Besides presenting a physical challenge—one that requires overcoming the hostile terrain of space—the Gravity Well also represents an ascent of achievement.

Toward the bottom lies our airline industry, generating $170 billion a year in revenue. Farther up, in low Earth orbit, or LEO, are more than a thou- sand satellites, monitoring crops and the weather.

Still farther, in middle Earth orbit or MEO, several dozen satellites provide our GPS.

At the next level, in geosynchronous orbit or GEO, more than 250 satellites enable our Internet, television, and telephone communications.

While governments were first to explore this terrain, it now supports a frontier economy, with basic, low-cost transportation increasingly provided by pri- vately owned companies. This economy is rapidly rising to higher revenues, as entrepreneurs develop more powerful reusable rockets and smaller, more sophisticated satellites to serve a variety of clients and customers on the ground.

Still farther up the Well lie the Lagrangian points, with a few more satellites. Farther up lies the Moon, where we Americans left footprints and then chose to pull back.