People have dreamed of being driven across the vast oceans of space by winds of light.
The idea of nudging reflective sails slowly towards the speed of light using nothing more than the punch of a photon might be our only chance of reaching another star inside of a single human lifetime.
It is also much harder said than done. Particles of light are not very hard to push. If you make a sail light that feels the inertia of radiation, it could damage its material.
Making a sail that can survive the dangers of such a long journey is going to require some clever solutions, and maybe the kind of solutions proposed in two studies published recently in the journal.
The innovations were developed by engineers from the University of Pennsylvania and the University of California at Los Angeles as part of the Breakthrough Starshot initiative.
The idea of a light sail has been around for a while, but we are just now figuring out how to make sure those designs survive the trip.
Waves of radiation exchange momentum with any objects they hit. The force they impart is going to be small because they don't have any resting mass.
The light that bounces off your body as you sunbathe is roughly equivalent to a tenth of a gram.
There are ways to get an object moving. A bigger sail can catch more light. One way to make the light hitting it more intense is by directing a lot of lasers at it.
There are some problems here. Bigger sails mean more people. The sail would be at risk of tears if the mass was trimmed because it would make it easier to push.
Some issues are presented by more light. The wavelength of radiation hitting the sail will appear to shift towards the red end of the rainbow, setting limits on the kinds of material that won't absorb too much.
Finding the right material to make the sails tough, lightweight, and capable of handling the heat produced by gigawatts of stretched out laser light has been the subject of previous investigations.
Engineers propose making a sail from two layers of compounds made up of molybdenum disulfide and Silicon nitride, both of which can be fabricated into sheets and have the kinds of optical properties to balance minimal absorption and emission of light as it stretches out.
A structural paper designed to handle the strain of increased photon pressure is the solution to the problem.
As the authors of the study point out, little research has been done into the stresses light pressure would place on this kind of structure.
The team demonstrated that a sufficient curvature is the way to go with a sail that could tow a few grams.
The researchers tinkered with the differences in acceleration time to find the right balance of mechanical and thermal stresses.
If a vessel can hit speeds of 20 percent the speed of light, it can cover 4.2 light years to Proxima Centauri within a couple of decades.
This technology may never be able to transport passengers. That will be fodder for science fiction for a while.
It might give us an up- close look at a planetary system that isn't our own within our lifetimes.
This research was published in two places.
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