Ad Astra: The past, present, and future of spacecraft

Spacecraft have come a long way since the Apollo era, and continue to evolve before our eyes.
Matthew S. Williams

On October 4, 1957, the Space Age officially began when the first artificial satellite (Sputnik I) launched from the Baikonur Cosmodrome in modern-day Kazakhstan and reached orbit. Almost immediately after, the United States and the Soviet Union began rapidly developing the technologies that would allow them to send humans to space.

These efforts bore fruit quickly with the Mercury and Vostok space capsules. These "tin cans," as they were nicknamed, were small, cramped, and provided few amenities for their one-person crew. Over the next decade, NASA and the Soviets would scale up these designs to accommodate larger crews on longer-duration missions.

This would eventually lead to the Apollo Program, which included the creation of three-stage rockets (like the Saturn V) and the Apollo spacecraft. By 1969, these efforts culminated with the Apollo 11 mission landing the first astronauts on the lunar surface (Neil Armstrong and Buzz Aldrin). By 1972, five more missions and ten more astronauts would follow.

Since then, spacecraft have been revolutionized with the invention of spaceplanes, reusable rockets, and commercial spacecraft. While the designs have matured and diversified, the basic premise remains the same: a "tin can" that seals astronauts inside to protect them from the hostile environment of space.

In the coming decades, we will likely witness further developments that will allow for missions to Mars, Venus, the asteroid belt, and perhaps even beyond. Given time, we may even witness the creation of spacecraft designed to achieve interstellar flight or ferry human beings beyond the solar system.

One quick note before we get into the crafts: By definition, the term "spacecraft" applies only to space vehicles designed to fly in "outer space," or altitudes beyond the Karman Line - 62 mi (100 km) above sea level.

Ad Astra: The past, present, and future of spacecraft
Source: NASA

Getting there first

In the wake of World War II, both the United States and the Soviet Union began developing rockets as part of their respective nuclear programs. However, related research was also conducted as part of their respective space programs. In addition to being a matter of prestige, getting to space (and getting their first) was also a matter of demonstrating technological dominance.

Much of their research was based on the wartime work of German rocket scientists, which were recruited after the war by both the U.S. and Soviet Union. The V-2 rocket, in particular, became the basis of early American and Soviet designs, giving rise to the U.S. PGM-11 Redstone rocket and the Soviet R-2 rocket by the early 1950s.

However, these rockets could only reach suborbital altitudes for a few minutes. By the late 1950s, both NASA and the Soviets managed to develop launch vehicles capable of sending payloads and crews to orbit — NASA's Mercury-Redstone and the Soviet R-7 Semyorka rocket. The next step was to develop spacecraft to keep astronauts safe in space and during reentry.

The Soviets achieved an early lead with the Vostok program, which sent six cosmonauts to space between 1961 and 1963. NASA quickly followed with Project Mercury, which also sent six astronauts to space (although technically, two of the flights were sub-orbital) between 1961 and 1963.

The Vostok capsule measured eight feet (2.43 meters) in diameter, 14.9 feet (4.55 meters) long, and weighed about 5.214 U.S. tons (4.73 metric tons). It was designed by Chief Designer Sergei Korolev, manufactured by Special Design Bureau 1 (OKB-1), and consisted of a spherical descent module for the cosmonaut and a biconical instrument module containing the engine system and propellant.

This simple design allowed for rapid production but came with several drawbacks. For starters, the descent module had no thruster capability since it was forced to separate from the engine system during reentry. This prevented the cosmonaut from controlling its path of reentry and orientation. This was why the descent module had to be spherical to ensure heat protection on all sides. But this design feature also resulted in it being more cramped inside.

Second, the cosmonaut would experience eight to nine times the force of Earth's gravity (8 to 9 g), pushing the limits of human tolerance. Sustained exposure to this kind of acceleration can cause even the most highly-trained people to blackout. Third, the descent module made very rough landings that could seriously injure or even kill anyone inside.

Ad Astra: The past, present, and future of spacecraft
Source: HPH/Wikimedia Commons

As a result, the cosmonaut was forced to use the ejector seat to exit the spacecraft at about 23,000 ft (7,000 m). Lastly, there were problems with the ejector seat that were never adequately resolved — something Korolev regretted deeply. The ejector seat also served as an escape mechanism in the event of a launch vehicle failure during the first 40 seconds after launch.

Beyond that, ground crews would manually shut down the booster, and the cosmonaut would eject once the rocket fell to ejection altitude. However, if a malfunction occurred during the first 20 seconds, the ejector seat wouldn't have enough time for its parachute to deploy. In the event of an ejection during those initial seconds, the cosmonaut was likely to land too close to the exploding booster and die.

The Mercury spacecraft was cone-shaped, with a convex base that measured 10.8 feet (3.3 m) long, six feet (1.8 m) wide, and weighed 3,000 pounds (1,400 kg) when fully loaded. The principal designer was Belizean-American rocket engineer Maxime Faget, who contributed to several later NASA programs - including Gemini, Apollo, and the Space Shuttle programs.

The conical shape allowed for maximum volume while also minimizing the heat shield's diameter. This consisted of an outer skin made of a tough nickel alloy (René 41) that could withstand the extreme reentry temperatures. The base carried another heat shield consisting of an aluminum honeycomb covered in fiberglass. The spacecraft also had a retropack of three rockets designed to brake the spacecraft during reentry.

The Mercury capsule was more spacious than Vostock — 100 cubic feet (2.8 m3) of volume — and had several amenities for the astronaut. This included a form-fitting seat and environmental controls that scrubbed the air of CO2 and odors, and collected urine. The spacecraft also had two main chutes (primary and reserve) and a drogue shoot to stabilize the spacecraft during free fall.

The launch escape system was also more reliable, consisting of three small solid-fuel rockets that would separate the capsule from the booster. The capsule would then deploy its parachute for landing at sea not far from the launchpad. This significantly increased the odds that the astronaut would survive in the event of a launch failure (compared to the Vostok spacecraft).

As noted, the Soviets achieved an early lead in the space race, which was partly due to the simpler design of their spacecraft. On April 12, 1961, the first man to go to space (Yuri Gagarin) launched as part of the Vostok I mission. Five more cosmonauts would follow between 1961 and 1963, including the first woman to go to space (Valentina Tereshkova). Her mission, Vostok 6, took place on June 16, 1963, and was the last flight of the program.

Ad Astra: The past, present, and future of spacecraft
Source: Air and Space Museum

The longest mission was Vostok 5, during which cosmonaut Valery Bykovsky remained in orbit for four days, 23 hours, and seven minutes. Gagarin established the record for distance, reaching a maximum altitude of 203 mi (327 km). The maximum number of orbits was also achieved by Vostok 5, which circled Earth 82 times.

The inaugural launch of the Mercury program was Freedom 7, in which astronaut Alan Shepard went to space on May 5, 1961, just three weeks after Yuri Gagarin. The final mission (Faith 7) launched on May 15, 1963, where astronaut L. Gordon Cooper Jr. established a record by spending over a day in orbit and circling the Earth 22 times.

The longest mission and the most orbits were accomplished by Cooper, who remained in space for one day, 10 hours, 19 minutes, and 49 seconds and orbited Earth 22 times. The highest altitude was accomplished by astronaut Wally Schirra who reached a perigee of 176 mi (283 km).

In short, the Soviets managed to get to space first and stay there longer, but NASA created a technically superior and safer spacecraft for its astronauts. This would eventually become apparent as both sides looked beyond Low Earth Orbit (LEO) and contemplated what their next goals should be.

Building a bridge

The next step for the American and Soviet space programs was to develop spacecraft that could accommodate larger crews and perform docking and rendezvous maneuvers in space. This would allow astronauts to conduct extra-vehicular activities (EVAs) and develop the necessary expertise to conduct missions beyond LEO and to the Moon.

To this end, NASA launched its second crewed space program, known as Project Gemini (1961-1966). This led to the creation of the two-stage Titan II rocket and the two-person Gemini spacecraft. Similar in profile to the Mercury spacecraft (conical in shape), this spacecraft measured 18 feet five inches (5.61 m) long and 10 feet (3.0 m) wide and weighed 7,100 to 8,350 lbs (3,220 to 3,790 kg).

The Soviets countered with the Voskhod program (1963-1966), which yielded the four-stage Molniya rocket (a modified R7 Semyorka) and the Voskhod spacecraft. Like its predecessor, the Voskhod consisted of a spherical descent module (for a crew of two to three) and a conical equipment module that housed the propellant and engines. The craft measured 16.4 ft (5 m) long and eight feet (2.43 m) wide and had an overall mass of about 12,535 lbs (5686 kg).

Once again, the Soviets managed to get there sooner. Between 1964 and 1965, two, one-day crewed missions were flown, and two dogs flew on a 22-day mission in 1966. The Soviet cosmonauts that went into space also accomplished two major firsts, including the first multi-person crewed mission (Voskhod 1) and the first spacewalk (Voskhod 2).

But the technical superiority of NASA's program and spacecraft quickly became apparent. Between 1965 and 1966, no less than ten flights were conducted with crews that spent between one day and 13 days in space. The crews also conducted spacewalks and rendezvous with other (uncrewed) space vehicles, something the Soviets would not accomplish for some time.

Ad Astra: The past, present, and future of spacecraft
Source: NASA

The Apollo Era

In 1961, NASA inaugurated two space programs: Project Gemini and Project Apollo. Both were in response to the Soviets taking an early lead with the Vostok Program. Whereas Gemini was intended to serve as the "bridge" between Project Mercury and missions beyond LEO, Apollo was NASA's attempt to win the "Space Race" by achieving something unprecedented and unequaled.

As President John F. Kennedy stated in his address to the Joint Session of Congress on May 25, 1961, the nation needed to commit to "landing a man on the Moon and returning him safely to the Earth" before the end of the decade. As he later stated in his famous address at Rice University, this goal would "serve to organize and measure the best of our energies and skills."

Between 1961 and 1964, NASA developed the heaviest and most powerful rocket to date, the three-stage Saturn V. This would be paired with the Apollo spacecraft, the most complex expendable vehicle developed by NASA until recently. This three-person spacecraft consisted of three modules: the Command Module (CM), Service Module (SM), and the Lunar Module (LM).

Once again, the spacecraft was conical in design when fully stacked inside its protective housing. In this configuration, the CM and SM were integrated to create the Command and Service Module (CSM), while the Lunar Module was mounted behind them. The LM consisted of two parts: the descent stage and the ascent stage.

While the descent stage contained the landing gears, rockets, fuel, and cargo hold, the ascent stage housed the crew cabin, controls, docking port, radar, communications antennas, and the ascent engine to return it to lunar orbit. The CSM measured 36.2 ft (11 m) long and 12.8 ft (3.9 m) wide and weighed 31.75 tons (28,800 kg), while the LM measured 23 ft (7.04 m) in length and 13 ft (4.22) in diameter and weighed up to 18.1 tons (16,400 kg).

Once the spacecraft reached cis-lunar space, the CSM would disembark from protective housing and attach the LM to its nose. The recombined spacecraft would establish lunar orbit while two crewmembers would transfer to the Lunar Module, leaving the third to pilot the CSM. The LM then descended to the lunar surface, where the two-person crew would conduct an EVA, perform various science experiments, and obtain samples to return to Earth.

Once the astronauts were aboard the LM again, the ascent stage would launch, leaving the descent section behind. Once in orbit, the ascent module would rendezvous with the CSM, the astronauts would return with their samples, and the ascent stage would be jettisoned. The CSM would return to Earth orbit, where the astronauts would jettison the SM, re-enter Earth's atmosphere, and land in the CM.

Ad Astra: The past, present, and future of spacecraft
Source: NASA/Magnus Manske

Between 1969 and 1972, the Apollo program sent six missions and twelve astronauts to the Moon. While the Soviets officially ceded the "Race to the Moon," considerable work was carried on in secret. This included the five-stage N1 rocket, a super-heavy launch system designed to compete with the Saturn V rocket.

The Soviets also came up with designs for a Soyuz-7 Lunar Orbital Spacecraft (LOK) and the Lunar Laning Craft (LK), which were analogous to the CSM and LM. The Soyuz-7 would carry two cosmonauts and the LK Lander, which would land one crew member on the lunar surface.

In terms of size, the LOK measured 33 ft (10.06 m) in length and 9.6 ft (2.93 m) in diameter and weighed 10.86 tons (9,850 kg). The LK measured 17 ft (5.2 m) long, 14.76 ft (4.5 m) wide, and weighed 7.2 tons (6,525 kg).

Unfortunately, budget constraints in the late 60s and early 70s, internal politics, and the loss of lead rocket engineer and spacecraft designer Sergei Korolev (who died in 1966) forced the Soviets to cancel the program. Four launch tests were attempted with the N1 between 1969 and 1972, the last of which resulted in an explosion that caused considerable damage to the Baikonur launch facility (aka Baikonur Cosmodrome).

The program did bear fruit in the form of the Soyuz spacecraft and rocket, which would become the mainstay of the Soviet and Russian space programs (see below). But for the sake of conducting a crewed lunar mission, the Soyuz-7 and LK Lander were admittedly less proficient than their Apollo counterparts.

A good example of this can be seen in the service life, volume, and power supplies of the lunar modules. NASA's Lunar Module was designed to support astronauts for up to 75 hours (three days), had an internal volume of 235 ft³ (6.7 m³), and was powered by two silver-zinc batteries.

Meanwhile, the LK Lander had a service life of 48 hours, an internal volume of 235 ft³ (6.7 m³), and was powered by dinitrogen tetroxide/unsymmetrical dimethylhydrazine chemical batteries. This trend existed throughout the Space Race, where Soviet designs were rugged and easy to produce rapidly but sacrificed sophistication for speed.

Ad Astra: The past, present, and future of spacecraft
Source: NASA/Wikimedia Commons

NASA's approach, meanwhile, was to crate spacecraft that boasted greater technical sophistication. This mirrored the development of military technologies during the Cold War in many ways. Whereas Soviet and Warsaw Pact military designers created weapons optimized for mass production, American and NATO designers sought to counter quantity with quality.

When the Apollo Era was close to wrapping up, both space agencies began contemplating what the future would hold. After the mad rush to send humans to space and reach the Moon first, NASA and their Soviet counterparts chose to slow down and catch their breath. What was needed at this point, they realized, were spacecraft that allowed their astronauts to go to space regularly and for longer periods.

The Space Shuttle Era

Having ceded the race to the Moon, the Soviets turned their attention toward the development of space stations. This resulted in the Salyut program, which deployed eight stations to orbit between 1971 and 1986. NASA, meanwhile, began working on a reusable spaceplane concept in 1972 that would result in the Space Shuttle Program.

This program was based on the Space Transportation System (STS) proposed by the Report of the Space Task Group in 1969. This report envisioned a series of reusable crewed space vehicles that would support operations in space beyond the Apollo program. Given the budget environment of the post-Apollo Era, the Space Shuttle was the only concept selected for further development.

This consisted of a reusable Orbital Vehicle (OV) launched using the Orbiter's three RS-25 engines, two solid rocket boosters, and an external fuel tank. These latter elements would break off and fall away once they were expended. When the mission was complete, the OV would reenter the Earth's atmosphere and glide its way onto a landing strip.

The fully-stacked Space Shuttle measured 184 ft (56.1 m) in height and 29 ft (8.7 m) in diameter and weighed 2240 tons (2.03 million kg) when fully fueled. The Space Shuttle Orbiter, meanwhile, measured 122.17 ft (37.237 m) in length, 58.6 ft (17.86 m) in width, and 78.1 ft (23.79 m) in terms of its wingspan, and weighed 120 tons (110,000 kg) when fully-fueled.

The interior of the Space Shuttle Orbiter was the largest of any spacecraft, with a pressurized volume of 32,898 ft³ (931.57 m³) and a habitable volume of 13,702 ft³ (388 m³). The Space Shuttle was capable of transporting an eight-astronaut crew and up to 30.3 tons (27,500 kg) of payload to LEO and 5 tons (2,270 kg) to Geostationary Orbit (GSO).

A total of six Space Shuttles were built between 1977 and 1985, including the Enterprise, Columbia, Challenger, Discovery, Atlantis, and Endeavour. The Enterprise was an unpowered glider launched by a Boeing 747 and used for atmospheric test flights and landings.

Ad Astra: The past, present, and future of spacecraft
Source: NASA/Wikimedia Commons

Fearing a possible "spaceplane gap," the Soviets began work on their own spaceplane in 1971 through the Buran Program. Like the Space Shuttle, the Buran consisted of a reusable orbital vehicle and an expendable launcher. This was the two-stage Energia super-heavy lift launch vehicle, which consisted of a core stage and four strap-on boosters — each containing a four-chamber RD-170 engine.

While the Orbiter element was extremely similar in appearance to the Space Shuttle, it had several distinct features. For example, the Buran Orbiter relied on its engines to provide propulsion in orbit, not for launch. Based on its technical specifications, the Orbiter was reportedly able to accommodate ten cosmonauts and deliver up to 110 tons (100,000 kg) to LEO and 22 tons (20,000 kg) to GSO.

Due to budget constraints (and the collapse of the Soviet Union in 1991), the program experienced several delays and was officially canceled by 1993. The first vehicle was not available until 1987, and only one (uncrewed) orbital test flight took place (on November 15, 1988). This prototype vehicle was destroyed in 2002 when its storage hangar collapsed.

The cancellation of the program, combined with a lack of successful crewed spaceflights, has prevented any accurate side-by-side comparisons between the Buran and Space Shuttle. However, the Soviet commitment to space stations not only led to the Salyut space stations and Mir but also to advancements in cargo delivery vehicles like the Progress spacecraft.

This spacecraft is essentially a cargo version of the Soyuz spacecraft. Development began in 1978 and has continued until the present day, resulting in many variations of this vehicle. With an interior volume of 270 ft (7.6 m) and the ability to deliver up to 5,300 lb (2,400 kg) to the ISS or LEO, this vehicle has been a workhorse to the Salyut, Mir, and ISS programs.

Meanwhile, the Space Shuttle Program went on to have a stellar record of service. Between 1972 and 2011, 133 successful launches were made that performed a variety of mission profiles. This included conducting experiments in orbit, delivering satellites, constructing the ISS, and ferrying crews and payloads to and from the ISS. 

Two missions were unsuccessful, including the Challenger Disaster (1986), which exploded during takeoff, and the Columbia Disaster (2003), which exploded shortly before landing. The program also demonstrated the viability and cost-effective nature of reusable spacecraft.

Between 1972 and 2011, when the program ended, the Space Shuttle cost American taxpayers a total of $196 billion ($250.52 billion today). Adjusted for inflation, that works out to $6.76 billion a year, or $1.45 billion a mission. Comparatively, the Apollo Program cost $175.52 billion between 1961 and 1972, which works out to around $15.95 billion a year, or $10 billion a mission.

These capabilities would become even more prominent during the next generation of spaceflight, characterized by bold new steps and the rise of the commercial space industry (aka NewSpace).

Moon to Mars

Beginning in the mid-2000s, NASA began preparing for its next major leap. With the success of the Space Shuttle Program and the ISS, NASA began work on a new generation of heavy launch systems and spacecraft that would allow for renewed missions to the Moon, the creation of a sustained human presence, and missions to Mars.

This began in 2004 with NASA's Vision for Space Exploration (VSE) plan and continued between 2006 and 2010 under the Constellation Program. This led to the preliminary designs for the Crew Exploration Vehicle (CEV), which would later be renamed the Orion Multipurpose Crew Vehicle (MPCV), or the Orion spacecraft.

The Orion is based on the same basic configuration as the Apollo CSM but has an increased diameter, an updated thermal protection system, and other modern technologies. The full Orion spacecraft includes the Crew Module (CM), the European Service Module (ESM), a spacecraft adapter, and an emergency Launch Abort System (LAS).

The Orion CM is a reusable space capsule that contains the crew habitat, storage for supplies and research instruments, and the docking port. It is larger than the Apollo CM  with a pressurized volume measuring 690.6 cu ft (20 m³)  and a habitable volume of 316 cu ft (9 m³) — and can support up to six crew members.

This is paired with the ESM, which provides propulsion, thermal control, and life support systems, including water, oxygen and nitrogen, and air recycling. It also provides long-term electrical power for the crew with four deployable solar arrays.

Unlike the Apollo spacecraft, the Orion will be capable of supporting crews for short-duration missions to the Moon (21 days) and long-duration missions to Mars (six months). During the latter, life support would be provided by another module integrated with the Orion (with the adapter) - like the Deep Space Transport (DST) or a similar system.

Ad Astra: The past, present, and future of spacecraft
Source: NASA

The commercial space era

Between 1970 and 2000, the average cost of sending payloads to space was about $8,400 per lb ($18,500 per kilogram). Thanks to the development of reusable rockets (like the Falcon 9 and Falcon Heavy), the cost is now $1,235 and $640 per lb ($2,719 and $1,410 per kg), respectively.

In addition, the commercial space sector has developed numerous spacecraft to meet the growing demands of space agencies and companies, which became necessary with the retirement of the Space Shuttle in 2011. A notable example is the Dream Chaser spaceplane, developed by the aerospace wing of the Sierra Nevada Company (SNC).

Similar in design and profile to the Space Shuttle, the Dream Chaser also relies on a booster to deploy it to space. Once there, it will rely on its own thrusters to perform maneuvers, dock with other spacecraft or stations in orbit, re-enter the atmosphere, and make a glide-landing an airstrip.

As part of the Commercial Resupply Services 2 (CRS-2) program, this multi-mission reusable space vehicle was developed to deliver crew and cargo to the ISS and other locations in LEO. This vehicle can operate autonomously, can be flown up to 15 times, and can accommodate 12,125 lb (5,500 kg) of pressurized and unpressurized cargo.

NASA has also contracted with SpaceX and Boeing through its Commercial Crew Program (CCP) to develop spacecraft that can deliver crews and cargo to the ISS. This led to two reusable spacecraft that can autonomously dock and return to Earth - the SpaceX Dragon 2 and the Boeing Crew Space Transportation Starliner (CST-100).

The Dragon 2 can accommodate four passengers in its pressurized cabin, which measures 330 ft³ (9.3 m³) in volume. Its Cargo Dragon version can deliver payloads of up to 7,291 lb (3,307 kg) to LEO and return 6,614 lbs (3,000 kg) to Earth. On November 16, 2020, it became the first private spacecraft to take humans to the ISS (the Crew-1 mission) and has delivered multiple crews since.

The CST-100, meanwhile, is slightly larger and can accommodate seven passengers in its 390 ft³ (11 m³) interior. While its cargo capacity is unspecified, the company has expressed that it exceeds the minimum payload capacity for ISS resupply - 5,511 lbs (2,500 kg) per mission — and can carry a mix of crew and cargo. 

It can reportedly be used up to 10 times (with a six-month turnaround) and features a weldless design, wireless internet, and tablet interfaces for the crew. Unfortunately, the Starliner has suffered setbacks due to technical errors during uncrewed test flights. NASA has indicated that further attempts will occur no earlier than May 2022.

Ad Astra: The past, present, and future of spacecraft
Source: Boeing

The future of spacecraft

Looking at the latest concepts and proposals, it is clear that the current trend of reusable spacecraft and spaceplanes is destined to continue into the foreseeable future. For example, Boeing has enjoyed considerable success with its X-37B Orbital Test Vehicle (OTV). This reusable spaceplane is similar in profile and design to the Space Shuttle (but one-fourth the size).

These similarities include the way it is launched to space atop a booster element, its fixed-wing configuration, its ability to return payloads (such as science experiments) from space, and its ability to glide back to Earth and land on an airstrip. It is also fully autonomous and can operate in LEO — 150 to 500 mi (240 to 800 km) above Earth's surface — for up to 270 days. To date, the X-37B has conducted six test flights with the US Air Force (USAF) and US Space Force (USSF).

Since the turn of the century, China's emergence as a space power has also led to the Shenzhou spacecraft, a crewed space vehicle created as part of the China Manned Space Program. Its design resembles the Russian Soyuz spacecraft but is larger in size and volume — measuring about 30.35 ft long and 9.2 ft wide (9.25 x 2.8 m) — and can accommodate three taikonauts in its cabin, which measures 494.4 ft³ (14 m³) in volume.

China has also developed an autonomous reusable spaceplane: the Chongfu Shiyong Shiyan Hangtian Qi (CSSHQ, or Chongfu). Very little is known about this vehicle except that it has many of the same attributes as the X-37B, such as its launch, reentry, and landing profile, and its reusability, and autonomous capability. During its only test flight (Sept. 6, 2020), the prototype reached a maximum altitude of 216 mi (348 km) and remained in orbit for 90 minutes.

Russia is developing the Orel spacecraft as a part of their Prospective Piloted Transport System (PPTS) program, which aims to develop a next-generation, partially-reusable crewed spacecraft that will replace their Soyuz and Progress spacecraft. According to its specifications, the Orel will be able to carry four to six passengers in its cabin — which measures around 635.5 ft³ (18 m³) in volume — and will remain in LEO for up to a year.

A lunar variant has also been proposed, which would be able to send a crew of four cosmonauts on a 14-day mission to lunar orbit. As part of the proposed Russian-Chinese lunar exploration program, the spacecraft would remain docked with the Lunar Orbital Station for up to 200 days and return 220 ft (100 kg) of cargo (including lunar samples) to Earth.

Reflecting its entry onto the space scene, the Indian Space and Research Organization (ISRO) has developed its own crew capsule. As part of the Indian Human Spaceflight Program (Ganganyaan), this 11,684.5 lbs (5,300 kg) spacecraft consists of a crew and service module (similar to the Apollo spacecraft) and can accommodate up to three astronauts in its 280 ft³ (8 m³) interior volume. 

For its maiden crewed mission, scheduled for 2023 at the earliest, the Ganganyaan spacecraft will fly a two or three-person crew to an altitude of 250 mi (400 km) for up to seven days.

But perhaps the most anticipated and ambitious development expected for the coming years is the Starship. This reusable vehicle is the spacecraft element of SpaceX's Starship and Super Heavy launch system, which will eventually become the backbone of the company and replace its fleet of Falcon 9 and Falcon Heavy rockets.

The Starship is also central to SpaceX CEO and founder Elon Musk's vision of sending regular missions to the Moon and Mars and the eventual creation of a Martian colony. This massive spacecraft measures 394 ft (120 m) tall, 30 ft (9 m) in diameter, and weighs a staggering 10 million lbs (5,000 metric tons) when fully fueled.

According to its technical specifications, the Starship has an interior volume of 38,800 ft³ (1,100 m³) and will be capable of lifting 100 tons (90 metric tons) of cargo to LEO. Musk has also indicated that each Starship, once they reach commercial production, will be able to transport 100 tons or 100 passengers to Mars each.

As part of the NASA's Human Landing System (HLS) program, a lunar variant — the Starship HLS — was selected to land astronauts on the Moon as part of the Artemis I mission (scheduled for 2025).

Speaking of ambitious, there are even interstellar concepts in the works like Breakthrough Initiatives' project, Breakthrough Starshot. This proposal incorporates a lightsail, an ultra-light sheet of reflective material (similar to a solar sail), and a gram-scale spacecraft (Star Chip) studded with sensors and electronics. This spacecraft will be accelerated by a gigawatt (GW) laser array to 20 percent of the speed of light, thus making it to Alpha Centauri in just 20 years.

The next generation

From their humble beginning as expendable capsules that could support a single astronaut or cosmonaut in space for a few days, spacecraft have evolved to become entirely reusable modules and spaceplanes capable of carrying multiple crewmembers to space and operating for weeks or even months at a time. These days, human crews are not even needed, thanks to the development of autonomous systems.

Another major change is how the field of designs and mission profiles has opened up. During the Cold War era, two superpowers produced spacecraft that were (in large part) iterations on a single theme. Thanks to ongoing research and development, the rise of new space agencies, and the arrival of the NewSpace industry, spacecraft designs have become much more diverse.

At this rate, next-generation spacecraft could be equipped with bioregenerative life support systems (BRLSS) that can sustain crews for months without replenishment. These same next-gen spacecraft are likely to rely on nuclear-thermal or nuclear-electric propulsion (NTP/NEP), giving them the ability to deliver crews and payloads to deep-space destinations in just a few weeks.

Such spacecraft could allow for rapid missions to Mars and the asteroid belt and enable next-next-generation missions that will go even further. Someday, we could be sending astronauts to explore the moons of Jupiter, Saturn, and every celestial body from Mercury to the very edge of the Solar System.

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