NASA has postponed until Sunday the launch of its $1.5 billion unmanned Parker Solar Probe, to allow engineers more time to investigate a red flag that was raised in the last moment before lift-off.The problem had to do with the gaseous helium pressure alarm on the spacecraft, officials said early Saturday. The next launch window opens at 3:31 (0731 GMT) on Sunday. NASA’s car-sized, $1.5 billion Parker Solar Probe was scheduled to launch on a Delta IV Heavy rocket from Cape Canaveral, Florida during a 65-minute launch window that opened at 3:33 am (0733 GMT). By coming closer to the Sun than any spacecraft in history, the unmanned probe’s main goal is to unveil the secrets of the corona, the unusual atmosphere around the Sun. Watch video for more details.