NASA called off its launch of space shuttle Endeavor due to a malfunction in one of its power units, Space.com reported. The plan is to try again Monday afternoon, with astronaut Mark Kelly, the husband of Rep. Gabrielle Giffords, in the cockpit. Giffords and President Obama had planned to attend Friday's launch and it is unclear if they will be on hand Sunday. The White House said Obama did spend about 10 minutes with Giffords anyway and met the shuttle's crew. Endeavour will journey to the International Space Station for a two-week visit to deliver a $2 billion astrophysics experiment designed to hunt for exotic subatomic particles.