Top ten spacecraft

Douglas Adams famously described space in The Hitchhiker's Guide to the Galaxy as unimaginably enormous. Compared with the distances involved in the universe, even the longest journeys on Earth are almost insignificant.

The enormous scale of space is encouraging for a growing human population because, at some point, humanity may want to expand beyond Earth and explore other parts of the solar system or even farther. However, the human body is poorly suited to the harsh conditions beyond our atmosphere. Reaching space therefore requires advanced spacecraft, protective systems, and extraordinary engineering.

This list looks at ten spacecraft and space vehicles that played important roles in human exploration. Some carried people into unfamiliar environments, while others traveled enormous distances and returned valuable information about the universe around us.

10. Mars Express and Beagle 2

Beagle 2 earns a place on this list largely because of its importance to Britain's contribution to planetary exploration. The small lander represented an ambitious attempt to investigate Mars, although its mission ultimately ended before it could perform its planned scientific work.

Britain had never operated its own crewed space program, but British scientists and engineers had long maintained a strong interest in space exploration. In 2003, Beagle 2 was given the opportunity to participate in a major international mission. The lander was carried toward Mars aboard the European Space Agency's Mars Express spacecraft.

The project was conceived by Professor Colin Pillinger, who became one of the most recognizable British figures associated with planetary science.

Beagle 2 was intended to land on the Martian surface and investigate its environment. Scientists hoped that its instruments would provide detailed information about the planet's surface and help investigate whether Mars may have supported life in the distant past.

Unfortunately, contact with Beagle 2 was never successfully established after its attempted landing. Later observations showed that the lander had reached the surface but had not fully deployed its equipment. Despite the unsuccessful outcome, the mission represented an important attempt to place British scientific technology on another planet.

9. Vanguard 1

Vanguard 1 is significant not only because of its age but also because it illustrates the growing problem of objects left behind in Earth's orbit.

The satellite was the fourth artificial satellite successfully placed into orbit and became one of the oldest human-made objects still orbiting Earth. Its continued presence also serves as an early example of the long-term consequences of placing hardware into space.

Thousands of inactive objects and fragments now occupy Earth's orbital environment. In addition to inactive satellites, there are many smaller pieces of debris that can be difficult to monitor. As the number of launches and abandoned objects increases, orbital debris has become an increasingly important issue for future space operations.

Vanguard 1 also achieved another technological milestone. It was the first satellite to use solar cells as a source of electrical power. Even after its primary battery stopped functioning, the satellite continued transmitting useful information for several years through its solar-powered system.

8. Prospero X-3

Prospero X-3 holds an important place in British spaceflight history. Its successful launch made Britain the sixth country to use a domestically developed rocket to place a payload into low Earth orbit.

The satellite was relatively simple and was developed as part of Britain's Black Arrow rocket program. It carried solar cells intended for testing as well as a tape recorder that operated hundreds of times before eventually failing.

Prospero also carried an FM transmitter. Although the transmitter was officially shut down in 1996, reports indicated that signals associated with the satellite could still be detected years later.

The satellite remains in orbit and was reportedly heard transmitting an FM signal as late as 2006. Its orbital lifetime was expected to extend for roughly a century, meaning that it could remain in space until the middle of the 21st century before atmospheric reentry eventually destroys it.

7. Mir

Long-term human habitation in space has been an enduring goal of space exploration, and the Soviet Mir space station played a major role in demonstrating that people could live and work in orbit for extended periods.

Although the International Space Station eventually became the primary international orbital laboratory, Mir came before it and established several important precedents. Construction of the station began with its central module and continued for approximately a decade as additional modules were attached.

Mir established a record for continuous human occupation of an orbital station. From September 5, 1989, until August 28, 1999, people were continuously present aboard the station, with crews conducting scientific experiments, maintenance, and other activities.

During its operational lifetime, Mir traveled billions of kilometers around Earth. The station became a major symbol of long-duration human activity in space and provided valuable experience for later orbital programs.

Toward the end of Mir's operational life, there were proposals to use the aging station for space tourism and transform it into an orbital destination. However, maintaining the station became increasingly difficult as its components aged.

On March 23, 2001, the approximately 124-ton space station was deliberately removed from orbit and entered the atmosphere, where it was destroyed during reentry.

6. Apollo 11

Apollo 11 is one of the most recognizable missions in the history of space exploration because it carried the first humans to the surface of the Moon.

The achievement was particularly remarkable because human beings are naturally adapted to Earth's atmosphere and gravity rather than the vacuum and radiation environment of space. Keeping astronauts alive during a journey to the Moon required sophisticated spacecraft systems, life support, navigation, propulsion, and communication equipment.

Apollo 11 successfully transported its crew from Earth to lunar orbit, delivered astronauts to the lunar surface, and then brought them back into lunar orbit. The crew subsequently returned safely to Earth.

The mission demonstrated that humans could travel beyond Earth orbit, operate on another world, launch from the lunar surface, and complete the return journey. Apollo 11 therefore became a defining milestone in the history of human space exploration.

5. Pioneer 10

Human exploration eventually moved beyond the immediate surroundings of Earth and toward the larger solar system. Pioneer 10 played an important role in this transition.

Pioneer 10 was the first spacecraft to travel through the asteroid belt and became one of the earliest human-made objects sent on a trajectory toward the outer solar system. Its journey also contributed to discussions about what it means for a spacecraft to leave the solar system.

The spacecraft was originally designed to study the asteroid belt and the environment around Jupiter. It used a radioisotope thermoelectric generator for electrical power. The power system was positioned away from sensitive scientific instruments to reduce interference.

Communication with Pioneer 10 gradually became weaker as the spacecraft moved farther from Earth. The final successful signal was received on January 23, 2003.

Pioneer 10 continued traveling outward long after its primary scientific mission had ended. It was expected to pass relatively close to the star Aldebaran after an extremely long journey lasting roughly two million years. By that time, the spacecraft would effectively serve as a distant artifact representing humanity's early attempts to explore beyond the solar system.

4. Vostok 1

Vostok 1 occupies a unique position in spaceflight history because it carried Yuri Gagarin, the first human into outer space and the first person to orbit Earth.

Before Gagarin's flight, scientists had already sent animals into space, but the effects of weightlessness and spaceflight on a human being were still uncertain. Sending the first person into orbit therefore represented both a major technological achievement and a considerable unknown.

Gagarin did not have normal manual control over the spacecraft during the mission because engineers were still uncertain about how he would respond to the conditions of space. An emergency procedure existed that could unlock the controls if necessary, but the flight was largely controlled automatically.

The launch also encountered an unexpected problem. The second stage of the rocket burned longer than planned, placing Vostok 1 into a different orbit from the one originally intended. If the braking engine had failed to operate correctly, Gagarin could have remained in orbit long enough to exhaust the spacecraft's available supplies before returning to Earth.

Fortunately, the return procedure succeeded. After approximately 108 minutes in space, Gagarin returned toward Earth, ejected from the reentry module, and landed safely. His historic flight made him an international figure and established a new chapter in human space exploration.

3. Manned Maneuvering Unit

The Manned Maneuvering Unit, or MMU, was a specialized device that allowed astronauts to move independently outside their spacecraft without remaining physically attached by a tether.

The system was not a conventional spacecraft, but it provided astronauts with independent mobility in open space. This made it particularly significant because an astronaut using the MMU could travel away from the main spacecraft and later maneuver back.

The MMU made its first operational appearance on February 7, 1984. Bruce McCandless became particularly famous for using the system during a later spacewalk, when he moved approximately 97 meters away from the Space Shuttle Columbia.

The unit used nitrogen expelled through 24 small thrusters to provide movement and directional control. Depending on the astronaut's activities, the system could operate for approximately six hours.

NASA eventually stopped using the MMU in 1986 following the Challenger disaster. The risks associated with untethered spacewalking were considered too significant, particularly because many missions that would have required such equipment were subsequently canceled or redesigned.

Modern astronauts generally remain connected to their spacecraft or use safer systems designed to assist with emergency recovery.

2. Space Shuttle Orbiter

For generations of aspiring astronauts, the Space Shuttle became one of the most recognizable symbols of human spaceflight. Despite the difficulties associated with its design and operation, the orbiter represented a remarkable engineering achievement.

Some critics argued that reusable spacecraft were unnecessarily complicated and did not provide enough advantages compared with traditional expendable vehicles. Nevertheless, the Space Shuttle introduced capabilities that were highly significant for human spaceflight.

The five orbiters were Columbia, Challenger, Discovery, Atlantis, and Endeavour. Together, they completed more than 120 missions and spent over 1,100 days in space. The fleet also completed thousands of trips around Earth, deployed numerous satellites, and docked with both the International Space Station and Mir.

The Shuttle played an important role in constructing and servicing the International Space Station, launching scientific instruments, deploying satellites, and carrying astronauts into orbit.

However, the program also experienced two devastating accidents. Challenger was destroyed during launch in 1986, killing all seven crew members aboard. In 2003, Columbia broke apart during atmospheric reentry, resulting in the deaths of another seven astronauts.

Despite these tragedies, the Space Shuttle remained an important part of human spaceflight history and influenced generations of people who became interested in space exploration.

1. Voyager 2

Voyager 2 is regarded as one of the most productive robotic spacecraft ever launched. Its mission has dramatically expanded humanity's knowledge of the outer solar system and eventually carried the spacecraft into interstellar space.

Launched in 1977, Voyager 2 was originally designed to investigate the outer planets. During its journey, however, it accomplished much more than initially expected. The spacecraft visited Jupiter, Saturn, Uranus, and Neptune, providing scientists with observations and measurements of worlds that had previously been studied only from a distance.

After completing its planetary encounters, Voyager 2 continued traveling outward and eventually entered interstellar space. Its journey has taken it billions of miles from Earth.

The spacecraft contains more than 65,000 individual components and has transmitted an enormous quantity of scientific information back to Earth. Despite its substantial technical complexity, Voyager 2 operates using only a few hundred watts of electrical power.

Its long operational life has been made possible by a radioisotope power system. As its available electrical power gradually declines, individual instruments can be switched off to extend the useful life of the remaining systems.

Voyager 2 also carries the famous Golden Record. The disc contains information about Earth and humanity, including sounds, images, greetings, and examples of music from different parts of the world.

If another intelligent civilization ever encounters the spacecraft and manages to interpret its contents, the record could provide a small introduction to the people and planet that created it. Even if no such encounter ever occurs, Voyager 2 will continue traveling through space long after its scientific mission has ended, carrying a physical reminder of humanity's early exploration of the universe.