Washington, Feb 4 (IANS): The head of US space agency NASA has said that its next-generation James Webb Space Telescope, the successor to the 24-year-old Hubble Space Telescope, is on track for a 2018 launch.

All four of Webb's science instruments and all 18 of its primary mirror segments have already been delivered to the NASA's Goddard Space Flight Centre in Greenbelt, Maryland, where the agency's flagship science project will be assembled once the telescope structure arrives.

"The recent completion of the critical design review for Webb, and the delivery of all its instruments to Goddard, mark significant progress for this mission," Xinhua quoted NASA Administrator Charles Bolden as saying in a statement Monday.

"The design, build, delivery and testing of these components took meticulous planning and action... It's very exciting to see it all coming together on schedule."

According to NASA, the James Webb Space Telescope will be the most powerful space telescope ever built, capable of observing the most distant objects in the universe, providing images of the first galaxies formed, and observing unexplored planets around distant stars.

The space agency said that the 18 mirror segments will be coupled to form the massive space telescope's 21-foot-wide main mirror and that the four science instruments will be located inside the heart of the telescope.

The science instruments include a near-infrared camera that will be Webb's primary camera, a near-infrared spectrograph that can analyse 100 objects at once, a mid-infrared instrument that sees light in the mid-infrared region of the electromagnetic spectrum or wavelengths longer than the human eye can see, and a fine guidance sensor and near-infrared imager and slitless spectrograph to improve the telescope's resolution.