A NASA spacecraft headed toward the asteroid belt will fly past Mars on Friday, aiming to get a boost from the planet's gravitational field and save some of the propellant it needs to complete the second half of a six-year voyage. The spacecraft, called Psyche after the rare asteroid it will explore, launched in October 2023. At the time, it set out on a 2.2-billion-mile journey to the metal-rich celestial rock, which scientists believe may hold clues about how the cores of planets like Earth