CAPE CANAVERAL, Fla.—The Hubble Space Telescope has been hit with computer trouble, with all astronomical viewing halted, NASA said Wednesday. The orbiting observatory has been idle since Sunday when a 1980s-era computer that controls the science instruments shut down, possibly because of a bad memory board. Flight controllers at NASA’s Goddard Space Flight Center in Maryland tried to restart the computer Monday, but the same thing happened. They’re now trying to switch to a backup memory unit. If that works, the telescope will be tested for a day, before the science instruments are turned back on and observations can resume. For now, the cameras and other instruments are in a so-called safe mode. Launched in 1990, Hubble is showing more and more signs of aging, despite a series of repairs and updates by spacewalking astronauts during NASA’s shuttle era. The idled computer was installed during the fifth and final service …