LOS ANGELES — The space shuttle Endeavour traveled 122,883,151 miles during its 25 missions, bursting out of the atmosphere at more than 17,000 miles an hour. On the last flight of its 20-year career, a three-day victory lap across the country on the back of a transport aircraft, it will log a few thousand miles more before touching down for the final time on Friday at Los Angeles International Airport.

But the final segment of Endeavour’s journey has proved perhaps the toughest yet: 12 miles through the dense urban landscape of Los Angeles, past streetlights and trees, to say nothing of city bureaucracy and politics, on its way to retirement at the California Science Center.

A path was cleared just days before the shuttle’s scheduled arrival, but not without controversy. A storm of criticism and threats of legal action arose in low-income neighborhoods in South Los Angeles over plans to remove hundreds of trees to make way for the bulky aircraft....