On October 16, at 09:34 UTC, a United Launch Alliance Atlas V 401 launched NASA’s Lucy probe into a solar orbit to eventually reach the Jupiter Trojan asteroids from SLC-41 at Cape Canaveral Space Force Station in Florida.

According to the Lucy mission, the Jupiter Trojans are asteroids that are probably remnants from the formation of the outer planets. Exploring asteroids in this region could give us clues to the history of the solar system and the origins of organic materials on Earth.

The Atlas V 401 rocket has one RL-10 engine on its Centaur upper stage, a four-meter class fairing, and no solid rocket motors on the first stage. Slightly less than one hour after launch, the Lucy spacecraft was deployed from the Centaur upper stage after two burns to put it in orbit and then send it out of Earth orbit. But it can’t head directly out to the Trojan asteroids just yet.

Lucy will gain speed from two Earth gravity assists, one in 2022 and the other in 2024, to send it out into an elliptical orbit that intersects the Sun-Jupiter Lagrange point 4, sixty degrees in front of Jupiter in its orbit. 

Any two bodies in a gravitationally bound system have five areas, called Lagrange points, that a third body (for instance, a spacecraft) can orbit in, so you have to specify which two bodies’ Lagrange point you are referring to, with the more massive body first. 

Lagrange points 4 and 5 are the most stable points of intersecting gravity wells between bodies because of their extended size. Sun-Earth’s L4 and L5 are stable but much less so than others. Objects stay there but not forever. Objects can stay at Sun-Jupiter L4/L5 for extremely long periods of time, essentially forever, without propulsion. The Coriolis force has time to act on objects in these bigger gravity wells. That’s what makes them good for trapping the remnants of the building blocks of the solar system which Lucy is designed to investigate.

If you want to know more about Lagrange Points and orbital mechanics in general, check out the show notes and the Patreon bonus content for this week.

Before it reaches Sun-Jupiter L4, Lucy will fly by an outer main-belt asteroid. Then it will reach Sun-Jupiter L4 and flyby four asteroids in this location in 2027 and 2028 and head back into the inner solar system for one more Earth flyby in 2031. This flyby will shift its elliptical orbit to allow flybys of the Sun-Jupiter L5, sixty degrees behind Jupiter. Once it reaches apogee again, it will fly by a binary asteroid at Sun-Jupiter L5 in 2033 and conclude its nominal mission after visiting seven asteroids. It could reach further asteroids in either Sun-Jupiter L4 or Sun-Jupiter L5 if the spacecraft is still functioning properly and the mission is extended.

More Information

Overview (SwRI)

Basics of Space Flight (NASA)