Landings, NASA, and the Soviet Space Program
Published on November 30, 2010
I recently wrote a blog post about NASA’s choice of using exclusively splashdowns landings during the space race and a (relatively brief) discussion of why this method was far less desirable than a land landing alternative. In retrospect, I realized that I only told half the story. Part of what makes the NASA “splashdown v. land landing” story an interesting one is a comparison to their Soviet counterparts who used exclusively land landing systems. (The image to the left shows cosmonaut Alexei Leonov during his spacewalk, Voskhod 2, March 1965.)
Throughout the Space Race, both the Americans and Soviets were launching capsule-style spacecraft. Try as they might, the Americans just couldn’t land their spacecraft on land. Which begs the question: what did the Soviets do that the Americans didn’t, or couldn’t? The comparison between the two programs in this critical mission phase is a pretty interesting one.
NASA’s choice of splashdown landing for its Mercury manned space program was based on simplicity. A parachute was more than enough to slow the re-entering non-aerodynamic spacecraft to a speed at which the astronaut inside could sustain the final drop into the ocean. With the Atlantic and Pacific as well as a huge Navy as its disposal, it would be crazy for NASA to waste time developing a complicated landing system. Especially as time became a factor. The Soviets, it is no stretch to say, were consistently leading the Americans in space.
Consider a few of the Soviet firsts relevant to manned spaceflight in the early Space Race: In 1957 the Soviets launched the first artificial Satellite, Sputnik, followed a month later by the significantly larger Sputnik 2, which carried a dog, Laika, into orbit. In 1961, Soviet cosmonaut Yuri Gagarin became the first man to orbit the Earth. In 1962 the Soviet Space Program launched the first dual-spacecraft mission; Adrien Nikolayev in Vostok 3 and Pavel Popovich in Vostok 4 flew within 4 miles of one another in orbit. In 1964, the Soviets launched the first mission with a multi-person crew. Vladimir Komarov, Konstantin Feoktistov, and Boris Yegorov flew the first mission in the second-generation Soviet program, Voskhod. In 1965, cosmonaut Alexei Leonov completed the first extra-vehicular activity (or EVA).
The American timeline shows a definite lag in accomplishments. The first American satellite in orbit, Explorer, was launched in 1958. John Glenn became the first American to orbit the earth in 1962. The first dual-spacecraft mission wasn’t until 1966.
While the Americans lagged behind their adversaries, they surpassed the Soviets with their technology. The American space program opened the closed loop of the spacecraft to give the astronaut an increased amount of control. Engineers and designers took care to ensure the comfort and safety of the American astronauts as missions progressed and new spacecraft were developed. The same can hardly be said of the cosmonauts. The Soviet cosmonauts had comparatively little control. Clever engineers orchestrated many of their ‘space firsts’.
The best example is perhaps the Soviet first of a dual-spacecraft mission in 1962. Although presented to the west as two spacecraft flying in formation in orbit, in reality the cosmonauts didn’t pilot their spacecraft to close the gap between them. Rather, the engineers launched the spacecraft one after another such that their orbits took them within 4 miles of each other. The cosmonauts remained passengers. The American’s first rendezvous between two manned spacecraft was achieved through manual control of the flight path. Commander Wally Schirra, with pilot Tom Stafford, manipulated the orbit of the Gemini 6 spacecraft to within feet of Jim Lovell and Frank Borman’s Gemini 7. (The image to the right is Gemini 6 taken from the window on Gemini 7 while both were in orbit, December 1965.)
The astronauts control stands in stark contrast to the cosmonauts lack thereof, but the one aspect of all missions that put both on equal footing was the lading phase. Both astronauts and cosmonauts were stuck in a predominantly passive role.
In initially developing the landing method, NASA took advantage of its natural geography. The launch site at Cape Canaveral (later Cape Kennedy) in Florida is one of the most southern points in the United Sates. This is advantageous in putting spacecraft in orbit as well as bringing the astronauts home. The climate is, for the most part, conducive to launches year round, and splashdowns at a more or less equivalent latitude is safe enough for the astronauts to open their spacecraft and enter the water if need be.
The cosmonauts had no such luxurious natural resources to take advantage of. The Soviet Space Program’s (now known as the Russian Federal Space Agency’s) launch site at the Baikonur Cosmodrome (sometimes referred to as Tyuratam for its proximity to the river of the same name) is actually in Kazakhstan. The site, leased to Russia by the Kazakh government in the 1950s, was the Soviet’s attempt to establish the southern most launch site possible within the Soviet Union. It was, however, still quite north; the site is on roughly the same latitude as Portland, Maine.
(The above image shows a comparison between the Soviet and American launch sites and the relative area surrounding each.)
Additionally, the Baikonur Cosmodrome is essentially land locked. The Caspian Sea is the nearest body of water, west and slightly south of the launch site. Open Russian waters lie significantly farther north in the Arctic Circle and include bodies such as the Barents Sea, The Laptev Sea, and the East Siberian Sea. None of these are hospitable places for a splashdown. If water breached their spacecraft at all, the cosmonauts inside would surely freeze. Similarly, rescue forces would have a hard time assisting the cosmonauts in the water if they needed it. Any hospitable bodies of water would have the Soviets operating in shared international waters, an undesirable position in which to be.
What The Soviets did have access to was a huge expanse of land, most of which is free from populated areas. Land landings were thus the lesser of two evils, a comparatively safe and viable option.
The first Soviet manned spacecraft, Vostok, had a spherical cabin for the cosmonaut attached to a conical instrument and engine module. Retro rockets would slow the spacecraft for orbit. Before gravity began the reentry phase in earnest, the conical module was jettisoned; only the spherical portion would return to Earth. Once reentry had been initiated, there was little the cosmonaut could do to control the spacecrafts path or orientation. Although the natural weighting of the spacecraft ensured it entered the atmosphere with its heavier end down, the spherical shape was intended to protect the cosmonaut from the heat of reentry on all sides. (The above photo shows the Vostok 1 spacecraft).
The Vostok spacecraft used a parachute to slow and control its rate of descent. Even so, the landing was expected to be unsurvivably harsh. To spare the life of the cosmonaut, an ejection system was used in addition to the parachute-controlled descent. The cosmonaut would eject from the spacecraft at 23,000 feet, replying on a personal parachute for his return to Earth. The spacecraft and its cosmonaut would land separately.
The first man to land with his system was Yuri Gagarin on his historic Vostok 1 flight. His landing was presented to the West as having followed mission parameters and schedules perfectly. In reality, the descent was a near disaster and quite perilous to Gagarin’s life. After a perfect fire of the spacecraft’s retrorockets, the instrument module failed to separate from the descent vehicle. It remained connected by a tether, which caused the unbalanced pair to tumble wildly into the atmosphere. The risk was high of the two spacecraft sections colliding, and the tumbling was affecting the orientation of the descent module. It needed to be free from the pull of the instrument module in order to settle into the heavy-end-down configuration that would ensure Gagarin’s safety. (The picture above is cosmonaut Yuri Gagarin.)
The trouble early in the descent stage forced Gagarin to eject from his spacecraft ahead of schedule. His own parachute opened first, causing him to land ten minutes after his spacecraft and roughly two miles away. Both spacecraft and cosmonaut landed in the Saratova, a region of Soviet Union not far from the Kazakhstan border. Gagarin’s landing position was also affected by the trouble in the initial phases of his descent. He landed on rural farmland. As he walked towards the curious onlookers who were confused by his spacesuit and helmet, one woman asked in dismay whether he’d come from space. Gagarin replied simply that she wouldn’t believe him if he told her.
Near fatalities aside, the mission proved that land landings could work; five more cosmonauts carried out five successful landing in like manner in following Vostok missions. Nonetheless, the method had its drawbacks and would become increasingly problematic with a multi-manned crew. The need for a new system became more urgent with the design of the second-generation spacecraft, Voskhod.
To call Voskhod a second-generation spacecraft is a misnomer. The Voskhod was really just a reconfigured Vostok even if it was presented to observers in the west as an entirely new spacecraft. For the Voskhod program, the space-consuming Vostok-era ejection seats were removed to accommodate the larger crew.
The first mission carried three cosmonauts. Even without ejection seats, the spacecraft was cramped; to make room for all three men, none were able to wear spacesuits meaning there was nothing protecting them in the even of depressurization. Writer Ben Evans draws the comparison that if the Mercury astronauts were ‘spam in a can’, then the Voskhod 1 cosmonauts were sardines.
The second Voskhod mission, Voskhod 2, afforded the crew comparative luxury. Pavel Belyayev and Alexei Leonov flew without a third since only two men could fit with pressure suits on. This was a necessity since Leonov would be leaving the spacecraft. (Belyayev actually remained inside the pressurized spacecraft since Leonov left through an airlock. Still, if the airlock failed, both cosmonauts would be exposed to the vacuum. As such, both had to be prepared.) (To the right is cosmonaut Alexei Leonov.)
The removal of the ejection seats had another consequence: the development of a soft landing system was absolutely imperative to the success of this program.
The solution was the soft landing system known as ‘Elburs’. The system built on the previously used parachute-controlled descent method, adding probes to the end of the parachute lines. The probes were the first piece of the spacecraft to make contact with the ground, triggering a solid propellant braking rocket on the underside of the spacecraft. The final stage of the descent, if everything prior went smoothly, was a soft touchdown on the ground.
The Voskhod 1 cosmonauts reported that the landing was so gentle they hardly felt it. The Voskhod 2 cosmonauts on the other hand ran into complications and found themselves faced with the real dangers of landing a capsule-style spacecraft on land.
Voskhod 2 began its retrofire sequence on schedule, but a faulty solar orientation sensor meant that the command was not properly processed. The spacecraft began rolling. Leonov and Belyayev optically reoriented their spacecraft prior to manually firing their retro rockets. This deviation from the automated schedule cost the cosmonauts valuable seconds. They fired their retrorockets late, still landing in Soviet territory, but over 2,000 km from their intended site.
Overshooting the landing zone on a body of water results in the same basic splashdown. The same is not the case when overshooting a land landing. Leonov and Belyayev landed in the forest of the Ural Mountains. Only when their hatch refused to open did they realize their spacecraft was wedged between two fir trees. They managed to rock the capsule enough to free the hatch, but they were still in the in a heavily wooded forest, forced to spend a snowy night before loggers could cut a path for the rescue effort to reach the cosmonauts. By morning, rescue helicopters had located the cosmonauts in time to scare away wolves that had been closing in on the men through the night.
The problems associated with the Soviet landings are indicative that the Soviet program was as much of a crash program as the US space effort in the 1960s. Perhaps more so. Reconfiguring a spacecraft and calling it new speaks to a much more desperate need to more forward in space than the Americans demonstrated. Gemini built off Mercury, but it was a new spacecraft. However, the Soviets did succeed in landing a blunt spacecraft on landing while sparing the life of the cosmonaut(s) inside.
The motivations behind each country’s pursuit of land landing were different, and I think here lies the reason for the Soviet success and the American failure. NASA wanted to give the astronauts increased control with a land landing system. The proposals added new components into a spacecraft that worked, thus complicated the system. Not to mention NASA had the perfectly viable splashdown landing as a backup. Even though splashdowns were less desirable, a new land landing system was never absolutely necessary. The Soviet Space Program on the other hand absolutely needed a way to land on land; it was never a matter of giving the cosmonauts control. The solution was fairly simple. In fact, NASA had tried a similar method in Gemini, but the system proved too problematic and it never went beyond the initial testing phase.
Perhaps it was necessity that made Soviets’ system work. Without another option, they had to find a way to make it work. And they did, crude as the ejection system may be. In light of the Soviets’ accomplishment, it seems that the primary reason NASA engineers failed to incorporate a land landing system into its space race era spacecraft is rooted in their attempt to open the closed system further. The spacecrafts of Space Race were largely automated, regulated with feedback loops, and capable of being entirely controlled by mission control. Adding a human element adds complexity, and giving the human control complicates the system as a whole still further. Perhaps if the Americans had sought a land landing system without pilot control they would have succeeded. But then that would stand in the face of everything the pilots turned astronauts fought for.
Suggested Reading/Selected Sources:
1. Burgess, Colin and Hall, Rex. The first Soviet cosmonaut team: their lives, legacy, and historical impact. UK: Springer Praxis. 2009
2. Evans, Ben. Escaping the bonds of Earth: the fifties and the sixties. UK: Springer Praxis. 2009
3. Gagarin, Yuri et al. Soviet Man in Space. Honolulu: University Press of the Pacific. 2001.
4. Hall, Rex and Shayler, David. The rocket men: Vostok & Voskhod, the first Soviet manned spaceflights. UK: Springer Praxis. 2001
5. Scott, David and Leonov, Alexei. Two Sides of the Moon. New York: Thomas Dunne Books. 2004.
Published on November 30, 2010
I recently wrote a blog post about NASA’s choice of using exclusively splashdowns landings during the space race and a (relatively brief) discussion of why this method was far less desirable than a land landing alternative. In retrospect, I realized that I only told half the story. Part of what makes the NASA “splashdown v. land landing” story an interesting one is a comparison to their Soviet counterparts who used exclusively land landing systems. (The image to the left shows cosmonaut Alexei Leonov during his spacewalk, Voskhod 2, March 1965.)
Throughout the Space Race, both the Americans and Soviets were launching capsule-style spacecraft. Try as they might, the Americans just couldn’t land their spacecraft on land. Which begs the question: what did the Soviets do that the Americans didn’t, or couldn’t? The comparison between the two programs in this critical mission phase is a pretty interesting one.
NASA’s choice of splashdown landing for its Mercury manned space program was based on simplicity. A parachute was more than enough to slow the re-entering non-aerodynamic spacecraft to a speed at which the astronaut inside could sustain the final drop into the ocean. With the Atlantic and Pacific as well as a huge Navy as its disposal, it would be crazy for NASA to waste time developing a complicated landing system. Especially as time became a factor. The Soviets, it is no stretch to say, were consistently leading the Americans in space.
Consider a few of the Soviet firsts relevant to manned spaceflight in the early Space Race: In 1957 the Soviets launched the first artificial Satellite, Sputnik, followed a month later by the significantly larger Sputnik 2, which carried a dog, Laika, into orbit. In 1961, Soviet cosmonaut Yuri Gagarin became the first man to orbit the Earth. In 1962 the Soviet Space Program launched the first dual-spacecraft mission; Adrien Nikolayev in Vostok 3 and Pavel Popovich in Vostok 4 flew within 4 miles of one another in orbit. In 1964, the Soviets launched the first mission with a multi-person crew. Vladimir Komarov, Konstantin Feoktistov, and Boris Yegorov flew the first mission in the second-generation Soviet program, Voskhod. In 1965, cosmonaut Alexei Leonov completed the first extra-vehicular activity (or EVA).
The American timeline shows a definite lag in accomplishments. The first American satellite in orbit, Explorer, was launched in 1958. John Glenn became the first American to orbit the earth in 1962. The first dual-spacecraft mission wasn’t until 1966.
While the Americans lagged behind their adversaries, they surpassed the Soviets with their technology. The American space program opened the closed loop of the spacecraft to give the astronaut an increased amount of control. Engineers and designers took care to ensure the comfort and safety of the American astronauts as missions progressed and new spacecraft were developed. The same can hardly be said of the cosmonauts. The Soviet cosmonauts had comparatively little control. Clever engineers orchestrated many of their ‘space firsts’.
The best example is perhaps the Soviet first of a dual-spacecraft mission in 1962. Although presented to the west as two spacecraft flying in formation in orbit, in reality the cosmonauts didn’t pilot their spacecraft to close the gap between them. Rather, the engineers launched the spacecraft one after another such that their orbits took them within 4 miles of each other. The cosmonauts remained passengers. The American’s first rendezvous between two manned spacecraft was achieved through manual control of the flight path. Commander Wally Schirra, with pilot Tom Stafford, manipulated the orbit of the Gemini 6 spacecraft to within feet of Jim Lovell and Frank Borman’s Gemini 7. (The image to the right is Gemini 6 taken from the window on Gemini 7 while both were in orbit, December 1965.)
The astronauts control stands in stark contrast to the cosmonauts lack thereof, but the one aspect of all missions that put both on equal footing was the lading phase. Both astronauts and cosmonauts were stuck in a predominantly passive role.
In initially developing the landing method, NASA took advantage of its natural geography. The launch site at Cape Canaveral (later Cape Kennedy) in Florida is one of the most southern points in the United Sates. This is advantageous in putting spacecraft in orbit as well as bringing the astronauts home. The climate is, for the most part, conducive to launches year round, and splashdowns at a more or less equivalent latitude is safe enough for the astronauts to open their spacecraft and enter the water if need be.
The cosmonauts had no such luxurious natural resources to take advantage of. The Soviet Space Program’s (now known as the Russian Federal Space Agency’s) launch site at the Baikonur Cosmodrome (sometimes referred to as Tyuratam for its proximity to the river of the same name) is actually in Kazakhstan. The site, leased to Russia by the Kazakh government in the 1950s, was the Soviet’s attempt to establish the southern most launch site possible within the Soviet Union. It was, however, still quite north; the site is on roughly the same latitude as Portland, Maine.
(The above image shows a comparison between the Soviet and American launch sites and the relative area surrounding each.)
Additionally, the Baikonur Cosmodrome is essentially land locked. The Caspian Sea is the nearest body of water, west and slightly south of the launch site. Open Russian waters lie significantly farther north in the Arctic Circle and include bodies such as the Barents Sea, The Laptev Sea, and the East Siberian Sea. None of these are hospitable places for a splashdown. If water breached their spacecraft at all, the cosmonauts inside would surely freeze. Similarly, rescue forces would have a hard time assisting the cosmonauts in the water if they needed it. Any hospitable bodies of water would have the Soviets operating in shared international waters, an undesirable position in which to be.
What The Soviets did have access to was a huge expanse of land, most of which is free from populated areas. Land landings were thus the lesser of two evils, a comparatively safe and viable option.
The first Soviet manned spacecraft, Vostok, had a spherical cabin for the cosmonaut attached to a conical instrument and engine module. Retro rockets would slow the spacecraft for orbit. Before gravity began the reentry phase in earnest, the conical module was jettisoned; only the spherical portion would return to Earth. Once reentry had been initiated, there was little the cosmonaut could do to control the spacecrafts path or orientation. Although the natural weighting of the spacecraft ensured it entered the atmosphere with its heavier end down, the spherical shape was intended to protect the cosmonaut from the heat of reentry on all sides. (The above photo shows the Vostok 1 spacecraft).
The Vostok spacecraft used a parachute to slow and control its rate of descent. Even so, the landing was expected to be unsurvivably harsh. To spare the life of the cosmonaut, an ejection system was used in addition to the parachute-controlled descent. The cosmonaut would eject from the spacecraft at 23,000 feet, replying on a personal parachute for his return to Earth. The spacecraft and its cosmonaut would land separately.
The first man to land with his system was Yuri Gagarin on his historic Vostok 1 flight. His landing was presented to the West as having followed mission parameters and schedules perfectly. In reality, the descent was a near disaster and quite perilous to Gagarin’s life. After a perfect fire of the spacecraft’s retrorockets, the instrument module failed to separate from the descent vehicle. It remained connected by a tether, which caused the unbalanced pair to tumble wildly into the atmosphere. The risk was high of the two spacecraft sections colliding, and the tumbling was affecting the orientation of the descent module. It needed to be free from the pull of the instrument module in order to settle into the heavy-end-down configuration that would ensure Gagarin’s safety. (The picture above is cosmonaut Yuri Gagarin.)
The trouble early in the descent stage forced Gagarin to eject from his spacecraft ahead of schedule. His own parachute opened first, causing him to land ten minutes after his spacecraft and roughly two miles away. Both spacecraft and cosmonaut landed in the Saratova, a region of Soviet Union not far from the Kazakhstan border. Gagarin’s landing position was also affected by the trouble in the initial phases of his descent. He landed on rural farmland. As he walked towards the curious onlookers who were confused by his spacesuit and helmet, one woman asked in dismay whether he’d come from space. Gagarin replied simply that she wouldn’t believe him if he told her.
Near fatalities aside, the mission proved that land landings could work; five more cosmonauts carried out five successful landing in like manner in following Vostok missions. Nonetheless, the method had its drawbacks and would become increasingly problematic with a multi-manned crew. The need for a new system became more urgent with the design of the second-generation spacecraft, Voskhod.
To call Voskhod a second-generation spacecraft is a misnomer. The Voskhod was really just a reconfigured Vostok even if it was presented to observers in the west as an entirely new spacecraft. For the Voskhod program, the space-consuming Vostok-era ejection seats were removed to accommodate the larger crew.
The first mission carried three cosmonauts. Even without ejection seats, the spacecraft was cramped; to make room for all three men, none were able to wear spacesuits meaning there was nothing protecting them in the even of depressurization. Writer Ben Evans draws the comparison that if the Mercury astronauts were ‘spam in a can’, then the Voskhod 1 cosmonauts were sardines.
The second Voskhod mission, Voskhod 2, afforded the crew comparative luxury. Pavel Belyayev and Alexei Leonov flew without a third since only two men could fit with pressure suits on. This was a necessity since Leonov would be leaving the spacecraft. (Belyayev actually remained inside the pressurized spacecraft since Leonov left through an airlock. Still, if the airlock failed, both cosmonauts would be exposed to the vacuum. As such, both had to be prepared.) (To the right is cosmonaut Alexei Leonov.)
The removal of the ejection seats had another consequence: the development of a soft landing system was absolutely imperative to the success of this program.
The solution was the soft landing system known as ‘Elburs’. The system built on the previously used parachute-controlled descent method, adding probes to the end of the parachute lines. The probes were the first piece of the spacecraft to make contact with the ground, triggering a solid propellant braking rocket on the underside of the spacecraft. The final stage of the descent, if everything prior went smoothly, was a soft touchdown on the ground.
The Voskhod 1 cosmonauts reported that the landing was so gentle they hardly felt it. The Voskhod 2 cosmonauts on the other hand ran into complications and found themselves faced with the real dangers of landing a capsule-style spacecraft on land.
Voskhod 2 began its retrofire sequence on schedule, but a faulty solar orientation sensor meant that the command was not properly processed. The spacecraft began rolling. Leonov and Belyayev optically reoriented their spacecraft prior to manually firing their retro rockets. This deviation from the automated schedule cost the cosmonauts valuable seconds. They fired their retrorockets late, still landing in Soviet territory, but over 2,000 km from their intended site.
Overshooting the landing zone on a body of water results in the same basic splashdown. The same is not the case when overshooting a land landing. Leonov and Belyayev landed in the forest of the Ural Mountains. Only when their hatch refused to open did they realize their spacecraft was wedged between two fir trees. They managed to rock the capsule enough to free the hatch, but they were still in the in a heavily wooded forest, forced to spend a snowy night before loggers could cut a path for the rescue effort to reach the cosmonauts. By morning, rescue helicopters had located the cosmonauts in time to scare away wolves that had been closing in on the men through the night.
The problems associated with the Soviet landings are indicative that the Soviet program was as much of a crash program as the US space effort in the 1960s. Perhaps more so. Reconfiguring a spacecraft and calling it new speaks to a much more desperate need to more forward in space than the Americans demonstrated. Gemini built off Mercury, but it was a new spacecraft. However, the Soviets did succeed in landing a blunt spacecraft on landing while sparing the life of the cosmonaut(s) inside.
The motivations behind each country’s pursuit of land landing were different, and I think here lies the reason for the Soviet success and the American failure. NASA wanted to give the astronauts increased control with a land landing system. The proposals added new components into a spacecraft that worked, thus complicated the system. Not to mention NASA had the perfectly viable splashdown landing as a backup. Even though splashdowns were less desirable, a new land landing system was never absolutely necessary. The Soviet Space Program on the other hand absolutely needed a way to land on land; it was never a matter of giving the cosmonauts control. The solution was fairly simple. In fact, NASA had tried a similar method in Gemini, but the system proved too problematic and it never went beyond the initial testing phase.
Perhaps it was necessity that made Soviets’ system work. Without another option, they had to find a way to make it work. And they did, crude as the ejection system may be. In light of the Soviets’ accomplishment, it seems that the primary reason NASA engineers failed to incorporate a land landing system into its space race era spacecraft is rooted in their attempt to open the closed system further. The spacecrafts of Space Race were largely automated, regulated with feedback loops, and capable of being entirely controlled by mission control. Adding a human element adds complexity, and giving the human control complicates the system as a whole still further. Perhaps if the Americans had sought a land landing system without pilot control they would have succeeded. But then that would stand in the face of everything the pilots turned astronauts fought for.
Suggested Reading/Selected Sources:
1. Burgess, Colin and Hall, Rex. The first Soviet cosmonaut team: their lives, legacy, and historical impact. UK: Springer Praxis. 2009
2. Evans, Ben. Escaping the bonds of Earth: the fifties and the sixties. UK: Springer Praxis. 2009
3. Gagarin, Yuri et al. Soviet Man in Space. Honolulu: University Press of the Pacific. 2001.
4. Hall, Rex and Shayler, David. The rocket men: Vostok & Voskhod, the first Soviet manned spaceflights. UK: Springer Praxis. 2001
5. Scott, David and Leonov, Alexei. Two Sides of the Moon. New York: Thomas Dunne Books. 2004.
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