America's X-37B vs. China's Shenlong: Top space planes and their shadowy role in orbital war

• The US X-37B and China's Shenlong are unmanned spacecraft that play secretive roles in space.
• Space-based technology has long given the US military an edge.
• A space plane like the Shenlong could be an attempt to threaten this advantage.

Just before the start of 2024, the United States and China launched what may be their most secretive spacecraft into orbit to little fanfare.

Commonly referred to as space planes, the American X-37B and the Chinese Shenlong are unmanned spacecraft so secretive that their launches were marked with little more than vague general statements from their governments.

The launches are the seventh and third missions for the respective spacecraft, and although they are highly classified, observers have had limited success in tracking some of their movements.

The missions demonstrate exceptional leaps in the development of space planes, and come at a time when both the Chinese and US militaries have ramped up their space operations — a new frontier that can determine the course of war.

Space-based technology has long given the US military an edge. It can track the movements of enemy weapons with powerful spy lenses and provide the navigation and communications systems ships, aircraft, and troops in the field depend upon.

Enter the space plane. From one vantage, they could be robot keepers who keep these large networks fueled and functional, but from another, they could be orbiting spies and saboteurs.

What's clear is that their missions are getting more complex, as is their centrality to the strategies of the two countries that fly them.

X-37B

A space plane is a reusable spacefaring craft that can maneuver in space independently and also fly and glide within Earth's atmosphere. They are sent into space via a detachable rocket booster, and contain a cargo bay to deploy satellites and other objects for use and experimentation.

After completing their mission, they independently return to Earth's atmosphere, land at a designated landing site on their own power, and prepare for their next mission. The most well-known space planes are the American Space Shuttle and the Soviet Buran. But in contrast to the Space Shuttle, the X-37B is owned and operated by the military.

The X-37B's origin begins in 1999, when the civilian space agency NASA awarded Boeing a contract to develop a small unmanned spacecraft capable of fitting inside the Space Shuttle. What they created was a small space plane measuring approximately 30 feet long and with a wingspan of 15 feet — roughly one-fourth the size of the now-retired Space Shuttle.

It also contains a cargo bay measuring about 7 feet by 4 feet, which, in addition to housing satellites and other space cargo also holds a solar panel enabling the space plane to recharge. Boeing says the plane's avionics automate its descent from orbit and landing.

In 2004, before a working prototype had even been built, the project was transferred to the US Defense Department, specifically the Defense Advanced Research Projects Agency. Glide tests on the first testing prototypes (known as the X-37A), began in 2005, with the first fully successful free glide occurring in 2006.

That same year, the project was transferred from DARPA to the United States Air Force Space Command, which then built another model, the X-37B. Also known as the Orbital Test Vehicle (OTV), two X-37Bs have been built.

They have flown seven flights so far, with each being longer than the previous one. Though most of the details of the flights and their results remain classified, some information has been released to the public.

The first flight began on April 22, 2010, and saw the first X-37B remain in orbit for a total of 224 days. The second flight, which was the second X-37B's inaugural mission, began on March 5, 2011, and was extended well beyond its original 270-day limit to a total of 468 days. The third flight, beginning on December 11, 2012, marked the first time an X-37B had been reused, and lasted 674 days.

The fourth flight began on May 20, 2015. Over the course of 717 days, the space plane tested new propulsion technology for satellites as well as the effects of radiation on certain objects.

The X-37B's fifth flight on September 7, 2017 was launched atop Space X's Falcon 9 rocket (all previous launches were with the Atlas V rocket). Over the course of 780 days — a little over two years — the space plane performed a number of activities and experiments, including the deployment of multiple CubeSat satellites, which NASA foresees as an orbiting sensory network that can solve complex tasks with a "powerful central spacecraft."

The sixth flight began on May 17, 2020, and lasted 908 days. It was the first mission conducted under the command of the newly formed U.S. Space Force and may have been one of the busiest missions yet. It exposed select materials to space, tested the effects of space radiation on seeds, and deployed FalconSat-8, a satellite built by US. Air Force Academy cadets to conduct five experiments.

The X-37B's most recent and current flight began on December 28, 2023. Its mission is classified, with the Space Force stating only that it will be "operating the reusable space plane in new orbital regimes, experimenting with future space domain awareness technologies, and investigating the radiation effects on materials provided by NASA."

The Space Force has not given the X-37B's flight path, but because it was launched atop SpaceX's Falcon Heavy rocket, there has been speculation that the space plane could be headed for a much higher orbit than previous missions, as the rocket is one of the most powerful in the world.

Shenlong

Named after the most important dragon god in Chinese mythology and first revealed in 2007, the Shenlong is thought to be a direct Chinese response to the X-37B.

The program is surrounded in such extreme secrecy that there are no known images of the space plane in its current form. Images of what is believed to be a Shenlong test prototype mounted under the fuselage of an H-6 strategic bomber in 2007 indicate that the craft is likely to be similar in appearance to the X-37B.

Though its specific capabilities remain classified, it is known that, like the X-37B, the Shenlong is unmanned, that it is deployed via a rocket, that it is capable of adjusting its position and maneuvering in space, and that it can carry and deploy satellites and other space objects.

Perhaps the most impressive thing about the Shenlong is the speed of its development. Though the exact start date is unknown, academic models of a Chinese space plane were reported as far back as 2000.

Years of modelling, wind tunnel testing, and prototype test fights via deployment from H-6 bombers followed, and in 2011, the Shenlong reportedly made its first suborbital flight.

On September 4, 2020, the Shenlong made its first orbital flight, which lasted two days and saw it release an object into orbit before returning to China on its own power. A second orbital flight began on August 4, 2022, and lasted nine months.

In addition to being considerably longer, the Shenlong's second flight was far more eventful. About two months into its flight, the space plane deployed a subsatellite and then practiced recovering it at least two (and possibly even three) times, a capability for so-called proximity operations that may allow it to snatch an enemy's satellite.

The Shenlong embarked on its third and current flight on December 14, 2023, just seven months after its second mission. In May, the Shenlong released an object from its cargo hold, and began proximity operations, possibly even recapturing it.

How much longer the Shenlong will remain in orbit, as well as its future plans more broadly, remain secrets that the Chinese government has shown little appetite for divulging. The government has only said that the space plane will eventually land in China, and that "reusable technology verification and space science experiments will be carried out as planned to provide technical support for the peaceful use of space."

The vague wording resembles previous statements, like those of its builder, China Aerospace Science and Technology Corporation, which has previously said that the Shenlong "will provide a more convenient and inexpensive way to access space for the peaceful use of space in the future."

Satellite threat

Given the immense secrecy of the crafts and what is known about their capabilities, it's easy to understand speculation that the two space planes could be orbiting weapons platforms.

The very fact that the US Department of Defense is in charge of the X-37B instead of NASA confirms that the US government believes that there is a military application for the space plane. Similarly, the fact that the Chinese government has been so silent on the Shenlong's activities despite its penchant for boasting about its other space accomplishments may be a tacit indication that there is more to the Shenlong than the 'peaceful use of space.'

One of the most impactful possible uses of the space planes is as anti-satellite assets. Both have deployed satellites from their cargo bays, and the Shenlong's proximity operations may be training runs for attacks on hostile satellites in orbit.

Proximity operations are murky. They could be dress rehearsals for disrupting or eavesdropping on an enemy's satellite, just as they could be drills for missions to refuel and repair one of the country's own satellites.

Satellites are among the most important assets for any first-rate military, as they are essential for secure communications, navigation, and intelligence gathering via orbital imaging and communication intercepts. They are even sometimes used to guide smart munitions to hostile targets as well.

Neutralizing an enemy's satellites would be one of the most important objectives in any potential conflict between the world's foremost military powers. China, the US, India, and Russia have each demonstrated a capability to destroy satellites in orbit with anti-satellite missiles, but each of those tests resulted in the creation of large debris fields in orbit that took sometimes took years to disappear. Such debris fields could also pose a very severe threat to friendly satellites as well. China's anti-satellite missile test in 2007 triggered a space debris cloud that was an inspiration for the blockbuster film "Gravity."

Having a way to neutralize or even capture satellites, then, could be a better alternative. Tapping into enemy satellites to eavesdrop or shut down their data streams and communications could also serve as a better alternative, and may also be possible with the assistance of space plane (similar to the tapping of underwater cables by submarines).

With the militarization of space seemingly fast becoming reality and with China's space program demonstrating that it can tow away satellites, it is likely that space planes will only become more important in the years ahead.

Benjamin Brimelow is a freelance journalist covering international military and defense issues. He holds a master's degree in Global Affairs with a concentration in international security from the Fletcher School of Law and Diplomacy. His work has appeared in Business Insider and the Modern War Institute at West Point.