A spaceplane is an advanced airplane that can not only fly in the Earth’s atmosphere but also in outer space. The technology has been in development for many decades, but as compared to conventional rocket engines, spaceplanes have not been able to see much success when it comes to space exploration.
At least not yet.
However, many experts believe that spaceplanes have the potential to make space travel safer, more affordable, and more accessible than ever. The various limitations faced by rocket engines, concerning passenger capacity, reusability, operational cost, and launching infrastructure could be overcome by spaceplanes.
Let's find out why.
What is a spaceplane?
A spaceplane is something of a hybrid between a conventional atmospheric aircraft and a craft that can maneuver in outer space. To this end, existing and proposed examples of them tend to combine features, like wings, that allow them to fly or glide in the Earth's atmosphere, while also being able to move around in the void of space.
The archetype for such a craft would be the now-retired NASA space shuttles.
To date, there are two main types of spaceplanes, or what can be considered "real spaceplanes". The first, like the Space Shuttle, is a craft that can be strapped to a rocket to be carried into space. The second, and hardest by far to develop, would potentially not need a launch vehicle and could take off horizontally and reach space through a progressive trajectory.
The degree to which such craft incorporate features of spacecraft or atmospheric craft entirely depends on their intended use once out of the Earth's atmosphere. For example, fully orbital-capable spaceplanes will tend to have more in common with more conventional spacecraft, while the suborbital kinds tend to be more akin to conventional fixed-wing aircraft in design.
However, being something of a jack of all trades, such craft will also have some unique features exclusive to them. For example, the need to reenter the Earth's atmosphere (and survive) means that such craft needs some special features typically absent on aircraft and only present on spacecraft designed to return to Earth.
Apart from the need to get into space in the first place, spaceplanes need some form of renewable power supply once in orbit, as they can't refuel. In most cases, this will involve the use of solar panels, batteries, or fuel cells. They also need the means to maneuver in space, provide life support for any crew, and have a way of communicating with the ground and other space-based craft/installations.
They also need to be designed in such a way as to protect their delicate electronics and living occupants, safe from being bathed in solar radiation. Assuming, that is, that such craft will carry a living crew.
For maneuvering in space, craft like the Space Shuttle had dedicated engines and maneuvering thrusters for propulsion and fine motor control of yaw, pitch, etc.
For the Space Shuttle, these engines used a toxic substance called a hypergolic propellent, consisting of a fuel and an oxidizer, which requires very special handling precautions. Spaceplanes will require other gases, like helium for pressurization and nitrogen for life support, to be safely stored on board the craft.
The re-entry process requires the craft to shed a lot of momentum very quickly, which inevitably produces a lot of heat. If no protection was provided to the craft during the process, it would quickly burn up. For this reason, most spaceplanes need to have some form of heat shielding on their underside — like the Space Shuttle's thermal protection system (TPS).
To date, most existing spaceplanes tend to be primarily rocket-powered to get into orbit and then rely primarily on t their aerodynamic design to glide safely back to Terra Firma after reentry (usually unpowered).
The most notable examples of spaceplanes that have successfully launched into orbit (and returned to Earth) include the Space Shuttle, the Buran (a Russian version of the Space Shuttle), and the X-37, to name a few.
All of the existing, retired, and planned space planes tend to make use of vertical rocket launch vehicles to overcome Earth's gravity, and this is unlikely to change for the foreseeable future. Some other launch strategies do exist, primarily high altitude, horizontal launch platforms from airborne carrier aircraft — like the X-15 or SpaceShipOne.
What are the benefits and drawbacks of spaceplanes?
One of the main benefits of spaceplanes is the fact that they would be, at least in theory, completely reusable. With a little maintenance pre-flight and refueling, of course. In theory, they should be able to provide frequent flights into space and back — much like commercial airliners today.
This is especially the case of a spaceplane that can be built that can take off and land using more conventional runways, rather than expensive rockets and rocket launch pads.
For uses like space tourism, this would be an incredibly attractive possibility and one that could make leisure trips to space an actual reality for more than the super-wealthy.
Another major benefit of spaceplanes is the ability to actually ferry stuff to and from space. This would prove very useful for repairing expensive orbiting spacecraft like satellites, space stations, or the Hubble Space Telescope, say.
Then there is the more aggressive potential of spaceplanes. Theoretically, spaceplanes could be used to test military equipment or intercept enemy satellites in space. Some elements of spaceplanes also overlap with hypersonic weapons so, in theory, they may also be useful interceptors for hypersonic missiles.
However, the potential for these craft relies on developers overcoming some very serious challenges for the technology.
One of the main drawbacks of developing spaceplanes is the fact that they are relatively expensive to develop. This is partly because of the fact that any craft needs to be able to survive frequent trips into and back from space.
There is also the technological problem of combining space and atmospheric propulsion systems on the same craft. The difficulty of this problem should not be underestimated.
Another major problem for spaceplanes is the, admittedly amazing, work of companies like SpaceX. The development of reuseable and recoverable rockets are, to no small degree, killing the motivation for the development of spaceplanes.
Spaceplane development is not cheap, and with the reduced need to bring stuff back from space, like old satellites, there is an ever-shrinking need for them beyond possible space tourism or as a special kind of taxi service.
Satellites, for example, are becoming increasingly cheaper to build and launch, and most are considered expendable once their useful life cycle is over. This is a trend that is unlikely to change, especially with the likes of SpaceX's Starlink satellite program that consists of thousands of mass-produced, small satellites.
However, even the likes of SpaceX's rockets require some time to get ready for launch. A true spaceplane that can take off and land like a conventional aircraft, reach space, and return safely, would be an incredibly useful piece of technology.
It might be the case that we need to wait a little more time for new propulsion systems to be developed before spaceplanes could ever become a reality. However, it will be interesting to see what the next few decades have in store for spaceplanes.
But, in short, if all the problems with them can be overcome, they could completely rewrite space travel forever. Especially if coupled with other systems, like skyhooks.
What are some examples of spaceplanes?
So, with that being said, let's take a look at some of the most notable examples of spaceplanes from past, present, and future. Here we will only consider examples of spaceplanes that have actually entered orbit and returned to Earth, or those that are being designed to provide that capability (sorry X-15).
The following list is not exhaustive and is in no particular order.
1. The Space Shuttle was the most successful spaceplane to date
Of all the spaceplane concepts and programs to date, by far the most successful was NASA's Space Shuttle program. Designated as a "partially reusable" low-Earth orbital spacecraft, several were built and the program completed 135 missions between 1981 and its final retirement in 2011.
Officially called the Space Transportation System (STS), the program can trace its origins to the 1960s, with NASA's plan for a system of reusable spacecraft. After years of research and development, the STS program was eventually given the green light in the early-1980s.
In total, six space shuttles were built with all accumulating a total of 135 space missions throughout the program's duration. The first, the Enterprise, was built in the mid-1970s and was used mainly for Approach and LAnding tests, she had, therefore, no orbital capability. The other four operational orbiters were the Columbia, Challenger, Discovery, and Atlantis.
Of these, only two now remain, with the Challenger and Columbia lost under very tragic circumstances. Not only were the craft lost, but these accidents cost the lives of 14 brave astronauts - much to the horror of the world. In 1991, a sixth and final orbiter, the Endeavour, was built to replace the then recently lost Challenger.
Operational missions for the craft ranged from the deployment of satellites, interplanetary probes, ferrying of scientific apparatus (like the Hubble Space Telescope), helping build and ferry crew back and forth to the International Space Station, conducting low-Earth orbit experiments, and adding its considerable weight to the Shuttle-Mir program with Russia.
All-in-all, the Space Shuttle fleet's total mission time was 1,322 days, 19 hours, 21 minutes, and 23 seconds. The STS system required the use of a vertical launch vehicle to actually get the Orbiter Vehicle (the shuttle) into space and consisted of a pair of recoverable booster solid rockets, and a large expendable fuel tank of liquid hydrogen and oxygen to fuel the boosters. These boost rockets would work in tandem with the shuttle's own three main engines to get the orbiter off the ground.
Despite the program's successes, all surviving craft were finally grounded in 2011, after which NASA relied on Russian Soyuz spacecraft to ferry astronauts and material to the ISS. That was until the launch of SpaceX's Dragon missions.
2. Dreamchaser is an interesting development
Currently under development by Sierra Nevada Corporation (SNC) Space Systems, the Dream Chaser is a modern example of a spaceplane under development. Called "America's Spaceplane" by Sierra Nevada Corporation, the Dream Chaser is intended for use as a multi-mission, space utility vehicle.
Designed as a potential reusable, lifting-body spaceplane, the craft was originally designed as a crewed vehicle. However, the current craft under development is primarily to be used as an unmanned cargo transporter. Once operational, a crewed variant is in the works that will be capable of carrying up to seven people, with less cargo, into low-Earth orbit.
NASA selected the Dream Chaser spaceplane to provide cargo delivery, return, and disposal services for the International Space Station under the Commercial Resupply Services 2 (CRS-2) contract. Under this agreement, Dream Chaser will provide a minimum of six cargo service missions to and from the space station.
Currently, Dream Chaser is able to deliver 5.5 tons of pressurized and unpressurized cargo, which can include a myriad of items, from food, to water, to science equipment, and everything in between. So long as the payload can be packaged and tucked inside the craft, it can, in theory, be delivered to space. She can also return to Earth carrying material or waste materials as a kind of space-to-Earth disposal vehicle.
Like the Space Shuttle that preceded it, Dream Chaser requires the use of a vertical launch vehicle to actually get into space. This is currently provided using the Vulcan Centaur rocket. However, Dream Chaser's unique selling point is the flexibility of its design to be mounted, theoretically, on a variety of launch vehicles.
A European Space Agency (ESA) variant has also been proposed that would piggyback on an Arianespace vehicle, but this is yet to be realized. After completing its supply missions, the Dream Chaser is then able to autonomously land horizontally on conventional runways.
To date, Dream Chaser has completed several key milestones in its development, but is yet to supply the ISS for real.
3. Little is know about the X-37B
One of the most interesting spaceplanes currently under development is NASA's semi-mysterious X-37B. An unmanned spacecraft, it has, to date, completed a series of test flights carrying undisclosed payloads on long-duration flights in Earth's orbit.
Development of the craft began in the late-1990s, with two initial vehicles planned: an "Approach and Landing Test Vehicle (ALTV)", and an "Orbital Vehicle". In 2004, the program was transferred to the U.S. Military under the governance of the Defense Advanced Research Projects Agency (DARPA). At that point, X-37B became a classified project.
The craft resembles, in passing, the venerable Space Shuttle, but is much smaller, at around 29 feet (8.8 meters) long and 9.5 feet (2.9 m) tall, with a wingspan just less than 15 feet (4.6 m). At launch, it weighs 11,000 lbs. (4,990 kilograms). She can operate at altitudes of between 110 to 500 miles (177 to 805 km).
Her cargo/payload bay is pretty impressive for the craft's size, at 7 feet long by 4 feet wide (2.1 by 1.2 m) — about the size of a pickup truck bed. However, and we stress this, what it is designed to carry is a closely guarded secret.
"The primary objectives of the X-37B are twofold: reusable spacecraft technologies for America's future in space and operating experiments which can be returned to and examined on Earth," states an X-37B fact sheet produced by the Air Force.
The X-37B, like its Space Shuttle predecessor, is primarily solar-powered and is able to launch vertically using a rocket-powered vertical launch vehicle. Once its orbital mission is complete, the X-37B reenters the Earth's atmosphere and cruises back to Earth to land like a conventional aircraft.
NASA's original ambitions for the Approach and Landing Test Vehicle phase of the project were completed by 2006, with a series of captive-carry and free-flight tests completed successfully. The "Orbital Vehicle" part of the original project was, as far as we know, never realized, but it served to inspire the design of the current X-37B.
The X-37B program is now run by the Air Force's "Rapid Capabilities Office", with mission control for orbital flights based at the 3rd Space Experimentation Squadron at Schriever Air Force Base in Colorado. The spaceplanes are being built by Boeing's Phantom Works division.
4. The Buran was Russia's answer to the Space Shuttle
Developed during the 1970s, the Buran program, also known as the "VKK Space Orbiter program", was basically a Soviet version of the much more successful Space Shuttle. Designed at the Central Aerohydromdynamic Institute of Moscow, the program finally came to a close with the fall of the Soviet Union in the 1990s.
The Buran program, much like the American Space Shuttle, consisted of the orbiter spaceplane, the K1, and its launch vehicle. It completed a single uncrewed spaceflight in 1988 and is, to date, the only such spacecraft to successfully touch down under automatic control, something NASA's space shuttle was not designed to do.
The K1 orbiter spaceplane ostensibly resembled the much more famous Space Shuttle and was lifted into space using expendable rockets. One key difference between the Buran system and NASA's is that only the K1 orbiter was recoverable, its entire launch vehicle, an Energia rocket, was completely sacrificial.
Buran was, by far, the most expensive endeavor of the Soviet Space program and one that ultimately was not successful. Two shuttles were built, but only one was completed. That orbiter's final appearance in public was at the 1989 Paris Air Show while carried on the back of an Antonov An-225.
After that, it was stored in a hangar at Baikonur. Sadly it was completely destroyed when the hangar collapsed in 2002 because of structural failure due to poor maintenance. The second, unfinished shuttle, the Burya, is located in a separate facility at the Baikonur cosmodrome. Its ownership is claimed by Kazakh businessman Dauren Musa, who has offered to return it to Russia in exchange for the skull of the last Kazakh Khan, a man named Kenesary Kasymov.
5. The Skylon really looks the business
Spaceplanes are not the reserve of the United States or the former Soviet Union, even the British are having a go at making one. Called Skylon, the British aerospace company, Reaction Engines, is hoping to build what might be the sleekest design for a spaceplane ever seen.
The company has been working on the project since the later-1980s when the official British spaceplane project for a Horizontal Take-Off and Landing (HOTOL) craft was canceled.
The Skylon is an ultra-sleek, single-stage-to-orbit spaceplane that hopes to be a leading light in the reusable spacecraft seen. The craft will be powered by a Synergetic Air-Breathing Rocket Engine (Sabre) that uses hydrogen as fuel and should be able to propel a spaceplane like Skylon from zero to hypersonic speeds by using the oxygen in the Earth's atmosphere.
The idea is for the engine to carry the craft to just the right velocity in the air and then finally into space with a little boost from the craft's onboard storage of oxygen — a little like a conventional rocket.
At present, the company is focussing on the development of the main propulsion system — the Sabre. The testbed engine is currently under development at a site at the foot of the Rocky Mountains, in Colorado, and has achieved simulated speeds of Mach 3.3. Engineers now hope to be able to push the engine up to Mach 5.5, which is more than 3,800 mph (6,200 km/h), or twice the cruising speed of the venerable Concorde and 50% faster than the SR-71 Blackbird.
This speed also happens to be right at the boundary of the capability of most materials used in aircraft production. The endeavor is backed by some of the biggest names in aerospace including, but not limited to, Rolls-Royce, Boeing, British Aerospace, as well as the UK and European space agencies.
6. RLV-TD is India's gambit at making the future of space travel
RLV-TD is another interesting spaceplane concept currently under development in India. An uncrewed craft, the RLV-TD is seen as the testbed for a potential future spaceplane being developed by the Indian Space Research Organization (ISRO).
The prototype craft made its first successful atmospheric flight in May of 2016 and was able to stay aloft for 770 seconds and reach a maximum altitude of 40 miles (60 km). This prototype vehicle was designed to test various experimental technologies on the craft and to gather data for a planned final version in a decade or so's time.
The RLV-TD consists of its main fuselage, a nose cap, double delta wings, and twin vertical tail fins. Flight controls are provided by a set of symmetrically planed active control elevons and rudders.
According to the ISRO, "this technology demonstrator was boosted to Mach no: 5 by a conventional solid booster (HS9) designed for low burn rate. The selection of materials like special alloys, composites, and insulation materials for developing an RLV-TD and the crafting of its parts is very complex and demands highly skilled manpower."
India's ambitious spaceplane project has a series of objectives that it hopes to achieve in the not too distant future. These include, but are not limited to:
- Hypersonic aero thermodynamic characterization of the craft's wing body
- Evaluation of the RLV-TD's autonomous Navigation, Guidance, and Control (NGC) schemes
- Integrated flight management
- Thermal Protection System Evaluation
The fully fleshed-out craft is expected to take off vertically like a rocket, reach Earth orbit to deliver its payload, renter Earth's atmosphere, and finally, land on a conventional runway. It is also hoped that the craft will be able to cut the cost of spaceflight by a whopping 80% once fully operational.
Future tests of the program will involve an air-drop test of the prototype to test the vehicle's autonomous landing capabilities. While currently still in its research and development phase, the RLV-TD's future is certainly looking bright.
7. China are also getting in on the act with its Chongfu Shiyong Shiyan Hangtian Qi
And finally, even the Chinese are having a go at making a spaceplane, too. Called the Chongfu Shiyong Shiyan Hangtian Qi (CSSHQ), roughly translated as the "Reusable Experimental Spacecraft", this spaceplane marks China's first-ever foray into developing anything of the kind.
The prototype craft was successfully launched in September of 2020 from its launch site in the Gobi Desert in northwestern China, using a Long March-2F rocket.
CSSHQ was able to reach low-Earth orbit, deploy a satellite, and then return safely to Earth at an airbase at Lop Nur.
The Xinhua report provided no information about the exact launch time, landing location, or what technologies the spacecraft tested. However, it did reveal some tantalizing information on the craft and its mission:
"The reusable spacecraft successfully launched by my country at the Jiuquan Satellite Launch Center successfully returned to the scheduled landing site on September 6, after flying in orbit for 2 days."
The report added that "The successful flight marked the country’s important breakthrough in reusable spacecraft research and is expected to offer convenient and low-cost round-trip transport for the peaceful use of space."
Other than that, precious little is known about the craft beyond its similarity to America's X-37B. For this reason, experts have speculated that, like the X-37B, its development might have military ambitions rather than be purely scientific.
And that spaceplane enthusiast is all for today. The development of spaceplanes has been something of an obsession over the last 50 years or so, but with pressure from the development of reusable rockets, a la SpaceX, is the fickle nature of funding slipping out of the fingers of spaceplanes?
While the benefits of true spaceplanes are not really in doubt, the technical challenges to make them a reality is likely to stifle their development for some time to come. Whatever the case, rockets are very wasteful and take time to prepare for launch.
If we are serious about making spaceflight a routine affair, then the development of spaceplanes will be an integral part of that. This is certainly a fascinating area of research to keep an eye on its future.