On August 17 the last GPS Block IIR satellite will be launched. It will be named SVN50/PRN21. This launch is the end of the aera of the Block IIR, "replenishment", satelites. The next satellite generation to be launched will be the Block IIF, "future", satellites. Of course the lifetime of 10 years will mean that we will use GPS Block IIR satellites for the next decade.
SVN50 will be placed into orbital plane/slot E3, replacing SVN40, a Block IIA satellite launched in July 1996 that is past its design life but still working well. SVN40 will be moved a little further along the orbital path. Successful launch and activation of the new satellite will bring the constellation to 31 operational satellites, not counting SVN49 which is still set unhealthy due to its signal anomaly.
Here it is important to note that SVN50 will not have any payload connected to the J2 auxiliary payload port that proved problematical with the L5 demonstration payload on SVN49, and possibly on other Block IIR/IIRMs.