Big science projects on the edge of doability

The Hubble Space Telescope, which was launched in 1990, forever changed how humanity views the cosmos. Along the way, the observatory has opened eyes to the expansion of the universe, the evolution of stars and the beginning of time. As Hubble’s expiration date nears, what’s next in the realm of big science? Check out seven projects that a consortia of scientists, government agencies, and private corporations are working on hard to get off the ground. Technological and budgetary hurdles may prove insurmountable for some.