NASA's Psyche Spacecraft Will Slingshot Past Mars on May 15 to Reach a Metal Asteroid

Level 3 — Intermediate

NASA is fine-tuning the trajectory of its Psyche spacecraft for one of the most important manoeuvres of the entire mission. On Friday, May 15, the probe will sweep just 2,800 miles above the Martian surface at roughly 12,300 miles per hour, borrowing energy from the planet's gravity to bend its course toward the asteroid belt.

Engineers call this technique a gravity assist, and it is essentially free propulsion. By matching Psyche's path to the moving target of Mars, the spacecraft picks up speed and tilts its orbital plane without firing its engines. NASA estimates the manoeuvre will save many months of cruise time and a substantial amount of xenon, the inert gas that feeds Psyche's solar-electric thrusters.

The spacecraft's destination is 16 Psyche, an unusual asteroid roughly 200 kilometres across that orbits between Mars and Jupiter. Most asteroids are rocky or icy, but 16 Psyche appears to be largely made of nickel and iron, prompting some planetary scientists to suggest it may be the exposed metallic core of a long-shattered protoplanet — a chance to study, from outside, the kind of dense interior we can never reach inside Earth.

Launched on October 13, 2023, atop a SpaceX Falcon Heavy rocket from Cape Canaveral, Psyche is expected to arrive at its target in August 2029 and then spend about 21 months mapping the asteroid in detail, measuring its gravity, its magnetism, and the chemistry of its surface.

trajectory: the path that a moving object follows through space

manoeuvre: a planned movement, often a careful or skilful one

propulsion: the force that pushes something forward

orbital plane: the flat surface in which an orbit lies

thruster: a small engine used to move or steer a spacecraft

asteroid belt: the region of space between Mars and Jupiter where many asteroids orbit

protoplanet: a young, partly formed planet

magnetism: the force that makes some metals attract iron

Level 4 — Advanced

On Friday, May 15, NASA's Psyche orbiter will execute the single most consequential manoeuvre of its 3.6-billion-mile cruise: a 2,800-mile-altitude gravity assist over Mars at a relative velocity of roughly 12,333 miles per hour. The encounter will not merely accelerate the spacecraft. It will also tilt its orbital plane out of the ecliptic by several degrees, a geometric correction that no realistic propellant budget could supply on its own.

Psyche relies on a Hall-effect solar-electric propulsion system, ionising xenon atoms and accelerating them through an electric field to produce a thrust that is exquisitely efficient but feeble in absolute terms. Across years of cruise, those gentle pushes accumulate to enormous delta-v; in a single afternoon, however, they cannot rival the free kick that a planet's gravity can deliver. Mission designers therefore architected the trajectory around two such kicks — an Earth flyby is no longer needed, but a Mars assist remains essential — exchanging mass and chemical complexity for years of patient flight.

The destination, 16 Psyche, is among the most enigmatic bodies in the solar system. Roughly 226 kilometres across at its widest, it shows the radar reflectivity and density signatures of a metal-dominated object, leading several planetary scientists to argue that it may be the exposed metallic core of a planetesimal whose rocky mantle was stripped away by ancient collisions. If so, the mission offers an unprecedented opportunity to probe, from outside, the kind of nickel-iron interior that lies forever beyond reach beneath Earth's silicate crust.

Arrival is scheduled for August 2029, after which the spacecraft will spend about twenty-one months in a sequence of progressively lower orbits, mapping the asteroid's gravity field, surface chemistry and any residual magnetism preserved from a long-extinct dynamo. For the broader planetary-science community, the May 15 flyby is more than a navigational waypoint; it is the moment when a long-deferred class of investigation — the in-situ study of a metallic small body — finally locks onto its trajectory.

ecliptic: the plane of Earth's orbit around the Sun, used as a reference

Hall-effect thruster: an electric rocket that uses a magnetic field to accelerate ions

delta-v: the total change in velocity a spacecraft can produce

feeble: extremely weak

enigmatic: mysterious or difficult to understand

planetesimal: a small body that can grow into a planet

dynamo: a process that generates a magnetic field by moving electric charges

in-situ: in the original or natural place

Level 1 — Absolute Beginner

Level 2 — Elementary

Level 3 — Intermediate

Level 4 — Advanced

NASA's Psyche Spacecraft Will Slingshot Past Mars on May 15 to Reach a Metal Asteroid

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