What is the danger that the small spacecraft plan "Break Through · Star Shot" flying at a speed of 20% of the speed of light has to face?

By irradiating a powerful laser beam from the ground to a super small space explorer that has been launched into space, we will accelerate it to 20% of the light speed and let it reach a planet that is several light years awayBreakthrough Starshot(Breakthrough · star shot) "plan is under way. Dr. Hawking and CEO of Facebook 's Zuckerberg have also expressed support In this plan, the planet of the star system, which is 4.37 light years away from the earthAlpha · CentauriWhatMake it reach 20 yearsIt is aimed to be aimed at, and research towards realization is being advanced, but on the other hand it has also been pointed out the existence of problems that can not be avoided.

Just how dangerous is it to travel at 20% the speed of light? | Ars Technica
http://arstechnica.com/science/2016/08/could-breakthrough-starshots-ships-survive-the-trip/

The Breakthrough Starshot plan is being advanced by a team led by Mr. Yuri Milner of Russia, and Dr. Hawking and Zuckerberg, as mentioned above, are named executives of the team. The essence of this plan is a laser beam irradiation facility that gives thrust to the spacecraft by irradiating a laser to the space from the ground with ultra compact and ultra light probing machine making full use of nanotechnology.

The spacecraft is extremely small with a core part size of a few millimeters and a weight of only a few grams, and by utilizing nanotechnology evolved according to "Moore's Law", the camera, sensor, It is planned to implement necessary equipment such as antennas for observation. And the core is fitted with a sail that receives laser light. Although this sail is about several meters in size, it is supposed to be a very thin one whose film thickness is only a few atomic number level, and the total weight combined with the core part and the sail can be kept within a few grams It is planned.


The laser beam irradiation facility installed on the ground gives thrust to the spacecraft. A mechanism that generates thrust by irradiating a prospecting machine accurately with powerful laser light with electric power of 100 gigawatt-hour class.


A spacecraft that gained powerful thrust reaches its target speed within a few minutes and plans to depart to the voyage to Alfa Centauri that will last for 20 years. Approximately 1000 explorers will be released to space in one launch.


You can see this overview by looking at the following movie.

Breakthrough Starshot Animation (Full)


Although it is a magnificent plan to fly at ultra-high speed which human beings have never realized and to leave the solar system greatly and go to deep space, there seems to be a big problem to be solved there.

Despite the ultra small spacecraft, which weighs just a few grams, the probe and the sail will have a lot of energy by pushing at a tremendous speed of 20% of the speed of light = about 60,000 kilometers per second. One of the biggest problems at that time is the existence of atoms and molecules drifting in outer space called "interstellar gas". Although space is a vacuum, it is not in a state where there is no substance at all. Hydrogen, helium, and in some cases atoms and molecules such as oxygen and iron, which are left behind in the process of the star birth, never attracted by gravity, are left behind, and objects colliding at high speed collide with each other , There is a danger that the damage that can not happen usually occurs.

ByPorter Hall

This danger was often regarded as a major problem when talking about "warp" that transcends space at a speed faster than the speed of light, but in reality it will cause problems even at speeds as high as 20% of the speed of light It is clarified from calculation. When a spacecraft that fly at ultra high speed collides with interstellar gas drifting in the space, heat is generated by the impact. Due to this heat, the material at the part where the material collided is melted, and in some cases it evaporates instantaneously.

As a matter of course, when the material evaporates, its part is missing and gives a big influence, but even if melting occurs, it will also be affected. Even if it is solidified by luck by escaping evaporation and again by lowering the temperature again, it is fully conceivable that the physical properties of the material change dramatically and it becomes impossible to demonstrate the required performance. The influence of the interstellar gas seems to give a dent of about 0.1 mm on the surface of the probe, but the influence due to the change of the physical property as well as the shape is not negligible.

Furthermore, the damage becomes prominent when it becomes "dust (Chile)" which is bigger than an atom or a molecule. Scientists estimate that when Chile collides, the part 1.5 mm from the surface is blown off by evaporation, and the melting will reach about 10 mm. Furthermore, as the size of Chile increases, the damage will be large, and it is believed that the explorer will be broken shattered only by a collision of about 15 microns (0.015 mm) in diameter. However, the probability of Chile colliding with a prospecting machine is very low, estimated to be 1/10 of 50, but it is no wonder whatever happens on the trip of the universe for 20 years Perhaps it should be considered.

ByJoe

Several measures are also considered to solve these problems. One of them is to reduce the risk of collision by reducing the diameter of the probe itself (= reduce the projected area in front) and cover the front with a protective material. In addition, it is conceivable to make the structure to deflect the impact well even when a collision occurs by making the shape shell type, but it is necessary to reduce the part of the sail which receives the thrust as well as the aircraft itself there is. The sail is an important structure for generating thrust and also serves as an antenna for communicating with the earth, so there is a limit to miniaturization. Therefore, it seems that there will be certain limitations in collision avoidance measures due to miniaturization of the airframe.

In addition, in order to avoid the problem due to heat during collision, the research team added "GraphiteWe are also considering means to add a layer of ". Graphite can effectively disperse heat and seems to be able to provide better heat protection than exposed silicon wafer.

In addition to the thermal problem, the change in momentum (momentum) caused by collision can not be ignored. The gas generated by evaporation produces the force to push back the spacecraft. The repeated application of this force can not ignore the possibility that the spacecraft will decelerate or it will not be able to reach the destination by deviating from the prescribed course.

In this way, it seems to be a fact that the problem which must be solved is settled on the grand plan which becomes the first human race. Nevertheless, science was a history of challenge to difficult, and I believe that it is hoped that by continuing to believe in the possibility of solving this problem, the problem will be cleared.

ByArs Electronica Center