An Earth-observation satellite developed by European and United States (US) space agencies set to lift off Saturday will measure sea level rise, tracking changes threatening to disrupt tens of millions of lives within a generation.If all goes according to plan, the payload will be hoisted into a low-Earth 1,300-kilometre (800-mile) orbit by a Space X Falcon 9 rocket, with lift-off from Vandenberg Air Force Base in California at 17:17 GMT.