For years before North Korea fired its first intercontinental ballistic missile this week, the Pentagon and intelligence experts had sounded a warning: Not only was the North making progress quickly, spy satellite coverage was so spotty that the United States might not see a missile being prepared for launch.

That set off an urgent but quiet search for ways to improve America’s early-warning ability — and the capability to strike missiles while they are on the launchpad. The most intriguing solutions have come from Silicon Valley, where the Obama administration began investing in tiny, inexpensive civilian satellites developed to count cars in Target parking lots and monitor the growth of crops.

Some in the Pentagon accustomed to relying on highly classified, multibillion-dollar satellites, which take years to develop, resisted the move. But as North Korea’s missile program progressed, American officials laid out an ambitious schedule for the first of the small satellites to go up at the end of this year, or the beginning of next.

Launched in clusters, some staying in orbit just a year or two, the satellites would provide coverage necessary to execute a new military contingency plan called “Kill Chain.” It is the first step in a new strategy to use satellite imagery to identify North Korean launch sites, nuclear facilities and manufacturing capability and destroy them pre-emptively if a conflict seems imminent.