Today, the Cassini automatic interplanetary station completed its space journey, which lasted almost 20 years. The station burned up in Saturn's atmosphere, but until the last moment it transmitted information from its sensors to NASA.

The device entered the atmosphere of one of the largest planets in the solar system on August 17. Cassini's mission was to explore Saturn, collecting data on the atmosphere, wind speed and temperature on the planet's surface.

Child of the Cold War

The history of the grandiose Cassini-Huygens mission began in 1982, when the European Science Foundation and the American National Academy of Sciences joined forces for joint research. Then European scientists proposed two joint projects: sending a satellite into the orbit of Saturn and a probe to the surface of the planet’s satellite, Titan. By 1986, a satisfactory conclusion about the potential of these missions was issued by NASA and the European Space Agency (EAS).

Although the project to explore Saturn and its moon was purely scientific in nature (unlike many other space projects that were directly or indirectly related to military developments), it was also not without politics. In those years, NASA had little regard for its European colleagues, belittling their scientific and research potential, and European space researchers willingly cooperated with the Soviet Union. It is enough to note that the first French cosmonaut took off on the Soviet Soyuz T-6 spacecraft.

NASA decided that it was time to correct the situation and that they needed to extend a hand of friendship to their European colleagues, since Soviet competition in the space industry was becoming increasingly felt. This is how the Cassini-Huygens project was born.

Long road in space

After the end of the Cold War, the project was going to be curtailed, but NASA insisted on its continuation: the agency feared that abandoning Cassini-Huygens would greatly disappoint its European colleagues, and this could affect other areas of cooperation.

On October 15, 1997, the device, on which representatives of 15 states worked, took off from Cape Canaveral. Both ideas - entering the orbit of Saturn and exploring Titan - were combined into one concept, "Cassini-Huygens", where "Cassini" is the name of the orbital station, and "Huygens" is the device designed to land on Titan.

The flight to Saturn lasted several years. One could say that he was accompanied by “many adventures,” but they were all part of complex calculations in which hundreds of specialists took part. Cassini-Huygens used the gravitational field of Venus for maneuver and acceleration, passed through the asteroid belt at great risk, and only reached the moons of Saturn in 2004.

• JPL-Caltech

In December 2004, the Huygens probe separated from the apparatus and headed towards Titan, where it landed on January 14, 2005. And Cassini entered the orbit of Saturn.

Seasons, geysers and cosmic dust

Thanks to Cassini, many discoveries were made, not to mention the photographs that were taken, including during the apparatus’s flight to Saturn. For example, scientists managed to obtain the most detailed portrait of Jupiter.

• Jupiter
• globallookpress.com
• NASA/ZUMAPRESS.com

In 2011, the device was able to film a hurricane that circled Saturn and closed, forming a ring in the planet’s atmosphere. Thanks to Cassini, previously unknown satellites of Saturn were discovered that rotate along with its rings: Metone, Pallene, Aegeon and others.

Enceladus turned out to be the most impressive of the discovered satellites of Saturn: by 2014, more than a hundred geysers were counted on its surface.

• Enceladus
• JPL-Caltech/Space Science Institute

According to scientists, there may be water under the icy surface of Enceladus. Theoretically, this suggests the possibility of the existence of life on Saturn's moon.

Delivered by Cassini to the surface of Titan, Huygens only worked for a very short time. But in the 219 minutes during which Cassini received its signal, Huygens managed to transmit about 350 photographs of Titan and a lot of data about the surface and atmosphere of the planet.

Cassini continued to amaze even in its final months of operation. In May 2017, the device captured the solstice on Saturn, which occurs once every 15 years. Scientists now know that the seasons on the planet change very quickly.

“During the Cassini solstice mission, we analyzed an entire season on Saturn at close range for the first time. The Saturn system changes significantly from winter to summer, and thanks to Cassini, we had a front-row view of this event,” said Linda Spilker, project scientist at JPL.

Also, thanks to Cassini, it was finally proven that there is no dust between the rings of Saturn, and the space between them is a “big void.”

On April 26, 2017, the Cassini spacecraft entered the last stage of its life, called the "Grand Finale" - the probe approached Saturn's largest moon Titan for the last time before ending its mission. Cassini has already sent the last photos it took to Earth, after which it came as close as possible to Titan, the most Earth-like moon of Saturn, the gravity of which allowed the device to accelerate and go on its last flight in orbit between the rings of Saturn and the upper layers of the atmosphere of the gas giant, NASA reports.

Researchers hope that during the final flight of the Cassini probe, the device will be able to collect the maximum amount of previously unknown information that will allow them to determine the length of Saturn's day, as well as the age of its rings. True, being in Saturn’s orbit will cause the probe to fall into the dense layers of the giant planet’s atmosphere, as a result of which it will simply burn up.

The Cassini probe set off on its final flight between Saturn and its rings - latest photos

The Cassini probe's final flight around Saturn will be the finale of a 12-year mission, during which it obtained many new photographs of the planet and also illuminated its hydrocarbon lakes and seas using its radars. But before complete combustion in the atmosphere of the gas giant, the device will have time to make another 22 flights between the rings of Saturn and their “lord,” collecting and transmitting data about this planet until its very end.

Let us recall that the Cassini probe first arrived at Saturn on June 30, 2004 and became the first artificial satellite of this planet. On January 14, 2005, the Huygens probe, which Cassini carried on board, first landed on Titan. On September 15, 2017, the research mission of the Cassini spacecraft will end - over the years of studying the Saturn system, the probe passed near this huge satellite 126 times, and each time it switched to a new trajectory that directed it to new research objects.

The Cassini probe is the last flight between Saturn and its rings (video):

On September 15, 2017, the Cassini spacecraft burned up in Saturn's atmosphere. This event united space lovers all over the Earth. Cassini was not just any satellite. He served as one of the main symbols of space research, and science in general. The same symbol as the Hubble telescope or the Large Hadron Collider.

Cassini was launched back in 1997. Just imagine - this is the year Titanic, Quake 2 and the first Fallout were released. During the work of Cassini, an entire generation grew up. Many modern astronomy lovers became interested in space thanks to Cassini. Therefore, today we remember the history of the mission and pay it the tribute it deserves.

From concept to launch pad

In 1980–1981, the pair made a historic flyby of Saturn. They took the first detailed photographs of the planet, its rings and satellites, and analyzed the atmosphere and magnetic field. The results amazed astronomers. It turned out that Saturn's rings consist of hundreds of thin rings forming a complex system. Titan, Saturn's largest satellite, was obscured by a layer of hydrocarbon haze that was opaque in the visible spectrum. The satellite Iapetus looked as if the designer of the solar system had forgotten to paint it: one of its hemispheres shone brightly, like fresh snow, the other was black, like soot.

Cassini assembly

The Voyagers were physically unable to stay near the planet and study it longer. To unravel the mysteries of Saturn and its moons, a fundamentally different mission was required. A device that could go into orbit around the planet and explore it for several years.

In 1982, scientists from NASA and ESA began the first consultations about a joint long-duration mission to the Saturn system. It would consist of an orbiter and a lander that would land on Titan and see what was happening on its surface. The mission was named after Giovanni Cassini, the famous 17th-century astronomer who discovered the four moons of Saturn and the gap in its rings.

The negotiations were not easy. At that time, relations between NASA and ESA were complicated by the cancellation of a number of joint projects. But in 1988, the partners finally agreed on the distribution of responsibilities. NASA was supposed to build the Cassini orbiter, ESA was supposed to build the Huygens descent probe for Titan. It was named after Christiaan Huygens, who discovered the rings of Saturn and Titan itself.

Model of the Huygens apparatus

Cassini's problems didn't end there. The total budget of the project exceeded three billion dollars (80% of the funds were allocated by NASA), and the American Congress has repeatedly threatened to deprive the project of funding. Even at NASA, not everyone supported the mission. But Cassini survived, thanks in no small part to the efforts of ESA lobbyists. Things even went as far as letters to US Vice President Al Gore asking him not to close the program. As a result, although with difficulty, the mission received the necessary funding.

The latest threat to Cassini is the green ones. Shortly before the launch, environmental activists began demonstrations at Cape Canaveral and filed a lawsuit demanding a ban on the launch. Cause? 32 kilograms of plutonium-238 on board the station. The fact is that the vicinity of Saturn reaches 100 times less sunlight than Earth. Therefore, to generate energy, Cassini was equipped with a radioisotope generator.

Environmental activists stated that in the event of an accident there would be radioactive contamination and demanded to “save the Earth” from Cassini. And no matter how much NASA experts explained that even in the event of an accident the plutonium would remain in a protected container, this could not convince the “greens.” Fortunately, the court did not take into account the environmental horror stories and did not cancel the launch.

Launch of the Centaur rocket with Cassini on board

Seven years in flight

Cassini launched on October 15, 1997 and headed towards... Venus. There is no mistake here. The mass of the station was almost six tons, which made it one of the largest interplanetary vehicles in history: only the Soviet Phobos weighed more. The rocket's power was not enough to send such a colossus directly to Saturn. So engineers took advantage of gravity. Cassini flew by Venus twice, then Earth, and finally Jupiter. These gravity maneuvers allowed the vehicle to achieve the required speed.

Flying past Jupiter, Cassini managed to study this gas giant. He discovered several new storms in its atmosphere and took the highest quality photographs of the planet at that time. At the same time, engineers checked the functionality of the station’s instruments.

"Portrait" of Jupiter made from several Cassini photographs

In the early summer of 2004, Cassini reached the vicinity of Saturn. On June 11, the craft passed Phoebe, one of the planet's most distant satellites, which orbits nearly 13 million kilometers from the gas giant (that's 36 times the distance between the Earth and the Moon). Cassini had only one chance to visit this unusual moon, and its trajectory was specifically designed for a close flyby.

On July 1, Cassini performed an extremely difficult maneuver, on the outcome of which the fate of the entire mission depended. It was successful. Cassini turned on its main engine for 96 minutes and slowed down so that the planet's gravity could pick it up. So it became the first artificial satellite of Saturn in history.

This is how Cassini saw Saturn

Thirteen years for Saturn

"I've seen things you humans wouldn't believe..." If Cassini could talk, it would definitely quote Blade Runner. From the very beginning of its operation, the device began to make discoveries, one more incredible than the other. For those who love statistics, let's say that during the 13 years of its stay at Saturn, the station took about 400 thousand photographs and sent over 600 gigabytes of information to Earth. Based on their results, about 4,000 scientific articles have already been written - and this number will grow, because Cassini data will be analyzed for many years to come. To describe all the achievements of the mission, a whole collection of essays would be required. We will only briefly mention the main milestones.

One of the mission's priority targets was Titan. In January 2005, the Huygens probe separated from Cassini and made a historic landing on its surface. The Huygens images showed complex terrain with areas resembling river beds and coastlines. Photographs from the surface show rounded stones with traces of liquid exposure.

Titan from both sides in the Cassini photo

Subsequently, Cassini completed over a hundred flybys of Titan. The device scanned the surface of the satellite with a radar, and shooting in the infrared range made it possible to look under its haze. It turned out that Titan has lakes, rivers, seas and even rains. But not from water, but from liquid hydrocarbons - a mixture of ethane and methane. The temperature on Titan is such that these substances can exist in three states at once (liquid, gas, solid) and perform the same role that water plays on our planet. This is the only body in the solar system besides the Earth where there is a full fluid cycle, and permanent bodies of water exist on the surface. More precisely, hydrocarbons.

Huygens landing on Titan, concept art

Recording of atmospheric wind on Titan made by Huygens during landing

Overall, conditions on Titan closely resemble early Earth in the pre-oxygen era. The satellite turned out to be a kind of time machine: it made it possible to study the processes that could lead to the emergence of life on our planet. Some scientists even make cautious assumptions that, despite the low temperatures, the simplest forms of life may already exist on Titan.

Mercator Plateau photographed by Huygens

Video of landing based on photographs from the device

But in the Saturn system there was an even more attractive target for astrobiologists - Enceladus. Before the Cassini mission, it was considered simply one of Saturn's many icy moons of little interest. But after Cassini’s first visit to Enceladus, these ideas had to be radically revised.

Enceladus, planet of giant geysers

It turned out that, despite its relatively small size (the diameter of the satellite is 520 kilometers, almost six times smaller than that of the Moon), Enceladus is one of the most geologically active bodies in the Solar System. Its south pole is densely dotted with geysers that constantly emit water into space. This water forms a separate ring around Saturn. The discovery of Enceladus geysers has become a scientific sensation. The Cassini program was urgently changed, and in subsequent years the device visited the satellite more than once. Several times Cassini flew directly through its emissions, analyzing their chemical composition.

Geysers of Enceladus

Data collected by Cassini showed that beneath Enceladus's icy surface lies a global ocean of liquid water. Its depth is estimated at 10 kilometers, the thickness of the ice above it ranges from 2 to 30 kilometers. Chemical analysis of the ejected water revealed salts, organic compounds and substances in it, indicating that active hydrothermal processes are taking place in the ocean of Enceladus. Now this satellite is considered the most suitable place for life in the solar system outside of Earth.

Cassini was able to solve the mystery of the “underpainted” Iapetus. It turned out that the differences in the color of the satellite are due to dust: meteorite impacts knock it out from the distant moons of Saturn, and it settles on the leading hemisphere of Iapetus (this is the hemisphere with which it moves “forward” in its orbit). Dust-covered areas heat up more than neighboring regions. As a result, ice evaporates from them and condenses where the surface temperature is lower: on the trailing side and in the circumpolar regions. A positive feedback is formed: dark areas become even darker, and vice versa.

Cassini also discovered another unique feature of Iapetus - the ring-shaped mountain range "Wall of Iapetus" that stretches along its equator. The unusual formation has a height of up to 13 kilometers, a width of up to 20 kilometers and a total length of about 1,300 kilometers. According to one theory, Iapetus once had a ring, and its particles fell to the surface and formed a wall.

Black and white Iapetus in Cassini images

But, of course, Cassini studied not only the satellites of Saturn, but also the planet itself. Over the years of the mission, the device captured several changes of seasons. They manifested themselves especially clearly in the hexagon - this is the name given to the amazing hexagonal-shaped vortex located at the north pole of the planet. The width of this formation is 25 thousand kilometers, approximately two diameters of the Earth. Cassini recorded how, with the arrival of summer in the northern hemisphere of Saturn, the hexagon changed color from dark blue to golden. The intensity of ultraviolet radiation increased, this triggered photochemical reactions, and compounds (tholins) began to be synthesized at the north pole, which changed the color of the storm.

Saturn's hexagonal vortex in 2016

Cassini has photographed Saturn's ring system many times. The images demonstrated their extraordinary complexity and variability. Numerous satellites of Saturn exert their gravity on the rings of the planet, which is why vortices, waves, kinks, loops and other structures are formed in them. Some small moons orbit directly within the rings. Their gravity accelerates the particles of the rings, which is why ruptures form in them. Other satellites play the role of “shepherds”. For example, the orbits of Prometheus and Pandora pass inside and outside the F ring. The gravity of a pair of satellites holds the particles of the rings in the same orbit, preventing them from scattering in different directions.

The highest quality photo of Saturn's rings

We must not forget about Cassini’s goal of popularizing space research. It turned out to be easy. Saturn is perhaps the most beautiful planet in the solar system, and its photographs have probably inspired many people to connect their lives with space.

One of Cassini's most famous images was taken on July 19, 2013. On that day, the device performed panoramic photography of the planet and its surroundings. At the time of photography, the Sun was exactly behind Saturn, effectively highlighting its rings. One of the pictures also showed our planet. From a distance of 1.5 billion kilometers, it appears as a pale blue dot.

“The Day the Earth Smiled”: the famous photo underwent extensive color correction to make the planets more visible. The earth is a barely noticeable point on the lower right under the rings

Cassini's final adventure

Cassini is often called the ideal space mission. The device operated well beyond its nominal four-year lifespan and completed all tasks without major incident. But, alas, any technology has a factor that limits its operating time. In the case of Cassini, these were the fuel reserves necessary for course corrections. Without it, control of the device would have become impossible. An uncontrolled station could crash into one of Saturn's moons and carry terrestrial microbes there. To exclude such a scenario, NASA decided to burn Cassini in the planet’s atmosphere.

But before this, the device had to survive the final adventure - 20 orbits at the outer edge of Saturn's rings, and then another 22 orbits between the planet's atmosphere and the inner edge of its rings. No vehicle has ever dived into this gap. The maneuver was considered very dangerous, but since the mission was already close to completion, NASA decided to take the risk.

Artist's impression of Cassini's final flight

As before, Cassini brilliantly completed all its tasks. He collected data that should solve the main mystery of Saturn - the age and origin of its rings. According to one version, they formed along with the planet. According to another, the rings are much younger and appeared as a result of the recent (by cosmic standards) destruction of one of Saturn’s moons. Cassini data will be analyzed for many more months, but preliminary results so far speak in favor of the second version.

Cassini had one last task to complete. During reentry, the vehicle used thrusters to keep its antenna pointed at Earth for as long as possible. Already falling apart, Cassini still continued to transmit data on the composition of the gas envelope and the magnetic field of Saturn. Even here, the device managed to exceed the target, surviving in such extreme conditions 30 seconds longer than the simulations predicted. At 11 hours 55 minutes 46 seconds universal time, NASA's deep space communications complex in Canberra received the last signal from Cassini. By that time, the device itself had already disintegrated into fragments and turned into a flaming meteor.

NASA said goodbye to Cassini without mourning. Still, this is not a disaster, but the end of a successful mission (NASA/Joel Kowsky)

The ending of the mission evoked conflicting emotions: pride, admiration, sadness and emptiness. Cassini has been in operation for so long that it is difficult to remember a time when it was not there. You can imagine what the mission participants, who had been working on the project since the 1980s, experienced as they watched the device’s signal disappear.

It becomes even sadder when you realize that you will have to wait at least a decade for the next such expedition to the distant planets of the solar system. Unfortunately, space exploration is a slow business, and there is no mission on the horizon comparable to Cassini's ambition. One can only be consoled by the fact that many new discoveries will be made based on the data collected by the station.

Cassini's legacy will live on for a very long time. The photographs he took of Saturn and its moons will remain with us forever. Thanks to Cassini, we were able to see in all their glory these cosmic bodies that were previously just dots in the sky for us.

About a space mission that was twice in jeopardy, but thanks to the common sense and judgment of American officials, it finally took place.

On September 15, 2017, the Cassini orbiter, one of the greatest examples of collaboration between an international team of scientists, will end its mission to study Saturn and its system. At approximately 15:00 Moscow time, the probe will enter the upper layers of the atmosphere of the gas giant, disintegrate into small pieces and burn up like a meteor. However, until the very end, Cassini will try to keep its antenna pointed at Earth in order to transmit “home” the latest data about the inner world of the “Lord of the Rings”.

Over almost 20 years of work in space, the interplanetary station has made many discoveries. Thanks to Cassini, we understood how the rings of Saturn were formed and what they consist of (in fact, the device confirmed the hypothesis of the American scientist Larry Esposito, who said that the rings consist of icy pieces of destroyed small satellites of the planet), we learned about the presence of an atmospheric phenomenon in the gas giant — an unusual hexagon, learned about the existence of thunderstorms and polar vortexes; The device helped to discover on the satellite of this giant planet - Enceladus - an ocean of liquid water hidden under a layer of thick ice, and also to explain the reason for the “two-facedness” of another satellite of Satun - Iapetus (one of its hemispheres shines like snow, the other black seems to be covered with soot).

Without exaggeration, we will say that Cassini completely changed our understanding of the appearance of Saturn and the structure of its satellites. To quote Jim Green, head of planetary exploration at NASA, in the tradition of great space explorers, this scientific vehicle has blazed a new trail, showing us new wonders and where our curiosity may take us in the near future.

How the Cassini-Huygens mission began

In the late 1970s and early 1980s, three NASA spacecraft (Pioneer 11, Voyager 1, Voyager 2) flew past Saturn and transmitted to the space agency's mission control center a series of photographs of this planet and its satellites taken from a relatively close distance . Scientists have been able to see the rings of a gas giant for the first time. It turned out that they consist of hundreds of thousands of small pieces of unknown origin and very different diameters, and some of the rings are even intertwined in some inexplicable way! What else amazed scientists was the satellite of the gas giant Titan. It was significantly different from the idea of ​​it that previously existed in the minds of scientists. It was a cold world, larger than Mercury, with a very dense atmosphere, so thick that none of the three probes was able to see its surface.

The data obtained only fueled the interest of astronomers in the “Lord of the Rings” and his companions. In 1982, a working group was created, which included representatives of NASA and ESF (European Science Foundation), to plan the program for the next “flagship” mission after Voyagers. At the group meeting, it was decided to jointly build a spacecraft to study Saturn and its system.

According to the scientists' plan, the device was supposed to consist of two parts: the Cassini orbital station (named after the French astronomer Giovanni Cassini, who in 1665 discovered four satellites of Saturn: Iapetus, Dione, Tethys, Rhea) and the Huygens lander ( named after the Dutch astronomer Christiaan Huygens, who discovered Titan and the rings of Saturn), intended for landing on Titan. The cost of the project was estimated at $2.5 billion, but then grew to almost $3.6 billion. NASA contributed most of the funds, about $3 billion.

Thus, the Cassini-Huygens project became one of the most expensive in the history of NASA and one of the first in which not only specialists from the United States took part, but also their colleagues from ESA (European Space Agency) and ASI (Italian Space Agency).

In 1984, work began on the creation of the Cassini-Huygens system, and in 1992 and 1994 the first problems arose. The mission was in jeopardy; the US Congress did not want to allocate additional money for the development of the research apparatus. But the first American woman astronaut, Sally Ride, who had enormous influence at that time, and her colleagues managed to convince congressmen, and the funds went into the NASA budget.

Three years later, in 1997, the Titan IVB launch vehicle was already standing at the Cape Canaveral Space Center in Florida, ready to launch into orbit one of the largest research vehicles ever built by humans.

Device design

The space explorer, whose mission is to reveal the greatness of Saturn, the origin, composition of its rings and the nature of its satellites, is a device 10 meters high and weighing about 6 tons at the time of launch (half the weight was fuel). It is equipped with 18 scientific instruments and cameras (12 installed on the station and 6 on the lander) capable of making precise measurements in any atmospheric conditions and photographing in different light spectra.

Cassini orbital station with the help of special filters, he can “see” Saturn and its moons at wavelengths that are inaccessible to the human eye (such filters help specialists find out exactly how the planet’s atmosphere reflects and absorbs certain wavelengths of sunlight). In addition, instruments on board the station can “feel” magnetic fields and tiny dust particles that humans would never feel.

Connection. The station can transmit data and receive information through a four-meter high gain antenna (HGA), or, in case of emergency, through one of two low gain antennas (LGA). All three instruments were developed by the Italian Space Agency.

The main antenna (HGA) is also used as an instrument to handle radio signals passing through the atmosphere of Titan, Saturn and the planet's rings. These signals are studied to determine the size of the ring particles and the atmospheric pressure of the gas giant.

Engines. The station has two sets of jet engines: two main ones for reaching the designed trajectory, and 16 spare low-thrust ones for probe orientation, small maneuvers and orbit correction. The Earth's envoy spent only 1% of the time on his way to Saturn with his engines running.

Generators. During the creation of Cassini, it was decided that the station would not operate on solar energy (due to the distance of Saturn from our star, solar panels are ineffective), but on the basis of radioactive plutonium-238. For this purpose, three radioisotope thermoelectric generators were developed, which contained 32 kg of radioactive plutonium. Experts considered that such a reserve of fuel should be enough until the end of the mission for maneuvers, braking, entering orbits, and providing energy for instruments.

Direct and remote sensing devices. These instruments are a variety of spectrometers and radars that can take measurements from great distances. They measure:

— electric charges of particles;
— plasma and solar wind in the planet’s magnetosphere;
— direction, size and speed of movement of dust grains located near the gas giant;
- infrared waves emanating from cosmic bodies to find out the temperature and composition of these objects;

— study the molecules of Saturn’s ionosphere;
— scan the surface of the gas giant’s satellites and model maps of this surface, measure the height of mountains and canyons on it using radio signals.

Magnetometer. The station has a special rod that can extend forward by 11 meters. This is a magnetometer. It is designed to measure the magnetic field around Saturn and compile a 3-D map of the planet’s magnetosphere.

Computer. All scientific instruments installed at the station are equipped with their own microcomputers. The main computer, the GVSC 1750A, developed by IBM, is protected from errors and failures by a multi-stage protection system.

Orientation system. Like the ancient sailors, the space probe navigates by the stars. In memory of the station's sensors, the NASA team laid out a star map of five thousand stars. Orientation in outer space occurs as follows: every second, sensors take at least ten wide-angle photographs of the starry sky, compare them with a map stored in memory, and determine the location of the device in outer space. Information about the movement of the station is updated at a frequency of 100 times per second.

Huygens lander- the brainchild of the European Space Agency. It was a device 2.7 meters wide and weighing about 320 kilograms with a thick protective shell that saved it from overheating during the descent to Titan.

Huygens was assembled from two parts: a protective module and a descent module. The protective module consisted of equipment responsible for separation from Cassini and a heat shield that prevented overheating when entering Titan's atmosphere. The descent module was equipped with three parachutes responsible for the descent, and a series of scientific instruments:

HASI- an instrument for measuring the atmosphere. The device was equipped with special sensors that, at the time of Huygens' descent, measured the physical and electrical properties of Titan's atmosphere;

DWE— a device for measuring wind speed on the surface of Saturn’s satellite;

DISR- a device for measuring the radiation balance (or imbalance) of Titan's thick atmosphere;

GCMS- the device was a universal gas chemical analyzer that identified and measured chemicals in Titan's atmosphere;

ACP— the instrument was intended to analyze aerosol particles extracted from Titan’s atmosphere;

SSP— a set of sensors designed to determine the physical properties of the surface of Titan at the point of descent. These sensors determined whether the surface was solid or liquid.

Path to Saturn

The Cassini-Huygens mission was launched on October 15, 1997. To launch such a heavy device into orbit, we recall that its weight was about 6 tons, specialists used one of the most powerful launch vehicles at that time, Titan IVB.

To give the Earth's envoy the required flight direction and the required starting speed, an additional Centaurus upper stage was placed between the rocket and the probe.

Instead of a direct route to Saturn (in this case, the device would need to be “filled” with 68 tons of additional fuel - a burden that no rocket in the world could handle), it was decided to pave a more complex route for the station: with two gravity maneuvers around Venus in 1998 and 1999, one near Earth in August 1999, and another near Jupiter in 2000. Each maneuver gave Cassini additional acceleration (due to the planet's own motion and gravitational attraction), which allowed the device to reach Saturn with almost zero fuel consumption. The only disadvantage of this method of transportation is time; using the gravity maneuver, scientists lost, on average, about four years, but this is a small price, given the importance of the mission.

Cassini spent almost the entire journey to Saturn with the instruments turned off; they “woke up” only when the device flew close to the planets or their satellites in order to capture these objects. During its gravity maneuver near Jupiter, the probe took about 30,000 photographs of this planet.

In January 2004, the NASA team gradually began to bring the device out of hibernation, turning on more and more instruments. As it approached Saturn, Cassini took stunning images of the planet. The cameras saw the majestic Saturn, whose shadow lay evenly on the rings of the planet. Earthlings have never seen the “Lord of the Rings” like this.

Cassini reached its destination on July 1, 2004. The device slipped between two thin outer rings F and G, and the station began to slow down, one of its main engines turned on, which worked for about 100 minutes, spending only 850 kg of fuel. During deceleration, Cassini was deployed in such a way that its main antenna served as a kind of protection for the apparatus’s fragile instruments from tiny dust particles. About 100 thousand hits were recorded on the station's body, but, fortunately, no serious collisions occurred, and the equipment remained undamaged.

When the engine stopped, it became clear that the scientists' dream had come true - the device ended up in Saturn's orbit safe and sound. The seven-year journey to the gas giant ended, and the station began exploring the planet and its moons.

Titan and the descent of the Huygens module

Cassini was not the first spacecraft to visit the planetary system of Saturn (Pioneer-11 and Voyagers did so before it), but it was the first to stay there. That is why the station carried with it unique equipment - the Huygens descent module. He was supposed to land on Saturn's largest moon Titan and conduct a series of studies.

Cassini's first encounter with Titan occurred the day after the vehicle entered orbit around Saturn. This was a zero flyby at a distance of almost 400,000 km from the satellite, a kind of “terrain reconnaissance” in front of the Huygens branch. True, Cassini began filming Titan back in May, when the station was just approaching The Lord of the Rings. Photography in the infrared range made it possible to identify some relief details on the satellite covered with a curtain of dense clouds. However, scientists were unable to understand what the light and dark spots in the photographs were. It was impossible to even distinguish where the hills were and where the depressions were.

Another, this time closer encounter with the giant satellite took place in October, when Cassini completed its first orbit around Saturn. This rapprochement has become more effective. The device approached Titan at a distance of 1200 km, which is 300 times closer than when it first “acquainted” with the object. The high-resolution photographs were simply mesmerizing. Titan appeared before scientists in all its glory. For the first time, experts saw what was under the veil of its dense atmosphere. The photo showed relief details, spots the size of a continent, reminiscent of the surface of the sea with bays and islands. This region was named Xanadu, its origin and geography still remains a mystery.

It was in this area with difficult terrain that Huygens was supposed to land. To land the module, Cassini again needed to approach Titan, this time at a distance of just over 2,000 kilometers. On December 25, Huygens was “shot” from Cassini, and on January 15, it “landed” on the surface of Saturn’s largest satellite.

The lander became the first man-made object to make a soft landing in the outer solar system.
During the descent, which took 21 days, the terrain began to be recognized only at an altitude of 74 km, and when the first images taken by the module at the hour of landing were received, scientists were very surprised. For example, in the photo they found dark drainage channels, indicating that methane rivers once flowed into them. It was found that Titan has large seas, although only at the poles.

The module was also able to record the sounds of wind on Titan, thanks to a microphone installed on board.

In total, Huygens transmitted more than 500 megabytes of information to Cassini; unfortunately, most of the data was lost due to a computer system failure.

The module worked on the surface of Titan for 72 minutes 13 seconds - that’s how long Cassini received signals from Huygens, then the orbital station disappeared over the horizon, and the signals stopped coming.

Enceladus

During its mission, Cassini was able to study Saturn's sixth largest moon, Enceladus, which attracted the attention of scientists because of the amazing geysers, the ejected substances of which became the main material for Saturn's E ring. These jets appear from the so-called cryovolcanoes, emitting water and volatile substances instead of lava. Cassini has identified more than 100 of these geysers, which emit 200 kg of water into space every second. Some of it settles on the surface of Enceladus in the form of snow, and some “flows” into the E ring. These geysers show that Enceladus is a geologically active world, heated from the inside. Since heating occurs at depth and there is ice on the surface, this means that the satellite must have deposits of water, which can be located in the subsurface ocean and have a depth of a couple of tens of kilometers.

The presence of an ocean of water below the surface may mean that Enceladus has everything it needs to begin life.

Other Cassini discoveries

In 2010, NASA management announced that despite the fact that the device’s service life had almost expired, it would continue to operate in Saturn’s orbit for another seven years, until 2017. During this time, the station made many discoveries.

1. Cassini collected a lot of useful data about Titan. He determined the location of hydrocarbon deposits, found out that the weather on Titan is temporary, and that most of its surface consists of frozen water. Cassini helped scientists understand that Titan is a very interesting world for research with a thin atmosphere, deposits of liquid methane and, probably, the presence of liquid water.

2. On Saturn’s other moons Dione and Rhea The automatic station found tectonic formations - cliffs and ice ridges. Cassini also discovered on these two satellites a rarefied atmosphere consisting of carbon dioxide and oxygen.

3. The interplanetary station helped scientists explain the “two-faced” effect of Iapetus- the third largest satellite of Saturn and discovered on its surface an unusual mountain range more than 13 km high and 20 km wide, encircling the satellite for almost 1300 km.

This satellite haunted astronomers for a long time. Scientists tried to understand the reasons why one pole of Iapetus is black and the other white. Cassini lifted the veil of secrecy. It turned out that such differences in color were due to dust. Meteorites that fall on the surface of the distant satellites of Saturn “knock it out” from there, and it settles on the leading hemisphere of Iapetus, that is, on the hemisphere with which it moves forward in its orbit. Dust-covered areas heat up more than neighboring regions, and the ice from them evaporates and condenses where the surface temperature is lower: on the trailing side and in the circumpolar regions.

Cassini's grand finale

The NASA team has prepared a very exciting ending for the Cassini mission. After 20 years of service, the device will burn up in Saturn's atmosphere. This will happen, according to scientists, on September 15, 2017. This ending was chosen deliberately by experts. The fact is that when Cassini runs out of all its fuel, its orbit will become less and less predictable, which means there will be a risk that the probe could collide with one of the giant’s two satellites - Enceladus or Titan, and bring living people onto them organisms. And as we know, these two objects are very active geological worlds that may have all the necessary conditions for the development of earthly life.

On April 26, 2017, the interplanetary station began performing a series of 22 orbits between Saturn and its rings, gradually approaching the gas giant's upper atmosphere. At the hour of its final flyby, the craft will plunge into Saturn, attempting to keep its antenna pointed at Earth while it transmits its final message. Then the journey will end, and Cassini will become part of the gas giant: the station will disintegrate into debris and burn.

At the time of this writing, Cassini has traveled a total of 7.9 billion kilometers and managed to transmit 635 gigabytes of data.

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September 15, 2017 at 04:55 PDT (11:55 UTC) the Earth stopped hearing the signal from the Cassini radio transmitter. Having completed an almost twenty-year flight and having worked for more than 13 years in the Saturn system, the American spacecraft entered the planet’s atmosphere, transmitting unique scientific data until the last second.

Cassini was launched on October 15, 1997 and entered orbit around Saturn on July 1, 2004. Over the course of 13 years, it made 293 orbits around the planet and made 162 close flybys of its moons. The device mapped their surfaces and measured their chemical composition, tracked the evolution of seasonal processes on Saturn and Titan, and studied the planet's rings, its magnetosphere, charged particles and waves in cosmic plasma.

A brief review of Cassini’s orbital “tour,” which lasted nine years longer than originally planned and consisted of several successive missions, was made in NK No. 7, 2017.

The "Grand Finale" of Cassini's twenty-year journey was planned seven years before it was to take place. The decision to send the device into the atmosphere of Saturn was due to fears of contamination of the planet's moons by terrestrial microorganisms - especially Enceladus with its subglacial ocean, from which polar geysers erupt. A meeting with representatives of the earth's biosphere, which could survive in a viable state on the spacecraft's structural elements, would distort the appearance of local life, if any.

Last five months

The final phase of the expedition began during Cassini's S99 flight program, which began on April 11. From May 25 to July 9, the command sequence S100 was practiced, and from July 10 to the end - S101, which included 10,657 individual commands.

On April 22, 2017, the last target flyby of Titan took place with a gravity maneuver, as a result of which the lowest point of the spacecraft’s orbit shifted under the ring system. Now the device had to make 22 orbits with an inclination from 62.4° to 61.7° with a period of 6.4–6.5 days, each time passing at the periapsis between the visible surface and the rings of Saturn and moving away approximately 1.27 million km from the planet at the apocenter.

The first “dive” took place on April 26 at the 271st orbit, when Cassini flew at an altitude of 2800 km above the cloud tops of the planet at a maximum speed of 33.957 km/s. The area under the rings turned out to be practically free of dust - the RPWS device for recording radio and plasma waves noted only a few particles 1 µm in size and below. This gave rise to hope for the success of all subsequent flybys and for the implementation of a scientific program that included mapping the gravitational and magnetic field of the planet, photographing and probing the rings and surface of Saturn from a minimum distance, and direct measurements of the composition of the upper atmosphere.

Of the 17 first flights, the lowest was on May 15 at an altitude of 2660 km, and the highest was on May 28 at an altitude of 3900 km above the clouds of Saturn. It also became the deepest penetration of the spacecraft into the inner ring D. To change the altitude of the periapsis between individual orbits, Titan flybys on May 23 at a distance of 118,000 km and on July 10 at a distance of 264,000 km, as well as two small corrections, were used. On May 10, the OTM-471 maneuver was carried out with a speed increment of only 21 mm/s by turning on the engines for 14 seconds. The last correction of OTM-472 was more significant - on July 15, the engines worked for 153.125 seconds and changed the spacecraft speed to 143.64 mm/s.

On August 11, Cassini passed 195,000 km from Titan, due to which the altitude of the spacecraft’s pericenter decreased by 1,200 km. Therefore, in the last five flights of the spacecraft, it “struck” along the very edge of the atmosphere at an altitude of 1710 km to 1630 km, and to maintain orientation, not flywheels were used, but low-thrust liquid propellant engines. The exact height of each span has not been published; We only know that the third of them was the record low on August 27. These five orbits served as rehearsals for Cassini's final entry into the atmosphere.

When crossing the plane of the rings at speeds from 33.6 km/s to 35.0 km/s, Cassini, as a rule, oriented its highly directional antenna forward along the velocity vector to protect the more “sensitive” parts from dust particles. When “diving” into the D ring on the 276th and 277th orbits, however, there was little dust, and on the 281st it was decided not to do this; the device passed safely through the lowest section of the ring and was not damaged. Cassini carried out most of its flights in autonomous mode with subsequent “reporting” of the results, but on orbits 273, 274, 275, 278, 280 and 284 it transmitted directly to Earth while crossing the plane of the rings.

Already in its first flyby, the ISS camera captured images of Saturn with a resolution 10 times better than in the previous 13 years. Photographing the planet, rings and satellites and probing them with VIMS, CIRS and UVIS spectrometers in various combinations was carried out on all subsequent orbits. In the rings, of particular interest were various edge effects, disturbances and small instabilities, known under the code name “propellers”. They were named after the great pilots of the 20th century - Bleriot, Santos-Dumont, Earhart.

Of the satellites, Titan and Enceladus were most often observed, especially its southern polar region with geysers, but there was time to photograph Dione at the 280th orbit and for very small satellites. The tiny Bebhionn - a double object with a diameter of only 6 km, extending at the apocenter 25 million km from Saturn - was captured on orbits 272, 273, 276, 280 and 282. The twice larger 14-kilometer Kiviuk, which is also suspected of a binary nature, photographed on July 28, August 9 and 16, and Trümr on August 23 and September 3–4. In addition, on June 6, spectrometry of the star ε Orionis was carried out during an eclipse by its satellite Tethys (Tethys).

On August 10 and 16, the ISS camera observed Neptune in the sky near Kiviuk. This meant that Cassini was able to image eight of the nine planets (including Pluto, but excluding Mercury).

The radio complex was used to determine the characteristics of Saturn’s gravitational field and to illuminate the rings, and the CDA cosmic dust analyzer tried to “catch” their matter. The RADAR device scanned them with a resolution from 4 km to 100 m on the 276th and 277th orbits, and also studied the atmosphere of Saturn: on the 288th orbit in passive mode, and on the 290th and 292nd in active mode . Scientists were interested in ammonia concentrations in the atmosphere below the ammonia cloud layer as evidence of Saturn's weather.

The 292nd orbit, also the 22nd in the Grand Finale series, began with the passage of the apocenter September 5 at 18:47 UTC onboard time. 9th of September at 00:09–00:14, the device sequentially passed the plane of the rings and the pericenter of the orbit and, 13 hours later, began transmitting the received information to Earth. 11 September, towards the end of its orbit, Cassini experienced the pull of Titan. The flight was one of the distant ones - at 19:04 UTC the device passed 119,049 km above the surface of the satellite - but the gravitational influence of Titan reduced the speed of the spacecraft by 29 m/s, as a result of which the pericenter of the orbit plunged into the atmosphere of Saturn.

The 293rd orbit has begun 12-th of September at 05:27 UTC onboard time. Over the past two days, the spacecraft has imaged Titan and Enceladus, which is setting beyond Saturn's northern horizon, the planet and individual features of its rings, including a compaction with the code name Peggy on the outer edge of the A ring, which may represent a forming small satellite. Finally, the VIMS spectrometer and other optical instruments observed the area of ​​the upcoming Cassini fall. The last photo was taken September 14 at 19:58 UTC.

At 21:45 UTC, according to the time the signal arrived on Earth, which corresponded to 20:22 onboard time, the last 14.5-hour communication session began. Cassini transmitted information at a frequency of 8.43 GHz at a speed of 66,360 bps, freeing its solid-state storage device from recorded data within 11 hours. The spacecraft signal reached the Long-Distance Network station in Goldstone with a power level of -128.06 dB, that is, 1.56.10-19 W. The latest photographs were accepted and promptly posted in raw form on the Cassini project website.

When you have finished resetting your data, September 15th at 07:14 onboard time, the spacecraft began a five-minute turn to such a position that the mass spectrometer of ions and neutral atoms INMS was located at the front of the spacecraft in the direction of flight and could directly measure the composition of the upper atmosphere of Saturn and its changes in altitude. On Earth, the 70-meter DSS-43 antenna near Canberra, capable of supporting reception at a speed of 124,426 bps, took over the baton. Cassini, however, immediately reconfigured the board so that in the last three and a half hours, scientific information was sent to Earth at a speed of 27,650 bps in near real time - just a few seconds after it was received on board. The transmission was carried out in the X- and S-band with reception on the 70-meter and, by way of reservation, on one of the 34-meter antennas in Australia. In addition, Doppler observations were carried out by the New Norcia station of the European Space Agency.

The instructions to the device for the final stage of the flight were simple. Cassini approaches the planet from the northern hemisphere. The entry point into the atmosphere is on the day side, 10° north of the equator. The device must carry out measurements with eight of 12 instruments (INMS mass spectrometer, CIRS and UVIS spectrometers, magnetospheric and plasma instruments MIMI, RPWS, MAG, CDA cosmic dust sensor and a highly stable radio complex generator) and transmit data to the last. This opportunity will be provided by on-board liquid propellant rocket engines with a thrust of 0.5N, supporting the orientation of the highly directional antenna to the Earth within ±0.1° from the specified one due to the issuance of short pulses.

Ballistics experts predicted that Cassini would feel the effects of Saturn's thin upper atmosphere at an altitude of 1915 km above the cloud tops and above a pressure level of 1 atm. Like all such boundaries, it was to a certain extent conditional. When flying outside the atmosphere, it is enough for the engines to fire once every few minutes, compensating for only a slight turning moment from the planet’s gravitational field. With increasing density of the gas shell and velocity pressure, the turning torque and operating frequency should increase. The conditional entry point was taken to be the moment when the duty cycle—the proportion of time during which liquid-propellant rocket engines operate—reaches 10%.

To cope with the effect of the atmosphere on the protruding elements of the Cassini structure, most notably the 11-meter magnetometer boom, the liquid-propellant rocket engines will gradually increase the duty cycle from 10 % to 100 %. This stage will take about a minute, during which the earthly vehicle will descend along a gentle trajectory to the 1500 km mark. Here the disturbing moments from the oncoming flow will become stronger than the stabilizing impulses of continuously operating engines. The device will begin to turn, going into an uncontrolled somersault, and the Earth will move away from the axis of its antenna. In another thirty seconds, the Earth probe will begin to collapse, and a couple of minutes later the planet’s atmosphere will absorb its debris.

The latest published forecast was that Cassini would begin re-entry on September 15 at 03:31 PDT (10:31 UTC) onboard time and lose orientation a minute later. 83 minutes 27 seconds after this, at 04:55:16 PDT (11:55:16 UTC), the last signal from the spacecraft will reach the Earth, and it will no longer hear Cassini.

In general, this prediction came true: the device was able to withstand the atmosphere of Saturn for 91 seconds, and in the last 20 seconds the engines worked at 100 % of their capabilities. The useful signal in the X-band with scientific information was interrupted at 11:55:39, and in the S-band at 11:55:47. According to telemetry data, it was clear that in these last 8 seconds Cassini began to slowly turn back. Then telemetry disappeared from the signal received on Earth and only the carrier frequency remained, but after 24 seconds it also stopped arriving. Having buried itself in the atmosphere of Saturn at an altitude of 1391 km at a speed of 34.449 km/s, the earthly apparatus ceased to exist.

“This is the final chapter of an amazing mission, but it is also a new beginning,” said NASA Associate Administrator Dr. Thomas Zurbuchen. “Cassini’s discovery of ocean worlds on Titan and Enceladus changed everything and shook our understanding of amazing places to look for life beyond Earth to its core.”

“Cassini may have left us, but its scientific gifts will keep us busy for many years to come,” said JPL project scientist Dr. Linda J. Spilker. “We have only scratched the surface of what we can learn from the mountain of data he has sent us over his lifetime.”

“The Cassini management team did an absolutely stellar job of bringing the spacecraft to its fitting end,” said project manager Earl H. Maize. “From designing the trajectory seven years ago to navigating 22 heart-stopping dives between Saturn and its rings, it was this fantastic group of scientists and engineers who came up with a fitting end to a great project.”

Over 20 years of flight, Cassini covered 7.9 billion km, received and executed 2.5 million commands as part of 101 stages of the flight program, carried out 360 maneuvers and corrections*, discovered six satellites of Saturn, took and transmitted 453,048 images to Earth, and a total of 635 GB of scientific information , on the basis of which 3948 scientific articles were published by the end of the expedition.