NASA's Psyche spacecraft used Mars as a free slingshot on 15 May 2026, gaining 1,000 miles per hour in speed and tilting its orbital plane by one degree, all without firing a thruster, to put it on course for a metal world that may be a planet's exposed iron core

On 15 May 2026, NASA’s Psyche spacecraft passed within 2,864 miles, or 4,609 kilometres, of Mars and left the encounter on a better path than the one it arrived on.

There was no large engine burn to do it. No dramatic use of onboard propellant. Instead, Psyche used Mars itself as part of the flight plan, taking a gravity assist that increased the spacecraft’s speed by about 1,000 miles per hour and shifted its orbital plane by roughly one degree relative to the Sun.

NASA confirmed the result in a 19 May 2026 mission update, after the flight team analysed radio signals between Psyche and the Deep Space Network. The manoeuvre put the spacecraft on course for asteroid Psyche, a metal-rich body in the main asteroid belt between Mars and Jupiter.

The asteroid is not simply another rock on the mission list. It may be the partial core of a planetesimal, one of the building blocks of early planets. If that interpretation is right, Psyche could give scientists a rare way to study material broadly related to the hidden iron cores of rocky planets such as Earth, without drilling through thousands of kilometres of mantle and crust.

How Mars gave the spacecraft speed

A gravity assist sounds like a shortcut, but it is really an exchange of motion.

As Psyche approached Mars, the planet’s gravity bent the spacecraft’s path. Because Mars itself is moving around the Sun, the encounter changed the spacecraft’s solar orbit. From Psyche’s point of view, Mars pulled it onto a new trajectory. From the wider view of the solar system, the spacecraft borrowed a tiny amount of orbital energy from the planet.

The word “borrowed” should be understood gently. Mars did give up a vanishingly small amount of momentum, but the planet is so massive compared with the spacecraft that the change to Mars is not meaningful in practice. For Psyche, however, the effect was large enough to matter.

The manoeuvre saved propellant and changed the spacecraft’s path in a way that would have been expensive to reproduce with thrusters alone. This is why gravity assists have been used across interplanetary exploration for decades. They allow mission designers to use planets not only as destinations, but as moving pieces of navigation infrastructure.

For Psyche, the Mars flyby was part of the route from Earth launch in October 2023 to arrival at asteroid Psyche in 2029. The spacecraft did not stop at Mars. It used the planet as a turn in the road.

The one-degree change mattered

The speed gain attracted the obvious attention, but the plane change was also important.

Objects in the solar system do not all orbit in exactly the same flat sheet. A spacecraft leaving Earth must be aimed not only outward or inward, but also into the correct orbital plane for its target. Changing that inclination can require substantial energy if done with propulsion.

NASA said Mars shifted Psyche’s orbital plane by about one degree relative to the Sun. A single degree may sound small on the page, but over interplanetary distances it is a serious navigation adjustment. It helped align the spacecraft with the path needed to reach the asteroid belt and eventually be captured by asteroid Psyche’s gravity.

That capture is expected in late July 2029, with the prime science mission beginning in August. Once there, the spacecraft will spend about two years orbiting the asteroid through a sequence of circular orbits, mapping the surface, measuring gravity and magnetism, and gathering composition data.

A practice run at Mars

The Mars flyby was not only a navigation event. It was also a rehearsal.

In the days before and during closest approach, Psyche’s instruments were powered on for calibration. Its multispectral imagers, magnetometers, and gamma-ray and neutron spectrometer used the encounter to test performance against a well-studied planetary target.

That matters because asteroid Psyche will be unfamiliar terrain. Before the spacecraft reaches it, engineers and scientists need to understand how the instruments behave in flight, how the cameras process real planetary scenes, and how the operations team handles fast-changing geometry during a close encounter.

As a result, the flyby produced thousands of Mars images. Some showed the planet as a thin crescent before closest approach, a result of the high phase angle from which Psyche viewed it. Others captured the south polar cap, wind-streaked terrain near craters, and an enhanced-colour view of the Huygens crater region.

Those images were not the main reason for the flyby. They were a useful by-product of a manoeuvre planned for navigation. But they also gave the Psyche team a large dataset for calibration before the asteroid encounter.

What kind of world Psyche is going to

Asteroid Psyche is about 173 miles, or 280 kilometres, across at its widest point. It has long been considered unusual because it appears to contain substantial metal, unlike the rocky or icy bodies visited by many previous missions.

The original scientific attraction was straightforward: if Psyche is the exposed core of a small early world, it could show scientists something they cannot directly observe inside Earth. Our planet’s core is inferred through seismic waves, magnetic-field studies, laboratory experiments and modelling. No spacecraft can visit it. A metal-rich asteroid, if it preserves core-like material, offers a different route into the same broad question of how rocky planets formed and differentiated.

But the mission is not based on the assumption that the answer is already known. Psyche may be a partial core. It may be a metal-rich body with a more complicated history. It may have mixed metal and silicate material in ways that challenge simple origin stories. The spacecraft is being sent because observations from Earth are not enough to settle the question.

This is why NASA describes the mission as a visit to a metal-rich asteroid, not as a guaranteed trip to a naked planetary core. The distinction matters. A good mission does not need the most dramatic hypothesis to be true. It needs a target interesting enough that the truth, once measured, will teach something either way.

A quiet kind of precision

The Mars assist was a reminder that interplanetary flight often advances through small, exact changes rather than obvious spectacles.

A thousand miles per hour is a large number in ordinary life, but in solar-system navigation it is part of a larger geometry measured over years. A one-degree tilt is barely visible without a diagram, yet it helps decide whether a spacecraft arrives at a distant asteroid. A flyby lasting hours can shape a mission’s path for the next three years.

Psyche will now resume its cruise toward the main asteroid belt, using its solar-electric propulsion system as needed along the way. The Mars encounter did not finish the mission. It made the rest of the mission possible on the planned route.

That is the quieter value of a gravity assist. It is not magic and it is not free in a physical sense. It is the careful use of planetary motion, planned years ahead, to make a distant target reachable.

On 15 May 2026, Mars did not become Psyche’s destination. It became the turning point that sent the spacecraft toward one of the more unusual bodies in the asteroid belt, and toward a test of whether a metal world can help explain the buried interiors of planets.