Return of the Shuttles: Boeing X-37 and its clones

Yes, I understand perfectly well that the purpose of the shuttle now is only to service the orbital station. Yes, I understand perfectly well that checking whether geraniums can bloom in zero gravity is another step in man's knowledge of the Universe. But we forget the main thing. It doesn't matter what happens on the station itself. It is much more important that we were able to build such a thing.

Jeremy Clarkson, "The shuttle's useless, but book me on the next flight," 2003.

The Space Shuttle program cost the United States $211 billion (almost $300 billion in 2025 prices) and the lives of 14 astronauts over 30 years. And although it was criticized for its overall high cost and the high cost of one launch ($450 million in 2011 prices), as well as for neglecting safety considerations, the shuttles performed many truly unique missions that, before their appearance, could only be read about in science fiction novels: the construction of the International Space Station; servicing satellites in orbit and returning them to Earth; launching interplanetary spacecraft from orbit; using manipulators in space, etc.

In addition, and this is even more important, the shuttles were embodied in metal and ceramics the maximum approximation to the image of spaceships that science fiction writers and filmmakers have been painting for 100 years - to elegant silver spaceplanes capable of independently leaving the atmosphere and returning to Earth. It is amazing that such incredible and technologically advanced ships rose into space only 20 years after Gagarin's flight. The first shuttle mission, STS-1, launched on April 12, 1981. It was symbolic.

"The shuttle is one of the most mysterious and stunning technological inventions of our time. And it is the only gift America has given the world worth remembering," wrote the TV presenter and journalist Jeremy Clarkson, who you probably know from the TV show Top Gear, in his weekly column for The Sun on February 9, 2003, eight days after the Columbia shuttle disaster.

It is not surprising that during the 1980s and 2010s, space agencies and private companies from many countries around the world developed their own spaceplane concepts, but once again the United States achieved success. Even before the landing gear of the space shuttle Atlantis, which carried out the last shuttle mission STS-135, touched down on the runway at the Kennedy Space Center in Florida on July 21, 2011, the Space Shuttle's successor, the Boeing X-37 spaceplane, was already in space on its second secret mission.

Let's figure out what the Boeing X-37 is, what it does in low-Earth orbit, which countries have already built its clones, which modern spaceplane projects are in active development, and which of them have a chance of reaching the stage of real operation. And let's start, of course, with the Boeing X-37.

Boeing X-37 (USA)

To be honest and brief, it is not known for certain what exactly the Boeing X-37 does in Earth orbit, why its missions last so long, and what secret tasks it performs. All information about the X-37 missions, which are carried out by the US Space Force on behalf of the Department of the Air Force Rapid Capabilities Office (which, in addition to the X-37, is also responsible for the development of the next-generation strategic bomber Northrop Grumman B-21 Raider), is classified. The Pentagon says very little about this program, limiting itself to general phrases like "this is an experimental test program to demonstrate the technologies of a reliable, reusable, unmanned space test platform" ("test-test", so in the original). All theories about the true goals of the Boeing X-37 missions, which from time to time appear in the public domain, are nothing more than theories. But information about the development and some characteristics of the Boeing X-37 is still available.

Boeing X-37. Development

The development of the Boeing X-37 began long before the Space Shuttle flights ceased - back in 1999. And the first impetus was the Challenger shuttle disaster in 1986. Initially, the development was taken over by NASA, which chose Boeing Integrated Defense Systems as the contractor (now this division is called Boeing Defense, Space & Security). The development was directly handled by the Boeing Phantom Works research and development division, which is currently working on the Boeing F-47 fighter jet, the Boeing MQ-28 Ghost Bat stealth fighter, and the Boeing X-51 Waverider hypersonic cruise missile.

In 2004, DARPA and the US Department of Defense took the X-37 under their wing and classified it. The original goals of the X-37 project were supposedly to rendezvous with satellites and repair them in orbit, but the Space Shuttle was doing much the same thing at the time.

Unlike the Space Shuttle, the Boeing X-37 is not a full-fledged spaceplane, because it is launched into orbit by a launch vehicle (a large "rocket" on which the Space Shuttle "hangs"; it is not a rocket at all, but a huge fuel tank for the shuttle's engines, i.e. the Space Shuttle launched into orbit almost independently), but it does land like an airplane. That is, it is half a spaceplane.

A scale model of the Boeing X-40 without engines and thermal protection, but with parachutes, was used as a research platform for the X-37, and it was 80% the size of the future X-37.

The first drop test, i.e. dropping a prototype from an airplane or helicopter to confirm its flight characteristics, took place on April 7, 2006, and used a full-size Boeing X-37A. During the first landing at Edwards Air Force Base in California, the shuttle rolled off the runway and suffered minor damage. The tests were moved to Plant 42 Air Force Base.

Interestingly, during the tests, the Boeing X-37A was dropped from a unique Scaled Composites Model 318 White Knight aircraft, created by Bert Rutan. This aircraft was used as a mothership during the tests and suborbital flights of the SpaceShipOne spacecraft of the same Bert Rutan. Recall that in 2004, SpaceShipOne crossed the Karman line three times.

On November 17, 2006, the U.S. Air Force announced the start of development of a full-fledged version of the shuttle, the Boeing X-37B Orbital Test Vehicle (OTV). A total of two shuttles were ordered.

Finally, on April 22, 2010, the USA-212 mission, also known as X-37B OTV-1, launched from the SLC-41 launch pad at Cape Canaveral Air Force Station, marking the first space flight of the Boeing X-37B space shuttle. No outside observer expected it to last a full 224 days. As it turned out, it was the shortest X-37 mission ever.

Boeing X-37. Missions

Initially, it was generally believed that the Boeing X-37 would be launched into orbit in the cargo bay of the same Space Shuttle, a kind of daruma doll (this is an original Japanese doll, the design of which the Russians stole and called "matryoshka") from the shuttles. Then the developers realized that it would be very expensive, so they redesigned the shuttle to launch under the main fairing of conventional launch vehicles. During the five X-37 missions, Atlas V 501 rockets from United Launch Alliance were used, the OTV-5 mission flew on a SpaceX Falcon 9 Block 4, and the most complex mission, OTV-7, to a high elliptical orbit (apogee 38,838 km) was carried out using a SpaceX Falcon Heavy.

The Boeing X-37 lands like an airplane, in automatic mode (just like the Buran 22 years before it, but there are nuances). The landing strip used is the US Space Force Vandenberg Air Force Base in Santa Barbara, California (yes, this is the same Santa Barbara, and yes, the shuttles were supposed to land here, but they never did), and the Shuttle Landing Facility strip at the Kennedy Space Center in Florida (most Space Shuttle missions landed here).

As of this writing, seven Boeing X-37B missions have been flown. All have been successful. The shortest, OTV-1, lasted 224 days, and the longest, OTV-6, lasted 908 days. The average mission duration is 1-2 years. Most information on mission objectives is classified.

It is known that during the OTV-2 mission, a retractable solar panel was used for the first time. During the OTV-5 mission, three cubesats separated from the Boeing X-37B, which were designated USA 295, 296 and 297, which the USA reported after the shuttle landed, i.e. in violation of the Convention on the Registration of Objects Launched into Outer Space. During the longest flight, OTV-6 (908 days), an additional service module with unknown experiments was on board the shuttle.

The most interesting is the latest Boeing X-37B mission, i.e. OTV-7. Firstly, because of the high elliptical orbit – perigee 323 km, apogee 38,838 km. Secondly, because it is the only mission, after the completion of which, the US Space Command posted the only photograph taken from the Boeing X-37B. Thirdly, it is the only mission, about which we know at least something. This is the NASA Seeds-2 experiment, on the effect of cosmic radiation on seeds during a long space flight.

Boeing X-37. Speculation

As we’ve already noted, most information about Boeing’s X-37 missions is classified. Officially, it’s an “experimental technology demonstration test program.” The U.S. Space Force only talks about testing avionics, control and navigation systems, thermal protection, engines, and the vehicle’s reentry mode, but… why has the X-37B been in orbit for so long?

Among the speculative versions of the Boeing X-37's use are the following: a spy platform (for example, to monitor the Chinese Tiangong-1 orbital station in 2012); a platform for launching weapons into orbit (the Pentagon denies everything); testing new generation reconnaissance sensors; testing the "impossible engine" EmDrive (radio frequency resonant cavity thruster), which violates the laws of classical physics; testing Hall effect engines (and it's true, such an engine from Aerojet Rocketdyne was actually tested in 2015); studying the possibilities of performing aggressive atmospheric maneuvers for orbit correction; etc.

None of these versions, except for testing the Hall effect engines, have been confirmed, so what the Boeing X-37B is actually doing in orbit is known only to the Pentagon. Interestingly, with such a long program, which has been going on for over 15 years, there have been no significant leaks of information about the X-37 missions.

Boeing X-37. Specifications

It is believed that there are three versions of the Boeing X-37. The first Boeing X-37A was used only for atmospheric drop tests. Both serial Boeing X-37Bs, which are a modification of the X-37A according to the test results, are flying into space in turn. Ship No. 1 has three flights, ship No. 2 has four. The next one, most likely, will fly the aircraft No. 1.

In addition, in 2011, Boeing began work on the X-37C - a 165% or 180% larger version of the X-37B. It could deliver up to 6 astronauts to orbit in a pressurized compartment. The Atlas V was planned to serve as the launch vehicle. The Boeing X-37C was a potential competitor to the Boeing Starliner. Unfortunately, the Starliner was chosen for the manned program, not the X-37C. As of now, work on the X-37C has been suspended.

Specifications of the Boeing X-37B

Boeing X-37 clones

The secret missions of the Boeing X-37 attract a lot of attention, so it is not surprising that some countries have decided to develop their own analogues of this space plane, which look almost like copies of it.

The motivation here seems to be the same as during the development of the Soviet Buran. "We don't know what that Space Shuttle does. We don't have the appropriate technologies, carrier and tasks for such a system. But if the USA has one, then we need one too!" This time, the catch-up is not the USSR, but China and India. In the case of Buran, development started in 1971 largely due to competition for resources and influence between different branches of the USSR government, and the same is partly true for the modern space race.

Shenlong and Reusable experimental spacecraft (China)

Even less is known about the Chinese space shuttles than about the American ones. It seems that we are talking about two programs - Shenlong, which was more of a concept study, and Reusable experimental spacecraft, which is a direct analogue of the Boeing X-37. Although it is possible that this is one joint program in two parts.

The only conditionally reliable photo of a scale model of Shenlong appeared in the Chinese segment of the Internet on December 11, 2007, but most likely it is a photo from 2005, taken during flight tests. Supposedly, the first drop test of the device took place on December 11, 2007, and the first suborbital flight on January 8, 2011. But then the Shenlong research program seems to have turned into a real space program, which has the conditional name Reusable experimental spacecraft.

Although the Reusable Experimental Spacecraft has already been in space three times, there is no reliable information about this ship or even a good quality photo of it. However, most experts are sure that it is an almost complete copy of the Boeing X-37B in both configuration and specifications.

Like the Boeing X-37, the Chinese shuttle takes off under the main fairing of a launch vehicle, in the case of the Reusable experimental spacecraft it is a two-stage Long March-2F rocket in the T configuration, the same one that launches the Chinese Shenzhou manned spacecraft (G configuration) and elements of the Tiangong 2 space station. Launches take place from the Jiuquan Cosmodrome in the Gobi Desert.

Interestingly, the unusual shape of the circular fairing of the Long March-2F/T launch vehicle for these missions provided additional information about the craft itself. It seems that it does not fit well under the 4.2 m diameter fairing, so additional protrusions were made for the wings, so the wingspan of the Reusable experimental spacecraft is approximately 4.5 m.

Like the Boeing X-37, the Chinese reusable shuttle lands like an airplane. Always at Lop Nor Air Base in western China. That's where it was "caught" by Planet Labs satellites during its first mission on September 6, 2020, though the photo quality leaves much to be desired.

Another uncertain image of the Reusable experimental spacecraft was taken by Austrian satellite observer Felix Scheffbanker. He even shot a video using his 14-inch reflector telescope. Felix estimates the shuttle to be 10 meters long, and the video also shows the spacecraft's solar panels.

The first short two-day mission of the Reusable experimental spacecraft took place on September 4-6, 2020, the next two missions in 2022-2023 and 2023-2025 lasted 276 and 266 days, respectively. The fourth shuttle mission is planned for 2025 (most likely for the second half of the year).

As with the Boeing X-37, the purpose of the Shenlong / Reusable experimental spacecraft is unknown. Versions include a space bomber (an idea that has been circulating in military circles since World War II) and assistance in the development of hypersonic cruise missiles.

RLV Technology Demonstration Programme (India)

But much more is known about the Indian Reusable Launch Vehicle–Technology Demonstration Programme (RLV-TD) and there are enough high-quality photos. Perhaps because RLV-TD is still just a series of various tests, it has not yet reached space flights.

The RLV-TD program began in 2006, when the Indian Space Research and Development Organization (ISRO) conducted the first ground tests of a hypersonic scramjet engine. Construction of large-scale prototypes of the RLV-TD, codenamed Pushpak ("Little Flower"), began in 2012.

The RLV-TD program consists of a series of experiments, two of which – the Hypersonic Flight Experiment (HEX) and the Landing Experiment (LEX) – have already taken place, and two – the Orbital Return Flight Experiment (OREX) and the Scramjet Propulsion Experiment (SPEX) – are still planned.

During the HEX01 experiment, which took place on May 23, 2016, the RLV-TD prototype was not hidden under the fairing, but was fixed on top of the first stage of the RLV-SB launch vehicle, which was powered by the HS-9 solid-propellant booster from the SLV-3 series rockets. The RLV-TD flew to an altitude of 70 km, then performed a series of maneuvers and splashed down in the waters of the Bay of Bengal at a distance of 450 km from the launch site. The mission lasted 770 seconds and was considered successful.

The RLV-LEX series of experiments, during which Pushpak was dropped from a helicopter from a height of 4.5 km, aimed to test autonomous landing, operation of the control system, radars, sensors, landing gear, brake parachutes, etc. In total, three such experiments were carried out in 2023–2024, the last on June 23, 2024. All of them were recognized as successful.

The next stages – the OREX and SPEX experiments, involve spaceflight and return from orbit. The launch vehicle is to be a GSLV with a PS-4 second stage from another PSLV launch vehicle. In this flight, the mini-shuttle will be hidden under a traditional fairing, in addition, a new, 1.6-fold enlarged version of the RLV-TD will be used. The dates of the new tests have not yet been announced, and the readiness status of the new RLV-TD prototype is also unknown.

As you can see, the shuttles are slowly coming back. The Boeing X-37 and some of its clones are already actively flying, although we have no idea what exactly they are doing in orbit. But, as they say, the X-37 is not the only one, in addition to purely military shuttles, commercial shuttles are also being developed, and what's more, some of them are due to launch soon. We'll talk about these rocket planes next time.