The cold glare of the stars is especially beautiful in the winter sky. At this time, the brightest stars and constellations become visible: Orion, Pleiades, Greater Dog with dazzling Sirius …
A quarter of a century ago, seven warrant officers of the Naval Academy asked an unusual question: how close is modern mankind to the stars? The research resulted in a detailed report known as Project Longshot (Long Range Shot). A concept of an automatic interstellar craft capable of reaching the nearest stars in a reasonable amount of time. No millennia of flight and "ships of generations"! The probe should reach the vicinity of Alpha Centauri within 100 years from the moment of its launch into space.
Hyperspace, gravity, antimatter and photonic rockets … No! The main feature of the project is its reliance on existing technologies. According to the developers, the Longshot design makes it possible to build a spaceship already in the first half of the 21st century!
One hundred years of flight with existing technologies. An unheard-of audacity, given the scale of cosmic distances. Between the Sun and Alpha Centauri lies a "black abyss" 4, 36 sv wide. of the year. Over 40 trillion kilometers! The monstrous meaning of this figure becomes clear in the following example.
If we reduce the size of the Sun to the size of a tennis ball, then the entire solar system will fit in Red Square. The size of the Earth in the selected scale will decrease to the size of a grain of sand, while the nearest "tennis ball" - Alpha Centauri - will lie on St. Mark's Square in Venice.
A flight to Alpha Centauri on a conventional Shuttle or Soyuz spacecraft would take 190,000 years.
A terrible diagnosis sounds like a sentence. Are we doomed to sit on our "grain of sand", not having the slightest chance of reaching the stars? In popular science magazines, there are calculations proving that it is impossible to accelerate a spaceship to near-light speeds. This will require "burn" all matter in the solar system.
And yet there is a chance! Project Longshot has proven that the stars are much closer than we can imagine.
A plate with a pulsar map is attached to Voyager's hull, showing the location of the Sun in the Galaxy, as well as detailed information about the inhabitants of the Earth. It is expected that someday the aliens will find this "stone ax" and come to visit us. But, if we recall the peculiarities of the behavior of all technological civilizations on Earth and the history of America's conquests by the conquistadors, one cannot count on "peaceful contact" …
The mission of the expedition
Get to the Alpha Centauri system in a hundred years.
Unlike other "starships" ("Daedalus"), the "Longshot" project involved entering the orbit of the star system (Alpha and Beta Centauri). This significantly complicated the task and lengthened the flight time, but would allow a detailed study of the vicinity of distant stars (unlike the Daedalus, which would have rushed past the target in a day and disappeared without a trace in the depths of space).
The flight will take 100 years. Another 4, 36 years will be required to transfer information to Earth.
Alpha Centauri Compared to Solar System
Astronomers pin great hopes on the project - if successful, they will have a fantastic instrument for measuring parallaxes (distances to other stars) with a basis of 4, 36 sv. of the year.
A century-old flight through the night will also not pass aimlessly: the device will conduct a study of the interstellar medium and will expand our knowledge of the outer boundaries of the solar system.
Shot to the stars
The main and only problem of space travel is the colossal distances. Having solved this issue, we will solve all the rest. Reducing the flight time will remove the issue of a long-term source of energy and high reliability of the ship's systems. The problem with the presence of a person on board will be solved. The short flight makes complex life support systems and gigantic supplies of food / water / air on board unnecessary.
But these are distant dreams. In this case, it is necessary to deliver an unmanned probe to the stars within one century. We do not know how to break the space-time continuum, therefore there is only one way out: to increase the ground speed of the "starship".
As the calculation showed, a flight to Alpha Centauri in 100 years requires a speed of at least 4.5% of the speed of light. 13500 km / s.
There are no fundamental prohibitions that allow bodies in the macrocosm to move at a specified speed, nevertheless, its value is monstrously great. For comparison: the speed of the fastest of the spacecraft (probe "New Horizons") after turning off the upper stage was "only" 16.26 km / s (58636 km / h) in relation to the Earth.
Longshot concept starship
How to accelerate an interstellar ship to speeds of thousands of km / s? The answer is obvious: you need a high-thrust engine with a specific impulse of at least 1,000,000 seconds.
Specific impulse is an indicator of the efficiency of a jet engine. Depends on the molecular weight, temperature and pressure of the gas in the combustion chamber. The greater the pressure difference in the combustion chamber and in the external environment, the greater the speed of the outflow of the working fluid. And, therefore, the efficiency of the engine is higher.
The best examples of modern electric jet engines (ERE) have a specific impulse of 10,000 s; at an outflow velocity of charged particle beams - up to 100,000 km / s. The consumption of the working fluid (xenon / krypton) is a few milligrams per second. The engine hums quietly throughout the flight, slowly accelerating the craft.
EJEs captivate with their relative simplicity, low cost and the potential to achieve high speeds (tens of km / s), but due to the low thrust value (less than one Newton), acceleration can take tens of years.
Another thing is chemical rocket engines, on which all modern cosmonautics rests. They have a huge thrust (tens and hundreds of tons), but the maximum specific impulse of a three-component liquid-propellant rocket engine (lithium / hydrogen / fluorine) is only 542 s, with a gas outflow velocity of just over 5 km / s. This is the limit.
Liquid-propellant rockets make it possible to increase the spacecraft speed by several km / s in a short time, but they are not capable of more. The starship will need an engine based on different physical principles.
The creators of "Longshot" have considered several exotic ways, incl. "Light sail", accelerated by a laser with a power of 3, 5 terawatts (the method was recognized as unfeasible).
To date, the only realistic way to reach the stars is a pulsed nuclear (thermonuclear) engine. The principle of operation is based on laser thermonuclear fusion (LTS), well studied in laboratory conditions. Concentration of a large amount of energy in small volumes of matter in a short period of time (<10 ^ -10 … 10 ^ -9 s) with inertial plasma confinement.
In the case of Longshot, there is no question of any stable reaction of controlled thermonuclear fusion: long-term plasma confinement is not required. To create jet thrust, the resulting high-temperature clot must be immediately "pushed" by the magnetic field overboard the ship.
The fuel is a helium-3 / deuterium mixture. The required fuel supply for an interstellar flight will be 264 tons.
In a similar way, it is planned to achieve unprecedented efficiency: in the calculations, the value of the specific impulse is 1.02 mln.seconds!
As the main source of energy for powering the ship's systems - pulsed engine lasers, attitude control systems, communications and scientific instruments - a conventional reactor based on uranium fuel assemblies was chosen. The electrical power of the installation must be at least 300 kW (thermal power is almost an order of magnitude higher).
From the point of view of modern technology, the creation of a reactor that does not require recharging for a whole century is not easy, but possible in practice. Already now, nuclear-powered systems are used on warships, whose core has a service life commensurate with the service life of ships (30-50 years). The power is also in complete order - for example, the OK-650 nuclear installation installed on the nuclear submarines of the Russian Navy has a thermal capacity of 190 megawatts and is capable of providing electricity to an entire city with a population of 50,000 people!
Such installations are excessively powerful for space. This requires compactness and precise compliance with the specified characteristics. For example, on July 10, 1987, Kosmos-1867 was launched - a Soviet satellite with the Yenisei nuclear installation (satellite mass - 1.5 tons, reactor thermal power - 150 kW, electric power - 6, 6 kW, service life - 11 months).
This means that the 300 kW reactor used in the Longshot project is a matter of the near future. The engineers themselves calculated that the mass of such a reactor would be about 6 tons.
Actually, this is where physics ends and the lyrics begin.
Problems of interstellar travel
To control the probe, an onboard computer complex with the makings of artificial intelligence will be required. Under conditions when the signal transmission time is more than 4 years, effective control of the probe from the ground is impossible.
In the field of microelectronics and the creation of research devices, large-scale changes have taken place recently. It is unlikely that the creators of Longshot in 1987 had any idea of the capabilities of modern computers. It can be considered that this technical problem has been successfully solved over the past quarter century.
The situation with communication systems looks just as optimistic. For reliable transmission of information from a distance of 4, 36 sv. year will require a system of lasers operating in the valley of the wave of 0.532 microns and with a radiation power of 250 kW. In this case, for each square. meter of the Earth's surface will fall 222 photons per second, which is much higher than the sensitivity threshold of modern radio telescopes. The information transfer rate from the maximum distance will be 1 kbps. Modern radio telescopes and space communication systems are able to expand the data exchange channel several times.
For comparison: the transmitter power of the Voyager 1 probe, which is currently at a distance of 19 billion km from the Sun (17.5 light hours), is only 23 W - like a light bulb in your refrigerator. However, this is quite enough for telemetry transmission to Earth at a rate of several kbit / s.
A separate line is the question of the thermoregulation of the ship.
A nuclear reactor of a megawatt class and a pulsed thermonuclear engine are sources of a colossal amount of thermal energy, moreover, in a vacuum there are only two ways of heat removal - ablation and radiation.
The solution could be the installation of an advanced system of radiators and radiating surfaces, as well as a heat-insulating ceramic buffer between the engine compartment and the ship's fuel tanks.
At the initial stage of the journey, the ship will need an additional protective shield from solar radiation (similar to that used on the Skylab orbital station). In the area of the final target - in orbit of the Beta Centauri star - there will also be a danger of the probe overheating. Thermal insulation of equipment and a system for transferring excess heat from all important blocks and scientific instruments to radiating radiators is required.
A graph of the ship's acceleration over time
Graph showing the change in speed
The issue of protecting the spacecraft from micrometeorites and cosmic dust particles is extremely difficult. At a speed of 4.5% of the light speed, any collision with a microscopic object can seriously damage the probe. The creators of "Longshot" propose to solve the problem by installing a powerful protective shield in the front of the ship (metal? Ceramics?), Which at the same time was a radiator of excess heat.
How reliable is this protection? And is it possible to use sci-fi protection systems in the form of force / magnetic fields or "clouds" of microdispersed particles held by a magnetic field ahead of the ship? Let's hope that by the time the starship is created, engineers will find an adequate solution.
As for the probe itself, it will traditionally have a multistage arrangement with detachable tanks. Manufacturing material for hull structures - aluminum / titanium alloys. The total mass of the assembled spacecraft in low-earth orbit will be 396 tons, with a maximum length of 65 meters.
For comparison: the mass of the International Space Station is 417 tons with a length of 109 meters.
1) Launch configuration in low-earth orbit.
2) 33rd year of flight, separation of the first pair of tanks.
3) 67th year of flight, separation of the second pair of tanks.
4) 100th year of flight - arrival at the target at a speed of 15-30 km / s.
Separation of the last stage, entering a permanent orbit around Beta Centauri.
Like the ISS, the Longshot can be assembled using the block method in low Earth orbit. The realistic dimensions of the spacecraft make it possible to use existing launch vehicles in the assembly process (for comparison, the mighty Saturn-V can carry a load of 120 tons to LEO at a time!)
It should be taken into account that launching a pulsed thermonuclear engine in near-earth orbit is too risky and careless. The Longshot project provided for the presence of additional booster blocks (chemical liquid-propellant rocket engines) for gaining the second and third cosmic speeds and withdrawing the spacecraft from the plane of the ecliptic (the Alpha Centauri system is located 61 ° above the plane of rotation of the Earth around the Sun). Also, it is possible that for this purpose a maneuver in the gravitational field of Jupiter will be justified - like space probes that managed to escape from the plane of the ecliptic, using "free" acceleration in the vicinity of the giant planet.
Epilogue
All technologies and components of a hypothetical interstellar ship exist in reality.
The Longshot probe's weight and dimensions correspond to the capabilities of modern cosmonautics.
If we start work today, it is highly likely that by the middle of the XXII century our happy great-grandchildren will see the first images of the Alpha Centauri system from close range.
Progress has an irreversible direction: every day life continues to amaze us with new inventions and discoveries. It is possible that in 10-20 years all the technologies described above will appear before us in the form of working samples made at a new technological level.
And yet the path to the stars is too far for it to make sense to talk about it seriously.
The attentive reader has probably already drawn attention to the key problem of the Longshot project. Helium-3.
Where to get one hundred tons of this substance, if the annual production of helium-3 is only 60,000 liters (8 kilograms) per year at a price of up to $ 2,000 per liter ?! Brave science fiction writers pin their hopes on the production of helium-3 on the Moon and in the atmosphere of giant planets, but no one can give any guarantees on this matter.
There are doubts about the possibility of storing such a volume of fuel and its dosed supply in the form of frozen "tablets" required to power a pulsed thermonuclear engine. However, like the very principle of operation of the engine: what more or less works in laboratory conditions on Earth is still far from being used in outer space.
Finally, the unprecedented reliability of all probe systems. The participants in the Longshot project write directly about this: the creation of an engine that can operate for 100 years without stopping and major repairs will be an incredible technical breakthrough. The same applies to all other probe systems and mechanisms.
However, you should not despair. In the history of astronautics, there are examples of unprecedented reliability of spacecraft. Pioneers 6, 7, 8, 10, 11, as well as Voyagers 1 and 2 - all of them have worked in open space for over 30 years!
The story with hydrazine thrusters (attitude control engines) of these spacecraft is indicative. Voyager 1 switched to a spare kit in 2004. By this time, the main set of engines had worked in open space for 27 years, having withstood 353,000 starts. It is noteworthy that the engine catalysts have been continuously heated up to 300 ° C all this time!
Today, 37 years after launch, both Voyagers continue their insane flight. They have long since left the heliosphere, but continue to regularly transmit data on the interstellar medium to Earth.
Any system that depends on human reliability is unreliable. However, we must admit: in terms of ensuring the reliability of spacecraft, we have managed to achieve certain successes.
All the necessary technologies for the implementation of the "stellar expedition" have ceased to be the fantasies of scientists who abuse cannabinoids, and have been embodied in the form of clear patents and working samples of technology. In the laboratory - but they exist!
The conceptual design of the interstellar spacecraft Longshot proved that we have a chance to escape to the stars. There are many difficulties to overcome on this thorny path. But the main thing is that the vector of development is known, and self-confidence has appeared.
More information on the Longshot project can be found here:
For the initiation of interest in this topic, I express my gratitude to "Postman".
