WASHINGTON -- NASAs Next Generation Space Telescope (NGST) is being revamped as engineers wrestle with cost and technology issues to keep the $1 billion observatory on track for launch before 2010.

The overhaul includes shrinking the NGSTs primary mirror diameter.

Project officials for the super telescope recently held a "cost summit," said Bernard Seery, NGST project manager at NASAs Goddard Space Flight Center. The optics, detectors, the spacecraft itself and the needed ground systems all received scrutiny as to cost and schedule, he said.

"People call it de-scope or re-scope. But what I actually perceive us doing is a re-optimization of all the parameters," Seery told SPACE.com.

In some areas, performance of NGST had to be reduced, while other areas were enhanced. "Id say weve come up with a new sweet spot for NGST," Seery said.

Several changes to the NGST program have come about as cost-saving measures.

Lack of available funds has caused cancellation of a risk-reducing, precursor flight experiment called NEXUS. Nixing the estimated $200 million NEXUS shakeout of technology now puts at a premium testing NGST on the ground.

"To do NEXUS we needed a lot of cash in fiscal years 2001 and 2002. We just couldnt get it. The agency [NASA] just doesnt have it," Seery said.

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To evaluate the very lightweight NGST on Earth, designers added mass back into the structure of the primary mirror to combat "gravity sag," Seery said.

Ultra-thin mirror technology is critical to building the Next Generation Space Telescope.

To counter that issue, a decision has been made to shave off a meter or so from the 26-foot (8-meter) diameter primary mirror. The design for NGSTs mirror diameter is now bouncing between 16.4 feet (5 meters) and 23 feet (7 meters), Seery said.

In another parameter change, NGST is likely to be operated at a different temperature than first considered.

"We actually found it might be cheaper to operate a little warmer than we had planned," Seery said. "Were looking across the whole spectrum of things, to figure out what constraints to remove, what assumptions to rethink. We want to figure out how to get a more robust system which can be ground tested."

NGST remains a very complex observatory, Seery said.

The intention is to launch NGST in the middle of 2009, possibly in late 2008 if testing goes smoothly. Some $600 million of U.S. monies are earmarked for the project. Additional funds for the now $1 billion program are coming from Canada and Europe.

One idea being kicked around is taking the NGST up on a space shuttle so astronauts can pop it over the side and check out the instruments in low Earth orbit. If the telescope proves ready for action, it would then be boosted out to the L-2 locale.

Seery said that a request for proposals to build the NGST should go out in late spring.

Ready to respond are contracting teams that have been engaged in the project for several years. One contractor team consists of Lockheed Martin Space Systems -- Missiles & Space Operations and Honeywell Corp., along with Jackson and Tull. The other team is TRW and Ball Aerospace.

Selecting the builder of NGST is anticipated to happen by this time next year, late fall to early winter, Seery said. "It will take a while no matter what we do. This is a big one," he said.

"The contractors will bid on something that we believe we can afford and understand how it will operate," Seery said.

John Mather, NASA head scientist for the NGST at the Goddard Space Flight Center, said the observatorys science objectives remain intact, despite the design alterations.

"If we cant afford to go as fast, we certainly still want to go there," Mather told SPACE.com. Although NGST costs and technical hurdles have bedeviled the project, he said the team members "have already caused several miracles to occur."

"Not only do we need to make a new observatory," Mather said, "we need to make it soon. Theres an opportunity sitting there to be making great discoveries...and Id like to see us making them as soon as possible."