Updated 1226 GMT (2026 HKT) February 10, 2021
Photos: The rockets that defined space travel1967: By now the US had set its sights on a moon landing, and NASA was busy designing a rocket for that purpose. It built the Saturn V, a huge and powerful rocket. At 111 meters (364 feet) tall, it was about the height of a 36-story building, and weighed 2.8 million kilograms (6.2 million pounds). The first Saturn V test launch was in 1967, but two years later it made its firstlunar landing mission, launching Apollo 11 (pictured). Hide Caption 8 of 15
Photos: The rockets that defined space travel1969:Apollo 11 lifted off from NASA’s Kennedy Space Center at 9:32am on July 16, carrying Neil Armstrong, Michael Collins and Edwin “Buzz” Aldrin. Four days later, Armstrong set foot on the moon. He was followed to the surface by Aldrin, while Collins remained in lunar orbit. The crew spent under three hours walking on the moon’s surface, collecting 47 pounds of lunar material to be analyzed back on Earth. Hide Caption 9 of 15
Photos: The rockets that defined space travel1973: Skylab was America’s first space station and crewed research laboratory. It was built using the modified stage of a Saturn V rocket, which was fitted with living quarters for three astronauts. Skylab launched into space on May 14, and spent six years in orbit, home to three successive crews. The longest stay for any crew on the station was 84 days. Hide Caption 10 of 15
Photos: The rockets that defined space travel1981: Columbia was the first space shuttle to fly in space. The shuttles were designed as reusable vehicles to ferry satellites and components into orbit, to build the International Space Station (ISS). But in 2003, on its 28th flight, the space shuttle broke up on its return to Earth, killing all seven astronauts on board. NASA suspended space shuttle flights for more than two years as it investigated the disaster.
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Photos: The rockets that defined space travel2010: The 2010s was the decade in which commercial spaceflight really took off. It started with Falcon 9, a rocket built by Elon Musk’s SpaceX, which launched the unmanned Dragon space capsule into orbit. The Dragon circled Earth twice before landing in the Pacific Ocean — becoming the first orbital spacecraft launched and recovered by a private company.Hide Caption 12 of 15
Photos: The rockets that defined space travel2017: US company Rocket Lab enters the commercial launch market with the maiden flight of its Electron rocket, lifting off from New Zealand’s Mahia Peninsula. The Electron, designed to offer cost-effective rocket launch services to the small satellite market, successfully reached space but failed to orbit.
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Photos: The rockets that defined space travel2020: SpaceX launched a Falcon 9 rocket on May 30, this time carrying two astronauts in a Crew Dragon capsule. The test mission reached the International Space Station (ISS) and returned safely on August 2. It was the first launch of an American crew since the conclusion of the Space Shuttle program in 2011. In November, a Crew Dragon returned to space with four astronauts on board for a six-month science mission on the ISS.Hide Caption 14 of 15
Photos: The rockets that defined space travel2020: NASA engineers have started to assemble the massive rocket designed to take the first woman and the next man to the moon in 2024, as part of the Artemis program. The first booster segment of the Space Launch System (SLS) was stacked on top of the mobile launcher in preparation for its maiden flight next year. Once fully assembled, the SLS rocket will stand taller than the Statue of Liberty and have 15% more thrust at liftoff than the Saturn V rocket — making it the most powerful rocket ever built.
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Photos: The rockets that defined space travel2020: Rocket technology has come a long way since the start of the space age. Humanity’s next giant leap is sending astronauts to Mars, with NASA hoping to do this by the mid 2030s. But to reach the red planet, explore the surface, and safely return home, new technologies must be deployed.One option being considered isnuclear-powered rockets. Thisdesign, by USNC-Tech, could travel from Earth to Mars in just three months, says the company. Click through to see the evolution of spacecraft, and how far we’ve come.
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Photos: The rockets that defined space travel1944: The first rocket capable of reaching the edge of space was the V-2, a long-range ballistic missile. Developed by German engineers during World War II, its full name — “Vergeltungswaffe Zwei” (Vengeance Weapon Two) — was given to it by Joseph Goebbels, the Nazi minister of propaganda. Despite being used as a lethal weapon the V-2, which was powered by a liquid ethanol fuel, signaled the dawn of the space age, with the Allies scrambling to acquire the technology once the war had ended. Hide Caption 2 of 15
Photos: The rockets that defined space travel1957: The Soviet Union won the first leg of the space race, launching its intercontinental ballistic missile, the R-7, on October 4. This put Sputnik — the world’s first artificial satellite — into orbit. The following month, a second satellite, Sputnik 2, was sent into space carrying a small dog called Laika, the first living creature in orbit. While she did not survive the mission, she blazed the way for all humans that followed.
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Photos: The rockets that defined space travel1958: Explorer 1 was the first US satellite to enter space, on January 31 from Cape Canaveral in Florida. It was launched on top of Jupiter C, a ballistic missile, and carried scientific instruments, such as a cosmic ray detector designed to measure the radiation environment in Earth’s orbit. The satellite made a total of 58,000 orbits then burnt up after entering the planet’s atmosphere in 1970.Hide Caption 4 of 15
Photos: The rockets that defined space travel1959: Despite only reaching the edge of space, the X-15, a rocket-powered plane, was crucial in informing the design and engineering of later American spacecraft, such as NASA’s space shuttles. The bullet-shaped plane completed 199 test flights over nine years, and was flown by just 12 pilots, including Neil Armstrong, who would go on to lead the first moon landing in 1969. It was the quickest manned aircraft ever to fly, reaching speeds of 4,520 miles per hour (7,274 kilometers per hour) in 1967. Hide Caption 5 of 15
Photos: The rockets that defined space travel1961: Pipping the US to the post, Soviet cosmonaut Yuri Gagarin became the first human in space, leaving Earth on April 12, aboard the Vostok 1 rocket — just 25 days ahead of the first manned American suborbital flight. His space flight, which lasted 1 hour 48 minutes, orbited Earth once before reentering the atmosphere. At 20,000 feet, Gagarin ejected himself and parachuted to ground, landing in Kazakhstan. Hide Caption 6 of 15
Photos: The rockets that defined space travel1962: In the fine art of one-upmanship, on February 20, the US sent John Glenn into orbit in the Mercury Atlas 6 rocket named Friendship 7. The spacecraft orbited Earth three times, reaching speeds of 28,000 kilometers per hour (17,000 miles per hour) and an altitude of 260 kilometers (161 miles). Four hours and 55 minutes later, it landed with a splash in the Atlantic Ocean. Glenn and his capsule were recovered by a US Navy ship 21 minutes later.
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Photos: The rockets that defined space travel1967: By now the US had set its sights on a moon landing, and NASA was busy designing a rocket for that purpose. It built the Saturn V, a huge and powerful rocket. At 111 meters (364 feet) tall, it was about the height of a 36-story building, and weighed 2.8 million kilograms (6.2 million pounds). The first Saturn V test launch was in 1967, but two years later it made its firstlunar landing mission, launching Apollo 11 (pictured). Hide Caption 8 of 15
Photos: The rockets that defined space travel1969:Apollo 11 lifted off from NASA’s Kennedy Space Center at 9:32am on July 16, carrying Neil Armstrong, Michael Collins and Edwin “Buzz” Aldrin. Four days later, Armstrong set foot on the moon. He was followed to the surface by Aldrin, while Collins remained in lunar orbit. The crew spent under three hours walking on the moon’s surface, collecting 47 pounds of lunar material to be analyzed back on Earth. Hide Caption 9 of 15
Photos: The rockets that defined space travel1973: Skylab was America’s first space station and crewed research laboratory. It was built using the modified stage of a Saturn V rocket, which was fitted with living quarters for three astronauts. Skylab launched into space on May 14, and spent six years in orbit, home to three successive crews. The longest stay for any crew on the station was 84 days. Hide Caption 10 of 15
Photos: The rockets that defined space travel1981: Columbia was the first space shuttle to fly in space. The shuttles were designed as reusable vehicles to ferry satellites and components into orbit, to build the International Space Station (ISS). But in 2003, on its 28th flight, the space shuttle broke up on its return to Earth, killing all seven astronauts on board. NASA suspended space shuttle flights for more than two years as it investigated the disaster.
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Photos: The rockets that defined space travel2010: The 2010s was the decade in which commercial spaceflight really took off. It started with Falcon 9, a rocket built by Elon Musk’s SpaceX, which launched the unmanned Dragon space capsule into orbit. The Dragon circled Earth twice before landing in the Pacific Ocean — becoming the first orbital spacecraft launched and recovered by a private company.Hide Caption 12 of 15
Photos: The rockets that defined space travel2017: US company Rocket Lab enters the commercial launch market with the maiden flight of its Electron rocket, lifting off from New Zealand’s Mahia Peninsula. The Electron, designed to offer cost-effective rocket launch services to the small satellite market, successfully reached space but failed to orbit.
Hide Caption 13 of 15
Photos: The rockets that defined space travel2020: SpaceX launched a Falcon 9 rocket on May 30, this time carrying two astronauts in a Crew Dragon capsule. The test mission reached the International Space Station (ISS) and returned safely on August 2. It was the first launch of an American crew since the conclusion of the Space Shuttle program in 2011. In November, a Crew Dragon returned to space with four astronauts on board for a six-month science mission on the ISS.Hide Caption 14 of 15
Photos: The rockets that defined space travel2020: NASA engineers have started to assemble the massive rocket designed to take the first woman and the next man to the moon in 2024, as part of the Artemis program. The first booster segment of the Space Launch System (SLS) was stacked on top of the mobile launcher in preparation for its maiden flight next year. Once fully assembled, the SLS rocket will stand taller than the Statue of Liberty and have 15% more thrust at liftoff than the Saturn V rocket — making it the most powerful rocket ever built.
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Photos: The rockets that defined space travel2020: Rocket technology has come a long way since the start of the space age. Humanity’s next giant leap is sending astronauts to Mars, with NASA hoping to do this by the mid 2030s. But to reach the red planet, explore the surface, and safely return home, new technologies must be deployed.One option being considered isnuclear-powered rockets. Thisdesign, by USNC-Tech, could travel from Earth to Mars in just three months, says the company.
Photos: The rockets that defined space travel1944: The first rocket capable of reaching the edge of space was the V-2, a long-range ballistic missile. Developed by German engineers during World War II, its full name — “Vergeltungswaffe Zwei” (Vengeance Weapon Two) — was given to it by Joseph Goebbels, the Nazi minister of propaganda. Despite being used as a lethal weapon the V-2, which was powered by a liquid ethanol fuel, signaled the dawn of the space age, with the Allies scrambling to acquire the technology once the war had ended. Hide Caption 2 of 15
Photos: The rockets that defined space travel1957: The Soviet Union won the first leg of the space race, launching its intercontinental ballistic missile, the R-7, on October 4. This put Sputnik — the world’s first artificial satellite — into orbit. The following month, a second satellite, Sputnik 2, was sent into space carrying a small dog called Laika, the first living creature in orbit. While she did not survive the mission, she blazed the way for all humans that followed.
Hide Caption 3 of 15
Photos: The rockets that defined space travel1958: Explorer 1 was the first US satellite to enter space, on January 31 from Cape Canaveral in Florida. It was launched on top of Jupiter C, a ballistic missile, and carried scientific instruments, such as a cosmic ray detector designed to measure the radiation environment in Earth’s orbit. The satellite made a total of 58,000 orbits then burnt up after entering the planet’s atmosphere in 1970.Hide Caption 4 of 15
Photos: The rockets that defined space travel1959: Despite only reaching the edge of space, the X-15, a rocket-powered plane, was crucial in informing the design and engineering of later American spacecraft, such as NASA’s space shuttles. The bullet-shaped plane completed 199 test flights over nine years, and was flown by just 12 pilots, including Neil Armstrong, who would go on to lead the first moon landing in 1969. It was the quickest manned aircraft ever to fly, reaching speeds of 4,520 miles per hour (7,274 kilometers per hour) in 1967. Hide Caption 5 of 15
Photos: The rockets that defined space travel1961: Pipping the US to the post, Soviet cosmonaut Yuri Gagarin became the first human in space, leaving Earth on April 12, aboard the Vostok 1 rocket — just 25 days ahead of the first manned American suborbital flight. His space flight, which lasted 1 hour 48 minutes, orbited Earth once before reentering the atmosphere. At 20,000 feet, Gagarin ejected himself and parachuted to ground, landing in Kazakhstan. Hide Caption 6 of 15
Photos: The rockets that defined space travel1962: In the fine art of one-upmanship, on February 20, the US sent John Glenn into orbit in the Mercury Atlas 6 rocket named Friendship 7. The spacecraft orbited Earth three times, reaching speeds of 28,000 kilometers per hour (17,000 miles per hour) and an altitude of 260 kilometers (161 miles). Four hours and 55 minutes later, it landed with a splash in the Atlantic Ocean. Glenn and his capsule were recovered by a US Navy ship 21 minutes later.
Hide Caption 7 of 15
Photos: The rockets that defined space travel1967: By now the US had set its sights on a moon landing, and NASA was busy designing a rocket for that purpose. It built the Saturn V, a huge and powerful rocket. At 111 meters (364 feet) tall, it was about the height of a 36-story building, and weighed 2.8 million kilograms (6.2 million pounds). The first Saturn V test launch was in 1967, but two years later it made its firstlunar landing mission, launching Apollo 11
(CNN)By 2035, NASA wants to land humans on Mars. But reaching the red planet, on average around 140 million miles away, will be a mammoth feat. Colder than Antarctica and with little to no oxygen, Mars is a hostile environment. The longer it takes astronauts to get there and the longer they stay, the more they are at risk.That’s why scientists are looking at ways to reduce trip time. Seattle-based company Ultra Safe Nuclear Technologies (USNC-Tech) has proposed a solution: a nuclear thermal propulsion (NTP) engine that could get humans from Earth to Mars in just three months. Currently, the shortest possible trip for an unmanned spacecraft is seven months, but a crewed mission is expected to take at least nine months. 
The idea of nuclear rocket engines dates back to the 1940s, but the technology has only recently been revisited as a solution for deep space exploration.Michael Eades, director of engineering at USNC-Tech, says that nuclear-powered rockets would be more powerful and twice as efficient as the chemical engines used today, meaning they could travel further and faster, while burning less fuel.”Nuclear technology will expand humanity’s reach beyond low Earth orbit, and into deep space,” he tells CNN. As well as enabling human space travel, it could open up space for galactic business opportunities, he says.
Faster space travel
Most rockets today are powered by chemical engines. These could get you to Mars, but it would take a long time — at least three years for a round trip — says Jeff Sheehy, chief engineer of NASA’s Space Technology Mission Directorate. NASA wants to get there faster, to minimize the crew’s time in outer space, he says. This would reduce their exposure to space radiation, which can cause health problems including radiation sickness, increased lifetime risk of cancer, central nervous system effects and degenerative diseases.
opes this tiny lunar rover will discover unexplored parts of the moonIt would also decrease the overall risk of the mission. “The longer you’re out there, the more time there is for stuff to go wrong,” he adds. That’s why the space agency is looking to develop nuclear-powered rockets. An NTP system uses a nuclear reactor to generate heat from a uranium fuel. That thermal energy heats a liquid propellant, usually liquid hydrogen, which expands into a gas and is shot out the back end, producing thrust. NTP rockets produce twice the thrust per unit of propellant than a chemical system — which is like saying it does “double the miles per gallon,” says Sheehy. This means the technology could get astronauts to Mars and back in less than two years. An illustration of a spacecraft with a nuclear-enabled propulsion system. Courtesy of NASA.However, one of the main challenges for building an NTP engine is finding a uranium fuel that can withstand the blistering temperatures inside a nuclear thermal engine. USNC-Tech claims to have solved this problem by developing a fuel that can operate in temperatures up to 2,700 degrees Kelvin (4,400 degrees Fahrenheit). Along with other companies developing similar technology, USNC-Tech has presented its development to NASA. While Sheehy would not comment on the specifics of any individual designs, he said the developments show that nuclear engines are feasible and could make “a good choice for human exploration to Mars.”
Is the nuclear option safe?
Shorter missions would limit the crew’s exposure to space radiation, but there is still concern about the radiation emitted from the nuclear reactor inside the spacecraft. This would be mitigated through the rocket’s design, Eades explains. The liquid propellants — stored between the engine and the crew area — block out radioactive particles, acting as “a tremendously good radiation shield,” he says. 
A rendering of the USNC-Tech NTP systems in line at a rocket hangar. The system is roughly 13 feet (four meters) long.The distance between the crew and reactor also provides a buffer, says Sheehy, and any NTP design would place the living quarters at the other end of the rocket to the reactor.To protect people on the ground, NTP spacecraft would not lift-off directly from Earth, Sheehy adds. Instead, a regular chemical rocket would hoist it into orbit, and only then would it fire up its nuclear reactor.Once in orbit, it could do little harm, he says, as blasts and thermal radiation cannot move through a vacuum.If disaster struck and the rocket’s reactor broke up, the pieces would not land on Earth — or any other planet — for tens of thousands of years, he says. By that time, the radioactive substance would have “naturally decayed to the point where it wasn’t hazardous anymore.”
Deep space exploration
Although USNC-Tech’s current goal for a one-way trip is five to nine months, nuclear-powered technology has the potential to cut journeys from Earth to Mars to just 90 days, says Eades.
Architects have designed a Martian city for the desert outside DubaiThese faster journey timescould open up a wealth of opportunities. USNC-Tech is hoping to develop its technology for government agencies like NASA and the Department of Defense, and for the commercial space market. The company says its concept could help to power space tourism and “rapid orbital logistics services,” such as transporting satellites or delivering spacecraft capable of repairing satellites out in space. Sheehy agrees that nuclear-powered rockets will be key to opening up the solar system but cautions that it could be at least two decades before they are used widely. Numerous demonstrations and tests would need to be carried out before a crew is sent to Mars in an NTP rocket, he says.”Nobody’s ever flown nuclear propulsion yet,” he says. “I think it’s going to have to be flown a few times … before somebody sells tickets.”
An earlier version of this story misidentified silicon carbide as one of the compounds contained in the rocket fuel. This has been changed to reflect new information.
