The last NASA Space shuttle mission is on the launch pad with the countdown continuing at T minus 3 hours. Whether or not it flies today depends on the appraisal of the weather which is currently very overcast on the Florida coast. If you want to watch it you can go via the web to NASA TV
The mission is to fly to the International Space Station to deliver supplies and spare parts for the next year. After that they hope to find some new way to keep the ISS going. The Shuttle has just a four person crew, the smallest since some of the earliest flights. This is because there is no backup shuttle to rescue the astronauts if Atlantis is damaged and unsafe to return. Instead the crew would have to wait on the space station to be returned up to a year later on Russian craft.