Three new satellites for the Russian global navigation system, or Glonass, entered orbit Tuesday after being launched by a Proton-M rocket from the Baikonur Cosmodrome, the Federal Space Agency said on its web site.

The latest additions increased the number of Glonass satellites in space to 20, with 19 active ones and one suspended for maintenance, the agency said. In order for Glonass to operate globally, it needs to have 24 operative satellites in orbit 19,000 kilometers above the Earth's surface.

Nikolai Testoyedov, head of Informatsionniye Sputnkoviye Sistemy, which produces the satellites, said Tuesday that six more satellites will be sent into orbit in two launches this year, giving the system the needed 24 working satellites and three in reserve.

Each satellite weighs 1,415 kilograms and has a service life of seven years.

Glonass is the Russian equivalent to the U.S. Global Positioning System.