Signals stopped Tuesday, Feb. 10. Silence was the sound of satellites colliding.

Hurtling forward at 17,500 miles an hour 500 miles above the earth, a dead Russian satellite smashed into a 1,200 pound, live U.S. satellite that was part of the Iridium global communications network. The collision left nothing but space debris... and the sound of silence.

The media treated the incident like a road accident, a quirky story of space junk gone bad. "Hey," the storyline went, "there's a lot up there. The Pentagon tracks about 18,000 pieces of space-garbage. Sometimes bad things happen. No biggie."

But the incident should serve as a cautionary tale about how incredibly dependent modern life is on the stuff in space. About the grave dangers that lurk in space. About how little is being done to ensure that America can protect and maintain access to our vital space assets.

For Americans, a day without space would look an awful lot like life in the 19th century.

For starters, you could kiss air travel goodbye. Today's commercial flights are almost wholly dependent on Global Positioning System (GPS) navigation. And the GPS system is dependent on satellites.

Your morning weather report would be almost worthless without the feeds from space-based weather satellites. And, in most cases, your cell phone, credit cards, and ATM wouldn't work very well without the space-based communications that support them.

Indeed, the entire global supply chain might grind to a halt. The shelves at the local Wall Mart would start looking bare very quickly.

Security would deteriorate quickly as well. Emergency services would be disrupted. People needing critical medical care or medicines might not get it in time. The military that protects us would be enfeebled, too -- no strategic communications, no space-based intelligence, no early warning of ballistic missile threats.

Everything that makes modern life convenient, comfortable, and safe might be compromised.

The satellite collision illustrates the vulnerability of space-based assets. Aside from accidental collisions, there are other ways to lose them.

One of the most devastating ways a foe could "reach out and touch" vital satellites is to detonate a nuclear weapon in space. The explosion would create an electro-magnetic pulse (EMP) that would burn out electrical systems anywhere in line-of-sight -- on earth and in space.

The explosion would also ionize a band in space, most likely at the low-earth-orbit level occupied by our most useful satellites. In 2004, the EMP Commission warned that a radiation belt like this would threaten "severe lifetime degradation or outright failure" among satellites in low-earth orbit. It could well fry any replacement satellites launched, too. Think of a decade without GPS.

There are lesser dangers as well. The Soviets tested anti-satellite weapons. Just two years ago, China successfully tested a satellite killer weapon. It's something they think about a lot. Reading some of the translated Chinese military writings about the utility of attacking satellites is very troubling.

Equally troubling is the thought of Iran in space. And three weeks ago, Tehran sent a satellite out there. It's a big deal, because once you have the ability to launch a satellite, you pretty much have the capacity to start knocking them down.

So far, the new administration's only response to this challenge has been to call for a treaty banning weapons in space. Treaties are hardly a panacea. Consider the nuclear nonproliferation treaty. A decade into it and membership in the Nuclear Powers Club has grown from six to nine -- with Iran now knocking at the door to become Member #10.

Rather than seek paper promises of good behavior, the administration would do better to (1) commit to ensuring America's access to space and (2) develop a better early-warning system that monitors threats to space-based assets.

For starters, they should move full speed ahead with a program like "Brilliant Eyes," the space-borne sensors that would let us spot anything headed into space from anywhere on the earth. Knowing "what goes up" is a good way to protect us from "what comes down."

James Jay Carafano is a senior fellow at The Heritage Foundation and the author of GI Ingenuity: Improvisation, Technology and Winning World War II.