Webb space telescope nears its destination almost a million miles from Earth, ready for critical mirror alignment

Thirty days outbound from Earth, the James Webb Space Telescope will slip into its parking orbit nearly a million miles from Earth on Monday, an ideal spot to scan the heavens in search of faint infrared light from the first generation of stars and galaxies.But getting there — and successfully deploying a giant sunshade, mirrors and other appendages along the way — was just half the fun.Scientists and engineers now have to turn the $10 billion Webb into a functioning telescope, precisely aligning its 18 primary mirror segments so they work together as a single 21.3-foot-wide mirror, by far the largest ever launched.Earlier this week, engineers remotely completed a multi-day process to raise each segment, and the telescope's 2.4-foot-wide secondary mirror, a half-inch out of the launch locks that held them firmly in place during the observatory's Christmas Day climb to space atop a European Ariane 5 rocket.Now fully deployed, the 18 segments currently are aligned to within about a millimeter or so. For the telescope to achieve a razor-sharp focus, that alignment must be fine-tuned to within 1/10,000th of the width of a human hair using multiple actuators to tilt and even change a segment's shape if required."Our primary mirror is segmented, and those segments need to be aligned to a fraction of a wavelength of light," said Lee Feinberg, optical telescope element manager at NASA's Goddard Space Flight Center. They were so precisely figured that if one was blown up to the size of the United States, the 14,000-foot-high Rocky Mountains would be less than 2 inches tall.But If Webb was aimed at a bright star today, the result would be 18 separate images "and they're going to look terrible, they're going to be very blurry," Feinberg said in an interview, "because the primary mirror segments aren't aligned yet."That's the next major hurdle for the Webb team, mapping out and then tilting each segment in tiny increments, merging those 18 images to form a single exactly focused point of light.