Lower than expected usage rates have forced NASA to decommission its three-year-old social networking website Spacebook. NASA plans to shut the site down on June 1 and archive all user accounts and content uploaded to the website, according to an internal email sent to employees last month. “When Spacebook came, we were on the initial cusp, but with Facebook and MySpace…the marketplace is a far more challenging space,” Sasi Pillay, NASA’s chief technology officer for information technology, said during a telework event inWashington. “Even getting some tools adopted internally is hard.” NASA launched Spacebook in June 2009 to facilitate collaboration…