Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with news on fascinating discoveries, scientific advancements and more.

CNN  — 

SpaceX’s hulking Falcon Heavy rocket returned to the skies Thursday evening, and this time it launched a mysterious spacecraft for the US military that will carry out cutting-edge research.

The rocket lifted off from NASA’s Kennedy Space Center in Florida at 8:07 p.m. ET, carrying the military’s X-37B space plane — which is uncrewed and operates autonomously — to unprecedented altitudes. The launch streamed live on SpaceX’s website. The side boosters returned to Earth and safely touched down.

It is not clear, however, exactly where the space plane is going.

The X-37B’s activities in space have long been the subject of fascination and speculation in the space community as amateur enthusiasts race to track its whereabouts and share theories about its activities.

Resembling a miniature NASA space shuttle with the windows blacked out, the reusable and fully autonomous X-37B has been known to carry out research on concepts such as relaying solar energy from space for use back on Earth and studying the effects of radiation on seeds used to grow food.

And this mission — the seventh trip to space for an X-37B plane — promises to be even more intriguing than earlier flights.

The X-37B orbital test vehicle concludes its sixth successful mission in 2022. Staff Sgt. Adam Shanks/US Space Force

A powerful ride

This launch marked the first time the space plane has hitched a ride on a SpaceX Falcon Heavy, one of the most powerful operational rockets in the world.

Previously, the X-37B has launched on the SpaceX Falcon 9 vehicle and the Atlas V rocket built by United Launch Alliance, a joint venture between Lockheed Martin and Boeing.

The Falcon Heavy produces more thrust than both of those rockets combined.

NASA's Lucy spacecraft, atop a United Launch Alliance Atlas 5 rocket for a mission to study the Trojan asteroids in the outer solar system, launches from Pad-41 at Cape Canaveral Space Force Station, in Cape Canaveral, Florida, October 16, 2021. REUTERS/Thom Baur Thom Baur/Reuters

These 2023 science and exploration missions seemed like fiction

The launch via the Falcon Heavy could indicate that X-37B is destined for more distant orbits, perhaps even to the moon or Mars, suggested Paul Graziani, CEO of COMSPOC, a company dedicated to tracking objects in space.

If it does travel much deeper into the cosmos than earlier flights, it could be far more difficult for sky-gazers on Earth to determine where the vehicle is.

If the military doesn’t want people to track the X-37B, Graziani added, the vehicle can be hidden in the glare of the sun or by various other means — including changing its position often. The X-37B has already proven on previous flights that it’s capable of making multiple maneuvers in space.

COMSPOC will attempt to search for the vehicle if the spacecraft winds up in geosynchronous orbit, which lies about 22,400 miles (36,000 kilometers) from Earth and is where most massive communications satellites operate. Geosynchronous orbit is where the company focuses its sensors for tracking satellites, said Graziani and Bob Hall, COMSPOC’s director of operations integration.

“I think it’s one of the most interesting things that’s happened in space in a long time, whatever it’s going to do,” Graziani said of the X-37B launch.

Space technology innovations

The X-37B makes it possible for the United States to carry out experiments to understand how to improve ongoing and upcoming space operations and push the boundaries of what’s possible, according to a statement by Gen. B. Chance Saltzman, chief of space operations.

Among the research on board this mission is a NASA experiment that aims to find ways to sustain astronauts on future deep-space missions. Called Seeds-2, it will “expose plant seeds to the harsh radiation environment of long-duration spaceflight” and build on research carried out on previous X-37B missions.

Learning how to grow food in the harsh, soilless environment of outer space could be crucial for astronauts on lengthy missions to the moon or beyond — places where it’s more difficult to deliver fresh supplies.

An illustration of the UK-designed CASSIOPeiA solar power satellite. Space-based solar power involves harvesting sunlight from Earth orbit then beaming it down to the surface where it is needed. Space Solar

This wild, futuristic space plan could help save the world. But some say it’s too far-fetched

It’s unclear how long the spacecraft will spend in orbit for this stint, though historically each X-37B flight has been longer than the last.

The last trip to space for the autonomous X-37B concluded in November 2022 after the spacecraft logged nearly 909 consecutive days in space. During that sixth mission, as CNN previously reported, the space plane carried experimental technology designed by the US Navy to convert solar energy and transmit it back to the ground, according to the military.

The X-37B has already spent more than 3,700 days in space on other uncrewed missions. When it returns to Earth, it will land on a runway, much like an airplane swooping down from the skies.

Challenging China

This launch came after more than two weeks of delays. SpaceX was prepared to lift off on December 10. The launch was pushed off twice because of weather and issues with the ground pad before SpaceX abruptly delayed the mission indefinitely to “perform additional system checkouts.”

But during the downtime, China — which the US government considers its chief competitor in a modern space race — sent its own secretive spacecraft into orbit.

Little about the spacecraft from China is known. Some in the industry speculate it is a doppelganger of the X-37B in form and function, though no official photos of the vehicle have been released.

China’s state-run Xinhua News Agency reported that the clandestine spacecraft launched aboard a Long March 2F rocket.

The agency’s post added only that during its stay in space, the vehicle will test out reusable space technology and carry out unspecified science experiments “for the peaceful use of space.”

It is not clear how long China’s space plane will spend in orbit.

ncG1vNJzZmivp6x7pLrNZ5qopV9nfXN%2FjmppaGpoZMSwvsudZqyokZiyuXnXbG6bZaOlrqSxjKmjmqaVYrqquMitmKuxXaiwr3vIp5uesF6dwa64