The US space agency is considering a Russian plan to keep crews aboard the International Space Station (ISS) for a year at a time.
The space station is currently limited to a two-person crew
The change would allow Russia to set aside room on its flights for more paying customers - either space tourists or European astronauts.
Currently, two Soyuz capsules blast off every year at six-month intervals.
The Russian space programme receives about $20m (£11m) from each customer who travels aboard its rockets.
Nasa has said it expects to make a decision within a few weeks.
The space station crew has been limited to two full-time residents since last year's suspension of space shuttle flights in the wake of the Columbia accident.
This left Russia's Soyuz capsules as the only means of transportation to and from the space station, reducing Russia's ability to sell seats on its rockets.
A Nasa team of doctors, engineers and other specialists has spent the past three weeks reviewing the Russian request.
However, the proposal would only affect the two men due to lift off in October, not the crew due to launch in a week.
Space station programme manager Bill Gerstenmaier said extending astronauts' time aboard the station could help lay the groundwork for eventual Moon missions or Mars trips.
Nasa wants to gather more medical and psychological data on the effects of long periods spent in space as it prepares for such missions.
The longest any person has spent in space is 14.5 months, a record set a decade ago by cosmonaut Valery Polyakov.
The Russian space agency recently announced that US millionaire Gregory Olsen would become the next space tourist, flying to the space station either this October or in April 2005.