Does anyone know what exactly is their plan, once they get there? How is that nano-thing going to slow down / take images / send data back to us? I couldn't find any information on this.

  • $\begingroup$ These things are t.b.d.. $\endgroup$ – ott-- Apr 14 '16 at 8:08
  • $\begingroup$ From what I gathered about communication: the swarm will spread out along the way (traveling at varied speeds) and relay the data back up the line towards Earth, nano-craft to nano-craft. $\endgroup$ – SF. Apr 14 '16 at 20:13
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    $\begingroup$ I am not sue they will slow down. From what I understood, its a fly-by. $\endgroup$ – Polygnome Aug 10 '16 at 8:48
  • $\begingroup$ @Polygnome That's what I've heard, too. How would they slow down without a propulsion system? There'd need to be a comparable laser system at the destination to do that. Can't think of any other way to remove approx 0.1 kilotons TNT equivalent kinetic energy per gram of vehicle mass $\endgroup$ – Everyday Astronaut Oct 27 '19 at 20:01
  • $\begingroup$ One option for slowing down is impacting something! But... that may hinder the transmission options... and would be like hitting a bulls-eye from the top of the empire state building if the target was in New Mexico. $\endgroup$ – Magic Octopus Urn Oct 28 '19 at 14:38

There seems to be very little published information at this stage.

There is a main page that has been set up for the initiative (Yuri Milner's Breakthrough Foundation).

The most interesting bits seem to be a list of challenges yet to be solved and a long page of research papers.

There's an interesting roadmap document too.

As for slowing down - no chance. As a page linked from the Challenges list says:

The nanocraft would traverse a distance of 1 AU in about 2500 seconds. To stabilize the image, the camera would need to “slew” at this rate.

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    $\begingroup$ Thanks, that is a nice list of challenges, I think this is not getting airborne in the next few days :) $\endgroup$ – Geek Dunkman Apr 14 '16 at 9:50
  • $\begingroup$ roadmap document link is broken $\endgroup$ – Everyday Astronaut Oct 27 '19 at 19:57

For reporting back from Alpha Centauri, the roadmap's pages 25-26 and figure 20 predict that an onboard 10 watt laser with narrow spread (and many assumptions, such as at most 40 photons per bit) could transmit from Alpha Centauri to a 30 m reflector mirror on Earth at 70 Mbps.

But the power source for a 10 W transmitter is heavy!

Plutonium-238's power density is 0.54 watts per gram, so sustained 10 W transmission needs an RTG of at least 18 grams. (Materials with more power density, such as polonium-210, would run out of power well before the end of the 20-year voyage.) Burst transmission could be lighter, accumulating the RTG's electrical energy in a supercapacitor, which stores 15 Wh/kg. So a 1 gram supercap stores 54 watt-seconds, enough for a 10 watt 5-second burst transmission; a 1-gram RTG would result in a duty cycle of 1:18, in other words 4 Mbps sustained from Alpha Centauri. But even that compromise of a power source weighs much more than the spacecraft.

More likely is an RTG+supercap a hundred times lighter, 0.02 grams. That gives an upper bound of 40 Kbps from Alpha Centauri. Because the bottleneck is that single 30 m mirror, if the swarm can stagger its broadcasts in sync, and if the mirror can switch its aim from one spacecraft to another fast enough, that number could become 40 Kbps per spacecraft, however many survive the voyage. (Edit: seen from Earth, the spacecraft won't have spread out enough to need re-aiming. They'll appear to be transmitting from the same point.)

(Less likely is replacing the RTG with a nonrechargeable battery, needed only at the destination. The longest shelf life we know of is 10 years, not nearly enough. Likewise, although a stored chemical energy propulsion system aka SCEPS has excellent shelf life, it hasn't yet scaled down even to Mars Rover size, nevermind milligram size.

Edit: Gram-size SCEPS have been attempted. Kyle Jiang at U. Birmingham built a millimeter-scale gasoline engine 15 years ago, but abandoned it because of technical difficulties. Around the same time, U. Berkeley built a gram-size 2.5 W butane-powered Wankel engine, and built parts for a 1 mm version (milligram-size), but nothing else that small.

For comparison, New Horizons transmitted from Jupiter at 38 Kbps, and from Pluto at 1 Kbps. Too bad NASA didn't build a giant receiving antenna for that, instead of waiting many years for its stored data to trickle back via radio.

So the full report back from A.C. could take many years.

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  • $\begingroup$ Well, the report back is already going to take at least a few years...we are limited by the speed of light, but this is a great summary of the technical challenges for communications. $\endgroup$ – called2voyage Aug 9 '16 at 20:25

They don't propose slowing down, which is part of why they don't expect high resolution. In fact, they seem to expect most of the acceleration will occur from the beginning, by the time they hit Pluto's orbit, they expect them to be going at a very high speed.

The communication is expected to be done via lasers. Maybe they can re-convert their reflective shield to assist in improving the laser focus, to increase the power received.

Last interesting bit is they are expected to remain in hibernation until they make their final approach, making communication during the deep void virtually impossible.

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    $\begingroup$ Seems like a plan with very few points of failure. $\endgroup$ – Magic Octopus Urn Oct 27 '19 at 1:29

Solar sails often suggest a couple of modes for slowing down.

1) Have a launch laser at the target location to slow it down the same way. Assumes much infrastructure.

2) Use the solar energy of the target sun to slow the sail down. I.e. Turn it around and spend a longer time decelerating as you get closer and closer.

3) There was a model, where the main sail had a second larger sail that would fly with it, during acceleration, but upon cruise would separate, and advance in front of the main sail. Then the launch laser would target the larger sail, to reflect the energy back on the smaller sail to slow it down. (Lots of tricky bits in that approach).

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    $\begingroup$ That last point sounds a lot like putting an electric fan on a sailboat to blow air on the sail... $\endgroup$ – Steve Apr 15 '16 at 15:37
  • $\begingroup$ @Steve Works awesome! Ever tried? Light is way cooler than air molecules. Idea is light hits the sail, running ahead of the main sail. Transfers momentum so it accelerates. So it stays ahead of the real sail. Then the reflected light hits the back side of primary sail and transfers momentum, slowing it down. Probably need active aiming as both sails will diverge as they slow down. Light! Momentum for ever! $\endgroup$ – geoffc Apr 15 '16 at 16:10
  • $\begingroup$ Do you have any links to more information? $\endgroup$ – Steve Apr 15 '16 at 16:57

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