Fly to Proxima: ready to accelerate to near the speed of light

  If you leave the earth at this moment and fly at the speed of light, you will reach the moon before the end of this sentence; to the sun, it will take 8 minutes.
  To reach the nearest star system-Proxima Centauri (or Centaurus), flying at the speed of light takes about 4 years and 3 months; it takes at least 80,000 years to ride the fastest rocket.
  However, an ambitious plan intends to launch human spacecraft to Proxima in the next 10 to 20 years; they will fly close to the speed of light and reach their destination within 20 years. The plan was funded by U.S. Silicon Valley billionaire Yuri Milner and was announced at a press conference attended by the late physicist Hawking in April 2016.
  This “Breakthrough Shooting Star” project has aroused widespread international attention. If it succeeds, it may be the most ambitious plan in human history. But many people bet that this is just a whim of some people, and it will die soon. Now that 3 years have passed, what happened to the plan?
The idea of ​​”Breakthrough Photostar” project

  In the universe, the distance between stars is often measured in light-years. In order to reach another star system during the lifetime of human beings, it is necessary to fly close to the speed of light. However, the existing technology that can propel a spacecraft to close to the speed of light is very limited.
  Although the technology is limited, the scientists have not given up. In fact, for decades, there was only one choice for the power of spacecraft-Light Sail. Just as the oncoming wind can put pressure on the sails and thus propel the boat, the light beam can also drive objects in motion. Make a spacecraft light enough, tie a sail on it, and illuminate it with a powerful light source. In space where there is almost no resistance, it can be accelerated to a considerable speed.
  The solar sail is designed to use sunlight. In the 17th century, the German astronomer Kepler first mentioned this idea in his letter to Galileo. However, in order to accelerate an object to close to the speed of light, the sunlight is still too weak, and we need lasers with energy millions of times stronger than it.
  The vision of the “Breakthrough Photograph” project is to deploy hundreds of small spacecraft in orbit around the earth, each equipped with a light sail and the minimum hardware required to record and transmit information. A huge laser array is arranged on the ground. The laser beam will be focused on the light sails of the spacecraft, accelerating them to one-fifth the speed of light (about 60,000 kilometers per second)—a speed that is thousands of times that of traditional spacecraft. In 20 years, these spacecraft will reach Proxima Centauri and send us images of the planets that may be habitable in the star system.
  To achieve this plan, there are many technical challenges: a material that can receive gigawatt lasers without spontaneous combustion must be invented; electronic devices that are light enough but precise enough to be able to emit images back 4 light years away must be manufactured. It is also necessary to ensure that the laser on the earth accurately hits the small light sails, allowing them to accelerate away from the earth and fly to their destinations at a very fast speed; finally, a huge power source must be built to provide electricity for the laser transmitter.
  Let’s take a look at how the team of scientists participating in the program will overcome these technical obstacles.
Technically huge challenge

  The first task facing the team is to create a lightweight light sail. The “Breakthrough Photostar” plan requires Light Sail to cover an area of ​​approximately 10 square meters, but the weight should not exceed 1 gram. This means that its thickness is less than 100 nanometers, which is only a few tenths of the diameter of spider silk. It is technically feasible to produce this gauze-like membrane, but it is a huge challenge to ensure that it is not burned under the irradiation of a strong laser.
  The point is that the material can hardly absorb any incident light, but reflects the light like a mirror. At present, the brightest metal can reflect 99% of the incident light, and the light sail used in the “Breakthrough Shooting Star” project needs to reflect more than 99.999% of the incident light. The materials used to make light sails must satisfy low density, high reflectivity and low absorptivity at the same time. There are currently three candidates that meet these conditions: one is silica (that is, quartz); the second is molybdenum disulfide; and the third is diamond. Of course, these materials must be cut into thin films. If you choose diamond material to make a light sail, imagine that there are big “diamonds” floating in the sky, it will be very spectacular.
  Scientists are intensively studying these materials, and it is estimated that there will be results around next year.
  At the same time, progress has been made in the construction of laser arrays. The “Breakthrough Photostar” project requires a power system with a power of about 60 gigawatts, which is equivalent to 20 nuclear power plants. In contrast, the power of an ordinary laser pointer is about 5 milliwatts, and a beam is enough to make pilots dazzle. The laser only needs a few watts of power.
  The laser irradiates a small spacecraft deployed in the Earth’s orbit, pushes it out of orbit, and accelerates it to one-fifth the speed of light within 10 minutes, after which there is no need for laser propulsion. At this speed, the spacecraft will fly over Mars in 20 minutes, pass Pluto in 7 hours, and reach Proxima in 20 years.
  The scientists initially envisioned the creation of a huge laser, but later discovered that it seemed more feasible to make a group of smaller laser arrays. The principle is to combine the “small” laser light produced by each laser into a “big” laser beam after multiple reflections and refractions, and then emit it. The technology for manufacturing lasers is mature, and what needs to be solved now is how to accurately combine a beam of lasers.
  Spaceships will be built next. These micro aircraft require a power supply, a micro thruster for heading correction, a camera, and a powerful transmitter to transmit these images back to the earth, but the total mass of each aircraft cannot exceed 1 gram.
  To achieve this is no easy task. However, fortunately, we have the ability to manufacture micro-satellites with a quality in the order of grams. The current main obstacle is how to transmit the signal back to the earth, which may require the establishment of a huge signal receiving station on the earth, in addition to the installation of a high-power signal transmitter on the miniature spacecraft.
  Overcoming these difficulties may take about 10 to 20 years.

Proxima b, the closest exoplanet to us.
Fired the first shot of interstellar war?

  These small spacecraft have to roam in space for more than 20 years, passing through many small galaxies on the way, and may encounter many unknown dangers. In addition, the small spacecraft is fast, and it is difficult to avoid some unexpected dangers. The biggest danger is collision. Asteroid. In the solar system, this is easy. On the one hand, these small spacecrafts carry micro thrusters that can change their course in time; on the other hand, they can also bombard asteroids with strong lasers on the ground to push them away. But if it’s too far, there will be nothing. The laser on the earth cannot reach it, and the spacecraft cannot communicate with the ground in real time (because the signal may take several months to go back and forth), so the course cannot be corrected in time. In this case, they can only resign themselves to fate. Fortunately, the small spaceship launches hundreds of ships at a time, as long as the last one arrives smoothly, so even if most of them are “distressed” halfway, it doesn’t matter.
  An important mission of the “Breakthrough Star” program is to investigate another star system and the habitable planetary world there. In 2016, astronomers discovered an exoplanet orbiting the star Centauri-Proxima Centauri b, which is the closest exoplanet to the earth. This discovery once excited the scientists involved in the project, but later studies have shown that the star Centaurus is prone to intense X-ray bursts and ultraviolet bursts, so its planet Proxima Centauri b is unlikely to be habitable.
  Nevertheless, some people believe that once human aircraft enters interstellar space, it will be easier to detect and receive signals from aliens, so it will greatly increase the chance of contact with alien life.
  But whether to contact aliens or not is a controversial issue in itself. Many celebrities, including Hawking, Musk (CEO of SpaceX, a US private space exploration company), and science fiction writer Liu Xinci, have warned that contact with aliens is very dangerous. Because from the perspective of the universe, human civilization is not necessarily the most advanced; in case alien civilization is stronger than us, after aliens discover us, they treat us as inferior species (just like European colonists used to American Indians as barbarians), humans on earth may be in danger of being enslaved or even genocide.
  And human activities in interstellar space may remind unfriendly aliens to notice our existence and reveal the location of our hiding place-the earth. Opponents of the “Breakthrough Star” plan even believe that the plan itself can be regarded as an act of war: a miniature fleet travels through interstellar space in an attempt to find a future colony.
  But supporters think this idea is absurd. They said that any advanced aliens may have known our existence from the radio and television radio waves that we have spread into space for decades, and our hiding place has long been leaked out. Besides, our spacecraft is so small and flies so fast, even if there are technologically advanced aliens, it is difficult for them to discover.
  Leaving aside the debate over whether contact with aliens is a blessing or a curse, the significance of the “Breakthrough Star” program is that it is the most ambitious space exploration program for mankind since the Apollo lunar exploration program. If it succeeds, it will be a great one. Achievement.