James Webb Telescope vs Hubble As NASA's Observatory Steps Closer to Launch

NASA's James Webb Telescope has undergone its final stage of testing and is now being prepared for transport to its launch site, the space agency announced on Thursday.

Webb, the successor to the Hubble Space Telescope, is due to be shipped to its launch site in French Guiana, South America, later this year once preparations conclude in September.

It will lift off aboard a European Space Agency (ESA) Ariane 5 rocket, though NASA is not clear on the exact date yet. The telescope has no launch date constraints, so it can launch on almost any day of the year.

Once Webb launches it will take a month to fly to its orbital location, around a million miles from Earth, and slowly unfold from its current compact size. It will then begin to power up and calibrate itself before peering into deep space.

NASA thinks Webb's first scientific operations will start around half a year after launch and will become the space agency's flagship astronomical observation tool.

Mark Voyton, Webb observatory integration and test manager at NASA's Goddard Space Flight Center, said in a NASA press release on Thursday: "To me, launching Webb will be a significant life event—I'll be elated of course when this is successful, but it will also be a time of deep personal introspection. Twenty years of my life will all come down to that moment."

Webb versus Hubble

The Hubble Space Telescope has provided us with some of the most stunning images of the cosmos since it began operating in the early '90s. But Webb will be even better suited for peering into deep space than its predecessor.

The James Webb Telescope is more sensitive and is capable of longer wavelength coverage than Hubble, meaning it will be able to look further away—that is, further back in time—than Hubble.

It also means Webb will be able to look for the formation of some of the first galaxies that have so far been unobserved.

The way the telescopes see the universe is also different. While the Hubble telescope primarily looks at optical and UV light, Webb will primarily look at infrared light. This is the type of light that is given off by the most distant objects in space.

At the heart of Webb's technological leap over Hubble is its enormous mirror, which it uses to capture the light from the most faint and distant parts of the universe. Its mirror is about 21.3 feet in diameter—much larger than Hubble's mirror, which is 7.8 feet in diameter.

The whole unit will also be bigger than Hubble, thanks to its huge sunshield that will protect Webb from heating up too much from sun exposure. The sunshield is about the size of a tennis court, 69.5 feet by 46.5 feet. Hubble, without that sunshield, is about 14 feet in diameter and 43.5 feet long.

The two telescopes will also be in different locations in space. Hubble operates in low Earth orbit at an altitude of around 340 miles.

Webb will not be in orbit around the Earth at all. Instead, it will actually orbit the sun at a distance of 1 million miles from our planet. The telescope is so sensitive that its sunshield must protect it not only from the sun's heat but also from the heat of the Earth and moon.

James Webb Telescope
The giant golden mirror of the James Webb Telescope seen here in November 2016 at NASA's Goddard Space Flight Center in Maryland. The telescope will be able to peer further into the cosmos than Hubble can. Alex Wong/Getty