The space probes Voyager 1 and Voyager 2 were launched 40 years ago. In just 12 years, they flew near the four major planets of the solar system - Jupiter, Saturn, Uranus and Neptune. Both space probes operate continuously and send data to Earth, although they are currently well outside Pluto's orbit.
Let's go back to 1965, when the competition for the lunar landing was underway, and NASA had the money and confidence to make a big dream come true.
At that moment, no one thought about Voyager, because everyone believed that space technology was not yet ready for travels long billions of kilometers outside the solar system.
But there was already money to recruit young and promising mathematicians working in science at the large California research center JPL, and two of this group of mathematicians formed the basis for the development of Voyager.
Michael Minovich and Gary Flandro were tasked with investigating possible flight paths for space probes in the solar system. This was a study under the slogan "Timely Discretion", which was supposed to continue until the moment when rocketry reached the required level of development.
No one expected any outstanding results, but these two young mathematicians established that between 1976 and 1979 there was a unique opportunity to launch a space probe into flight near four major planets without large expenditures of fuel. It was an opportunity that arose once every 176 years. It was during these three years that the planets were located in such a way that it was possible to use the gravity of one planet to fly the probe further to the next planet.
This was a fortunate discovery. The last time this happened was in 1801, when we were busy with Napoleon's wars and the Copenhagen naval battle. But the next time it will happen in 2153.
NASA did not let this opportunity pass: plans for a large expedition to the solar system were quickly drawn up.
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It was planned to send at least four space probes and in addition to explore distant Pluto. In 1976-77, it was planned to send two probes to Jupiter, Saturn and Pluto, and in 1979 - two more probes to Jupiter, Uranus and Neptune.
But the American Congress, having learned that this project was worth more than a billion dollars, did not like it. It was a lot of money at the time. Congress wanted to allocate money for just two space probes, which will take advantage of the planet's favorable position to explore Jupiter and Saturn.
NASA prepares for the "Great Walk"
NASA committed a small act of civil disobedience, which, however, is now forgiven.
Voyager 1 accurately carried out the official plan, which was limited to visiting only Jupiter and Saturn, which made it possible to study Jupiter's moon Io and Saturn's large moon Titan at close range.
But it also meant that Voyager 1 was given an orbit from which it was impossible to fly further to Uranus and Neptune. Scientists had a secret idea to keep Voyager 2 in stock. He got a slow track and therefore flew for Voyager 1 all the time. While Voyager 1 was solving its tasks, Voyager 2 was allowed to complete the initial mission and fly to four large planets, that is, to take the “Great Walk,” as this expedition was later called.
This decision had a funny consequence: Voyager 2 was launched before Voyager 1. As a result, the fast Voyager 1 was the first to reach Jupiter and Saturn. And the slow Voyager 2 was supposed to be content with second place, but it got the opportunity to become the first probe to reach Uranus and Neptune.
Big oversight leads to extra work
Therefore, Voyager 2 was launched on August 20. And although it was a "slow" probe, it nevertheless reached a speed of 52 thousand kilometers per hour, as a result of which it flew past the Moon's orbit in less than 10 hours.
Two weeks later, the fast Voyager 1 was launched, and now everyone hoped for a smooth flight to Jupiter. But then there was a failure, as a result of which a considerable number of engineers had to work overtime over the next 12 years.
The control center forgot to send a routine message to Voyager 2. When the Voyager 2 computer did not receive the expected message, it was written in its instructions that this could only happen if the onboard receiver malfunctioned. It was believed that the control center simply could not forget about this operation.
Voyager 2 dutifully switched to a spare receiver, but it did not have the appropriate setting and could only receive signals in a very narrow frequency range of 96 hertz, and this created problems.
The control center naturally sent signals on a very specific frequency, but since Voyager was moving very quickly relative to Earth, due to the Doppler effect, it received a signal on a different frequency. Therefore, the receiver was tuned to receive signals in the 100,000 hertz range.
Voyager 2 was silent
The first reaction was to transfer Voyager 2 to the main receiver, but this receiver immediately broke completely. As a result, NASA was unable to send commands to the space probe.
This turned out to be a much more serious problem than expected. The speed relative to the Earth was easy to calculate, but much worse was that even very small changes in the probe temperature of less than 0.3 degrees changed the frequency range of the receiver so much that contact with the Earth was interrupted. It was found that even when one instrument was turned on or one of the control engines was used, the space probe's temperature changed.
Over the years, NASA engineers developed a complete mathematical model for Voyager that could calculate the probe temperature to within one hundredth of a degree. The model was developed during the entire flight of the probe to Neptune, communication with it was interrupted for several days.
Voyager sends first images to Earth
In March 1979, Voyager 1 reached Jupiter, and scientists were literally amazed at the fantastic photographs sent to the center: clouds and a red spot on Jupiter, Io's orange moon and white, all ice-covered Europa.
Jupiter's Great Red Spot. Photo taken by Voyager 1
Scientists learned what "Instant Science" means when journalists at JPL immediately asked for explanations about photos that were received just a few hours ago and therefore were not carefully analyzed by experts.
For many scientists who are accustomed to a quiet life and suddenly found themselves in a large audience in front of dozens of journalists wishing to get an answer, this was a real test.
Rainy weather over Australia creates problems
During the probe's flight over Australia, where a large tracking station is located, heavy rain created problems. Voyager sent its data to Earth only at 3.6 cm, and radio waves of such a short length barely passed through rain clouds. Because of this, data disappeared in a few hours.
But the unexpected event only happened a few days later, when Voyager 1 was on its way from Jupiter to Saturn.
For reliable navigation, it is necessary to know exactly the position of Voyager, and this had to happen, in particular, by photographing Io's satellite along with the mass of stars in the background. Therefore, a slow shutter speed was used, as a result of which Io in the photograph looked like an illuminated white disk.
The task of analyzing the photographs on a computer was performed by a young employee of the navigation team Linda Morabito. She discovered that there was something over Io that looked like a cloud. Io has no atmosphere, so no one expected clouds a few hundred kilometers above the surface.
Tidal forces and volcanic activity
It was immediately suspected that it was a volcanic eruption, but experts who could study the photos were on a weekend getaway. Therefore, it took a full three days before NASA could tell that the first active volcanoes outside the Earth were discovered.
The news was of particular relevance to three American scientists. Just a week ago, they published an article in Science predicting the existence of volcanoes as a consequence of the powerful tidal forces of Jupiter and neighboring moons Europa and Ganymede acting on Io.
Four months later, Voyager 2 approached Jupiter. Scientists were now ready to watch the volcanoes on Io and take a closer look at Europa's undamaged ice surface. Today it is believed that this ice surface hides the sea, the depth of which can reach 100 km and in which life can exist.
And thanks to Voyager's measurements, we now know that tidal forces cause Io's solid surface to move up and down in elevation changes of up to 100 meters. Therefore, it is not surprising that the heat generated as a result of this leads to powerful volcanic activity.
Voyager 1 flies close to Titan
It was a quiet time before Voyager 1 flew to Saturn in November 1980. Scientists could again just sit and gaze with delight at the fantastic photographs of Saturn's rings. However, the greatest expectations were associated with the flight near Titan. This flight past Titan ruled out Voyager 1's ability to continue its flight to Uranus and Neptune.
But the only thing that could be seen was a completely impenetrable orange cloud cover. However, the composition of the atmosphere was studied, which is mostly carbon dioxide with a small amount of methane. The surface pressure was 1.6 times stronger than the earth's.
Measurements have shown that large amounts of organic molecules are generated in the orange haze around Titan when methane is exposed to light from the sun. This means that Titan, in any case, receives many molecules, which are a prerequisite for the emergence of life. Unfortunately, the measurements showed a temperature of minus 180 degrees. It's chilly for life, but it's a temperature that makes it possible to find methane on the sea surface.
It still had to take 30 years before the Cassini space probe using radar was able to see the famous methane seas at the north and south poles of Titan despite the cloud cover.
Voyager 2 faces challenges again
Voyager 2 flew to Saturn in August 1981, and at first everything went well despite problems with the receiver. He photographed the small moon Enceladus, which, as we know today, erupts huge geysers from cracks in the ice-covered surface, and took pictures of the icy moon Hyperion, which closely resembles a washing sponge.
But then the problems started. The turntable with scientific instruments got stuck, a lot of data was lost. Again the engineers had to work extra, but the situation continued to deteriorate because NASA had 108 instead of 200 due to staff cuts.
The heavy workload has led to physical and mental fatigue of many employees.
But the problems were identified, they were related to the transmission that controls the turntable. The problem was the lubrication. When the platform turned quickly, the grease flew off the gears in zero gravity, which meant that the metal parts touched each other. Small metal shavings appeared and came off, blocking the movement. The problem could be avoided by turning the platform slowly.
Flight to Uranus
Fortunately, there was enough time to solve this problem, because Voyager 2 had to fly from Saturn to Uranus for almost five years. Nevertheless, it was a difficult time, because, as already mentioned, the flight to Uranus was not entirely calm.
Three large tracking stations in California, Spain and Australia had to be upgraded to receive critical signals from Voyager's small transmitter, which was only 20 watts. One way is to electronically connect large 64-meter parabolic antennas with smaller 34-meter antennas so that they can function as one large one.
Another problem was the high speed at which Voyager 2 flew past Uranus. The photographs turned out to be very blurry, since the sunlight in the Uranus region is so weak that it is necessary to keep the frame for a long time. All this helped to find ingenious solutions - in addition to what was done with the turntable (In the end, it all ended with the fact that instead of turning only one platform, fearing that it would jam again, they began to turn the entire space probe).
Accident when meeting Uranus
When Voyager 2 flew up to Uranus in January 1986, the only thing that could be seen was a large bluish-green ball with no visible signs of clouds. What Voyager saw appeared to be a layer of haze in a deep atmosphere composed of light hydrogen and helium, with small amounts of methane and other carbohydrates.
But Voyager's flight was remembered for something different.
Photo of Uranus from Voyager 2
On January 28, 1986, NASA was supposed to submit the first photographs of Uranus' small satellites - in particular, Miranda, where, as it turned out, there are sheer ice cliffs almost 10 kilometers high. But the press conference did not take place, because other footage appeared on the television screens of the audience. The explosion of the space shuttle Challenger was shown, in which seven astronauts died.
Time and again showed a white cloud of steam from the explosion and two rocket auxiliaries flying in different directions. After that, no one wanted to participate in the press conference on Uranus. Therefore, Voyager 2 quietly left Uranus and began its three-year journey to Neptune.
Goodbye and a new beginning
In August 1989, Voyager 2 flew up to Neptune, the final target of the Great Walk that Congress never allowed.
This time it was about a real spacecraft festival in Pasadena, where JPL is located. It was attended by thousands of people who were rewarded with interesting photographs of a beautiful blue Neptune with white clouds driven by the storm at a speed of 2,000 km per hour.
It remains a mystery how a planet at such a great distance from the Sun and with a very low temperature - minus 215 degrees = could have enough energy to create such powerful storms.
Soon it was time to say goodbye to Voyager 2. and this goodbye were photographs of the large icy moon Triton, which surprised by the presence of geysers. At least 50 sites have been found with long, dark traces of some form of eruption.
Some photographs show that the geysers reach a height of 8 kilometers, where they encounter a jet stream in a very rarefied atmosphere. She stretches sheer geysers, turning them into long streaks of smoke. The geysers are believed to be so dark because they not only contain steam, but also contain dust and organic matter.
The flight has just begun
The flight past Neptune was the end of the Great Walk, a journey that can rightfully be compared to landing on the moon. But this was not a farewell to the solar system, which neither Voyager 1 nor Voyager 2 had yet left.
To mark the completion, a farewell photograph of all the planets in the solar system was taken in 1990. On them, the Earth is visible as a small "light blue dot". This snapshot of our Earth from a distance of 6 billion km has become a kind of symbol showing how little space we actually occupy in the universe.
Both Voyager probes are now far from Pluto's orbit and from the Kuiper belt, which is made up of small icy planets. But they still have a journey of thousands of years before they reach the last outpost of our solar system, namely the Oort Cloud, which is considered the birthplace of many comets.
Voyager 1 set a record for traveling 141 AU from the Sun (one AU is the distance from Earth to the Sun).
The slow Voyager 2 traveled only 116 AU. Both probes are constantly sending data to Earth, which are now mainly related to the solar wind and the solar magnetic field.
Scientists hope to keep in touch with both old space probes until 2025. These two probes are almost eternal representatives of humanity, although they are unlikely to be found by any other civilization.
Earthlings' message
Both Voyagers carry with them a message from the Earthlings, written on a gold-plated 30-centimeter plate mounted on board.
The message was developed by a commission led by renowned astronomer and astrobiologist Carl Sagan (Carl Sagan, 1934 - 1996). Since the probability that these probes will ever be found is infinitely small, we can take this message as a message to ourselves.
It includes both pictures and sounds, which are encrypted on the plate. This is a series of pictures describing how the contents of the plate can be reproduced. Play should be done at 16 2/3 rpm using the needle that is attached to the plate. It's old-fashioned, but technically sound, if the recipients can figure out the series of pictures.
Henrik og Helle Stub