Worst-ever orbital collision leads to calls for tighter regulation.A cloud of debris spreading through low Earth orbit following the collision of two satellites poses a new risk to many scientific missions and may signal the demise of the Hubble Space Telescope. NASA is monitoring the increased threat carefully, and if it is as bad as some fear, the agency may have to cancel the proposed shuttle-servicing mission slated for later this year. Without that mission, the telescope's days are numbered, even if none of the new debris comes anywhere close to it.At 04:56 GMT on 10 February an active communications...