The tardigrades had already been coaxed into an anhydrobiotic state, during which their metabolisms slow by a factor of 10,000. This allows them to survive vacuums, starvation, dessication and temperatures above 300 degrees Fahrenheit and below minus 240 degrees Fahrenheit.
Once in orbit, the tardigrade box popped open. Some were exposed to low-level cosmic radiation, and others to both cosmic and unfiltered solar radiation. All were exposed to the frigid vacuum of space.
Back on Earth, tardigrades that had basked in cosmic radiation revived and reproduced at rates comparable to an unexposed control group. Those dosed with solar radiation were less likely to wake -- but that even a few survived, wrote Rettberg's team in findings published today in Current Biology, was remarkable.
The next task is the find out how water bears survive so well. http://blog.wired.com/wiredscience/2008/09/invertebrate-as.html