GERLACH, Nev. — Wedge Oldham, a 49-year-old software engineer from Los Angeles, finds nothing sweeter than spending a fall weekend in the Black Rock desert, barking rocket launching commands like “Are we good to go?” into the hot dusty wind. Nerves jangling, he awaits the moment when Carpe Diem, his homemade 18-foot-long rocket, hurls itself heavenward with 737 pounds of thrust, shockwaves — or “mach diamonds” — surging from its supersonic exhaust. With dazed exuberance he watches it recede into deep blue sky, and then, with the release of parachutes, gently drift four miles away, preserved for another flight. At...