A Laser-Powered Sail Vehicle Can Reach Alpha Centauri In 20 Years- But - It Cannot Bear Masses Greater Than 1 Gram

 

In the  June issue of Physics Today  (p. 12) I found an intriguing article ('Putting Holes In A Sail To Reach The Stars') detailing how a laser-powered (reflective) mylar sail can actually receive enough momentum from a powerful laser to reach the nearest star.  That would be Alpha Centauri 4.3 light years distant.

What really excited me is when I read:  

 "A high-powered laser fired for less than an hour from Earth's surface could provide enough momentum to accelerate a photonic sail to a fifth of the speed of light and reach Alpha Centauri within 20 years . Fig. 1)

The underlying physics principle is easy enough to grasp.  

Since photons possess momentum, p =  Ec  - then if the light (e.g. from lasers) is intense enough (high enough energy E) it can impart momentum to an object to propel it, i.e. after reflection.  In this case the object would be a sail made up of photonic crystal membranes.  The composition- design of such a sail is shown in Fig. 2 below (Phys. Today, p. 13):

Here we have a 60 mm x 60 mm sample of the larger sail which has a repeating pattern of oval-shape holes, imaged here by a scanning electron microscope.  As noted in the Figure caption: "Different hole sizes reflect different wavelengths of light, which allow the sail to continue reflecting laser light even when it is Doppler -shifted." Adapted from L. Norder et al., Nat., Commun., 16, 2753, 2025)

Basically, all that's required is a sail optimized to reflect as much light as possible and lightweight enough to make use of the resulting energy. as the piece observes:

"Photons reflect off the sail which is then propelled because of conservation of momentum. But as the sail picks up speed the laser light becomes Doppler shifted. To reflect as long as possible - and accelerate as m,uch as possible, a sail needs o reflect across a range of wavelengths".

And that is where the sail design of Fig. 2 comes in.

The one downer?  

"To reach relativistic speeds the payload and the sail need to have masses of no more than 1 gram each."

So hey, if any interested hardy microbes are interest in going to Alpha Centauri - and are able to hibernate for 20 years- maybe they can apply.

See Also:

NASA says that warp drive is getting closer to reality