When it comes right down to it, space exploration is pretty darn expensive! The cost of building and servicing launch vehicles is bad enough, but once you factor in the cost of fuel, it gets downright prohibitive. It is little wonder why, until recently, only federal space agencies were able to do go into space.
To reduce the associated costs and make space exploration more accessible, space agencies all over the world are looking to make spacecraft reusable. Much like reusable rockets, which are being pursued by aerospace companies like SpaceX and Blue Origin, spaceplanes are expected to cut the costs of going into space significantly.
Granted, this is not an entirely new concept. Since the dawn of the Space Age, designs for reusable spaceplanes have been on the books. But it's only been since the closing of the Apollo Era that these and other concepts have been pursued — mainly out of necessity.
And with the age of renewed space exploration upon us, many of the old ideas are being picked up, dusted off, and reevaluated for modern use. Let's take a look at the history of the idea and where it might lead us.
As with everything else that has to do with space exploration, the history of reusable spacecraft began shortly after World War II. At the time, the United States and the Soviet Union got in a competitive deadlock that would last for almost five decades.
Both had taken possession of German technology and expertise at the end of the war. This included advancements in jet propulsion and rocketry, which both sides attempted to leverage to gain an advantage over the other.
In addition to setting new speed records for aircraft, the US and Soviets both wanted to send artificial satellites and crewed spacecraft into orbit. The ultimate goal was not only to prove the superiority of their respective economies but to avoid being left at a disadvantage militarily.
Immediately after WWII, Soviet and American scientists began pursuing experimental rocket-powered aircraft. In many respects, this was a continuation of experiments conducted by Germany during the war.
Faced with overwhelming odds in the air, German scientists were tasked with investigating other methods of propulsion to create fighter and bomber aircraft that were superior to anything the Allies could muster. In addition to jet engines, rockets were also tested extensively.
For the latter, the military applications appeared limited. Rocket aircraft were difficult to maneuver once airborne, and takeoff and landing were very difficult for pilots to perform. But when it came to speed, they were unmatched.
For this reason, American and Soviet aerospace engineers experimented with a number of reusable aircraft that were capable of achieving altitudes and speeds that were unheard of before and they were successful too. These experiments helped pave the way towards orbital spacecraft and launches.
Examples include the Bell X-1, an experimental aircraft developed jointly by the National Advisory Committee for Aeronautics (NACA, the predecessor to NASA) and the U.S. Army Air Forces, and the U.S. Air Force (USAF).
On Oct. 14th, 1947, this aircraft flew its fiftieth sortie, piloted by legendary test pilot Capt. Charles "Chuck" Yeager. On this sortie, the X-1 became the first aircraft to achieve a velocity of 700 mph (1,126 km/h).
In other words, Yeager and the X-1 became the first pilot and aircraft to break the sound barrier (Mach 1). In the years following, the sound barrier would be broken many times more with the X-1 and its variants.
The Cold War Peaks
By the late 1950s and throughout the 1960s, the development of experimental aircraft and spacecraft reached a pinnacle. This reflected the progress that was being made with the respective US and Soviet space programs, both of which were pursuing rockets and spacecraft that could reach the Moon.
It was within this historical context that the North American X-15 design began conducting test flights, eventually culminating in the aircraft reaching speeds of up to Mach 6.7 (or 5,140 mph or 8,270 km/h) and altitudes of over 66 miles (100 km).
Between 1957 and 1963, the USAF and Boeing also looked into the creation of a military spaceplane that would be able to be conduct everything from reconnaissance and rescue operations to satellite maintenance and sabotage.
The result was the X-20 Dynamic Soarer (Dyna-Soar), a single-pilot spacecraft that would be launched into space by a single-stage rocket and then land on an airstrip under its own power. While the program would be abandoned just as construction began, the design would inform future concepts like the Dream Chaser.
In 1965, the Soviets also began work on a reusable spaceplane through the Experimental Passenger Orbital Aircraft (EPOS) program, also known as "Spiral". This eventually led to the Mikoyan-Gurevich MiG-105, a crewed horizontal take-off and landing (HOTOL) spaceplane.
The project was halted in 1969 but resumed in 1974 in response to the U.S. Space Shuttle program. The first test flight was conducted in 1976 and a total of eight flights were made until 1978 when EPOS was canceled in favor of the Buran program.
The space shuttle era
By the early 1970s, a changing budget environment and the end of the "Space Race" forced both NASA and the Soviet Union to investigate ways to reduce the associated cost of space launches. It was from this point to the second decade of the 21st century that earlier designs for reusable spaceplanes were finally developed.
For the United States, this resulted in the Space Shuttle Program, which ran from 1983 and ended with the retirement of the remaining Space Shuttles in 2011. Officially, the program was known as the Space Transportation System (STS) and was based on plans for reusable spacecraft drafted in 1969.
The system consisting of a reusable orbiter vehicle that would be launched into space using two solid-fuel rockets and an external fuel tank. The Space Shuttle fleet consisted of six orbiter vehicles, named the Space Shuttle Atlantis, Columbia, Challenger, Discovery, Endeavour, and Enterprise.
The Space Shuttle fleet began making operational flights in 1982 (with the Space Shuttle Columbia) and conducted a total of 135 flights, the last being made by the Space Shuttle Atlantis in 2011.
Among other things, these missions involved the deployment of satellites, the Hubble Space Telescope, and aiding in the construction of the Soviet/Russia space station Mir. Two shuttles and their crews were lost during their 15 years of service - the Challenger in 1986 and the Columbia in 2003.
During this same period, the Soviets developed their own reusable spaceplane system in response to the Space Shuttle program. Known as Buran, this system consisted of an orbital vehicle — which was very similar in design to the Space Shuttle — and the Energia launch system — an expendable fuel tank with up to four solid-rocket boosters.
The program officially ran from 1974 to 1993 and consisted of only one uncrewed test flight. The program was canceled in the wake of the Soviet Union's collapse due to lack of funding, and the prototypes were retired, the majority of which are part of museum exhibits. The Buran spacecraft was destroyed in 2002 when the hanger it was stored in collapsed.
While the retirement of the Space Shuttle program marked the end of an era, the lessons learned from this and other designs have gone on to inform the creation of a new generation of spaceplanes. At the same time, the rise of the commercial aerospace industry has also led to a great deal of innovation.
Beyond the use of reusable rockets (as exemplified by SpaceX's Falcon 9 and Falcon Heavy launch systems), spaceplanes are another way in which the new commercial space industry is looking to make space exploration more cost-effective and accessible.
For example, the efforts at the NASA Langley Research Center during the 1960s and 1970s with Horizontal Landing (HL) concepts have been realized in the form of the HL-42 reusable spaceplane, also known as the Dream Chaser, being developed by Sierra Nevada Corporation Space Systems. The design resembles that of the Space Shuttle orbiter but is much smaller and lighter.
In the coming years, this spaceplane will be used to send crew and cargo to Low Earth Orbit (LEO) and the ISS. It will be launched using the ULA's Vulcan Centaur rocket and be able to land on a runway under its own power. The development of the spacecraft is on schedule and the first flight is expected to take place in late 2021.
There's also the Boeing X-37B — aka. the Orbital Test Vehicle (OTV) - which began as a NASA project in 1999 but was transferred to the US Department of Defense in 2004. This reusable robotic spacecraft is capable of long-duration flights for classified purposes, while also serving as a demonstrator for autonomous and reusable space technologies.
Similar to other spaceplanes, the OTV is sent to space using a rocket and re-enters Earth's atmosphere and lands under its own power. The first test (a drop test) took place in 2006 and there have been five orbital missions of increasing duration since.
For the sixth flight (OTV-6), a joint USAF/US Space Force mission, an X-37B launched on May 17th, 2020, and delivered a number of scientific payloads into orbit. These included a sample plate designed to test the reaction of certain materials to conditions in space, a sample of seeds, and a space-based solar collector designed by students from the US Naval Research Laboratory (NRL).
In 2005, the Italian Space Agency and the Italian Aerospace Research Center initiated the Program for Reusable In-orbit Demonstrator (PRIDE) in response to the ESA's desire to create a reusable spaceplane. The ESA eventually adopted PRIDE, which led to the design of the Intermediate eXperimental Vehicle (IXV).
This suborbital re-entry prototype spacecraft was developed for the sake of validating the ESA's work in the field of reusable launchers. On Feb. 11th, 2015, the IXV conducted its first 100-min spaceflight and became the first spacecraft to perform a full atmospheric reentry from orbital speed.
China, which has been emerging as a space power in its own right since the turn of the century, is also pursuing some next-generation innovation with spaceplanes. In 1992, as part of China's Project 921 for crewed spaceflight, designs for reusable spacecraft began to be considered.
This led to the creation of the Shenlong Space Plane ("Divine Dragon" in Chinese), which is similar to the X-37B. the spaceplane would be launched into space by a rocket booster (or possibly a maglev inductor). By 2007, images began to emerge of the Shenlong undergoing testing and the first suborbital flight is believed to have taken place by 2011.
On Sept. 4th, 2020, the Shenlong launched for its inaugural space flight and returned two days later. The details of the mission remain shrouded in secrecy, but the state-owned news site Xinhua reported success almost immediately after launch:
“The test spacecraft will be in orbit for a period of time before returning to the domestic scheduled landing site. During this period, it will carry out reusable technology verification as planned to provide technical support for the peaceful use of space.”
In the commercial sphere, SpaceShipOne stands as a shining example of reusable spaceplane technology. Aerospace company Scaled Composites began work on the aircraft in 1994 and the first successful crewed flight was conducted in 2004 — for which it was awarded the US $10 million Ansari X Prize.
SpaceShipOne pioneered the concept of air-launched rocket-powered aircraft capable of conducting sub-orbital spaceflight. The air launch entails being carried to deployment altitude by a carrier aircraft (the "White Knight"), being released and engaging its own engines, and gliding home.
Using a hybrid rocket motor, SpaceShipOne was able to achieve speeds of up to 900 m/s (3240 km/h; 2013 mph) while the wings and tail booms are capable of "feathering" (adjusting their angle) to assist with controlled landings.
The design would be expanded on with the construction of SpaceShipTwo. This suborbital spacecraft was built by The Spaceship Company, a subsidiary of Virgin Galactic (which acquired Scaled Composites in 2012).
With the help of the White Knight Two, this spacecraft is also air-launched, and uses a hybrid rocket motor and feathered wings to achieve suborbital flights and controlled landings. As of 2018, SpaceShipTwo has successfully conducted its first spaceflight and is expected to be used as a cargo and space tourism vehicle in the coming decade.
On Dec. 3rd, 2020, the Alabama-based aerospace startup AEVUM unveiled the RAVN-X, an autonomous suborbital spaceplane that is capable of sending a payload to LEO in just three hours. Its first mission is scheduled to take place by 2021, where it will launch payload for the U.S. Space Force (after completing flight testing).
The company has already earned about $1 billion in military contracts, but the largest market for this technology is expected to be telecom and satellite internet companies.
Spaceplanes of the future
Even more exciting than the current generation of spaceplanes that are now entering service are those that are planned for the future. Much like the innovative ideas we see today, these future spaceplanes are being developed by both private industry and national space agencies.
This reflects the growing presence of the New Space industry in space exploration, as well as the increased presence of emerging space powers — like China, India, and the European Union.
For example, there's the ESA's Space Reusable Integrated Demonstrator for Europe Return (Space RIDER), an uncrewed orbital spaceplane that would provide low-cost missions to LEO. The project was approved in 2016 and is expected to mount a two-month-long mission by 2022.
This is to be followed by several missions that will demonstrate a range of capabilities and orbits. By 2025, the ESA hopes to privatize the Space RIDER and transfer operational control of the spacecraft over to Arianespace.
And as of 2018, the Japanese Aerospace Exploration Agency (JAXA) began working on their Winged Reusable Sounding (WIRES) rocket. At present, it is unclear if this vehicle will be a recoverable first-stage vehicle or a crewed spaceplane. However, the WIRES profile is likely to become more detailed as development continues.
In the private sector, some very impressive concepts are being pursued. For example, there's SpaceX's Starship, a super-heavy reusable spacecraft that is intrinsic to Elon Musk's vision of mounting commercial missions to LEO, the Moon, and even to Mars (with the long-term goal of establishing a colony there).
The idea was first announced in 2013 and was referred to by Musk as the "Mars Colonial Transporter" (MCT). Over the next few years, the concept would evolve and become more detailed, and several name-changes would occur.
In 2016, a substantially more detailed plan was released for the spacecraft, which was now known as the Interplanetary Transport System (ITS). By 2018, the project changed names again, becoming the Big Falcon Rocket (BFR), and the design was updated considerably.
Based on the current iteration, the launch system will consist of a second-stage orbital spacecraft (the Starship) and a first-stage rocket (the Super Heavy). After being launched to space, and undergoing orbital refueling, the Starship will travel to deep-space destinations.
Upon reaching its destination, the Starship will rely on maneuvering fins and its own engines to make controlled landings. Its engines will also provide the necessary thrust for the return trip home, where it will land again using the same process. The system will be entirely reusable and will be the heaviest launch system ever created.
After conducting multiple "hop tests" using a scaled prototype (the Starship Hopper), a full-scale orbital test vehicle known as Starship Mk.1 was unveiled on September 28th, 2020. Multiple prototypes have been tested to failure and two prototypes (SN5 and SN6) successfully completed ~500 ft (150 mt) hop tests between August and September of 2020.
A high-altitude test, where the SN8 flew to an altitude of 7.8 mi (12.5 km; ~41,000 ft) followed by a "belly-flop" maneuver, took place on Wednesday, Dec. 9th, 2020. The flight went off without a hitch and the SN8 managed to reach apogee and pull off the ambitious maneuver.
Unfortunately, the SN8 had trouble reigniting its engine just before touching down and was descending too fast when it landed. This resulted in the SN8 exploding on the landing pad.
During the test, the rocket exploded on landing, but SpaceX claimed they had gotten all of the information they needed from the attempt and were satisfied with the result. The assembly of the booster element, the Super Heavy, also began in early November at the South Texas Launch Facility near Boca Chica, Texas.
A flight around the Moon using the entire operating system is currently slated for 2023. Musk has also indicated that he hopes to send the first crewed Starship to the Moon by the early 2020s, and to Mars as early as 2026.
In recent years, UK-based Reaction Engines announced the development of a new spaceplane concept known as the Skylon. This reusable spaceplane has the advantage of being a Horizontal Take-Off and Landing (HOTOL) concept that does not need an expendable booster to be sent into space.
The key to the Skylon spaceplane is the SABRE engine, an air-breathing rocket propulsion system that runs on hydrogen/oxygen fuel. Basically, the engine cycles between using jet turbines to take oxygen in from the atmosphere and using liquid oxygen (LOX) fuel once it reaches orbit.
This allows the engine to rely on its jet element to take off and land and its rocket element to achieve the hypersonic speeds necessary to reach LEO.
In 2016, the Indian Space Research Organization (ISRO) began developing and testing a launch system known as the Reusable Launch Vehicle (RLV), a two-stage-to-orbit system consisting of a launch rocket and a reusable spaceplane.
Similar in concept to the SABRE engine, the spaceplane is expected to rely on air-breathing supersonic combustion ramjet (scramjet) engines as well as rocket engines. These could allow the spaceplane to achieve orbit without relying on an expendable booster.
Bristol Spaceplanes, another UK-based aerospace provider, is pursuing the creation of a fleet of reusable spacecraft for commercial purposes. Currently, their plan is to develop a small sub-orbital spaceplane called the Ascender, a concept that would use existing technology and to pave the way for later vehicles.
This will be followed by the Spacecab, a fully-reusable carrier spaceplane that would air-launch the smaller Ascender (similar to Virgin Galactic's system). The third and final step in this process will be the Spacebus, a heavy-lift spaceplane that could transport as many as 50 people to and from "space hotels" and air-launch satellites or smaller spacecraft (like the Ascender or the Spacecab).
Last, but not least (for the sake of this list, at any rate), there is the XS-1 "Phantom Express." This project is a collaborative effort to create a reusable spaceplane between Boeing and DARPA as part of the latter's Experimental Spacecraft (XS) program.
The spaceplane will be powered by Aerojet Rocketdyne (AR-22) engines and will deliver payloads either from a cargo hold or (in the case of satellites or small spacecraft) an externally-mounted rocket. In this respect, it will reduce costs by combining reusability with single-stage-to-orbit (SSTO) capability.
Looking at all of these current and future concepts (and the history of their development), a certain pattern becomes clear. From the very beginning of the Space Age, mission planners and engineers have played with the idea of reusable spaceplanes.
At the time, the ideas were placed aside in favor of expendable space capsules and heavy boosters that could be manufactured more rapidly and did not require the same level of maintenance. Since the early Space Age was all about "getting there first", spacecraft that could be manufactured and placed into service faster were naturally favored.
However, once the Moon Landing occurred and the Space Race began to cool down, spaceplanes became the favorite of mission planners looking to cut costs and create a sustainable human presence in space.
Today, almost seven decades later, we are finally realizing their potential. In addition to offering cheaper launch costs by using reusable components, they also offer flexibility that expendable boosters do not.
As the Space Shuttle demonstrated, spaceplanes can deliver satellites and payloads to orbit, conduct vital experiments and research there, and transport crews to space and bring them home again. While it still costs a pretty penny to launch these spaceplanes into orbit, that is rapidly changing.
With advancements in propulsion and hybrid-engine technology, we may soon be able to create SSTO spaceplanes that can do it all!