Let's say the earth ends. The sun is about to explode as an asteroid the size of Texas is approaching the planet. The major cities are populated by zombies, and in the countryside, farmers are hard at work planting corn because other crops are dying. We urgently need to leave the planet, but the trouble is that no wormholes have been found in the Saturn region, and superluminal engines from far, far away galaxy didn't bring. The nearest star is more than four light years away. Will humanity be able to achieve it with modern technology? The answer is not so obvious.

It is unlikely that anyone would argue that a global environmental catastrophe that will endanger the existence of all life on Earth can only happen in the cinema. Mass extinctions have occurred on our planet more than once, during which up to 90% died. existing species. The Earth experienced periods of global glaciation, collided with asteroids, went through bursts of volcanic activity.

Of course, even during the most terrible disasters, life never completely disappeared. But the same cannot be said about the species that dominated at that time, which were dying out, making way for others. Who is the dominant species now? Exactly.

It is likely that the opportunity to leave native home and go to the stars in search of a new one can someday save humanity. However, it is hardly worth hoping that some cosmic benefactors will open the way to the stars for us. It is worth figuring out what our theoretical possibilities are to reach the stars on our own.

space ark

First of all, traditional chemical propulsion engines come to mind. IN currently four terrestrial vehicles (all of which were launched back in the 1970s) managed to reach the third space velocity, sufficient to leave the solar system forever.

The fastest of them, Voyager 1, has moved away from Earth at a distance of 130 AU in the 37 years since its launch. (astronomical units, that is, 130 distances from the Earth to the Sun). Each year, the device overcomes approximately 3.5 AU. The distance to Alpha Centauri is 4.36 light years, or 275,725 AU. At this rate, it would take the spacecraft almost 79,000 years to reach the neighboring star. To put it mildly, the wait will be long.

Photo of the Earth (above the arrow) from a distance of 6 billion kilometers, taken by Voyager 1. The spacecraft traveled this distance in 13 years.

You can find a way to fly faster, or you can just accept and fly for several thousand years. Then only the distant descendants of those who set off on the journey will reach the end point. This is precisely the idea of ​​the so-called ship of generations - the space ark, which is a closed ecosystem designed for a long journey.

In fiction, there are many different stories about the ships of generations. They have been written about by Harry Garrison (Captured Universe), Clifford Simak (Generation Achieved), Brian Aldiss (Nonstop), from more contemporary writers- Bernard Werber ("Star Butterfly"). Quite often, the distant descendants of the first inhabitants generally forget about where they flew from and what is the purpose of their journey. Or even begin to believe that the whole existing world comes down to a ship, as, for example, is told in Robert Heinlein's novel Stepchildren of the Universe. Another interesting story featured in the eighth episode of the third season of the classic " Star Trek where the crew of the Enterprise tries to prevent a collision between a generational ship whose inhabitants have forgotten their mission and the inhabited planet it was headed for.

The advantage of the generation ship is that this option will not require fundamentally new engines. However, it will be necessary to develop a self-sustaining ecosystem that can exist without outside supplies for many thousands of years. And do not forget that people can simply kill each other.

Conducted in the early 1990s under a closed dome, the Biosphere-2 experiment demonstrated a number of dangers that can lie in wait for people during such travel. This is the rapid division of the team into several groups hostile to each other, and the uncontrolled reproduction of pests, which caused a lack of oxygen in the air. Even the usual wind, as it turned out, plays essential role- without regular rocking, trees become brittle and break.

To solve many of the problems of a long flight will help technology, immersing people in prolonged suspended animation. Then neither conflicts are terrible, nor boredom, and the life support system will require a minimum. The main thing is to provide it with energy for long term. For example, with the help of a nuclear reactor.

Related to the theme of the ship of generations is a very interesting paradox called Wait Calculation, described by scientist Andrew Kennedy. According to this paradox, new, more quick ways movement, allowing later ships to overtake the original settlers. So it is possible that by the time of arrival, the destination will already be overpopulated by the distant descendants of the colonialists who set off later.

Installations for suspended animation in the movie "Alien".

Riding on a nuclear bomb

Suppose we are not satisfied that the descendants of our descendants will reach the stars, and we ourselves want to expose our face to the rays of an alien sun. In this case, you can not do without a spacecraft capable of accelerating to speeds that will deliver it to a neighboring star in less than one human life. And here the good old nuclear bomb will help.

The idea of ​​such a ship appeared in the late 1950s. The spacecraft was intended for flights inside the solar system, but it could well be used for interstellar travel. The principle of its operation is as follows: a powerful armored plate is installed behind the stern. From the spacecraft in the direction opposite to the flight, low-power nuclear charges are evenly ejected, which are detonated at a small (up to 100 meters) distance.

The charges are designed in such a way that most of the explosion products are directed to the tail of the spacecraft. The reflecting plate takes over the impulse and transmits it to the ship through the shock absorber system (without it, overloads will be fatal for the crew). The reflective plate is protected from damage by a flash of light, gamma radiation and high-temperature plasma by a coating of graphite lubricant, which is re-sprayed after each explosion.

The NERVA project is an example of a nuclear rocket engine.

At first glance, such a scheme seems insane, but it is quite viable. During one of the nuclear tests on Eniwetok Atoll, graphite-coated steel spheres were placed 9 meters from the center of the explosion. After testing, they were found intact, proving the effectiveness of the graphite protection for the ship. But signed in 1963 "Treaty on the prohibition of nuclear weapons tests in the atmosphere, outer space and under water" put an end to this idea.

Arthur Clark wanted to equip spaceship Discovery One from the movie " space odyssey 2001 "something like a nuclear explosive engine. However, Stanley Kubrick asked him to abandon the idea, fearing that the audience would consider it a parody of his film Dr. Strangelove, or How I Stopped Being Afraid and Loved the Atomic Bomb.

What speed can be developed with a series of nuclear explosions? Most of the information exists about the Orion explosive project, which was developed in the late 1950s in the United States with the participation of scientists Theodore Taylor and Freeman Dyson. It was planned to accelerate the 400,000-ton ship to 3.3% of the speed of light - then the flight to the Alpha Centauri system would have lasted 133 years. However, according to current estimates, a ship can be accelerated to 10% of the speed of light in a similar way. In this case, the flight will last approximately 45 years, which will allow the crew to survive before arriving at their destination.

Of course, the construction of such a ship is a very expensive business. Dyson estimates that Orion would have cost about $3 trillion in today's dollars to build. But if we find out that a global catastrophe will threaten our planet, then it is likely that a ship with a nuclear pulse engine will become humanity's last chance for survival.

gas giant

A further development of the Orion ideas was the Daedalus unmanned spacecraft project, which was developed in the 1970s by a group of scientists from the British Interplanetary Society. The researchers set out to design an unmanned spacecraft capable of reaching one of the nearest stars during a human lifetime, conducting scientific research and transmitting the information received to Earth. The main condition for the study was the use in the project of either existing or foreseen technologies in the near future.

The target of the flight was Barnard's Star, located at a distance of 5.91 light years from us - in the 1970s it was believed that several planets revolved around this star. We now know that there are no planets in this system. The developers of the Daedalus aimed to create an engine that could deliver the ship to its destination in a time not exceeding 50 years. As a result, they came up with the idea of ​​a two-stage apparatus.

The necessary acceleration was provided by a series of low-power nuclear explosions occurring inside a special propulsion system. Microscopic granules from a mixture of deuterium and helium-3, irradiated by a high-energy electron beam, were used as fuel. According to the project, up to 250 explosions per second should have occurred in the engine. The nozzle was a powerful magnetic field created by the ship's power plants.

According to the plan, the first stage of the ship worked for two years, accelerating the ship to 7% of the speed of light. The Daedalus then jettisoned its spent propulsion system, shedding most of its mass, and launched its second stage, which allowed it to accelerate to its final speed of 12.2% of light. This would have made it possible to reach Barnard's Star 49 years after launch. It would take another 6 years to transmit a signal to Earth.

The total mass of the Daedalus was 54,000 tons, of which 50,000 were thermonuclear fuel. However, the alleged helium-3 is extremely rare on Earth - but it is abundant in the atmospheres of gas giants. Therefore, the authors of the project intended to produce helium-3 on Jupiter using an automated plant "floating" in its atmosphere; the entire mining process would take approximately 20 years. In the same orbit of Jupiter, it was supposed to carry out the final assembly of the ship, which would then launch to another star system.

The most difficult element in the whole Daedalus concept was precisely the extraction of helium-3 from the atmosphere of Jupiter. To do this, it was necessary to fly to Jupiter (which is also not so easy and fast), establish a base on one of the satellites, build a plant, store fuel somewhere ... And this is not to mention the powerful radiation belts around the gas giant, which additionally would make life difficult for technicians and engineers.

Another problem was that the Daedalus was unable to slow down and orbit Barnard's Star. The ship and the probes it launched would simply pass by the star along a flyby trajectory, overcoming the entire system in a few days.

Now international group of twenty scientists and engineers, acting under the auspices of the British Interplanetary Society, is working on the project of the Icarus spacecraft. "Icarus" is a kind of "remake" of Daedalus, taking into account the knowledge and technology accumulated over the past 30 years. One of the main areas of work is the search for other types of fuel that could be produced on Earth.

At the speed of light

Is it possible to accelerate a spaceship to the speed of light? This problem can be solved in several ways. The most promising of them is an annihilation engine based on antimatter. The principle of its operation is as follows: antimatter is fed into the working chamber, where it comes into contact with ordinary matter, generating a controlled explosion. The ions generated during the explosion are ejected through the engine nozzle, creating thrust. Of all the possible engines, the annihilation engine theoretically allows you to achieve the highest speeds. The interaction of matter and antimatter releases an enormous amount of energy, and the speed of the outflow of particles formed during this process is close to the speed of light.

But then there is the question of fuel extraction. Antimatter itself has long ceased to be science fiction - scientists first managed to synthesize antihydrogen back in 1995. But it is impossible to get it in sufficient quantities. Currently, antimatter can only be obtained with the help of particle accelerators. At the same time, the amount of the substance they create is measured in tiny fractions of grams, and its cost is astronomical sums. For one billionth of a gram of antimatter, scientists from the European Center for Nuclear Research (the same one where the Large Hadron Collider was created) had to spend several hundred million Swiss francs. On the other hand, the cost of production will gradually decrease and may reach much more acceptable values ​​in the future.

In addition, we will have to come up with a way to store antimatter - after all, when it comes into contact with ordinary matter, it is instantly annihilated. One solution is to cool the antimatter to ultra-low temperatures and use magnetic traps to prevent it from coming into contact with the walls of the tank. On this moment The record storage time for antimatter is 1000 seconds. Not years, of course, but taking into account the fact that for the first time antimatter was kept for only 172 milliseconds, there is progress.

And even faster

Numerous science fiction films have taught us that you can get to other star systems much faster than in a few years. It is enough to turn on the warp drive or hyperspace drive, lean back comfortably in your chair - and in a few minutes you will be on the other side of the galaxy. The theory of relativity prohibits travel at speeds faster than the speed of light, but at the same time leaves loopholes to get around these restrictions. If we could tear or stretch space-time, we could travel faster than light without breaking any laws.

The gap in space is more commonly known as a wormhole, or wormhole. Physically, it is a tunnel connecting two distant regions of space-time. Why not use such a tunnel to travel into deep space? The fact is that the creation of such a wormhole requires the presence of two singularities at different points in the universe (this is what is beyond the event horizon of black holes - in fact, gravity in its purest form), which can break space-time, creating a tunnel that allows travelers " cut" path through hyperspace.

In addition, to maintain such a tunnel in a stable state, it is necessary that it be filled with exotic matter with negative energy - and the existence of such matter has not yet been proven. In any case, only a super-civilization can create a wormhole, which will be many thousands of years ahead of the current one in development and whose technologies, from our point of view, will look like magic.

The second, more affordable option is to "stretch" the space. In 1994, Mexican theoretical physicist Miguel Alcubierre suggested that it was possible to change its geometry by creating a wave that compresses the space in front of the ship and expands it behind. Thus, the starship will be in a "bubble" of curved space, which itself will move faster than light, thanks to which the ship will not violate fundamental physical principles. According to Alcubierre himself, .

True, the scientist himself considered that it would be impossible to implement such a technology in practice, since this would require a colossal amount of mass-energy. The first calculations gave values ​​in excess of the mass of the entire existing Universe, subsequent refinements reduced it to "only" Jupiter.

But in 2011, Harold White, head of research group Eagleworks, at NASA, performed calculations that showed that if you change some parameters, then creating an Alcubierra bubble may require much less energy than previously thought, and it will no longer be necessary to recycle the entire planet. White's group is now working on the possibility of an "Alcubierre bubble" in practice.

If the experiments show results, this will be the first small step towards creating an engine that allows you to travel 10 times faster than the speed of light. Of course, a spacecraft using the Alcubierre bubble will travel many tens or even hundreds of years later. But the very prospect that this is actually possible is already breathtaking.

Flight of the Valkyrie

Almost all proposed starship designs have one significant drawback: they weigh tens of thousands of tons, and their creation requires a huge number of launches and assembly operations in orbit, which increases the cost of construction by an order of magnitude. But if humanity still learns to get a large amount of antimatter, it will have an alternative to these bulky structures.

In the 1990s, writer Charles Pelegrino and physicist Jim Powell proposed a design for a starship known as the Valkyrie. It can be described as something like a space tractor. The ship is a bundle of two annihilation engines connected to each other by a heavy-duty cable 20 kilometers long. In the center of the bundle are several compartments for the crew. The ship uses the first engine to gain speed close to light, and the second - to extinguish it when entering orbit around the star. Thanks to the use of a cable instead of a rigid structure, the mass of the ship is only 2100 tons (for comparison, the mass of the ISS is 400 tons), of which 2000 tons are engines. Theoretically, such a ship can accelerate to a speed of 92% of the speed of light.

A modified version of this ship, called the Venture Star, is shown in the movie Avatar (2011), one of whose scientific consultants was just Charles Pelegrino. Venture Star takes off on a journey, accelerating with lasers and a 16-kilometer solar sail, before braking at Alpha Centauri with an antimatter drive. On the way back, the sequence changes. The ship is capable of accelerating to 70% the speed of light and flying to Alpha Centauri in less than 7 years.

Without fuel

Both existing and future rocket engines have one problem - fuel always makes up most of their mass at the start. However, there are designs for starships that will not need to take fuel with them at all.

In 1960, physicist Robert Bassard proposed the concept of an engine that would use hydrogen in interstellar space as fuel for a fusion engine. Unfortunately, as attractive as the idea is (hydrogen is the most abundant element in the universe), it has a number of theoretical problems, ranging from how hydrogen is harvested to a calculated maximum speed that is unlikely to exceed 12% of the speed of light. This means that it will take at least half a century to fly to the Alpha Centauri system.

Another interesting concept is the application of a solar sail. If you build a huge super-powerful laser in Earth orbit or on the Moon, then its energy could be used to disperse a starship equipped with a giant solar sail to sufficiently high speeds. True, according to the calculations of engineers, in order to give a manned ship weighing 78,500 tons a speed of half the speed of light, a solar sail with a diameter of 1000 kilometers would be required.

Another obvious problem with a starship with a solar sail is that it needs to be slowed down somehow. One of her solutions is to release a second, smaller sail behind the starship when approaching the target. The main one will disconnect from the ship and continue its independent journey.

***

Interstellar travel is a very complex and costly undertaking. To create a ship capable of covering space distance in a relatively short period of time is one of the most ambitious tasks facing humanity in the future. Of course, this will require the efforts of several states, if not the entire planet. Now it seems like a utopia - governments have too many worries and too many ways to spend money. A flight to Mars is millions of times easier than a flight to Alpha Centauri - and yet, it is unlikely that anyone will now dare to name the year when it will still take place.

Either a global danger threatening the entire planet, or the creation of a single planetary civilization that can overcome internal squabbles and want to leave its cradle can revive work in this direction. The time for this has not yet come - but this does not mean that it will never come.

On April 12, 2016, the famous British physicist Stephen Hawking and Russian businessman and philanthropist Yuri Milner announced the allocation of $100 million to finance the project Breakthrough Starshot. The goal of the project was to develop technologies for creating spacecraft capable of making an interstellar flight to Alpha Centauri.

Thousands of science fiction novels describe giant photonic starships the size of a small (or large) city, leaving on an interstellar flight from the orbit of our planet (less often, from the surface of the Earth). But, according to the authors of the project Breakthrough Starshot, everything will happen completely differently: on one significant day two thousand of some year, not one or two, but hundreds and thousands of small starships the size of a fingernail and weighing 1 g will start towards one of the nearest stars, Alpha Centauri. And each of them will have the thinnest solar sail with an area of ​​16 m 2 , which will carry the spaceship with ever-increasing speed forward - to the stars.

"Shoot to the Stars"

Project basis Breakthrough Starshot became the article of the professor of physics at the University of California at Santa Barbara Philip Lubin "Plan for interstellar flights" ( A Roadmap to Interstellar Flight). The main stated goal of the project is to make interstellar flights possible already during the lifetime of the next generation of people, that is, not in centuries, but in decades.

Immediately after the official announcement of the program Starshot a wave of criticism from scientists and technical experts in various fields hit the authors of the project. Critical experts noted numerous incorrect assessments and simply "blank spots" in terms of the program. Some comments were taken into account and the flight plan was slightly adjusted in the first iteration.

So, the interstellar probe will be a space sailboat with an electronic module StarChip weighing 1 g, connected by heavy-duty slings to a solar sail with an area of ​​16 m 2, a thickness of 100 nm and a mass of 1 g. Of course, the light of our Sun is not enough to accelerate even such a light structure to speeds at which interstellar travel will not last millennia. Therefore, the main highlight of the project starshot- this is acceleration with the help of powerful laser radiation, which is focused on the sail. According to Lyubin, with a laser beam power of 50–100 GW, the acceleration will be about 30,000 g, and in a few minutes the probe will reach a speed of 20% of the speed of light. The flight to Alpha Centauri will last about 20 years.

Questions without answers: a wave of criticism

Philip Lubin in his article gives numerical estimates of the points of the plan, but many scientists and specialists are very critical of these data.

Of course, in order to work out such an ambitious project as Breakthrough Starshot, years of work are required, and $100 million is not such a big amount for work of this scale. In particular, this applies to ground-based infrastructure - a phased array of laser emitters. Installing such a capacity (50-100 GW) will require a huge amount of energy, that is, at least a dozen large power plants will need to be built nearby. In addition, it will be necessary to remove a huge amount of heat from the emitters for several minutes, and how to do this is still completely unclear. Such questions without answers in the project Breakthrough Starshot a huge number, but so far the work has just begun.

“The scientific council of our project includes leading experts, scientists and engineers in various relevant fields, including two Nobel laureates, - says Yuri Milner. - And I heard very balanced assessments of the feasibility of this project. In doing so, we certainly rely on the combined expertise of all members of our scientific council, but at the same time we are open to a wider scientific discussion.”

Under star sails

One of the key details of the project is the solar sail. In the original version, the sail area was initially only 1 m 2, and because of this, it could not withstand heating during acceleration in the laser radiation field. The new version uses a 16 m 2 sail, so that the thermal regime, although quite severe, should not, according to preliminary estimates, melt or destroy the sail. As Philip Lubin himself writes, it is planned to use not metallized coatings, but fully dielectric multilayer mirrors as the basis for the sail: “Such materials are characterized by a moderate reflection coefficient and extremely low absorption. For example, optical glasses for fiber optics are designed for high light fluxes and have an absorption of the order of twenty trillion per 1 micron of thickness. Achieving a good reflection coefficient from a dielectric with a sail thickness of 100 nm, which is much less than a wavelength, is not easy. But the authors of the project pin some hopes on the use of new approaches, such as monolayers of a metamaterial with a negative refractive index.

solar sail

One of the main elements of the project is a solar sail with an area of ​​16 m 2 and a mass of only 1 g. Multilayer dielectric mirrors are considered as the sail material, reflecting 99.999% of the incident light (according to preliminary calculations, this should be enough to prevent the sail from melting in a radiation field of 100- GW laser). A more promising approach that makes it possible to make the sail thickness smaller than the reflected light wavelength is to use a metamaterial monolayer with a negative refractive index as the base of the sail (such material also has nanoperforations, which further reduces its mass). The second option is to use a material with a low absorption coefficient (10 −9) rather than a high reflectance, such as optical materials for light guides.

“In addition, you need to take into account that the reflection from dielectric mirrors is tuned to a narrow range of wavelengths, and as the probe accelerates, the Doppler effect shifts the wavelength by more than 20%,” says Lubin. - We have taken this into account, so the reflector will be adjusted to approximately twenty percent of the emission bandwidth. We have designed such reflectors. Larger bandwidth reflectors are also available if needed.”

Laser machine

The main propulsion system of the starship will not fly to the stars - it will be located on Earth. This is a ground-based phased array of laser emitters with a size of 1×1 km. The total power of lasers should be from 50 to 100 GW (this is equivalent to the power of 10–20 Krasnoyarsk HPPs). It is supposed to focus radiation with a wavelength of 1.06 μm from the entire array into a spot with a diameter of several meters at distances up to many millions of kilometers using phasing (that is, changing the phases on each individual emitter) (the ultimate focusing accuracy is 10 −9 radians). But such focusing is greatly hindered by the turbulent atmosphere, which blurs the beam into a spot about an arc second (10 −5 radians) in size. An improvement of four orders of magnitude is expected to be achieved using adaptive optics (AO), which will compensate for atmospheric distortions. The best adaptive optics systems in today's telescopes reduce blur to 30 milliseconds of arc, leaving about two and a half orders of magnitude more to reach the intended target. “In order to defeat small-scale atmospheric turbulence, the phased array must be broken down into very small elements, the size of the radiating element for our wavelength should be no more than 20–25 cm,” explains Philip Lubin. - This is at least 20 million emitters, but this number does not scare me. For feedback in the AO system, we plan to use many reference sources - buoys - both on the probe, and on the mother ship, and in the atmosphere. In addition, we will track the probe on its way to the target. We also want to use the stars as a beacon to adjust the phasing of the array when receiving a signal from the probe upon arrival, but to be sure, we will track the probe.”

Arrival

But then the probe arrived in the Alpha Centauri system, photographed the surroundings of the system and the planet (if any). This information must somehow be transmitted to Earth, and the power of the probe's laser transmitter is limited to a few watts. And in five years, this weak signal must be received on Earth, separating stars from the background radiation. As conceived by the authors of the project, the probe maneuvers at the target in such a way that the sail turns into a Fresnel lens, focusing the probe signal in the direction of the Earth. According to estimates, an ideal lens with ideal focus and ideal orientation amplifies a signal with a power of 1 W to 10 13 W in isotropic equivalent. But how can one consider this signal against the background of much more powerful (by 13–14 orders of magnitude!) star radiation? “The light from the star is actually quite weak, because the linewidth of our laser is very small. The narrow line is a key factor in reducing the background, says Lubin. - The idea of ​​making a Fresnel lens out of a sail based on a thin-film diffractive element is quite complicated and requires a lot of preliminary work to understand exactly how best to do it. This item is actually one of the main ones in our project plan.”

Interstellar flight is not a matter of centuries, but decades

Yuri Milner ,
Russian businessman and philanthropist,
founder of the Breakthrough Initiatives Foundation:

Over the past 15 years, there have been significant, one might say, revolutionary advances in three technological areas: the miniaturization of electronic components, the creation of a new generation of materials, and the reduction in cost and increase in laser power. The combination of these three tendencies leads to the theoretical possibility of accelerating a nanosatellite to almost relativistic speeds. At the first stage (5–10 years), we plan to conduct a more in-depth scientific and engineering study in order to understand the extent to which this project is feasible. The project website has a list of about 20 serious technical problems, without which we will not be able to move forward. This is not a definitive list, but based on the opinion of the scientific council, we believe that the first stage of the project has sufficient motivation. I know that the star sail project is subject to serious criticism from experts, but I think that the position of some critical experts is connected with a not entirely accurate understanding of what we really propose. We finance not a flight to another star, but quite realistic multi-purpose developments related to the idea of ​​an interstellar probe only in a general direction. These technologies will find application both for flights in the solar system and for protection against dangerous asteroids. But setting such an ambitious strategic goal as interstellar flight seems justified in the sense that the development of technology over the past 10–20 years probably makes the implementation of such a project a matter not of centuries, as many assumed, but rather of decades.

On the other hand, a phased array of optical emitters / radiation receivers with a total aperture of one kilometer is an instrument capable of seeing exoplanets from a distance of tens of parsecs. Using receivers with tunable wavelength, it is possible to determine the composition of the atmosphere of exoplanets. Are probes really necessary in this case? “Of course, the use of a phased array as a very large telescope opens up new possibilities in astronomy. But, adds Lubin, we plan to add an infrared spectrometer to the probe as a longer-term program in addition to the camera and other sensors. We have a great photonics group at UC Santa Barbara that is part of the collaboration.”

But in any case, according to Lubin, the first flights will be made within the solar system: “Because we can send a huge number of probes, this gives us many different opportunities. We can also send similar small ( wafer scale, that is, on a chip) probes on conventional rockets and use the same technology to study the Earth or planets and their satellites in the solar system.

The editors would like to thank the Troitsky Variant - Science newspaper and its editor-in-chief Boris Stern for their help in preparing the article.

Kinematics of interstellar flights

Let the flight there and the flight back consist of three phases: uniformly accelerated acceleration, flight at a constant speed and uniformly accelerated deceleration.

The proper time of any clock has the form:

where is the clock speed. The earth clock is motionless (), and their own time is equal to the coordinate. Astronauts' watches have a variable speed. Since the root is integral remains less than one all the time, the time of these clocks, regardless of the explicit form of the function , always turns out to be less than . As a result .

If acceleration and deceleration are relativistically uniformly accelerated(with the parameter of its own acceleration ) during , and uniform motion - , then according to the clock of the ship the time will pass:

, Where - hyperbolic arcsine

Consider a hypothetical flight to a star system Alpha Centauri, remote from the Earth at a distance of 4.3 light years. If time is measured in years, and distances are in light years, then the speed of light is equal to one, and the unit acceleration of light year / year² is close to free fall acceleration and approximately equal to 9.5 m / s².

Let the spaceship move half the way with unit acceleration, and slow down the other half with the same acceleration (). Then the ship turns around and repeats the stages of acceleration and deceleration. In this situation, the flight time in the earth's reference system will be approximately 12 years, while according to the clock on the ship, 7.3 years will pass. Max Speed the ship will reach 0.95 of the speed of light.

In 64 years proper time, a spacecraft with unity acceleration could potentially travel (back to Earth) to Andromeda Galaxy, removed by 2.5 million St. years. On Earth, during such a flight, about 5 million years will pass. By developing twice as much acceleration (to which a trained person may well get used to under a number of conditions and using a number of devices, for example, suspended animation), you can even think about an expedition to the visible edge of the universe (about 14 billion light years), which will take astronauts about 50 years; however, returning from such an expedition (after 28 billion years according to earth clocks), its participants run the risk of not finding alive not only the Earth and the Sun, but even our Galaxy. Based on these calculations, in order for the astronauts to avoid future shock upon returning to Earth, a reasonable radius of accessibility for interstellar expeditions with a return should not exceed several tens of light years, unless, of course, any fundamentally new physical principles of movement in space-time are discovered. However, the discovery of numerous exoplanets gives reason to believe that planetary systems are found near a sufficiently large proportion of stars, so astronauts will have something to explore in this radius (for example, planetary systems ε Eridani And Gliese 581).

Suitability of various types of engines for interstellar flights

The suitability of different types of engines for interstellar flight was reviewed at the meeting British Interplanetary Society in 1973 by Tony Martin. Electric rocket engine with a nuclear reactor has a small acceleration, so it will take centuries to reach the desired speed, which allows it to be used only in ships of generations. Thermal nuclear propulsion type NERVA have a sufficient amount of thrust, but a low speed of the expiration of the working mass, on the order of 5-10 km / s, so a huge amount of fuel will be required to accelerate to the desired speed. Thus, a ship with such an engine will be several orders of magnitude slower than a ship with an electric propulsion engine. For a flight to a neighboring star on such a ship, it will take tens and hundreds of thousands of years (a flight to Alpha Centauri at a speed of 30 km / s will take 40 thousand years). A ramjet would require a huge diameter funnel to collect rarefied interstellar hydrogen, which has a density of 1 atom per cubic centimeter. If a super-powerful electromagnetic field is used to collect interstellar hydrogen, then the force loads on the generating coil will be so great that it seems unlikely even for the technology of the future to overcome them.

Interstellar expedition projects

Starship-rocket projects

Orion Project

The rocket ship designed by the Daedalus project turned out to be so huge that it would have had to be built in outer space. It was supposed to weigh 54,000 tons (almost all the weight is rocket fuel) and could accelerate to 7.1% of the speed of light, carrying a payload weighing 450 tons. Unlike the Orion project, designed to use tiny atomic bombs, the Daedalus project involved the use of miniature hydrogen bombs with a mixture of deuterium and helium-3 and an ignition system using electron beams. But huge technical problems and concerns about nuclear propulsion meant that the Daedalus project was also put on hold indefinitely.

The technological ideas of Daedalus are used in the Ikarus thermonuclear starship project.

Starship projects driven by the pressure of electromagnetic waves.

In 1971, in the report of G. Marx at a symposium in Byurakan proposed to be used for interstellar travel x-ray lasers. Later, the possibility of using this type of propulsion was investigated NASA. As a result, the following conclusion was made: “If the possibility of creating a laser operating in the X-ray wavelength range is found, then we can talk about the real development of an aircraft (accelerated by such a laser beam) that can cover the distances to the nearest stars much faster than all known currently systems with rocket engines. Calculations show that with the help of the space system considered in this paper, it is possible to reach the star Alpha Centauri ... in about 10 years.

In 1985, R. Forward proposed the design of an interstellar probe accelerated by energy microwave radiation. The project envisaged that the probe would reach the nearest stars in 21 years.

At the 36th International Astronomical Congress, a project was proposed for a laser spacecraft, the movement of which is provided by the energy of optical lasers located in orbit around Mercury. According to calculations, the path of a starship of this design to the star Epsilon Eridani(10.8 light years) and back would take 51 years.

The advantage of a solar sailboat is the lack of fuel on board. Its disadvantage is that it cannot be used to sail back to Earth, so it is good for launching robotic probes, stations and cargo ships, but not very suitable for manned return flights (or astronauts will need to bring a second laser with a supply of fuel to install at the destination , which actually negates all the advantages of a sailboat).

Annihilation engines

Theoretical calculations by the American physicists Ronan Keane and Wei-ming Zhang show that, based on modern technologies it is possible to create an annihilation engine capable of accelerating a spacecraft to 70% of the speed of light. The engine they proposed is faster than other theoretical developments due to the special design of the nozzle. However, the main problems in creating annihilation rockets ( English) with similar engines are obtaining the required amount of antimatter, as well as its storage. As of May 2011, the record storage time for antihydrogen atoms was 1000 seconds (~16.5 minutes). Estimated NASA 2006 production milligram positrons cost about 25 million US dollars. One gram of antihydrogen would be worth $62.5 trillion, according to a 1999 estimate.

Direct-flow engines powered by interstellar hydrogen

The main component of the mass of modern rockets is the mass of fuel needed for the rocket to accelerate. If it can somehow be used as working body and fuel surrounding the rocket, it is possible to significantly reduce the mass of the rocket and achieve high speeds due to this.

Another disadvantage of a thermonuclear ramjet is the limited speed that a ship equipped with it can achieve (no more than 0.119 c= 35.7 thousand km/s). This is due to the fact that when trapping each hydrogen atom (which can be considered stationary relative to the stars in the first approximation), the ship loses a certain momentum, which can be compensated by the engine thrust only if the speed does not exceed a certain limit. To overcome this limitation, it is necessary to utilize the kinetic energy of trapped atoms as completely as possible, which seems to be a rather difficult task.

Let's say the screen caught 4 hydrogen atoms. During the operation of a thermonuclear reactor, four protons turn into one alpha particle, two positrons and two neutrinos. For simplicity, we will neglect neutrinos (taking into account neutrinos will require an accurate calculation of all stages of the reaction, and the losses on neutrinos are about a percent), and we will annihilate positrons with 2 electrons left from hydrogen atoms after the removal of protons from them. Another 2 electrons will be used to turn the alpha particle into a neutral helium atom, which, thanks to the energy received from the reaction, will be accelerated in the engine nozzle.

The final reaction equation without taking into account neutrinos:

4edit] Photon engine on magnetic monopoles

If some options are true grand unification theories, such as model "t Hooft - Polyakova, then it is possible to build a photon engine that does not use antimatter, since magnetic monopole hypothetically catalyze proton decay on positron And π 0 -meson :

π 0 quickly decays into 2 photons, and the positron annihilates with an electron, as a result, the hydrogen atom turns into 4 photons, and only the mirror problem remains unresolved.

A photon engine based on magnetic monopoles could also work in a direct-flow scheme.

At the same time, magnetic monopoles are absent in most modern theories of the Grand Unification, which casts doubt on this attractive idea.

Interstellar Spaceship Braking Systems

Several methods have been proposed:

1. Braking on internal sources- missile

2. Braking due to a laser beam sent from the solar system.

3. Braking magnetic field using Zubrin's Magnetic Sail on superconductors.

Generation ships

Interstellar travel is also possible using starships that implement the concept of " generation ships» (for example, by type O'Neill colonies). In such starships, a closed space is created and maintained. biosphere capable of maintaining and reproducing itself for several thousand years. The flight takes place at low speed and takes a very long time, during which many generations of astronauts have time to change.

Dangers of the external environment

This problem was considered in detail by Ivan Korznikov in the article "Reality of interstellar flights". The collision with interstellar dust will occur at near-light speeds and will resemble microexplosions in terms of physical impact. At speeds greater than 0.1 C, the protective screen must have a thickness of tens of meters and a mass of hundreds of thousands of tons. But this screen will reliably protect only from interstellar dust. A collision with a meteorite will have fatal consequences. Ivan Korznikov calculates that at a speed of more than 0.1 C, the spacecraft will not have time to change its flight path and avoid a collision. Ivan Korznikov believes that at sublight speed, the spacecraft will collapse before reaching the target. In his opinion, interstellar travel is possible only at significantly lower speeds (up to 0.01 C).

Energy and resources

Interstellar flight will require large reserves of energy and resources that will have to be carried with you. This is one of the little-studied problems in interstellar astronautics.

For example, the most advanced Daedalus project to date with a pulsed thermonuclear engine would have reached Barnard's Star (six light years) in half a century, spending 50 thousand tons of thermonuclear fuel (a mixture of deuterium and helium-3) and delivering a useful mass of 4 thousand to the target. tons.

FTL movement

IN science fiction works often mention the methods of interstellar flights, based on moving in space faster than the speed of light in a vacuum. Although