Apr 13, 2016 06:39 Theodore Kim Posted on: Breakthrough Initiatives

I believe one reason for the choice of this design (having lasers on the ground, at a high altitude in Chile's Atacama desert) was because it would prevent someone from having a 100GW laser canon in space that could be used as a weapon! That, and of course the much lower costs of basing it on earth rather than on space. However, it would still be a fantastically powerful anti-sat weapon capable of (literally) blowing away anything the passes overhead (almost everything except geo-sync orbits over the other hemisphere). That's why governments will need/want to be involved (if they secretly aren't already :(
However, there is another application that I propose. Not only would it be, as a telescope, be able to spot any potential asteroids heading our way but a 100GW laser could do serious damage to them, "pushing" them or more realistically ablating their surface so that they are gradually nudged off course. Think of it as an "earth-defense" laser :)

Apr 13, 2016 08:10 Theodore Kim Posted on: Breakthrough Initiatives

To continue with my earlier post, it could also be used for laser launched spacecraft from the ground (using the atmosphere or water as the working fluid) or possibly for spacecraft propulsion in near earth space. Further away it could be used to illuminate solar arrays for deep space probes and for a possible lunar base during the 2 week lunar night or if one is at the lunar poles (in perpetual "darkness").
Lastly, although I believe that this will particular implementation of the project will not be achieved within this generation, it could very well be achieved in the next generation IF the laser array was placed ON THE FAR SIDE OF THE MOON. No problems with atmospheric conditions and better collimation of the beam would allow for longer propulsive phase for the star wisp. Being on the far side of the moon would also mean it could never pose a threat to earth or local satellites. Regrettably it'll be away before launch costs come down to the point where this becomes practical, hence "for the next generation".

Apr 13, 2016 09:03 Rj Hillan Posted on: Breakthrough Initiatives

The lasers even at 100GW would not have the power to deflect the kind of asteroids we would need to be worried about, the 100GW lasers will have little kinetic power when compared to other forms currently used. This is why the spacecraft is going to be roughly an inch long (give or take a few cm). however it can damage spacecraft and pose health risks, it wouldn't be a very successful weapon in orbit so no government would attempt to use it as one.
This challenge will be more of a political challenge when creating protocols and such for the powerful beam array and its power generation.

Apr 13, 2016 10:43 Angeliki Kapoglou Posted on: Breakthrough Initiatives

How much simpler the laser-beamed interstellar probes concept would be (both from policy and technical perspective) if we built the array on the Moon? Maybe not much. but someone needs to check this :)

Apr 14, 2016 17:58 Louis Scheffer Posted on: Breakthrough Initiatives

The policy objectives (can't be used for attack of Earth or its satellites) could also be achieved by a space-based laser, if solar powered and outside the Earth's orbit. The architecture would be a thin plate with solar cells on one side and adjustable lasers on the other. With no storage, it would need to be somewhat bigger (say 5 km on a side) which would give less power but longer acceleration times (since it's a bigger aperture it can keep focus longer). Phasing would be much easier. Expense is an obvious problem.

Apr 15, 2016 12:49 Mike Gorman Posted on: Breakthrough Initiatives

--> I can't sign up with an email address with an Australian (*****.com.au) domain, can this be corrected please? -->

Policy won't mean much unless there is a clear governance model and the means to strictly implement it. Governance starts from the top and requires transparency. One quality required for mega-projects is a "trust" surplus. Projects such as this must manage trust in a similar way to how they manage risk, or in a similar way many organistions today manage health, safety and environment. A culture of trust needs to be engendered from the beginning. Trust management contributes to the bottom line, helping to control cost and quality (vendors trust the project, the project trusts the vendors) and contributing as public relations collateral for the project. Intent, Scope, Governance, Trust, Risk, and Cost need to be outlined in the organisational and project charters. The sponsors and leadership will need to sign up to the charters and they need to be openly published .

Apr 15, 2016 14:10 Theodore Kim Posted on: Breakthrough Initiatives

Okay, so putting it on the far side of the moon, while it would satisfy the policy requirements, would be much more expensive than putting it in the Atacama desert in Chile.

But what about Antarctica?

Possibly the only place on earth that's drier than the Atacama desert is the (high?) regions in Antarctica (not only is there very little precipitation but the intense cold freezes out all the water vapor). So this may be an even better site to base the beamer array in terms of performance (don't know if the optical turbulence caused by winds is more than could be compensated for). As for the policy problems, basically all satellites in equatorial and low earth orbits (expect polar ones) would be safe because the array, being at the pole, couldn't point below the horizon. That includes, for now, the ISS and manned launches. (BTW Alpha Centauri is in the southern skies right?).

While this would be more expensive than placing it in Chile, it would be much cheaper than on the moon (or in space). Power would be a problem during the long sun-less winters, perhaps fuel cells could be used? However the cold temperatures may be an advantage over Chile for the electronics and sensors. Also, during the long winter night, it might be capable of keeping the array pointed for a lot longer than 12 hours (I realize this is probably not a requirement for the launcher but it may be useful for other things, like optical communications with the probe or use as an observatory).

So keep your parkas ready!

- By the way, in my earlier post about using the array as an asteroid deflection system, I'm not sure the light pressure would be sufficient to impart enough energy to make it worthwhile. However, a 100GW beam, hitting the surface of an asteroid, might be able to vaporize part (especially if there are volatiles like in a comet!) and impart a thrust that aways. I mean if the sail has to be 99.999% reflective to keep it from melting then an asteroid should heat up very well.

Apr 16, 2016 16:27 Karen Pease Posted on: Breakthrough Initiatives

Antarctica is windy in most locations. Even if it wasn't, it'd still be a poor location. It's very expensive not just to build there, but to operate there. Not to mention that in most locations, manmade structures gradually sink into and are buried under the ice.

For megascale construction, one has to keep things simple, even if there are more "technologically ideal" locations. Otherwise, your costs rapidly become unrealistic.

As for using it to deflect asteroids by heating one side, there's some technical plausibility to that. It depends in part on the capacity factor of your laser - can you fire it 20% of the time or 0,0002% of the time?

Apr 24, 2016 13:00 Mihai Ionescu Posted on: Breakthrough Initiatives

HIGH-POWER LASERS
There are several N x PW (1,000,000 GW) lasers operational in 2016 in the world, like the 2x 10PW ELI-NP laser in Magurele, Romania, the most powerful one built so far (becoming operational this year), the LFEX laser in Osaka, Japan, operational from 2015, which has a power of 2PW, or the Petawatt Laser in Austin, Texas, which is operational since 2008, with a power of 1.1PW. Please note that these PW lasers produce high-energy trains of laser pulses with a duration (of each individual pulse) from 10-20 femtoseconds to 10-20 picoseconds, with pulses fired at a repetition rate of 1-10 KHz. The cost of building a 2x 10PW laser is around $300 million. Another Nx 10PW laser is under construction in Czech Republic, anticipated to become operational in 2018. So, no beam array needs to be purposely built, as ground-based PW laser facilities are available today.

LASER BEAM FACILITIES
Although beam-time could be requested, in principle, at any of these facilities for powering nanocrafts (as for any other scientific program), none of them have any off-atmosphere high-accuracy laser beam targeting equipment available today. Furthermore, the beam-shots timing has to be scheduled depending on clear-sky weather conditions at the respective facilities, as well as on other constraints, like the safety of airplanes or satellites that could intersect the laser beam path (it can destroy such vehicles in flight, something that has already been demonstrated on small drones, with less powerful lasers).

LASER BEAM TARGETING
All these PW laser facilities are located in the northern hemisphere, between 30-50 degrees Latitude, which makes Alpha Centauri not visible from any of them. The best technical solution for powering the nanocrafts could be the use of optical deflector high-accuracy laser beam targeting equipment placed on-board geostationary satellites with fixed position above these locations. This solution reduces to the minimum the atmosphere thickness the laser beam has to go through, allowing the powering of nanocrafts heading towards the Alpha Centauri or any other star system. The cost of launching a geo-stationary satellite is $40-50m, with the cost of the satellite itself around $50-80m.

HEAVIER NANOCRAFTS
The use of laser beams 10,000 times more powerful than initially considered, may allow the use of heavier nanocrafts (in the pounds/kg range), with better reflective solutions for the sail (based on technologies available today), larger sails and improved protection for the main body, allowing similar flight dynamics and performance for nanocrafts heavier than the grams range, initially considered.

THE SOLAR SYSTEM
This solution may even allow the same concept to be used for extending the solar system exploration in an cost-effective way and placing all the planets within days or weeks of travel time reach, for nanocrafts in the pounds/kg weight range, for quick planetary flyby missions.

PW laser facilities websites:
ELI-NP: http://www.eli-np.ro/
LFEX: http://www.osaka-u.ac.jp/en/apru2015/tour/institute-of-laser-engineering
Texas Petawatt Laser: http://texaspetawatt.ph.utexas.edu/

Aug 17, 2016 14:05 Breakthrough Initiatives Posted on: Breakthrough Initiatives

On Apr 24, 2016 13:00 Mihai Ionescu Posted on: Breakthrough Initiatives
"HIGH-POWER LASERS
There are several N x PW (1,000,000 GW) lasers operational in 2016 in the world, like the 2x 10PW ELI-NP laser in Magurele, Romania, the most powerful one built so far (becoming operational this year), the LFEX laser in Osaka, Japan, operational from 2015, which has a power of 2PW, or the Petawatt Laser in Austin, Texas, which is operational since 2008, with a power of 1.1PW. Please note that these PW lasers produce high-energy trains of laser pulses with a duration (of each individual pulse) from 10-20 femtoseconds to 10-20 picoseconds, with pulses fired at a repetition rate of 1-10 KHz. The cost of building a 2x 10PW laser is around $300 million. Another Nx 10PW laser is under construction in Czech Republic, anticipated to become operational in 2018. So, no beam array needs to be purposely built, as ground-based PW laser facilities are available today."

Answer:

The increase in laser power seems to follow Moore’s law, a built-in premise for StarShot. The mentioned lasers have indeed peak power of 20 PW, 2-3 orders of magnitude above the requirements for the beamer. However, the average power for the 2x 10PW ELI-NP laser in Magurele, Romania (the most powerful at present) given in the specifications is for the pulse duration of 50 fs:
Two outputs with 0.1PW at 10Hz x 50fs = 100 W average
two outputs with 1PW at 1 Hz x 50 fs = 100 W average
two outputs with 10PW at 1shot/min x 50 fs = 17 W average
http://www.eli-np.ro/scientific-papers/SPIE_ELI-NP_87801H.pdf or
https://www.researchgate.net/publication/260669642_Extreme_Light_Infrastructure_Nuclear_Physics_ELI-NP_Present_status_and_perspectives
Extreme Light Infrastructure Nuclear Physics (ELI-NP): present status and perspectives

The present lasers do not yet satisfy the beamer requirements. We need a continuous average power of about 15-100 GW for at least 10 minutes.

– Prof. Sasha Buchman, Breakthrough Initiatives