an interceptor will miss its target.

SSTS possesses another interesting attribute: It is unique among U.S. military space programs because it is on schedule and on budget. Moreover, it is a true spiral development program. Two demonstration satellites are scheduled to be launched in fiscal 2007. A full constellation will begin deploying in 2012.

The House Appropriations defense subcommittee cut the funding for the Block 12 program. As if that was not enough, the subcommittee inserted language in the authorization bill that prohibits the Missile Defense Agency from beginning work on the operational STSS constellation.

The logic for gutting a successful space program, one that will improve the effectiveness of virtually every missile defense program the Defense Department is deploying, escapes me. The only explanation I can come up with is that they just don’t get it.

Two individuals who do get it are U.S. Sens. Ted Stevens (R-Alaska) and Daniel Inouye (D-Hawaii) , representing the two states most directly threatened by North Korean missiles. It is largely due to their foresight and determination that the United States has any missile defenses today. Without question, these leaders understand the importance of the STSS program. They are aware that without STSS the military will not be able to guarantee a fully effective defense of Alaska, Hawaii or the lower 48 states.

Stevens and Inouye need to rise to the defense of the STSS program. The Senate Appropriations Committee must reject the House subcommittee actions in the clearest terms and affirm the value of the STSS program. This successful program must be allowed to proceed on schedule.

Daniel Goure is vice president of The Lexington Institute, Arlington, Va.