There is currently a 60-percent chance that weather at the launch site will delay today's launch. Weather conditions are expected to improve slightly on Wednesday and Thursday.
The seven STS-120 crew members, including ESA astronaut Paolo Nespoli, arrived at Kennedy Space Center on Friday.
As well as exchanging a member of the Station's permanent crew, and the challenging operation of repositioning a set of solar arrays, the STS-120 crew is responsible for the safe delivery of the Italian-built Node 2 connecting module - an important step in the continued construction of the International Space Station.
Nespoli's mission has been named 'Esperia' after the Ancient Greek name for the Italian peninsula. During the 14-day mission Nespoli will play a key role as the intravehicular activity (IVA) astronaut for three of the five scheduled spacewalks, including the installation of Node 2. He will also conduct a joint ESA/ASI programme of human physiology and biology experiments, as well as a number of educational activities.
Nespoli's mission stems from six flight opportunities granted to the Italian Space Agency (ASI) for their provision of three pressurised cargo containers (Multi-Purpose Logistics Modules, or MPLMs) to NASA under a bilateral agreement. The close cooperation between ESA and ASI led to the assignment of Nespoli, a member of the European Astronaut Corps, for this ASI flight opportunity.
The countdown to launch of STS-120 and the Esperia Mission can be viewed on NASA TV - coverage starts at 12:30 CEST (10:30 GMT): http://www.nasa.gov/multimedia/nasatv/