Russia launched three additional GLONASS satellites on March 1, 2010.  The launch was originally scheduled for September 2009, but had to be postponed when problems emerged with a similar satellite already in orbit and sent the three new satellites back to the factory for pre-launch repairs.  The GLONASS constellation now includes 23 operational satellites, two of which are being used in a reserve capacity.  A 21-satellite constellation provides 98.5% global availability.  With three additional satellites expected to launch in August and another launch scheduled for November, the GLONASS constellation could reach 99.5% global availability by the end of 2010. 

As a comparison, the current GPS constellation maintained by the United States includes 32 satellites and reached full operational capacity in 1995.  It takes a minimum of 24 operational satellites to provide complete global availability.