NASA is changing strategy away from manned missions towards investigating the origins of the solar system.
Space probes are picking off scientific targets with a view to finding out more about how the Sun and planets developed in the first 10 million years after the star's birth.
Top of the list are the asteroid 16 Psyche and another group of asteroids trapped in the gravitational pull of Jupiter.
NASA experts believe these battered relics are the remnants of the first generation of planets that populated the solar system long before the Earth was on the scene.
Psyche is of special interest as the 'rock' is unique to astronomers.
Is asteroid a planet core?
The 130-mile wide asteroid is made of iron and nickel – the same as the Earth's core – and is the only metal object so far found in the solar system.
Scientists believe the asteroid is all that is left of the metal core of a long-destroyed planet that was roughly the size of Mars. The theory is the planet was buffeted by strikes from other celestial objects billions of years ago, and may have exploded to leave the core floating in space.
A space probe is due to take off on a seven-year flight for Psyche in 2023. On arrival, the satellite will investigate the asteroid's features for six months.
In 2021, another mission will launch for six asteroids orbiting Jupiter. These cold and lifeless rocks are thought to be material left over from when the solar system first formed.
The NASA program including the voyages to Psyche and Jupiter's asteroids – codenamed Discovery – will cost £365 million.