The USD 8.8 billion James Webb Space Telescope is scheduled for launch in 2018 and aims to provide an unprecedented look at far-away planets and the first galaxies formed.
A successor to the Hubble Space Telescope launched in 1990, it is a joint project of NASA, the European Space Agency and the Canadian Space Agency.
All 18 of its primary mirror segments and four science instruments are now housed at NASA Goddard Space Flight Centre facilities in suburban Maryland.
"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," NASA administrator Charles Bolden said yesterday.
"It's very exciting to see it all coming together on schedule."
The project has gained support from US lawmakers despite a number of delays and cost hikes that delayed delivery from its initial 2013 date and pushed spending way over its primary budget of USD 3.5 billion.