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A recent question about Project Starshot's communication asks about one of the seemingly insurmountable problems with this project.

There is however another problem that has bugged me ever since I first heard about the project. We are told the craft will consist of an electronics module with a mass of about 1g, attached to a sail of about 1 m^2 which is just a few atoms thick. Then we accelerate the entire craft with a laser, pushing it up to 20% of the speed of light in a few minutes.

A quick calculation shows that we need of the order of 60,000 G to reach that speed. Hence, during acceleration our 1 g mass will weigh 60 kg.

What kind of technology do they envisage to produce a sail that will hold that kind of weight, without tearing or just collapsing under the strain?

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    $\begingroup$ It's fantasy. Per the WP page, "at least a dozen off-the-shelf technologies will need to improve by orders of magnitude." $\endgroup$ – Russell Borogove Sep 19 '17 at 1:56
  • $\begingroup$ @Russell but is there even any imaginable technology that can do this? $\endgroup$ – hdhondt Sep 19 '17 at 2:00
  • $\begingroup$ Imaginable @hdhondt? Sure, I can imagine some amazing things. Part of point of Starshot is to get people doing the blue-sky thinking that could lead to some breakthroughs, imagination certainly enters into it. Putting it into practice is the hard work. $\endgroup$ – GdD Sep 19 '17 at 9:53
  • $\begingroup$ Just give them a few billion in funding and they'll solve all these pesky problems. They promise. $\endgroup$ – Russell Borogove Sep 19 '17 at 18:10
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    $\begingroup$ A 1 gram package at the center of a 1m sail presents a nearly insurmountable structural challenge. However if you treat the whole 1m^2 sail like a big printed circuit board then you could (arguably) distribute 1g worth of components across its surface. Other speculation: A composite sandwich with two strong (graphene?) layers separated by an aerogel filler would make a structure stiff enough to resist deforming under the loads imposed by a few dozen milligram-sized discrete components distributed across an area. Speculation, but the sort of thing that makes you say "Worth exploring further." $\endgroup$ – Kengineer Sep 19 '17 at 21:32
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You're looking at it wrong.

Yes, pulling 1g payload with a 60,000g acceleration would be a tremendous engineering challenge. (I wouldn't call it impossible, though—that's not too far beyond gun accelerations and we routinely fire electronics out of guns.)

However, that's not how you do something like this. You do not want to pull a payload!! Rather, your probe needs to be spread over the sail surface. If you could somehow spread the probe totally evenly across the sail the only force would be compressive and since it would be incredibly thin that's not that much force even given the acceleration in question.

In practice the limit is going to be how thin you can spread the probe.

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  • $\begingroup$ I think "You're looking at it wrong." is a bit strong, I am not sure there are right and wrong ways to look at something so hypothetical. Looking at things from several different ways is often important when something is so new and different and unexplored. Can you support your assertion that spreading out the mass is the "right way" to do this? At 0.2c every hydrogen atom collision can take out many other atoms by sputtering and leave structural damage. I have a hunch some thickness for the important bits might be necessary. $\endgroup$ – uhoh Sep 25 '17 at 4:09
  • $\begingroup$ @uhoh I suppose that's another challenge then: making components that are just a couple of atoms thick, and evenly spread across every square micron of the sail (to avoid spots where g forces would be concentrated). But at least this is a possible way out. $\endgroup$ – hdhondt Sep 25 '17 at 6:00

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