Author Topic: Breakthrough Starshot  (Read 36804 times)

Offline Eric Hedman

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Re: Breakthrough Starshot
« Reply #40 on: 04/12/2016 11:02 PM »
I wonder how lasers of this power hitting a small target won't vaporize it.  If it doesn't reflect 99.999999999% of the light there will be an insane amount of energy absorbed into this tiny spacecraft.  I don't know of any material that can reflect that high a percent of the light hitting it.

Could they make the sail out of some kind of reflective ablative?
I'm not an expert, but I think that would add significant mass drastically reducing the acceleration possible.

Offline Remes

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Re: Breakthrough Starshot
« Reply #41 on: 04/13/2016 12:00 AM »
I wonder how lasers of this power hitting a small target won't vaporize it.  If it doesn't reflect 99.999999999% of the light there will be an insane amount of energy absorbed into this tiny spacecraft.  I don't know of any material that can reflect that high a percent of the light hitting it.
Not all of the electric energy is converted to light. Some of the light will be scattered in the atmosphere. Even the best lasers diverge and therefore only a small amount of the light hits the target. The sail might be quite huge.

100E9W electric power.
30E9W light power
1E9W scattering, divergence, ...
1E7W 1% is absorbed
10W per square meter, if the sail is 1km˛ big.

Albeit 10W is quite something on a very thin foil. But the divergence losses are in my guess rather optimistic.
« Last Edit: 04/13/2016 12:12 AM by Remes »

Offline the_other_Doug

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Re: Breakthrough Starshot
« Reply #42 on: 04/13/2016 12:19 AM »
And yes, you might be able to accelerate a gram-mass probe with this energy source.  But, um... how much does a many-square-kilometer light sail mass?  You gotta include the mass of the sail...
-Doug  (With my shield, not yet upon it)

Offline ChrisWilson68

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Re: Breakthrough Starshot
« Reply #43 on: 04/13/2016 01:18 AM »
Well, it will be useful when the Kzinti show up.

Offline yg1968

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Re: Breakthrough Starshot
« Reply #44 on: 04/13/2016 01:26 AM »
A few links to the archived video of the press conference:

http://livestream.com/breakthroughprize/starshot



« Last Edit: 04/13/2016 11:28 PM by yg1968 »

Offline gospacex

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Re: Breakthrough Starshot
« Reply #45 on: 04/13/2016 01:34 AM »
By what magic the probe is not instantly vaporized by multi-gigawatt laser beams?

Offline Robotbeat

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Re: Breakthrough Starshot
« Reply #46 on: 04/13/2016 02:03 AM »
By what magic the probe is not instantly vaporized by multi-gigawatt laser beams?
Dielectric mirrors can achieve ridiculously high reflectivity. And for the part that is absorbed, you have a very, very large area to radiate heat from.

But there's another problem: The laser array they showed wouldn't work due to the "thinned array curse."

They'd be wasting 95% of the laser power due to the thinned array curse. Either that, or they're assuming a small aperture. Small aperture makes everything harder since it means you need to accelerate much faster, thus requires a much more powerful laser.

I still think an orbital laser, or a bunch of them, would be better. Perhaps a very large inflatable mirror with an active-optics secondary mirror to adjust for imperfections in the inflatable mirror. (MMOD of the inflatable mirror would be a smaller problem than normal, since you'd be accelerating for on the order of minutes and could afford to keep it inflated with an external gas supply in case of holes.)
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline savuporo

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Re: Breakthrough Starshot
« Reply #47 on: 04/13/2016 02:12 AM »
I still think an orbital laser, or a bunch of them, would be better. Perhaps a very large inflatable mirror with an active-optics secondary mirror to adjust for imperfections in the inflatable mirror.
We all know that wouldn't be permitted, since Diamonds are Forever came out.
Orion - the first and only manned not-too-deep-space craft

Offline ChrisWilson68

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Re: Breakthrough Starshot
« Reply #48 on: 04/13/2016 06:36 AM »
They mentioned 60000g acceleration (probably peak initial).

According to Wikipedia, the electronics in artillery shells is rated to survive under acceleration of 15,500 g, and presumably the electronics are there to steer the shell, so the sensors and actuators have to be able to survive that acceleration too.  So, it's conceivable that something can survive this order-of-magnitude of acceleration and still sense and interact with the outside world.  Obviously, though, the artillery shell only has to endure that acceleration for orders of magnitude less time, since its final speed is orders of magnitude less than .2c.

Offline R7

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Re: Breakthrough Starshot
« Reply #49 on: 04/13/2016 07:12 AM »
^The artillery shells have slightly different problem; how to contain microchips without braking them inside a macroscopic object doing 5-digit acceleration plus shock vibrations. In this concept the chip itself is the "ammunition". Its microscopic nature should make it more robust.

Having said that I have problems imagining a thin sheet a few meters wide (they mentioned four meters in the pressconf) weighing just one gram remaining steady and flat while inside laser beam pushing it 60000g. Wouldn't even minor misalingment or a wrinkle in the sail cause instant folding, warping, tumbling and whatnot of destructive kind? I guess one could spin stabilize the sail before launch but is it enough? Also the beam would have to be very uniform over the sail in order not to flip it.

Did some BOTE calc for the fun. Assuming 4m diameter disc weighing one gram the required beam intensity to accelerate the craft at 60000g is 7GW/m2. Further assuming 99,9999% reflectivity on the mirror side the craft absorbs 7kW/m2. If the other side is perfect black body it can reradiate the heat at required rate if the craft can survive about 600K. Not horribly hot, but is hextuple-9 reflectivity within realm of possible idk.
« Last Edit: 04/13/2016 07:39 AM by R7 »
AD·ASTRA·ASTRORVM·GRATIA

Offline Oli

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Re: Breakthrough Starshot
« Reply #50 on: 04/13/2016 07:47 AM »
Making a planetary flyby in another star system at 0.2c? What if the 1g probe's course is slightly altered by interstellar dust or similar? Does it have its own propulsion? How is it supposed to navigate?

IMO this is one of those "Moore's law will fix everything" concepts.
« Last Edit: 04/13/2016 07:47 AM by Oli »

Offline R7

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Re: Breakthrough Starshot
« Reply #51 on: 04/13/2016 08:13 AM »
1. Making a planetary flyby in another star system at 0.2c?
2. What if the 1g probe's course is slightly altered by interstellar dust or similar?
3. Does it have its own propulsion?
4. How is it supposed to navigate?

1. Cool huh?
2. Then the probe ends up in slightly different place than planned. The plan is to shoot out large number of them. Perhaps spread the flotilla a bit like a shotgun pattern to increase odds that at least some ends up in the right place.
3. Photon thrusters are mentioned, but given the miniature attainable power levels they are probably for orienting only.
4. Poorly? I guess it could trim its trajectory a bit acting as a solar sail.
AD·ASTRA·ASTRORVM·GRATIA

Offline Oli

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Re: Breakthrough Starshot
« Reply #52 on: 04/13/2016 09:01 AM »
1. Making a planetary flyby in another star system at 0.2c?
2. What if the 1g probe's course is slightly altered by interstellar dust or similar?
3. Does it have its own propulsion?
4. How is it supposed to navigate?

1. Cool huh?
2. Then the probe ends up in slightly different place than planned. The plan is to shoot out large number of them. Perhaps spread the flotilla a bit like a shotgun pattern to increase odds that at least some ends up in the right place.
3. Photon thrusters are mentioned, but given the miniature attainable power levels they are probably for orienting only.
4. Poorly? I guess it could trim its trajectory a bit acting as a solar sail.

2. A slightly different place? This is space we're talking about. You won't fit anything but primitive optics on a 1g probe, so you must get close.
4. With navigation I mean knowing its location and trajectory in space with sufficient accuracy.

Offline Star One

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Breakthrough Starshot
« Reply #53 on: 04/13/2016 01:41 PM »
Further article with an explanation from Milner as to why he proposes the lasers be on the ground & not in space.

http://www.centauri-dreams.org/?p=35402
« Last Edit: 04/13/2016 01:49 PM by Star One »

Offline notsorandom

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Re: Breakthrough Starshot
« Reply #54 on: 04/13/2016 02:17 PM »
Making a planetary flyby in another star system at 0.2c? What if the 1g probe's course is slightly altered by interstellar dust or similar? Does it have its own propulsion? How is it supposed to navigate?

IMO this is one of those "Moore's law will fix everything" concepts.
I think from reading into previous proposals similar to this one that it is a numbers game. Each individual probe has a small chance of ending up on target. However because these things are so small they are inexpensive to build and get into space. A good percentage of them could end up off target but enough would be on target to make it worthwhile. This also appears to be how they will deal with interstellar dust impacts at 0.2C. Many will be destroyed in relativistic collisions but some will make it through. Just build and launch enough of them and some will make it there.

Offline Burninate

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Re: Breakthrough Starshot
« Reply #55 on: 04/13/2016 02:20 PM »
https://en.wikipedia.org/wiki/Starwisp

I don't understand how the numbers given could possibly be feasible, even if starwisps are probably the fastest way to return data from nearby stars.

Offline Oli

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Re: Breakthrough Starshot
« Reply #56 on: 04/13/2016 04:48 PM »
I think concepts for better telescopes are more promising. For example NASA's "glitter telescope".

http://www.space.com/29677-floating-cloud-space-telescope-glitter-tech.html
« Last Edit: 04/13/2016 04:50 PM by Oli »

Offline Star One

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Re: Breakthrough Starshot
« Reply #57 on: 04/13/2016 07:26 PM »
Ancestors
April
18h18 hours ago
April ‏@prillyp
@plutokiller My daughter thinks you could test the star shot tiny satellites on getting images of Planet9. Ok? (I ❤️ having a science kid!)
Mike Brown
Mike Brown –  ‏@plutokiller

@prillyp I HAD THE SAME THOUGHT THIS MORNING!!!!!!!!
7:31 p.m. - 12 Apr 2016
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Online Zed_Noir

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Re: Breakthrough Starshot
« Reply #58 on: 04/13/2016 07:40 PM »
After reading through the entire thread. All I can think of is the Motie "Crazy Eddie Probe" from the CoDominion Universe from Larry Nivens & Jerry Pournelle.

Online Silmfeanor

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Re: Breakthrough Starshot
« Reply #59 on: 04/13/2016 09:08 PM »
it instantly reminded me of the star probe to the brown dwarf in Charles Stross's Accelerando, using a laser bank in the asteroid belt, with the starwhisp being made of computronium.

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