Gram-scale StarChip components | Protective coating

Apr 13, 2016 00:49 Posted on: Breakthrough Initiatives

As a metallurgist, I find beryllium copper to be an odd choice for a protective coating. It is a high strength copper alloy with 0.5-3% Be, but has high density (because of its low Be content), and is not a particularly good conductivitor (20-40 IACS [pure Cu], because of the Be in solid solution).
What are the requirements for the coating? THe text says "able to withstand the collisions with particles in the interstellar medium within a range of sizes" but how does it translates in terms of mechanical properties ? If toughness (or energy absorption) - expressed per unit mass (specific values) - are the main criteria, then many better alloys are available. Metallic nano- or microfoams may also be a good choice.

Apr 13, 2016 06:22 David Theil Posted on: Breakthrough Initiatives

At a typical interstellar medium density of 1 atom per cubic cm these can be ignored from a momentum consideration. Dust particles of order 10^-14 g in mass have density of roughly 10^-12 per cubic cm in the local bubble. A cm sized spacecraft could expect to encounter a few million of these beasties on the way to Alpha Cen (roughly 1 parsec.) At a speed of 6x10^9 cm/s (0.2c) each one will deposit about 10^5 ergs into our little spacecraft...not enough to raise the temperature all that much if averaged over the whole 1 gram mass (assumed heat capacity of silicon), BUT presumably enough to sputter away some protective coating. I would want to do some lab experiments to see how different coatings respond to such collisions. Even the LHC can't produce 10^16 eV particles. This is going to be a tough thing to test and will have to rely on modeling.

Apr 13, 2016 12:34 Dwayne Fries Posted on: Breakthrough Initiatives

One factor that I would recommend as a previous submariner, the strength of the hull to be greater than sea pressure at great depths doesn't come from a strong metal, rather, a soft metal that is able to bend under pressure and normalize correctly without the pressure.

Apr 13, 2016 18:55 Karen Pease Posted on: Breakthrough Initiatives

I can't imagine that any material would make more sense than carbon aerogel. You want the initial impact to be as far ahead of your sensitive components as possible. Carbon aerogel is also very heat tolerant.

If not an aerogel, then the only other reasonable option I can think of is a whipple shield.

Apr 14, 2016 01:20 Götz Thorwarth Posted on: Breakthrough Initiatives

David, based on sputtering alone you may want to give diamond-like carbon a spin - it is very tough to sputter, quite dense, and amorphous. High energy ion impact may graphitize it to a certain degree but not completely.

Apr 14, 2016 13:28 Andrey Revyakin Posted on: Breakthrough Initiatives

Regarding the damage to the sails... This may be a bit naiive but... Let's assume that the cost of the nano-spaceship itself is negligible compared to the cost of the laser (this may not be true -- e.g. if the entire space ship has to be nano-printed).

Assuming the spaceship is cheap, why not send as swam of ships (100, 1000), so that at least a few will make it to the target. This way one can also statistically sample the observation and use some kind of co-operativity between the ships to repair each other.

Obviously, if the power entire beam has to go on one sail, this won't work.

Apr 15, 2016 04:12 Ryan Whitchurch Posted on: Breakthrough Initiatives

Karen Pease,
Are there any secondary roles the carbon aerogel could offer the mission? I'm not very familiar with the material, but a quick review indicates that useful properties abound, such as:

Apr 16, 2016 16:25 Karen Pease Posted on: Breakthrough Initiatives

@Ryan Whitchurch:

That's actually not a bad idea. If you're going to bring it you might as well dual-use it. Carbon aerogel is really amazing stuff. It makes silicon aerogel look like lead by comparison:

In a vacuum the lighest carbon aerogels are a fraction of the mass that an equivalent volume of air would be on Earth.

The key with decelerating debris in space is, "start early". A particle starts to break up after its first collision. That's the basis for whipple shields. Aerogel is basically a continuous whipple shield.

If you could double that up for other purposes, like energy storage, that would be brilliant.

Apr 19, 2016 17:47 Micky Badgero Posted on: Breakthrough Initiatives

Karen Pease, the carbon nanogel idea is great. The problem at 20%c is as much hydrogen atoms as dust particles. Project Daedalus used 9mm of beryllium, but had a large volume over which to disperse the impact cone. I have looked at shielding for a somewhat larger probe than Starchip (kg sized) of three layers: beryllium to ionize anything coming in; polyimide aerogel to stop the ions and; boron nitride to stop anything solid enough to make it through the first two layers. Carbon areogel is less comlicated and would probably work as well or better for a gram sized probe.

Ryan Whitchurch, the advantage of carbon nanogel for capacitors is the large surface area exposed to the electrolyte. I think trying to make it into a capacitor would make it too heavy though. If you look at the mass budget for a one-gram star probe, there's not much room for liquid.

Apr 21, 2016 20:59 Posted on: Breakthrough Initiatives

It occurs to me that the high energy physics community (particle accelerators) has a lot of experience with materials encountering atoms travelling at near lightspeed, and in engineering electronics and physical structures to withstand such erosion.

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