Why is the STS space shuttle program ending in 2010?

I have read that the Constellation series of human space flight rockets arnt going to be ready until 2014, so why is nasa ending the space shuttle program in 2010. I have heard obvious reasons like the shuttles are gettin old but i still dont see why they cant just be reffited. With the space shuttles retired,... show more I have read that the Constellation series of human space flight rockets arnt going to be ready until 2014, so why is nasa ending the space shuttle program in 2010. I have heard obvious reasons like the shuttles are gettin old but i still dont see why they cant just be reffited.

With the space shuttles retired, does it mean that the ISS will be relying on the russian soyuz rockets to conduct crew changes and some resupply needs?

Also related to this questions, what other human spaceflight vehicles are there, reusable and expendable?

Thank you.
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