Two Ships Passing in the Night
On one side, you have the European Space Agency's (ESA) Mars Express, a veteran orbiter that has been studying the Red Planet since 2003. It’s one of the most successful and long-running missions in Martian history, providing invaluable data for over
two decades. On the other side is NASA's Psyche, a newcomer launched in October 2023 on a groundbreaking mission to visit a metal-rich asteroid, also named Psyche, located in the main asteroid belt between Mars and Jupiter. Psyche's journey is a long one, and to get there efficiently, it needed a little help from a neighbor.
The Gravity Assist Slingshot
Interplanetary missions often use a technique called a 'gravity assist' to save fuel and time. By flying close to a planet, a spacecraft can use its gravitational pull to get a slingshot effect, increasing its speed and adjusting its trajectory. On May 15, 2026, it was Psyche’s turn to use Mars for this purpose. The plan was for Psyche to pass just 4,500 kilometers above the Martian surface to get the boost it needed for its long journey to the asteroid belt. While these flybys are primarily for navigation, they also present a golden opportunity to test and calibrate a spacecraft's scientific instruments against a known target.
A Spontaneous Idea, a Powerful Collaboration
When the team behind ESA’s Mars Express heard about Psyche's planned flyby, they had an idea: what if they could coordinate observations? They wondered if the paths of the two spacecraft would cross in a way that would allow them to point their cameras at the same patch of Martian surface at roughly the same time. Weeks in advance, teams from ESA and NASA began coordinating, exchanging detailed trajectory data and observation timelines. This wasn't a simple task. It required precise planning to ensure both the veteran orbiter and the passing spacecraft were looking at the same place, a region of ancient highlands called Noachis Terra.
Two Views Are Better Than One
The result was a unique set of paired observations. Mars Express, from its orbit of about 6,000 km, captured an image of the cratered landscape. A little under two hours later, Psyche, having already completed its closest approach and now receding from the planet at an altitude of 41,000 km, captured an image of the very same region. The two images offered different perspectives; Mars Express viewed the surface from an angle, while Psyche looked almost straight down. But beyond just being a neat comparison, this exercise served a critical engineering purpose. By comparing the brightness, color, and detail in Psyche's images with the well-understood data from Mars Express's camera, scientists can fine-tune the calibration of Psyche's instruments. This ensures that when the spacecraft finally arrives at its mysterious asteroid destination in 2029, its cameras will be working optimally.
More Than Just Pretty Pictures
The collaboration provided more than just a camera test. The entire suite of Psyche's instruments, including its gamma-ray and neutron spectrometer, were powered on for the flyby. This gave scientists a 'dress rehearsal' for operations at the asteroid Psyche, allowing them to test the instrument performance and data pipeline against the known properties of Mars. Furthermore, by having Mars Express track Psyche during its flyby, engineers were able to verify the spacecraft's trajectory with even greater accuracy. This kind of cross-agency support is becoming increasingly vital in space exploration, maximizing the scientific return on investment and demonstrating the power of international cooperation.
