Details of a new vision for America's space programme are expected on Monday.
President Barack Obama has cancelled the American project designed to take humans back to the Moon.
It is widely thought the new approach will see the commercial sector being given the task of launching astronauts.
The Constellation programme envisaged new rockets and a new crewship called Orion to put astronauts on the lunar surface by 2020.
In doing so, President Obama will scrap the rockets currently being developed by the US space agency to replace the shuttle and go back to the Moon.
But in his federal budget request issued on Monday, Mr Obama said the project was "over budget, behind schedule, and lacking in innovation".
It is anticipated Nasa chief Charlie Bolden will outline the new vision to coincide with Mr Obama's 2011 budget request to Congress.
It was draining resources from other US space agency activities, he added.
Pre-announcement briefings have trailed the likelihood of the agency getting a $6bn increase in its funding over the next five years.
He plans instead to turn to the private sector for launch services.
Some of this money will be used by Nasa to incentivise private companies, to help them bring forward a new generation of launchers to carry humans into orbit.
As well as being a customer for these rockets, the agency would also set and oversee standards in the nascent market, especially in matters that concern crew safety.
Entrepreneurs are waiting to sell astronaut 'taxi services' to Nasa
In addition, the funding boost would enable America to extend the operation of the International Space Station from 2015 to at least 2020.
The changes, if confirmed, fit broadly with ideas put forward by a special panel convened last year by Mr Obama to review US human spaceflight options.
The Augustine committee argued strongly in favour of giving the commercial sector a greater role in the nation's space programme. The panel members thought such an approach could reduce costs and even speed up the adoption of new technologies.
Bretton Alexander, president of the Commercial Spaceflight Federation, said the details that were starting to emerge about Mr Obama's space plans were very encouraging.
"At a time when job creation is the top priority for our nation, a commercial crew programme will create more jobs per dollar because it leverages millions in private investment and taps the potential of systems that serve both government and private customers," he said.
"We have a tremendous opportunity here to jump-start private activity in low-Earth orbit that will further lower the cost of access to space and unleash the economic potential of space long promised."
The vision thing: When will humans go back to the Moon?
But there are major bi-partisan concerns in Congress about the proposed new path, and the impact it could have on jobs tied up with current Nasa programmes.
The agency has been working to produce two new rockets - known as Ares-1 and -5 - and a new crewship called Orion. These are intended to replace the shuttle but have the capability also to take astronauts back to the Moon by 2020.
If this multi-billion-dollar project - known as Constellation - is now abandoned, there will be considerable fall-out on Capitol Hill.
The Congressional delegations from Alabama, Florida and Texas - the states most involved in Constellation - will want assurances about their workforces' future.
One issue of key interest will be what plan, if any, the Obama vision has for a new heavy-lift rocket, without which astronauts cannot get beyond the space station, to go to destinations such as the Moon or Mars.
Without a heavy-lift rocket, humans will not go beyond Low-Earth Orbit
Ares-5 was supposed to have been that vehicle, but many critics have argued that Nasa could get the same capability faster, and much more cheaply, if it just modified elements of the current shuttle launch stack.
Several versions of this Shuttle-Derived Heavy Launch Vehicle (SDHLV) have been proposed, including a powerful rocket dubbed Jupiter.
This launcher has been designed by a largely anonymous group of Nasa and industry engineers in their spare time.
It is built around the solid rocket boosters and external tank used by the shuttle to get into orbit today. Additional thrust is achieved by placing shuttle engines under the tank.
A capsule, or some other payload, is then placed above the main tank.
