The James Webb Space Telescope, launched Christmas Day and already 667,000 miles away from Earth, passed its last major test before it can become fully operational, unfurling the 21-foot mirror it will use to see 13.7 billion years into the past to the formation of the first stars and galaxies, and perhaps to the brink of the Big Bang itself.

After countless delays and cost overruns, NASA’s $10 billion successor to the Hubble Space Telescope will give us a more complete picture of the universe. Not only is Webb more advanced than the Hubble, it will orbit farther away — peering out into space from a distance of 1 million miles away from Earth.

Its destination is Lagrangian point 2, an area where the Earth’s gravity and the sun’s gravity cancel each other out. It’s a sort of cosmic eye of the storm, where Webb can always face away from the sun and have a clear view of the universe.

Webb is set to reach its new home within the next two weeks and then will undergo months of instrument alignments and tests before it starts its mission. It also needs to chill — literally. Once at L2, it will slowly cool to minus 388 degrees Fahrenheit, which is necessary for its sensitive instruments to scan the infrared spectrum.

While Hubble peered at the visible spectrum, and sent back remarkable images of stars, nebulae and faraway galaxies, Webb will search the heavens for clues not visible to the naked eye, no matter how good your vision.

Thus far, everything has gone so well that Webb has enough fuel for a life expectancy of about 20 years. A million things could have gone wrong, as they did when the Hubble was first launched and NASA engineers discovered a flaw that left it nearsighted and necessitated a repair mission to correct. Webb is too far away for any last-minute rescues. The engineers who built Webb had to get it right on the first go, with almost no margin for error, and it looks as if they’ve succeeded. (And it probably helped that they could build on what engineers learned in deploying Hubble.)

Perhaps not wanting to jinx things, NASA officials aren’t quite declaring victory yet.

“It’s not downhill from here. It’s all kind of a level playing field,” project manager Bill Ochs said after Webb’s mirror deployed last weekend.

When you’re playing with $10 billion of taxpayer money and aren’t going to get a do-over if anything goes wrong, that’s the prudent attitude to take. The true “mission accomplished” will come after Webb starts sending back data.

When can we expect the fruits of these efforts? Sometime during the middle of the summer.

As NASA’s manned space program continues to struggle, the unmanned program continues to expand our knowledge of the universe we inhabit. We all thought Hubble gave us a good picture, but likely we haven’t seen anything yet.