Introduction

Since antiquity, humankind has dreamed about launching a rocket to fly out of the Earth’s atmosphere and upward into space to the Moon and beyond.  However, only in the last half-century have rockets and powerful enough engines been developed to allow artificial satellites and humans to reach space. In the 1920s, the development of primitive rocket engines for propulsion opened up new opportunities for scientists and engineers to advance the space flight field. In the 1950s and 1960s, there were rapid advances in the design of rocket engines and reliable launch vehicles, allowing satellites and humans to reach orbit. Since then, humans have traveled into space, walked on the surface of the Moon, launched thousands of satellites (many into deep space), and operated orbiting space stations. Humans will likely return to the Moon in this decade, colonize Mars within another decade, and reach other planets in the solar system within another two decades.

The engineering challenges of reaching space should not be underestimated. First, overcoming Earth’s gravity to reach space requires a velocity of at least 11.2 kilometers per second (25,020 miles per hour). Then, when reaching space, it is an incredibly harsh environment for humans – it is a vacuum with no air, extreme temperatures ranging from extreme cold to extreme heat, and harmful radiation. Distances are vast – the nearest star system to our solar system, Alpha Centauri, is approximately 4.37 light-years away, roughly 41 trillion kilometers (25.5 trillion miles). The vastness of space and the universe as a whole is best summed up by a quote from the extraordinary scientist, astronomer, and professor Dr. Carl Sagan: “Even these stars, which seem so numerous, are as sand, as dust, or less than dust, in the enormity of the space in which there is nothing.” The recent photograph of the Earth taken from the Orion spacecraft, as shown below, eminently makes the point. All of what we are and what we know is just a speck of dust in the universe, and our existence has been just a momentary blip in the Brief History of Time.

The Quest for Space

Rockets were invented in China in the 9th century, during the Tang Dynasty (618–907 AD), not long after the discovery of gunpowder. They were called “fire arrows” and were first employed as fireworks and weapons of war. They consisted of a simple tube filled with gunpowder and attached to a shaft with feathers resembling an arrow. When ignited, the expanding gases from the burning gunpowder were expelled out of the rear of the tube, creating thrust and propelling the arrow forward. These fire arrows and similar rocket-based weaponry spread from China to other parts of Asia and eventually to the Middle East and Europe.

In his science fiction novels from the 1860s, the novelist Jules Verne imagined rockets leaving the Earth and landing on the moon, and his books popularized widespread interest in the potential for space flight. While Verne’s novels were groundbreaking and sparked interest in space travel, they also reflected the limited scientific knowledge in the 19th century. The concept of using a cannon to launch a spacecraft to the Moon was based more on creative storytelling than scientific feasibility. Nonetheless, Jules Verne’s contributions to science fiction and his ability to inspire generations of readers and future scientists and engineers with his imaginative tales of space travel.

A challenge in reaching into the higher atmosphere and space is that rocket engines must be designed to work in a vacuum, so the spacecraft they power must carry fuel and an oxidizer, usually liquid oxygen (LOX). In 1903 in Russia, Konstantin Tsiolkovsky published a technical paper (in Russian) about rocket flight titled: “The Exploration of Cosmic Space by Means of Reaction Devices.” See also: “Study of Outer Space by Reaction Devices,” NASA TT F-15571. In 1929, he also proposed the concept of multistage rockets and suggested the possibilities of space travel. Tsiolkovsky’s visionary ideas and dedication to the exploration of space had a profound impact on the development of rocket technology, and they laid the groundwork for the eventual human exploration of space.

In the U.S., in 1914, Robert Goddard received two patents, one for a rocket using liquid fuel and the other for two-stage or three-stage rockets that used solid fuel. In 1919, he published a technical paper titled: “A Method of Reaching Extreme Altitudes.” This paper influenced many working in rocketry, including Hermann Oberth and a young Wernher Von Braun, who was later to be part of NASA’s rocket and spaceflight programs. In addition, Goddard tested rocket engines in a vacuum chamber and built and flew the first successful liquid-propellant rocket engine in 1926. By the mid-1930s, his rockets were flying at supersonic speeds and reaching heights of nearly two miles. Goddard’s achievements in rocket propulsion significantly advanced the field of rocketry, and his work was to set down both the theoretical and practical foundations for the scientific exploration of space. For this reason, Robert Goddard is often called the “Father of Rocket Propulsion.”

Other rocket pioneers include Hermann Oberth in Germany, who in 1929 fired up his first liquid-fueled rocket engine. Although it lacked a cooling system, it operated successfully for a short time. Rocket engines are extremely powerful and can create massive amounts of thrust. However, historically, they have not always been as reliable as air-breathing engines because they must operate at extremely high pressures and temperatures and are designed to produce large amounts of thrust for relatively short periods. Nevertheless, by the late 1930s, powerful rockets had been developed as long-range weapons, and several countries started ballistic missile programs. The German V-2 rocket (Vergeltungswaffe 2) was one of the world’s first long-range guided ballistic missiles. It was used primarily against Allied targets in Western Europe. While thousands of V-2 ballistic missiles were launched during WW2, they had poor guidance systems, and most missed their targets.

After WW2, engineers in the U.S. exploited the V-2’s rocket engine components to help develop their rocket program by 1948, launching a two-stage rocket to an altitude of over 200 miles. Oberth’s assistant was Wernher von Braun, who would become a leader in advancing the technology of rockets. was brought to the U.S. after WW2 along with other scientists as part of Operation Paperclip. After developing ballistic missiles for the U.S. Army, von Braun’s group became part of NASA. Their work was instrumental in developing NASA’s human space program, including the moon landings.

In 1936, James Hart Wyld built and tested the first regeneratively cooled liquid rocket engine, which used a double-walled rocket nozzle, allowing fuel to circulate as a coolant. Overheating was one of the major problems with early rocket engines in that they became so hot that they often melted. With the regenerative system, the fuel circulates in a cooling jacket around the combustion chamber and expansion nozzle before entering the combustion chamber, igniting it with the oxidizer. This design became so successful that it is the basis of nearly all modern liquid-propellant rocket engines. In most modern designs, the rocket engine’s nozzle uses many interwoven internal pipes or other cooling channels in which the fuel is first pumped.

Following the X-1 aircraft was the X-15 research rocket-powered aircraft, as shown below, which was flown 199 times from 1959 to 1968. This program gave much new understanding of transonic, supersonic, and hypersonic flight at the edges of the Earth’s atmosphere. Hypersonic flight is usually defined as airspeeds at more than Mach 5. The X-15 still holds the official world record for the highest speed ever recorded by a piloted, powered aircraft, at a speed of 4,519 miles per hour (7,274 km/h) or Mach 6.72 at 102,100 feet (31,120 m), which was set in 1967.

First Steps into Space

The late 1950s and 1960s saw tremendous technical growth in the field of astronautical engineering and rocketry, not all of it being known to the public. Then, in 1957, the surprise launch of the Soviet Union’s Sputnik-1 became the first artificial satellite in space. Shortly after, the Soviets launched Sputnik II, carrying a slightly heavier payload. It had four external antennas and broadcast radio pulses around the Earth. The success of the Sputnik launches precipitated an era of political and military uncertainty in the U.S., triggering the Sputnik Crisis and then the so-called “Space Race.”

In 1958, the U.S. Government formed the National Aeronautics and Space Administration (NASA) to replace the National Advisory Committee for Aeronautics (NACA). This new organization soon launched its first satellite, Explorer 1. During this mission, the satellite carried out an experiment developed by Professor James Van Allen to detect the existence of radiation zones encircling Earth, which became known as the Van Allen radiation belts. Explorer 3 and Explorer 4 were also successfully launched in 1958.

Project Mercury was started in 1958 and was the first human spaceflight program in the U.S., running until 1963. However, Yuri Gagarin was the first human to fly in space in April 1961 when his Vostok 1 rocket carried him into space to complete one orbit of the Earth. The Soviet Union had secretly pursued the Vostok program in parallel with Project Mercury in the U.S. Several uncrewed Vostok missions had been launched before Gagarin’s flight to test various types of rockets and space capsules, but not all were successful. The first woman in space was Valentina Tereshkova, who flew in June 1963 aboard the Soviet Vostok 6.

In May 1961, the U.S. launched its first astronaut, Alan Shepard, on a suborbital flight. This mission was the third flight of the Mercury-Redstone (MR-3) rocket that von Braun and the NASA engineers had developed. Shepard’s Freedom 7 capsule was launched from Cape Canaveral in Florida, reaching an apogee altitude of 115 nautical miles and a speed of 5,100 mph before parachuting and splashing down in the Atlantic Ocean. Alan Shepard was later to walk on the surface of the Moon as the commander of Apollo 14.

In February 1962, John Glenn became the fifth astronaut to fly in space and the first American to completely orbit the Earth, circling it three times during a five-hour flight. The giant leap for humankind was never about stepping on the Moon for the first time but attaining Earth’s orbit! The Friendship 7 mission’s success allowed NASA to accelerate its efforts on the Project Mercury program. This program set down the foundations for the subsequent Gemini and Apollo programs that were to reach their peak during the 1960s.

In 1963, NASA started to launch a series of communications satellites into orbit to demonstrate the feasibility of geosynchronous satellite communications from the Earth’s surface. The Gemini spacecraft program was also started, the capsule carrying two astronauts. The Gemini program aimed to develop space travel techniques to learn enough to eventually land astronauts on the Moon.

Ten Gemini missions were flown between 1965 and 1966, placing the U.S. firmly in the lead over the Soviet Union regarding spacecraft developments. The second piloted Gemini mission, Gemini IV, was in space for four days, and one of the astronauts, Edward H. White, Jr., performed the first spacewalk. The Gemini program was to provide essential information on human space activities. The program also included astronauts such as Neil Armstrong, John Young, and Edwin “Buzz” Aldrin, who would later walk on the Moon’s surface.

To the Moon!

In 1961, U.S. President John F. Kennedy laid down a National challenge by the end of the decade of landing a human on the Moon and returning them safely to the Earth. The Apollo program was successful despite a significant setback in 1967 with the Apollo 1 cabin fire that killed the crew during a pre-launch test. The Apollo 8 mission proved the feasibility of leaving Earth and orbiting the Moon, followed by further lunar landing preparations with the Apollo 9 and Apollo 10 missions, but without landings.

The Apollo 11 flight in July 1969 led to Neil Armstrong and Buzz Aldrin, Jr. successfully landing and walking on the surface of the Moon. After launching the three-stage Saturn V rocket, the spacecraft circled the Earth in a parking orbit. The third stage reignited for a translunar injection to send the spacecraft to the Moon, as shown in the schematic below. The next step was to undock with the third stage, dock with the Eagle lunar module, and pull it out, after which the stage was discarded to fly off into a solar orbit.

After reaching the Moon, the spacecraft went into orbit, and the lunar module then undocked to begin the descent to the Moon, leaving Michael Collins to continue orbiting in the command module. The descent stage contained the rocket engine, fuel, science, and exploration equipment. After less than a day on the surface, the two astronauts returned to orbit on the ascent stage with about 50 lb (23 kg) of rocks and other lunar samples. After a transearth burn, the spacecraft made it back to Earth in 44 hours, followed by a re-entry through the atmosphere, and eventually, the command module parachuted into the sea.

Five further Apollo missions through 1972 (Apollo 12 through Apollo 17) sent astronauts to explore the Moon. Unfortunately, the lunar landing mission for Apollo 13 was aborted after an oxygen tank exploded en route to the Moon, crippling the spacecraft. However, after six days during which the spacecraft circled the Moon, the Apollo 13 crew eventually returned safely to Earth.

The Apollo missions to the Moon were launched using a Saturn V (always pronounced as “Saturn Five”), a three-stage liquid-fueled rocket, as shown in the photograph below. The advantage of a multi-stage rocket is that it uses less fuel to take a payload into orbit, especially for high orbital altitudes, because the remaining weight of the rocket is substantially reduced after each stage and its rocket engines are jettisoned.

The first stage of the Saturn V used RP-1 (a specially densified kerosene) and liquid oxygen (LOX) as the propellant to power its five rocket engines, and the second and third stages used cryogenic liquid hydrogen (LH) and LOX. The Saturn V was 85% propellant by mass on the launch pad. The first stage of this rocket produced over 3,000 tons of thrust at liftoff. During the first stage burn, the propellant flow rate to all five F-1 rocket engines was about 15 tons per second, in the ratio of one ton of RP-1 to two tons of LOX.

Exploring the Planets

Starting in 1962, the first Mariner spacecraft were sent from Earth to map the surface of Mars, Venus, and Mercury, and more missions continued to be launched until 1973. There were ten Mariner spacecraft, seven of which were successful. This program also accomplished the first planetary flyby and gravity assist maneuver, including using “solar sails” to help propel it.

In 1977, two Voyager spacecraft were launched to send back detailed images of Jupiter and Saturn. Voyager 2 then continued to Uranus and Neptune. Both spacecraft are still active, exploring interstellar space and sending back data. Voyager 1 has completed 45 years in space and, as of June 2023, was 23.3 billion km (14.5 billion miles) from the Earth. However, the nuclear fuel used for the Voyager spacecraft will eventually be depleted. So they will be “condemned to wander the universe for eternity but remain the most distant emissary of humankind,” quoting Carl Sagan.

Communication & Earth Observation Satellites

Satellites now give real-time weather information, digital telecommunications, the internet, and GPS navigation systems that allow us to pinpoint our location within a few feet of nearly anywhere on the planet. While the 1970s saw a significant increase in the number of communications and navigation satellite launches, there was also a substantial decline in crewed space flights. Nevertheless, by 1980, satellite communications were becoming commonplace, and since then, the capacity has expanded exponentially to carry digital television and internet services to any home with a satellite receiving dish. Most communication satellites operate in geostationary or geosynchronous orbits, which are orbits with periods equal to the Earth’s rotational speed (about 24 hrs) at an altitude of approximately 22,300 miles (35,780 km).

The 1970s also saw the launch of satellites to support the Global Positioning System (GPS) or Navstar, which provides geolocation and time information to a GPS receiver anywhere on the surface of the Earth. GPS has been one of the most successful technologies used by humankind and is available to anyone with a GPS receiver; one is even included in almost every automobile, smartphone, and smartwatch.

Landsat satellites have accumulated continuous imagery records of the Earth’s surface since 1972. The first satellite, the Earth Resources Technology Satellite, was renamed Landsat 1 in 1975. Subsequently, Landsat 8 was launched in 2013. Landsat instruments have acquired millions of images publicly available through the U.S. Geological Survey (USGS). The imagery is used for agriculture, cartography, geology, forestry, regional planning, etc. In addition, it has become a unique record of human activity on Earth regarding urban expansion, deforestation, and melting of the polar ice caps. The most recent, Landsat 9, was launched in 2021.

Era of the Space Shuttle

In 1981, the Space Shuttle program initiated a new period of human space flight with reusable components. The central reusable part, the Orbiter, was launched with the help of two external solid rocket boosters, which were jettisoned after about 90 seconds into the flight. The boosters then parachuted into the sea, were recovered, and reused. The Orbiter’s flight to low-Earth orbit continued using its three main engines, followed by jettisoning the large external fuel tank. On returning to Earth, the Obiter re-entered the atmosphere and landed like a supersonic glider on a runway, although it had a steep glide angle.

Despite its engineering complexity, the Space Shuttle was a very successful concept. It was used for military and commercial purposes, including the deployment of communications satellites, interplanetary probes, various science experiments, servicing of the Hubble Space Telescope, and construction of the International Space Station and its subsequent servicing. The Orbiters were retired in 2011 after 30 years of service and 135 cumulative missions. Unfortunately, the Shuttle concept had two catastrophic failures, one during launch and the other during re-entry with the Orbiter. Engineers had predicted during the design process that because of the complexity of the concept, there was a 1:50 chance of failure.

The 1980s and 1990s also saw the Space Shuttle being used as a launch vehicle for the further exploitation of space as well as a better understanding of the human environment on Earth. It launched various satellites for geographic, oceanic, and atmospheric studies, including weather forecasting. The Space Shuttle launched the Hubble Space Telescope (HST) into low Earth orbit in 1990, and the telescope still remains operational for astronomy research. Another space telescope, the Kepler Space Telescope, was launched in 2009 into an orbit around the Sun. The Kepler telescope provided much information about our universe, and scientists discovered thousands of new planets, but it ran out of fuel and was retired in 2018.

In December 2021, the James Webb Space Telescope (JWST) was launched into space by NASA, and it will be able to view objects too distant for the Hubble Space Telescope. The JWST is expected to make many future advances in understanding astronomy and cosmology, such as observations of the first stars. The JWST operates approximately 930,000 miles (1,500,000 km) beyond Earth’s orbit around the Sun compared to the Hubble, which orbits only 340 miles (550 km) above the Earth.

Space Stations

In 1971, the Soviet Union launched the first space station, Salyut 1, to test the feasibility of astronauts being able to rendezvous with a space station and conduct scientific research. However, the station was unsuccessful and was deorbited after only a few months. In 1972, Skylab was launched by a Saturn V rocket and became the second space station to orbit the Earth. Skylab was very successful, and for about six years, it allowed scientific experiments to be performed by visiting astronauts.

The International Space Station (ISS) is a habitable satellite parked in a low Earth orbit. The Space Shuttle launched the first ISS components in 1998, which consisted of modules, external trusses, solar arrays, and other components. It is a microgravity and space environment research laboratory and has been occupied by astronauts since November 2000. The ISS flies in Low Earth Orbit (LEO) with an orbital period of just over 90 minutes. The ISS is big and low enough to be seen from Earth with the naked eye on a dark night; the reflecting solar panels look like a bright star that quickly arcs across the horizon. Crew members use the ISS to conduct various types of science experiments, and it is expected to remain operational for many more years. Eventually, the ISS will be deorbited and burn up in the Earth’s atmosphere.

Air-Launched Rockets

Other types of space vehicles may be carried to relatively high altitudes using a conventional airplane and then released into flight, much like the X-15 was originally launched. At this point, the rocket engines ignite and power the vehicle upward and into space. An example of this less conventional launcher design type is the Pegasus, as shown below.

Pegasus is released from its carrier aircraft at approximately 40,000 ft (12,000 m) and then boosts its way into space. The vehicle consists of three solid-propellant stages and an optional monopropellant fourth stage. The first stage also has wings, which create lift in the atmosphere and help the vehicle reach altitude quicker before being jettisoned. The vehicle continues as a pure rocket until the payload reaches orbital speeds and altitudes. The Pegasus can only carry relatively small payloads of about 1,000 lb (455 kg) into a low Earth orbit.

Virgin-Galactic has recently designed an air-launched vehicle capable of delivering about 1,100 lb (500 kg) to low orbital altitudes. White Knight Two, the mothership, carries a spacecraft as its payload known as Space Ship Two to a cruising altitude, where the rocket separates, ignites its boosters, and begins to climb out of the atmosphere.

Commercial Space Ventures

During the last decade, commercial and privately funded companies, such as Space Exploration Technologies Corporation (SpaceX) and Blue Origin, have developed launchers with a reusable first stage, thus proving the technical feasibility of reusing many components, including rocket engines. In addition, advances in computing and miniaturization of electrical and other components have brought small satellites (i.e., those weighing 100 kg or 220 lb or less) to the forefront of commercial and research activities. The Planet company is notable for its fleet of 3U CubeSats or nanosatellites, which provide daily global coverage in the visible spectrum with a ground resolution of approximately 15 ft (5 m). SpaceX has also begun to launch nanosatellites as part of a low-cost global communications network called Starlink.

Currently, two commercial spacecraft companies in the U.S. are performing frequent launches, United Launch Alliance (ULA) and SpaceX. ULA is operated by Lockheed-Martin and Boeing, providing spacecraft launch services to the Department of Defense and NASA. ULA operates expendable launch systems based on the Atlas and Delta launch system families, which have been used for decades to carry a variety of payloads, including telecommunications satellites and probes for interplanetary exploration.

SpaceX aims to create technologies to reduce space transportation costs and enable the colonization of outer space. It has developed the reusable Falcon series of launch vehicles, the first stage that can be landed back at the launch site. The Falcon 9 uses the remaining fuel to reignite its engines in a series of decelerating burns to return to Earth. These burns help adjust the rocket’s speed and reorient the vehicle into the proper position to enter the Earth’s atmosphere and toward the final landing spot.

The SpaceX Dragon spacecraft has been designed to supply the ISS with cargo. The crewed version of the Dragon has now flown three times, with the first four astronauts being launched to the ISS on November 15. 2020. Another four astronauts flew on September 18, 2021, the first all-civilian mission, with the crew conducting science and medical experiments and public outreach activities for three days.

SpaceX has also developed the Falcon Heavy, the World’s most powerful operational launch vehicle, which first flew successfully in February 2018. It can lift nearly 200,000 lb (91,000 kg) of payload into orbit, more than twice the next closest operational launch vehicle, the ULA Delta IV Heavy. The first stage of the Falcon Heavy comprises three Falcon 9 nine-engine cores, with 27 separate rocket engines that generate more than 2,300 tons of thrust at liftoff.

NASA Space Launch System (SLS)

The NASA Space Launch System (SLS), a photograph shown below, is a heavy-lift expendable launch vehicle under development since 2011. The contractors for the vehicle include Aerojet Rocketdyne, Northrop Grumman, Boeing, and United Launch Alliance. The first uncrewed launch was scheduled for August 29, 2022, but a problem with one of the rocket motors and two back-to-back hurricanes in Florida delayed the launch. The SLS finally lifted off for its flight debut on November 16, 2022. This test flight propelled the Orion capsule, without any astronauts on board, on a round-trip mission beyond the moon, covering a distance of over 1.3 million miles and splashing down successfully back on Earth 26 days later.

In the long term, the SLS will become the primary launch vehicle of NASA’s deep space exploration plans. It is a huge launch vehicle, almost 322 ft (98 m) tall, and so comparable in size and weight to the mighty Saturn V. It holds 700,000 gallons (nearly 3.2 million liters) of propellant comprising cryogenic liquid hydrogen (LH) and oxygen (LOX). It has four first-stage RS-25 rocket engines, the same ones used previously on the Space Shuttle. Two solid-fuel boosters burn PBAN (ammonium perchlorate and aluminum powder). At the point of liftoff, the SLS weighs 5.8 million lb (2.6 million kg).

SpaceX Starship

The Starship is a super heavy-lift launch vehicle developed by SpaceX. It stands at 120 meters (394 feet) in height and has a liftoff mass of 5,000 metric tons, making it one of the largest and most powerful rockets ever developed, surpassing the thrust of NASA’s SLS. As shown in the photograph below, the Starship is a two-stage-to-orbit launch vehicle. The first stage, known as Super Heavy, serves as a booster to propel the second stage, also named Starship, into space.

Both the Super Heavy booster and Starship spacecraft are powered by Raptor rocket engines, which burn a combination of liquid methane and liquid oxygen (Methalox). A key design goal for both Super Heavy and Starship is full reusability and is intended to perform controlled landings. In a fully reusable configuration, Starship is designed to have a payload capacity of 150 tonnes (330,000 lbs) to low Earth orbit. When expended (not recovered), it could carry up to 250 tonnes (550,000 lbs) to orbit. One of the unique features of Starship is its ability to be refueled in orbit. SpaceX plans to launch tanker Starships to refill Starships already in low Earth orbit so as to reach the Moon and Mars.

Deep Space & Beyond

Ventures into deep space and beyond our solar system may start to infringe on the final frontier, whatever that is. For example, it has become clear that with our current technology, it is impossible to send astronauts into deep space, hoping they can safely return to Earth. The distances in deep space are enormous, and then some. Alpha Centauri, the Earth’s nearest Sun-like star system, is located 4.37 light-years away from the Earth, so about 25,000,000,000,000 miles (40 trillion km) away. Interstellar probes and robotic explorers like Voyager 1 and Voyager 2 are still sending back data. Voyager 1 and 2 were designed to take advantage of a rare planetary alignment to study the outer solar system up close. Voyager 1 flew past Jupiter, Saturn, and Saturn’s largest moon, Titan. Voyager 2 targeted Jupiter, Saturn, Uranus and Neptune. However, it has taken several decades for them to get where they are now, which is just beyond our solar system, and it will take them another 400,000 years to get to the nearest stars. However, these robotic probes carry the vision and inspiration of humankind, with the hope that one day, humans may be able to head out there too.

Summary & Closure

Human ingenuity and innovation have overcome the engineering challenges of reaching space. The ability to successfully engineer rockets and spacecraft has made it possible for humans to reach space and study other planets as well as our planet. Research activities in space have led to many new technologies that benefit everyone on Earth. The ability to launch satellites into low Earth orbit has given us a unique perspective on our planet, including its weather and the effects of humankind on the environment. With continued advancements in space technology, there is expected to be continued exploration of our solar system and beyond, with human missions to the Moon and Mars being a step toward this goal.

In the coming decades, humankind will likely explore space like never before, partly because commercial space endeavors have revitalized the public’s interest in space. New space technologies, including reusable launch vehicles and more efficient rocket engines, have significantly reduced the costs of launching payloads into space. In addition, commercial companies continue to develop technologies to make spaceflight more affordable and accessible. Another significant development in the last decade is how more national space agencies have become involved in space exploration. International cooperation between space agencies and commercial partners has become the norm, and space activities are no longer limited to the traditional space-faring nations. The growth of the commercial space industry, including the development of space tourism, is also expected to drive scientific discovery and the possibilities of living and working in space.