Yes, Edward raises very good points. Another problem I saw when reading the technical proposal was the acceleration of the 2 gram size spacecraft. It was stated to be 10000 g’s. Another challenge and a bit more than someone dropping a cell phone.

Yo, Blair– anxiously awaiting your blog-post on served & targeted adverts in the blogosphere!

Edward: well said… “It just may not work quite as advertised.”

At 0.3C, it would take much less than a ‘tiny rock’. I have a video where engineers put a small satellite into a chamber and fire a mass equivalent to a small pebble at Earth orbital velocity at the craft. There are a few small pieces left, but everything else is dust.

I got interested in solar sails in the late 1970s. Even back then, this kind of idea had been proposed. One method for slowing down at the destination was to have the sail built in two parts: in inside disk and an outer ring. The ring would break away as the sail neared the destination, and the laser would shine on it, the light would bounce back to the disk and the payload would slow to an orbital speed. One downside to this idea was that the outer ring would accelerate away at a higher rate than the payload would slow down, reducing the effectiveness of the reflected light as time went on.

Another suggested way of slowing down was to use the star’s light as a breaking force. Speeds approaching relativistic speeds would likely overwhelm the breaking force of the destination star, so the travel speed would be limited to the breaking power of that star. This probably would require an even slower approach speed, as the gravitational attraction of the star would also have to be accounted for.

I like the article’s suggestion, however, of having a second laser source at the destination, such as Mars. This may require that we have a serious presence at Mars, though.

So, the article and the video suggested that they were moving from science fiction to science reality, but there is a bit of a problem, so if you want to continue believing that this is possible with current technology, take this as a *** SPOILER ALERT! *** and read no further.

Let’s talk heat dissipation. First, the laser array needs to dissipate a lot of waste heat. For every gigawatt of power sent by the laser, 3 gigawatts will have to be dissipated if the power source is 25% efficient (current solar arrays can be made this efficient). That requires a big radiator for every one of the 70 proposed gigawatts. Fortunately, current solar arrays can dissipate that much on their back sides. But it takes a big array of solar panels. Big. Really big.

For other power source types, imagine a standard Earth-bound power plant with all that steam being emitted from the cooling towers. A standard power plant like that is about 1 gigawatt, so we have to do around the equivalent of 70 of those cooling towers using only radiative cooling. This is a bit tricky.

Second, the worse problem is cooling the poor solar sail. Not all of the light is going to be reflected off the reflective sail. To save weight and maximize the acceleration per gigawatt of laser power, the reflective material, such as aluminum or silver, would be so thin that some of the energy will pass right through. But not all of the energy will reflect or pass through, some will be absorbed into the thin material and heat it up. At 70 GW, it won’t take too much absorption for the sail to (!) melt away.

One proposal that I read, lo those many years ago, was to grow radiative “hairs” on the back side of the sail, and these fibers would increase the surface area that radiates away the heat. The paper that proposed that idea seemed to conclude that the increased light that can shine on the sail more than makes up for the additional weight of the radiative hairs. But … 70 GW is still a lot of power, and it still would heat up that sail quite a bit.

My conclusion is that 70 GW is overpowered, especially considering that it takes them 10 minutes to get to 30% of the speed of light, according to the embedded video. A possible solution is to use a lower power laser, one that does not overwhelm the solar sail material, and station multiple lasers along the longer acceleration route to make up for the lost power of the spreading beam, due to distance. Lasers are not exactly perfectly parallel light, they spread out over distance. Using multiple power sources over the track of the acceleration is how they get subatomic particles up to relativistic speeds in the laboratory — they do it all the time. It is also how a mass driver works/will work (mass drivers have been built in the laboratory, too).

Do not abandon all hope, ye who read this far. Just because the system needs a little work does not mean it is impossible in the long run. It just may not work quite as advertised.

The world consumes 19TW of electricity. If the nighttime part of that capacity were to be beamed to the Moon, collected and then revealed for interstellar propulsion then much greater than CubeSats could be sent.

2nd try.