For the first time, an experimental treatment made from human embryonic stem cells has shown evidence of helping someone, partly restoring sight to two people suffering from slowly progressing forms of blindness.CAPE CANAVERAL, Fla. — NASA says a third spacewalk is now needed to restore a crucial cooling system at the International Space Station.
Space station astronauts didn't make much progress during Saturday's urgent spacewalk. The crew had to hammer loose a stuck connector. Then, an ammonia leak erupted. In the end, Douglas Wheelock and Tracy Caldwell Dyson were unable to remove the ammonia coolant pump that failed last weekend.
NASA originally estimated two spacewalks would be needed to replace the failed pump. After Saturday's trouble, managers say three will now be necessary. The next spacewalk won't be attempted until Wednesday at the earliest. Engineers need to figure out the next step.
NASA says the space station remains in stable condition.
