By Jonathan Amos
Science correspondent, BBC News, Kennedy Space Center
The US space agency (Nasa) will try again in the next few hours to launch its shuttle Endeavour into orbit.
Sunday's attempt at a lift-off was thwarted by thick, low cloud over the Kennedy Space Center.
If it does get away this time, Endeavour should make a small piece of history by becoming the last shuttle to launch in darkness.
It will be delivering a connecting unit and a large bay window to the International Space Station (ISS).
Endeavour is fuelled and ready to go, with mission control reporting no technical issues with the orbiter.
Weather forecasters say there is a 60% chance of favourable conditions holding over the Space Coast at the time of launch, which is scheduled for 0414 local time (0914GMT).
NODE 3 - 'TRANQUILITY'
Key unit connects and helps manage other ISS modules
Multiple docking ports for visiting vehicles or future modules
7m by 4.6m; a mass of 14 tonnes, but will be fitted out in orbit
Sophisticated life support systems will include air cleaning unit
Cupola to be fixed to an Earth-facing port once in orbit
Panoramic views provide ideal control room for robotic arm
Named after Sea of Tranquility, the Apollo 11 landing site
If the shuttle does not make it off the pad on Monday, it will be stood down for a few days to give ground crews a rest and allow a rocket on the nearby Cape Canaveral Air Force Station the opportunity to launch.
The main purpose of Endeavour's 13-day mission is to fit the Node 3 and Cupola modules to the ISS. Once this is done, the platform will be 90% complete.
The mission is an important moment for the European Space Agency's (Esa) contribution to the station project. Both the modules were manufactured in Italy by Thales Alenia Space.
Node 3, also known as Tranquility, will house the station's core life-support systems.
It will also store a treadmill the crew must use regularly to exercise their bodies and maintain bone density.
One of the risks of living in microgravity conditions is that bones tend to lose strength over time.
The Cupola will afford spectacular views of Earth
The Cupola is an observation tower that will be used to control robots working on the exterior of the platform.
It is constructed in the shape of a dome, with six trapezoidal side windows and a circular top window of a little under 80cm, making it the largest window ever built for space.
The Cupola is travelling into orbit attached to the end cone of Node 3 but once in orbit will be transferred to a berthing point that looks straight down to Earth.
The spectacular views from the Cupola mean it is likely to become a popular place on the station for astronauts to relax.
Endeavour's crew get ready for the launch
Esa's project manager on Node 3 and the Cupola, Philippe Deloo, told the BBC: "I heard that on orbit the most favourite past-time of the crew when they're off duty is to watch out the window and look at Earth.
"The psychological effect of being able to look outside, to look at the Mother Earth, is something that has long been put forward as an argument to have windows on the station."
Endeavour's crew is commanded by George Zamka, a colonel in the US Marine Corps; and includes the British-born mission specialist Nicholas Patrick.
Dr Patrick will conduct the three spacewalks to install the two modules with colleague Bob Behnken.
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