Three astronauts launched aboard a Chinese National Space Administration rocket in the early hours of Tuesday morning from the Gobi Desert. They are now en route to China’s recently completed Tiangong space station. Although another three astronauts were already aboard Tiangong since before it was completed, once docked the Shenzhou-15 mission trio will soon replace them for a six-month stay—the first crew swap-out for the station in what will be a continuously occupied, decade-long projected lifespan. As notes, “This will be a first for China, which has never supported two crews on the orbiting outpost simultaneously before.”

The launch represents a major milestone in the country’s literal and figurative ascendance as a space superpower, and comes barely two weeks after the successful launch of NASA’s unmanned Artemis I launch, the first in a series leading to Americans’ return to the lunar surface.

[Related: How Tiangong station will make China a force in the space race.]

As reported by The New York Times and elsewhere, the newcomers will finish installing facilities and equipment aboard Tiangong in near-zero gravity as the station travels in low-Earth orbit roughly 240 miles above the planet’s surface. China plans to replace Tiangong’s astronauts every six months, who will conduct a range of experiments and research as the country aims to solidify itself as a major spacefaring force. Among the first, is testing the effects of low gravity and space radiation on seed production and growth, as well as studying how spiders spin webs in free fall—similar to previous experiments conducted on the ISS. From there, a host of additional experiments will be conducted by a rotating Tiangong staff in the months and years ahead.

Unlike traditional stateside NASA launches, The New York Times reports a particularly substantial level of military security surrounding the event. No civilian or journalist photography was allowed, and those approaching the site were sent text messages beginning at 50 miles away, including one reading, “Those stealing secrets will surely be caught, and will be decapitated once caught! Everyone catch enemy spies, and make great contributions by seizing them!”

Despite lofty aspirations to eventually travel to both the moon and Mars, China is currently pursuing those goals alone. NASA has prohibited cooperation with the nation since 2011 in response to human rights and security concerns, and China’s astronauts have never visited the International Space Station. The NY Times explained that European researchers are however participating in a few experiments heading for Tiangong, including one with a high-energy cosmic radiation detector. A United Nations program is also reportedly offering experiment opportunities for teams from Saudi Arabia, Mexico, Peru, and India.

[Related: Why the SLS rocket fuel leaks weren’t a setback.]

China’s space aims remain ambitious, with an eye to mine near-Earth asteroid and Martian samples, as well as land astronauts on the moon by the end of the decade. By 2040, the country hopes to develop a nuclear-powered rocket—something many stateside are also working hard to achieve.