The aim of the ambitious Breakthrough Starshot project (which is supported by Russian Grand Master Yuri Milner) is to send a “mini” spacecraft to the Alpha of the Centaur at a speed of 1/4 to 1/5 of that light so that it gets there in 20 to 50 years. However, in addition to acceleration, there is also the issue of slowing down: The boat will slow down enough to collect data on the star and its planets as it passes – and the proposal of a theoretical physicist of the Goethe-Universität Frankfurt is the the use of ‘magnetic sails’ as space brakes for the purpose of slowing down the craft.
The Breakthrough Starshot and other similar ideas for the use of small-scale vessels are based on the use of innovative acceleration modes: In the case of the Breakthrough Starshot, this is the use of powerful lasers. However, slowing down is a difficult task, since such a small boat (just a few grams) can not be equipped with conventional braking systems, so Professor Claudiu Gros of the Institute of Theoretical Physics estimates that a slowdown could be achieved using magnetic sails – at least for relatively slow spacecraft.
“Slowly in this case it would mean a cruising speed of about 1,000 km per second, which is just 0.3% of the speed of light, but it’s about 50 times faster than Voyager spacecrafts,” Gross explains. According to his calculations, a magnetic sail is required: A large, extremely conductive loop, about 50 km in diameter, where a strong magnetic field is generated when current is being fed. In this magnetic field, ionized hydrogen will fall, gradually slowing down the craft. The whole idea, as Gross has shown, is functional, despite the very low particle density observed in the interstellar space (0.005 to 0.1 particles per cubic centimeter).
His research has shown that magnetic sails of this kind can slow down “slow” spacecraft, weighing up to 1,500 kg. However, such a trip would take many years – for example 12,000 years for the seven known planets of TRAPPIST-1. However, slower craft of the size of a car could be dispatched with the same laser that, based on the ambitions of the Breakthrough Starshot program, would allow shipments of just a few grams to the Alpha of the Centauri. Also, while thousands of years of missions do not make much sense, things are different in times where time is a secondary issue – like the “The Genesis Project” proposed by the same scientist in 2016, which would send simple, unicellular organisms (either in a mine or as a “plan” in a mini genetic laboratory) on other planets to create life there. For such vessels, what would have been important would not have been when they would arrive there, but that they could slow down and get into orbit around the target planet.