Is a Hawking-Milner StarShot Possible?

Original author: Ethan Siegel
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Common sense dictates that for a flight to another stellar system, either a new type of propulsion system is needed, patience stretched out over several generations, or overcoming the laws of physics. But if you refuse to send a person or a traditional spacecraft - can you think of a better, innovative and simple technology? The year before last, a team of scientists wrote a paper on how an array of lasers can be combined with the concept of a solar sail in order to create a spaceship with a “laser sail”. In theory, the existing technologies, together with extremely light spaceships (“cosmic chips”), can allow us to reach the nearest stars in a single human life.

The advantages of this project are amazing:

• Most of the energy such a ship receives not from a one-time rocket fuel, but from lasers capable of recharging.
• The masses of cosmochips are extremely small, so they can be accelerated to very high speeds, close to the speed of light.
• With the current successes of miniaturization of electronics and the creation of very light and durable materials, we really can create useful devices and send them in many light years.

The idea is not new, but the development of new technologies - already available, and those that will be available in 20-30 years - makes this opportunity realistic.



Moreover, since billionaire Yuri Milner donates $ 100 million to the project as part of the Breakthrough Initiative , it seems that mankind will still reach for the stars. This concept was approved by many serious scientists, because technology is developing very quickly. Nanomaterials are getting better, and we can expect that we can build a sail weighing 1 gram and 1 m² in size, capable of reflecting a laser beam. One of the recent advances in the manufacture of lasers has been the ability to assemble lasers into a large array capable of focusing them on a single target. Further improvements in laser power and collimationmeans that a laser can accelerate a target to an acceleration radically exceeding the capabilities of lasers in the 1990s.



Having built a huge array of lasers in space, aiming it at these one-gram reflecting sails and constantly shooting at them, we will be able to accelerate these cosmic chips to speeds of more than 60,000 km / s, that is, about 20% of the speed of light. With such a speed, they will reach the nearest star system in 22 years, and we will be able to fly to the 100 nearest known systems for 100 years. The size of the laser array will require a giant: about 100 km², which corresponds to about 2/3 of the state of Liechtenstein. But with him the problem is only in cost, and not in technological limitations.



Looks too good to be true. In fact, when describing the project was not mentionedseveral of its drawbacks :

• An array of lasers are going to be built on the surface of the Earth, and not in space. It is easier to create and maintain, not to mention the fact that it will cost 50 times less, but the atmosphere scatters light, and therefore only a fraction of it will reach the cosmic chips. Less light means less acceleration, and low travel speed makes the project less attractive.

• A stream of any type entering a structure such as a sail will cause an angular momentum and cause it to rotate. It is not clear how it will be possible to keep such a sail from spinning and spinning out of control without the use of a heavy stabilizing mechanism on board.

• Even if you reach the goal, you will not be able to slow down or transmit information to Earth. For the time being, the energy available to such a small cosmochip will not be enough to transmit anything to Earth that we can detect.

• And finally, money: $ 100 million seems like a lot of money, but it is less than 1% of the cost of such a project, not to mention the development of technology that does not yet exist.

There is hope to solve some of these problems, but so far from a scientific point of view, they have not been completely worked out. Will there be any improvement in laser collimation technology? Will we build such a huge (or powerful) array that it will be able to transfer a sufficiently large amount of energy to the laser sail? Will we build a sail thinner and larger in area, so that it can get more momentum? Can a sail, even with a reflectivity of 99.9995%, withstand a gigawatt laser, or will it be destroyed with 0.0005% of absorbed energy?



What about the problem of rotation; Will we invent and develop nanogyroscopes capable of stabilizing the sail against rotation? If not, will we be able to direct it towards another star system, or will it fly to where it will turn out, while an error of even 0.1% leads to a miss by the target of billions of kilometers? What about transmission problems; Will we put a tiny amount of plutonium-238 into the generator of each ship? Will we hope for a new, not yet developed information transfer technology? If we take into account that most of the instruments, even from Voyager ships, which are at a trifling distance of 0.002 light years, cannot communicate with Earth, how can we hope that a single-gram chip can send us a message from distances of 1000 times more?


A logarithmic distance scale showing the Voyager spacecraft, our solar system, and the star closest to us for comparison.

The last problem may be the most difficult. As planetary scientist Bruce Betts says:

If you could fly into the forest, and see how a tree falls, but you could not tell anyone about it, would it have any significance?

This is perhaps the most difficult problem of the project: do we spend tens of billions of dollars just to deliver one-gram artifacts from Earth to deep space, never to receive messages from them again?

I'm not saying that this is not necessary, just let's be honest about the problems the project has. If we do this, we must do it correctly and put as much sense as possible into this attempt. This is an amazing opportunity that needs to be explored further, but the $ 100 million and our most modern technologies do not even begin to bring us closer to our goal.

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