Recently, the Einstein Probe (EP) satellite mission released the first batch of scientific images taken in orbit. These 11 scientific images, including observations of the center of the Milky Way, transient sources, the Crab Nebula, and the elliptical galaxy M87, showcase a cosmic "firework."
"We chose a path never taken before, destined to be filled with hardships and challenges. Fortunately, we have a group of idealistic young minds. I am honored to be able to encourage them. They are the future of Chinese space science!" On the eve of China's Youth Day, researcher and chief scientist of the EP satellite, Yuan Weimin from the National Astronomical Observatory of the Chinese Academy of Sciences, reflected on the journey with the EP satellite in an interview with the "China Science Daily."
From the "Three Musketeers" led by Yuan Weimin in 2011 to the "big family" of over 70 people at the satellite launch in 2024, this research team, mainly composed of post-80s and post-90s generations, started from original concepts, successfully broke through a series of key detection technologies, and finally turned their dreams into reality.
"Standing tall" at the launch site
On January 9, 2024, the EP satellite was successfully launched. On the eve of the launch, Yuan Weimin's family also came to cheer him on, but he did not have time and energy to take care of them. "Teacher Yuan is busy worrying about his 'second daughters'!" joked the young people in the team. Jokes aside, with the power of role models, the entire research team stood tall.
Members of the National Astronomical Observatory's EP Satellite Experiment Team posed for a group photo at the Xichang Satellite Launch Center. Photo provided by the National Astronomical Observatory.
At that time, it started raining as soon as the satellite was mounted on the rocket and transported to the launch tower. Everyone's hearts skipped a beat. They were concerned that if it leaked, the measures to maintain the cleanliness of the instruments through nitrogen gas would be affected.
In response, the team immediately established an inspection system, sending people to the launch tower to check for leaks every 2 hours, continuously for 24 hours.
"At the moment, it is drizzling, the cable window is intact without leaks, temperature is 19.94 degrees Celsius, humidity is 39.52%, meeting requirements." "At this time, the rain has stopped, the cable window is intact without leaks, temperature is 19.69 degrees Celsius, humidity is 40.56%, meeting requirements." They tirelessly reported these details in their work WeChat group day and night, without rest or food.
Fortunately, their concerns did not materialize, and the carefully protected instruments ultimately operated successfully in orbit.
Half an hour before launch, a seemingly minor but crucial action that could determine success or failure had to be completed, which was removing the protective cover of the Wide-field X-ray Telescope (WXT). Also for protection, the telescope was placed together with the cover in the satellite fairing, and could only be removed through a small window in the fairing.
Two bold and meticulous young individuals, Ma Xiaohao and Chen Yifan, used a "fishing" method to remove the protective cover. "This work was extremely dangerous, the rocket had been fueled, so it had to be completed quickly and evacuated as soon as possible." Yuan Weimin was also impressed by the courage and dedication of the young people.
In the "pre-battle mobilization," Yuan Weimin once again introduced the EP satellite logo that the team was very familiar with. As early as July 2023, the National Astronomical Observatory established the "EP Star Sea Pioneer Technology Task Force," with a deep blue logo on the red team flag standing out. At the Xichang Satellite Launch Center, this flag accompanied them in their battle.
The many Chinese elements on the logo deeply inspired the team members. "We pay tribute to the significant contributions of Chinese civilization to world astronomy, and always keep in mind the mission to seize the technological high ground!" Yuan Weimin said.
Yuan Weimin conducted "pre-war mobilization" before the launch of the EP satellite. Image provided by the National Astronomical Observatory.
"Sealing the Gap" for the Core Payload
WXT is one of the core payloads of the EP satellite. Zhang Chen, a researcher at the National Astronomical Observatory and head of the EP satellite payload WXT, introduced that this payload originated from a preliminary idea 13 years ago. In 2011, based on the principle of biomimetic micro-pore array X-ray focusing imaging of "lobster eyes," he sketched out a blueprint for the "Chinese Space Station X-ray All-sky Monitor (XASM)."
"It was so bad!" he exclaimed upon seeing the sketch again.
However, the dream of the EP satellite began with this drawing. In 2012, the EP satellite project was proposed; in 2015, it was selected as one of the key support projects of the Chinese Academy of Sciences; in 2017, the project was approved; and in 2023, the satellite rolled off the production line, with its weight and size nearly doubled.
Chen Yong, a researcher at the Institute of High Energy Physics of the Chinese Academy of Sciences and head of the X-ray Telescope (FXT) following the EP satellite payload, experienced the excessive "major transformation" of the FXT. At the end of 2016, he attended the EP satellite mission requirements analysis meeting for the first time. "The initial idea was to have only one FXT, but after it was completed, it turned into two, exceeding all expectations in various aspects," he recalled.
Researchers and FXT. Image provided by the National Astronomical Observatory
After multiple rounds of efforts, the domestically developed "Lobster Eye" telescope has been successfully produced, with its observation sensitivity and spatial resolution increased by more than 10 times compared to similar devices. On February 3rd this year, the "Lobster Eye" successfully started up, marking the first large-scale application of Lobster Eye optical technology in a space project; on February 19th, a global alert "Transient Source" was first released in the astronomer telegram.
Known as the "Swift Wind in the Sky," FXT moves swiftly in the sky like the wind. On February 28th this year, FXT observed the Crab Nebula, paying tribute to the Chinese astronomer of the Song Dynasty who observed the "Guest Star of Tian Guan" in 1054.
In fact, the team's achievements are inseparable from those down-to-earth efforts. When assembling the "Lobster Eye," Zhang Chen had to manually fill a very small gap between the lens and the frame with special sealing glue.
"During that time, he would quietly 'fill the gap' at his workstation every day," recalled Liu Yuan, a researcher at the National Astronomical Observatory and chief engineer of the EP satellite scientific application system.
Like a wave in the sea
Since the payload was fully activated in late February this year, the EP satellite has detected 17 new transient sources and 168 stellar flares, guiding several telescopes internationally for follow-up observations.
Sun Hui, assistant researcher at the National Astronomical Observatory and scientist at the EP satellite science center, told Science China, on March 15th, after the EP satellite detected an X-ray source, it attracted the attention of astronomers worldwide, leading to the organization of 6 global discussion meetings at the fastest pace.
"The time zones were so challenging! In the end, we had to schedule the meetings at 9 p.m. Beijing time, 6 a.m. in the U.S., and noon in Europe, which often led to discussions among Chinese scientists until midnight," Sun Hui said.
Liu Yuan explained that from April to June this year, the research team will complete all WXT and FXT calibration observations. Subsequently, from June to December, they will continue on-orbit testing, followed by transitioning to the on-orbit scientific operation phase.
"It's rare in life to have the opportunity to work on such a challenging scientific project," said Liu Heyang, a postdoctoral fellow at the National Astronomical Observatory and scientist at the EP Science Center. In 2020, Liu Heyang, who had no plans to work in Beijing, joined the team without hesitation after receiving an invitation call from his mentor Yuan Weimin.
Yuan Weimin assigned him as the "project manager," with the task of completing the test of the "Lobster Eye X-ray Imager" (LEIA) to be launched by the "Lijian-1" rocket developed by the Institute of Mechanics of the Chinese Academy of Sciences in 2022.
"I used to work on theory, and I didn't have much experience in engineering." He overcame his social anxiety while learning, eventually growing together with the EP satellite. "Just as the song 'Me and My Motherland' sings, I and our EP satellite are like the sea and the waves, sharing both the sorrows it brings us and the joy it brings!"
