- Part 2 -
At some point in our lives, each of us asked this question: how long to fly to the stars? Is it possible to carry out such a flight in one human life, can such flights become the norm of everyday life? There are many answers to this difficult question, depending on who is asking. Some are simple, others are more difficult. To find a definitive answer, there are too many things to consider.
Unfortunately, no real estimates exist that would help find such an answer, and this frustrates futurists and interstellar travel enthusiasts. Whether we like it or not, space is very large (and complex) and our technology is still limited. But if we ever decide to leave our "home nest", we will have several ways to get to the nearest star system in our galaxy.
The closest star to our Earth is the Sun, quite a "average" star according to the Hertzsprung-Russell "main sequence" scheme. This means that the star is very stable and provides enough sunlight for life to develop on our planet. We know that other planets revolve around the stars near our solar system, and many of these stars are similar to our own.
Possible habitable worlds in the Universe
In the future, if humanity wishes to leave the solar system, we will have a huge selection of stars to which we could go, and many of them may well have favorable conditions for life. But where are we going and how long will it take us to get there? Keep in mind that this is all speculation and there are no landmarks for interstellar travel at this time. Well, as Gagarin said, let's go! Promotional video:
Reach for the star
As already noted, the closest star to our solar system is Proxima Centauri, and therefore it makes a lot of sense to start planning an interstellar mission with it. Part of the Alpha Centauri triple star system, Proxima is 4.24 light years (1.3 parsecs) from Earth. Alpha Centauri is, in fact, the brightest star of the three in the system, part of a close binary system 4.37 light years from Earth - while Proxima Centauri (the faintest of the three) is an isolated red dwarf 0.13 light years away. from a dual system.
And while conversations about interstellar travel suggest all kinds of faster-than-light (FAS) travel, from warp speeds to wormholes to subspace engines, such theories are either highly fictional (like the Alcubierre engine) or only exist in science fiction. … Any mission to deep space will stretch over generations of people.
So, starting with one of the slowest forms of space travel, how long does it take to get to Proxima Centauri?
Modern methods
The question of estimating the duration of travel in space is much easier if existing technologies and bodies in our solar system are involved in it. For example, using the technology used by the New Horizons mission, 16 hydrazine mono-fuel engines, you can reach the Moon in just 8 hours and 35 minutes.
There is also the European Space Agency's SMART-1 mission, which was propelled towards the Moon using ion thrust. With this revolutionary technology, a variant of which the Dawn space probe also used to reach Vesta, the SMART-1 mission took a year, a month, and two weeks to reach the moon.
From a fast rocket spacecraft to an economical ion drive, we have a couple of options for getting around local space - plus you could use Jupiter or Saturn as a giant gravity slingshot. Nevertheless, if we plan to get a little further, we will have to build up the power of technology and explore new possibilities.
When we talk about possible methods, we are talking about those that involve existing technologies, or those that do not yet exist, but which are technically feasible. Some of them, as you will see, are time-tested and confirmed, while others are still in question. In short, they represent a possible, but very time consuming and costly scenario of travel even to the nearest star.
Ionic movement
Currently, the slowest and most economical form of engine is the ion engine. Several decades ago, ionic propulsion was considered the subject of science fiction. But in recent years, ion propulsion support technologies have moved from theory to practice, and with great success. The SMART-1 mission of the European Space Agency is an example of a successful mission to the Moon in 13 months of spiral motion from Earth.
SMART-1 used solar-powered ion thrusters, in which electricity was harvested by solar panels and used to power Hall effect thrusters. It took just 82 kilograms of xenon fuel to get the SMART-1 to the moon. 1 kilogram of xenon fuel provides a delta-V of 45 m / s. This is an extremely effective form of movement, but far from the fastest.
One of the first missions to use ion propulsion technology was the Deep Space 1 mission to Comet Borrelli in 1998. The DS1 also used a xenon ion engine and consumed 81.5 kg of fuel. For 20 months of thrust, DS1 developed speeds of 56,000 km / h at the time of the comet's passage.
Ion engines are more economical than rocket technologies because their thrust per unit mass of rocket fuel (specific impulse) is much higher. But ion thrusters take a long time to accelerate a spacecraft to significant speeds, and top speed depends on fuel support and power generation.
Therefore, if ion propulsion is used in a mission to Proxima Centauri, the engines must have a powerful source of energy (nuclear energy) and large reserves of fuel (although less than conventional rockets). But if you start from the assumption that 81.5 kg of xenon fuel translates into 56,000 km / h (and there will be no other forms of movement), you can make calculations.
At a top speed of 56,000 km / h, Deep Space 1 would take 81,000 years to travel 4.24 light years between Earth and Proxima Centauri. In time, this is about 2700 generations of people. It's safe to say that the interplanetary ion drive will be too slow for a manned interstellar mission.
But if the ion thrusters are larger and more powerful (that is, the rate of exit of the ions will be significantly higher), if there is enough rocket fuel, which is enough for the entire 4.24 light years, travel time will be significantly reduced. But all the same there will be much longer than the period of human life.
Gravity maneuver
The fastest way to travel in space is to use gravity assist. This method involves the spacecraft using the relative motion (i.e., orbit) and gravity of the planet to alter its path and speed. Gravitational maneuvers are an extremely useful technique for space flight, especially when using Earth or another massive planet (like a gas giant) for acceleration.
The Mariner 10 spacecraft was the first to use this method, using the gravitational pull of Venus to accelerate toward Mercury in February 1974. In the 1980s, the Voyager 1 probe used Saturn and Jupiter for gravitational maneuvers and acceleration to 60,000 km / h, followed by an exit into interstellar space.
The Helios 2 mission, which began in 1976 and was supposed to explore the interplanetary environment between 0.3 AU. e. and 1 a. That is, from the Sun, the record for the highest speed developed using a gravitational maneuver holds. At that time, Helios 1 (launched in 1974) and Helios 2 held the record for the closest approach to the Sun. Helios 2 was launched by a conventional rocket and put into a highly elongated orbit.
Due to the large eccentricity (0.54) of the 190-day solar orbit, at perihelion Helios 2 managed to reach a maximum speed of over 240,000 km / h. This orbital speed was developed only by the gravitational attraction of the Sun. Technically, the perihelion speed of Helios 2 was not the result of a gravitational maneuver, but the maximum orbital speed, but the device still holds the record for the fastest artificial object.
If Voyager 1 was moving towards the red dwarf Proxima Centauri at a constant speed of 60,000 km / h, it would take 76,000 years (or more than 2,500 generations) to cover that distance. But if the probe were to reach the record speed of Helios 2 - a constant speed of 240,000 km / h - it would take 19,000 years (or more than 600 generations) to travel 4,243 light years. Much better, though not nearly practical.
Electromagnetic motor EM Drive
Another proposed method for interstellar travel is a resonant cavity radio frequency motor, also known as EM Drive. Proposed back in 2001 by Roger Scheuer, a British scientist who created Satellite Propulsion Research Ltd (SPR) to implement the project, the engine is based on the idea that electromagnetic microwave cavities can directly convert electricity into thrust.
While traditional electromagnetic motors are designed to propel a specific mass (such as ionized particles), this particular propulsion system does not depend on the reaction of the mass and does not emit directional radiation. In general, this engine was greeted with a fair amount of skepticism largely because it violates the law of conservation of momentum, according to which the momentum of the system remains constant and cannot be created or destroyed, but only changed under the action of force.
Nevertheless, recent experiments with this technology have clearly led to positive results. In July 2014, at the 50th AIAA / ASME / SAE / ASEE Joint Propulsion Conference in Cleveland, Ohio, NASA's advanced jet scientists announced that they had successfully tested a new electromagnetic motor design.
In April 2015, scientists at NASA Eagleworks (part of the Johnson Space Center) said they had successfully tested the engine in a vacuum, which could indicate a possible application in space. In July of that year, a group of scientists from the Space Systems Division of the Dresden University of Technology developed their own version of the engine and observed tangible thrust.
In 2010, Professor Zhuang Yang of Northwestern Polytechnic University in Xi'an, China, began publishing a series of articles about her research on EM Drive technology. In 2012, it reported a high input power (2.5 kW) and a fixed thrust of 720 mn. In 2014, she also conducted extensive tests, including internal temperature measurements with built-in thermocouples, which showed that the system was working.
According to calculations based on the NASA prototype (which was given a power rating of 0.4 N / kilowatt), an electromagnetic-powered spacecraft can make a trip to Pluto in less than 18 months. This is six times less than what was required by the New Horizons probe, which was moving at a speed of 58,000 km / h.
Sounds impressive. But even in this case, the ship on electromagnetic engines will fly to Proxima Centauri for 13,000 years. Close, but still not enough. In addition, until all the dots are dotted in this technology, it is too early to talk about its use.
Nuclear thermal and nuclear electric propulsion
Another possibility to carry out an interstellar flight is to use a spacecraft equipped with nuclear engines. NASA has studied such options for decades. A nuclear thermal propulsion rocket could use uranium or deuterium reactors to heat hydrogen in the reactor, converting it into ionized gas (hydrogen plasma), which would then be directed into the rocket nozzle, generating thrust.
A nuclear-powered rocket includes the same reactor, which converts heat and energy into electricity, which then powers the electric motor. In both cases, the rocket will rely on nuclear fusion or nuclear fission to create thrust, rather than the chemical fuel that all modern space agencies operate on.
Compared to chemical engines, nuclear engines have undeniable advantages. First, it is practically unlimited energy density compared to rocket fuel. In addition, the nuclear engine will also generate more thrust than the amount of fuel used. This will reduce the amount of fuel required, and at the same time the weight and cost of a particular apparatus.
Although thermal nuclear power engines have not yet entered space, their prototypes have been created and tested, and even more have been proposed.
Yet despite the advantages in fuel economy and specific impulse, the best of the proposed nuclear thermal engine concepts has a maximum specific impulse of 5000 seconds (50 kNs / kg). Using nuclear engines powered by fission or fusion, NASA scientists could deliver a spacecraft to Mars in just 90 days if the Red Planet is 55,000,000 kilometers from Earth.
But when it comes to travel to Proxima Centauri, a nuclear rocket will take centuries to accelerate to a significant fraction of the speed of light. Then it will take several decades of the way, and after them many more centuries of inhibition on the way to the goal. We are still 1000 years from our destination. What's good for interplanetary missions, not so good for interstellar missions.
- Part 2 -