The model of the JWST is on display in Washington DC.
The James Webb Space Telescope (JWST) is intended to replace the ageing Hubble telescope.
It will be larger than its predecessor, sit farther from Earth and have a giant mirror to enable it to see more.
Officials said the JWST - named after a former Nasa administrator - was on course for launch in June 2013.
The full-scale model is being displayed outside the Smithsonian National Air and Space Museum in the US capital, Washington DC.
It was recently shown off in Seattle at the American Astronomical Society meeting.
The $4.5bn (£2.3bn) telescope will take up a position some 1.5 million km (930,000 miles) from Earth.
It will measure 24m (80ft) long by 12m (40ft) high and incorporate a hexagonal mirror 6.5m (21.3ft) in diameter, almost three times the size of Hubble's.
Hubble, launched in 1990, has sent back pictures of our solar system, distant stars, and remote fledgling galaxies formed not long after the Big Bang.
But scientists say the JWST will enable them to look deeper into space and even further back at the origins of the Universe.
"Clearly we need a much bigger telescope to go back much further in time to see the very birth of the Universe," said Edward Weiler, director of Nasa's Goddard Space Flight Centre.
Martin Mohan of Northrop Grumman, the contractor building the telescope, said that the team was making excellent progress.
"There's engineering to do, but invention is done, more than six years ahead of launch," he said.
When ready, the JWST will be launched by a European Ariane 5 rocket. It is expected to have a 10-year lifespan.
Until then, the 17-year-old Hubble telescope will continue to do its work. Nasa plans to send astronauts on the space shuttle to service it in 2008.
The model on display at The International Society for Optical Engineering's (SPIE) Astronomical Telescopes and Instrumentations conference, May 2006.
NASA has unveiled the new telescope that will replace the Hubble Space Telescope in Washington D.C. called the James Webb Space Telescope JWST. Currently, NASA has a life-sized model on display to the public which is as tall as a two story house and weighs several tons.

Researchers at NASA say that the Webb telescope will be able to see farther than Hubble "to the beginning of time."

"It will find the first galaxies and will peer through dusty clouds to see stars forming planetary systems, connecting the Milky Way to our own Solar System," said a statement posted on NASA's website. It will be sent into space where it will orbit nearly 2,000,000 miles from Earth.

JWST will have a large mirror, 6.5 meters (21.3 feet) in diameter and a sunshield the size of a tennis court.

Northrop Grumman is contracted to build the telescope and will be jointly operated by NASA, the European Space Agency and the Canadian Space Agency. It is scheduled to launch in 2013 from Arianespace's ELA-3 launch complex at European Spaceport located near Kourou, French Guiana.