Earlier government estimates said that Mir, which has been in orbit for more than 10 years, would be decommissioned in the middle of next year. Russian space officials insist it could stay up for another two years.
The United States and other countries want Russia to dedicate its resources to the International Space Station, which has been delayed by funding shortages on the Russian side.
NASA is paying the Russian Space Agency up to $60 million to make sure it completes a service module on time.
Astronauts and cosmonauts cannot live on the space station until the service module and its life-support systems are in orbit.
It costs Russia about $13.6 million each year to keep the Mir in orbit. But Russia's sentimental attachment to the Mir has made it tough for it to let go of the accident-prone station.