NASA's "Psyche" deep space probe is preparing to conduct a bold close flyby of Mars. It will use the "slingshot" effect of Mars' gravity to accelerate towards one of the most peculiar metallic asteroids in the solar system - the asteroid of the same name "Psyche". On Friday, May 15, Eastern Time, the probe will pass by at an altitude of only about 2,800 miles (about 4,500 kilometers) from the surface of Mars at a speed of about 12,300 miles per hour (about 19,800 kilometers). By changing its flight trajectory and increasing its speed, it will provide a key boost for the long journey to the main asteroid belt.
The "Lingshen" probe was launched on October 13, 2023. It relies on solar electric propulsion and xenon gas to continue to slowly accelerate, gradually increasing its speed during the multi-year mission. Through Mars gravity assistance, the mission team can significantly save propellant consumption while obtaining sufficient speed and orbital inclination changes to enable the probe to reach the target asteroid in subsequent years. This type of planetary flyby is not only a key link in orbit design, but also provides engineers and scientists with a valuable opportunity to comprehensively test and calibrate the flight control system and scientific payload before reaching the final target.
During the upcoming flyby, the mission team of "Psychia" plans to use the multispectral imager to conduct thousands of observations of Mars to obtain image and spectral data to verify the performance of the imaging system and optimize subsequent observation strategies in the asteroid orbit. The probe has begun to send back images before the flyby. In the first batch of "raw" images released since May 7, Mars is still just a faint light in the distant starry sky. Subsequent engineers will process a large number of images taken during the flyby by adjusting the brightness and contrast, and are expected to produce a time-lapse sequence showing the entire close flyby process in the next few weeks.
In order to ensure the accurate implementation of the flyby, the mission team performed an orbit correction maneuver on February 23. The probe was continuously fired for about 12 hours, fine-tuning the flight orbit and slightly increasing the speed so that it could fly from the predetermined altitude as planned when it arrives at Mars in May. Sarah Bairstow, head of mission planning, said that the flight control team has written all the operations that the detector needs to perform throughout May into the flight computer. "This time we can not only calibrate the camera with a target much larger than 'a few pixels' during flight for the first time, but also allow other scientific instruments to participate in the observation."
Since the "Psyche" is approaching from the night side of Mars, the appearance of Mars seen by the probe will be different from the "full red disk" familiar to the public on the ground. According to the description of Jim Bell, the leader of the mission imager, the probe is approaching Mars at a very high "phase angle", that is, "catching up with the planet from the night side, only a thin crescent moon barely outlined by sunlight can be seen." Before and after the flyby, the probe will first see a slender "Mars crescent". After the flyby, it will have the opportunity to take a view close to the "full Mars". This is not only conducive to the calibration of the imaging system, but also expected to produce a batch of highly ornamental photos.
Scientists are also interested in using this opportunity to detect faint rings of dust that may exist around Mars. Research speculates that when the two small satellites of Mars - Phobos (Phobos) and Deimos (Deimos) - are continuously hit by micrometeors, they may eject fine dust particles into space and form a thin dust "ring" or "annular cloud" near the orbit of Mars. If the illumination angle is suitable during the flyby, these dusts are expected to be revealed in the processing of imaging data by the "Spirit Star", providing new clues for understanding the small Martian satellite and its microenvironment.
This flyby is not only an imaging experiment, but also a multidisciplinary comprehensive observation exercise. The magnetometer on the probe is expected to record the interaction between the Martian magnetic field and charged particles from the sun, while the gamma ray and neutron spectrometer will monitor changes in cosmic ray flux during the flyby, accumulating experience for subsequent detection of high-energy particles and surface materials in asteroid orbits. In addition, the imager will also perform a "satellite search" mode and carry out observation exercises similar to "micro satellite search" around Mars in order to more efficiently search for potential micro satellites after arriving at the "Psyche" asteroid.
Although the scientific gains are promising, the mission team emphasized that the primary purpose of this flyby is still to "borrow Mars' power." As Lindy Elkins-Tanton, the project’s lead researcher, said, the fundamental reason for the flyby is to “get a little help from Mars, accelerate the flight and tilt the orbit in the direction of the asteroid Psyche.” If the instrument testing and calibration can be successfully completed on this basis, it will be the “icing on the cake.”
During the flyby, the mission control center will closely track the radio signals sent back by the "Psyche" through NASA's Deep Space Network (DSN) to accurately evaluate the flyby effect. Subtle changes in the speed of the detector will be reflected in the Doppler frequency shift of the radio signal. Based on this, engineers can quickly invert the new orbit parameters after the flyby and confirm whether the detector has accurately headed towards the main asteroid belt. Through joint observations with the Mars on-orbiter and the ground bureau, the team also hopes to further optimize the orbit measurement and navigation strategies of future deep space missions during the planetary gravity-assisted process.
Multiple spacecraft currently operating near Mars will coordinate to support this operation. These include NASA's "Mars Reconnaissance Orbiter" (MRO), the "Mars Odyssey" orbiter, and the two Mars rovers "Curiosity" and "Perseverance" operating on the surface of Mars. The European Space Agency's (ESA) "Mars Express" and "ExoMars Trace Gas Orbiter" will also participate in observations and measurements. Scientists plan to compare the observation data obtained by the "Lingshen" during its flyby with the data accumulated over the years by existing missions to Mars to further improve the calibration of the "Lingshen" scientific instruments and help future probes close to Mars better design communication and navigation solutions.
According to the mission plan, the "Psyche" probe will continue to rush outward to the main asteroid belt after being boosted by Mars' gravity. It is expected to arrive at its eponymous metallic asteroid by the end of 2029 and enter orbit, launching a long-term investigation of the internal composition and evolutionary history of this rare celestial body. As the first asteroid exploration mission with metals as its main research target, "Psyche" is expected to reveal ancient remnants similar to planetary cores, providing an unprecedented window for humans to understand the formation process of terrestrial planets and the evolution of the early solar system.