I Thoughts on Breakthrough Starshot?

[greswd]

Now in the pop science news is about how "disco balls" could be the key to interstellar travel.

https://www.newscientist.com/articl...ropelled-by-laser-could-fly-to-a-nearby-star/

What do you guys think of this project? Its feasibility, cost, usefulness etc..

 

[russ_watters]

The "project" is at this point just a research project:
https://en.wikipedia.org/wiki/Breakthrough_Starshot

They have a long way to go before such a thing will even be possible, much less feasible:
"According to The Economist, at least a dozen off-the-shelf technologies will need to improve by orders of magnitude.[18]"

Doesn't sound very realistic to me.

 

[Chronos]

The problems with light sails are myriad and have been well publicized. See https://www.inverse.com/article/14246-5-big-questions-about-the-starshot-nanocraft-technology for discussion on some of these issues. It still looks like wishful thinking [emphasis on the wish part] to me. The concept appears feasible and probe costs could be manageable, but, the power issue still looms large: where will the trillion dollars for the laser come from?

 

[greswd]

The problems with light sails are myriad and have been well publicized. See https://www.inverse.com/article/14246-5-big-questions-about-the-starshot-nanocraft-technology for discussion on some of these issues. It still looks like wishful thinking [emphasis on the wish part] to me. The concept appears feasible and probe costs could be manageable, but, the power issue still looms large: where will the trillion dollars for the laser come from?

Do you think a more durable craft equipped with a "slow burning" rocket thrust would be more feasible?

 

[rootone]

If 'feasible' means could it be done, then yes,
but then we are back to the problem that it would take decades to go the nearest star system.
Centuries to go anywhere that is seriously interesting.

 

[greswd]

If 'feasible' means could it be done, then yes,
but then we are back to the problem that it would take decades to go the nearest star system.
Centuries to go anywhere that is seriously interesting.

but if accelerated over a long period of time it could still reach a pretty fast speed.

 

[rootone]

Yes, but since it's going fast when it gets to the destination there isn't much time to collect interesting data.
The New Horizons probe though managed to collect a big set of data in a couple of days while passing through the Pluto system.

 

[Chronos]

I think the idea is severely constrained by energy demands. I have zero faith we could build, much less sustain a device of such power. The economics and politics just do not work for me.

 

[Astronuc]

Now in the pop science news is about how "disco balls" could be the key to interstellar travel.
. . . .
What do you guys think of this project?

Another nutty idea. What power lasers and where are they located? On orbit? Problems with dispersion over 'long' distances. Sending back information from 4+ light-years away would seem infeasible. I would think a local star's radiation (and solar wind) would swamp any signal generated.

Statements like ". . . , sending back pictures of anything interesting once it arrived," are just silly.

 

[greswd]

I think the idea is severely constrained by energy demands. I have zero faith we could build, much less sustain a device of such power. The economics and politics just do not work for me.

is that due to the low momentum-energy ratio of light?

 

[Chronos]

The logistics and economics of building and powering a 100 gigawatt laser array would be enormous. And, as already noted, how will the probe transmit its data back to earth? I'm unaware of any technology, real or imagined, capable of such a feat. We aren't talking about a light day here, as in the case of the solar system, we are talking 4 light years. Bear in mind signal strength falls by the square of distance.

 

[skeptic2]

The logistics and economics of building and powering a 100 gigawatt laser array would be enormous. And, as already noted, how will the probe transmit its data back to earth? I'm unaware of any technology, real or imagined, capable of such a feat. We aren't talking about a light day here, as in the case of the solar system, we are talking 4 light years. Bear in mind signal strength falls by the square of distance.

The Earth bound laser would be one of the minor problems. Traveling at 0.2 c, even a dust particle could cause major damage to a probe. If the probe were to reach Proxima Centauri the path loss for the transmission, assuming a transmit gain of 10 dB and a receive gain of 40 dB would be 292 dB. http://www.qsl.net/pa2ohh/jsffield.htm With a receive sensitivity of -130 dBm it would still need a transmit ERP of 162 dBm or 10^13 watts using a frequency of 74 MHz for minimum path loss. A power supply capable of supplying that amount of power would also be needed. Inasmuch as the probe would already have to have a power supply that large, it might as well be used to propel the probe with a laser pointed backwards. Nevertheless the probe would have a mass of many thousands of tons. Then there is the problem of dissipating that much heat in a vacuum.

 

[rootone]

... the probe would already have to have a power supply that large, it might as well be used to propel the probe with a laser pointed backwards..

A very good point, and whilst not actually plausible, that concept eliminates some modes of power wastage.

 

[Sue Rich]

I've always had a vision of a ring-like ship that has a powerful center generator that creates its own power, by simply rotating rapidly, causing electricity and immense power. The only time any other source needed would be on take off and landing.

 

[rootone]

Simply rotating does not generate power.
To generate electricity you need to be rotating in a magnetic field which itself is not rotating.

 

[Sue Rich]

Sorry, rotating was just the best word I could find to describe what I meant. Thanks for the clarification.

 

[Sebastiaan]

The logistics and economics of building and powering a 100 gigawatt laser array would be enormous. And, as already noted, how will the probe transmit its data back to earth? I'm unaware of any technology, real or imagined, capable of such a feat. We aren't talking about a light day here, as in the case of the solar system, we are talking 4 light years. Bear in mind signal strength falls by the square of distance.

Sure thing but the question is, does it has to because perhaps the whole Starshot is just a ruse to build a 100 GW Laser array . There are many more applications you can do with just shooting light-sails to other stars. Technically you can use it to light up anything that flies over. Or you can use it to transfer huge amount of power to orbital systems or planetary vessels traveling to other planets. I bet this is the true reason why they are so invested in this.

Still if they manage to build it, it will be quite the spectacle to send probes into outer space.

 

[Tom.G]

Hmm... I wonder what the aperture of that 100 GW Laser would have to be to avoid flashover. I've seen a large desktop size Laser support a sustained electrical arc in air when focused.

 

[stefan r]

Hmm... I wonder what the aperture of that 100 GW Laser would have to be to avoid flashover. I've seen a large desktop size Laser support a sustained electrical arc in air when focused.

I assumed the lasers would be located in space.

 

[IsometricPion]

I read up on this a few months ago. I am pretty sure that they had in mind to build the 100 GW worth of laser power as a (phased?) array of ~10,000 10 Megawatt lasers on the ground. The sails themselves would weigh only of order a gram each. It was my understanding that, for the sail sizes they had in mind, this would require about an order of magnitude improvement in density. Similar improvements in reflectivity an miniturization of electronics would be necessary. I don't remember any mention of sending back pictures. If any communication were possible, I think the idea would be to modulate the reflected laser light. The idea being to more or less constantly send these probes and thus have a relay system for communication back to Earth (so it is only necessary to be able to communicate with the nearest functional sail, not directly with Earth).

edit: 1 Million 10 KW lasers, possibly pictures could be sent via the same relay system, besides advances in laser technology, cooling of the lasers could be trouble, as they should all fit into a few to a few hundred Km², link to the Breakthrough Initiatives' forum where they have discussed some of the challenges: http://breakthroughinitiatives.org/challenges/3

 

[stefan r]

cooling of the lasers could be trouble, as they should all fit into a few to a few hundred Km²,...

A gigawatt per square kilometer is a kW/m². The solar constant is 1.36 kW/m².

2 lasers positioned next to each other would not be that much better than a laser on each of Earth's poles.

 

[IsometricPion]

According to http://breakthroughinitiatives.org/forum/26?page=1, I was wrong. Dissipating the heat is not considered a big problem.

Also, the website links to two interesting arxiv articles:
A Roadmap to Interstellar Flight - This seems to be the most comprehensive recent analysis to which they link.
Starship Sails Powered by Cost-Optimized Directed Energy - This seems to focus on cost, and indicates an interstellar flight precursor mission is all that is currently feasible.

 

[Sebastiaan]

A gigawatt per square kilometer is a kW/m². The solar constant is 1.36 kW/m².

2 lasers positioned next to each other would not be that much better than a laser on each of Earth's poles.

Although the amount of energy transmitted would be the same, the quality of the phased array central spot size will be negetively effected. According to this powerpoint presentation, there is something called the fill factor, which depend a lot on how close the lasers are position from each other. Only if they can manage a high fill factor, most of the enrgy can be focusted and therefore deliver effective force to the laser sail. The problem to achieving a high fill factor is that the phased array will not be able to supply powr to low elivations as there is simply noo room.