NASA is looking at June 28 for the 135th and final launch of the space shuttle Atlantis. Atlantis will journey to the International Space Station to deliver supplies, logistics, and spare parts. The shuttle will also fly a system that will test robot-powered refueling on existing spacecraft, and return a failed ammonia pump module.

Atlantis, as the Associated Press reported, was originally scheduled as an emergency backup mission for the crew of the Endeavor, which will launch in April. If all goes well with Endeavor, however, Atlantis will proceed as its own separate mission.

President Obama signed in October the 2010 NASA Authorization Act, which added an additional flight to the space shuttle fleet before its retirement. As AP points out, however, Congress has yet to hand over the several hundred million dollars NASA needs for the Atlantis mission. Initial funds are available in the existing budget, but not enough and Congress is set to appropriate the funds in March.

NASA, however, needs to get the space shuttle Discovery off the ground prior to Atlantis. After several delays due primarily to cracks, Discovery is now scheduled for a February 24 liftoff.  And to prevent further cracks, NASA technicians have been adding radius blocks to the shuttle’s stringers, or support beams, which will provide added structural support to those areas. NASA said that technicians had completed radius block work on 61 of 94 stringers, with modifications continuing through the weekend. NASA will roll Discovery out to the launchpad on January 31.

Meanwhile, NASA has to replace one of the astronauts who was scheduled to travel to the ISS next month via Discovery; Astronaut Steve Bowen will replace astronaut Tim Kopra on the STS-133 mission. This was prompted by a biking accident which happened earlier this week.