Apr 13, 2016 13:58 Karen Pease Posted on: Breakthrough Initiatives

Clearly you have to use a chemical laser or similar. When you're talking about these sorts of power outputs, even if your laser was 99% efficient (which of course doesn't happen) its internal heat would very rapidly become unmanageable.

Clearly deuterium fluoride has cost and toxicity issues, so we can rule it out, but I think COIL could be a reasonable approach. The efficiency is acceptable and it has very good beam quality. With any chemical laser, you have all the time in the world to generate your feedstocks, then you burn them quickly when you need power in a manner similar to a rocket engine. So you need feedstocks that can be stored as cheaply as possible, preferably open tanks (or at least unpressurized / not temperature regulated tanks). And they need to be cheaply and efficiently regenerable.

The iodine for COIL, that's easy - elemental iodine is solid, you can store it in a big heap and feed it in on screws or belts. It's $30/kg, though, so I'm not sure if that would be a limiting factor or not. If your laser burns into a tank of water, then you'll accumulate iodic acid. iodine can be recovered from it by a number of processes - for example, dehydrating it back to iodine pentoxide and reducing it with carbon monoxide.

On the other side of the equation, you have to generate excited oxygen. COIL does this by reacting chlorine with a mixture of potassium hydroxide and hydrogen peroxide. Producing H2O2 (anthraquinone process) and converting KCl to KOH and Cl2 is straightforward enough (chloralkali process), but storing large quantities of chlorine and concentrated H2O2 are less than ideal. So a better chemical oxygen generation reaction may be desirable.

From a completely different approach, ElectriCOIL uses arc discharges to create the oxygen. It's simpler and more efficient, but you really don't want to have to pay for the hardware to store/generate those sorts of power levels, discharged over the whole launch timeperiod. The cost would be astronomical.

1TJ is the energy content of about 24 tonnes of gasoline. After taking into account losses and the lower energy content of the chemicals in question, your total storage needs to be on the order of hundreds of tonnes. Assuming a net 20% system efficiency (incl. recovery) and industrial power rates of $0,05/kWh then one firing would cost $70k. So the power is eminently affordable. It's the capital costs that you have to control.

Apr 14, 2016 12:25 Theodore Kim Posted on: Breakthrough Initiatives

Okay, this is going to INCREASE costs substantially but I think for good reason: Put it on the FAR side of the moon!

First you must realize this project won't be practical for awhile, if only to develop nanobots capable of repairing damage from relativistic dust impacts. (Launching lots of probes and hoping one survives as per one proposal, is not optimal). Also, the superlaser launcher is an insanely powerful anti-sat weapon which would allow one to rule near earth space. (Current military lasers blow drones out of the sky, this is a million times more powerful). Since almost all orbits carry their satellites overhead, only geo-sync sats on the other side of the earth are safe. This would absolutely block international approval of the project.

Well, since this project isn't going to be ready soon anyway, why not use that time to wait until we can put it on the moon? In fifty years, it will be a lot cheaper to build on the FAR side of the moon and that brings many advantages. No atmospheric distortion, geologic stability, slow rotation (two week pointing time) and abundant solar power just adds to the principal advantage of being unable to be used against the earth (and near earth objects out to the moon's orbit). Another plus is perhaps improved beam purity (from more widely spaced lasers?) which may make it possible to keep it "locked on" far further than the planned 1 million km. If it can do ten times this distance the acceleration and reflectivity requirement of the sail would be reduced (from 99.999% to 99.99%). (Or the payload could be ten times larger, etc.).

So perhaps the additional costs for putting this on the moon is worth it (especially if a lot of it can be built there using lunar material and robots).

Apr 14, 2016 13:28 Karen Pease Posted on: Breakthrough Initiatives

No, putting things in space is not going to "make them cheaper", with launch costs on the order of thousands of USD per kg. And while they have been trending downward, the trend is not exactly spectacular. Space operation also introduces numerous new difficulties, such as outgassing, cooling difficulties, etc.

KISS principle here.

And "nanobot" is not a synonym for "magic". There's nothing about making robots nanoscale that makes engineering challenges go away - it actually makes them harder.

And if you're going to put it in space, there's no point to subsequently lowering it back down into a different gravity well.

Apr 15, 2016 12:18 Luka Marinovic Posted on: Breakthrough Initiatives

As Pete Worden suggestion, I'm posting my suggestion for a Light beam here:

1. You don't need a power for laser, 'cause we already have it! It's the Sun!
Just check the movie "Diamonds are forever": https://www.youtube.com/watch?v=xt_Kn4DggPg
In essence, a big enough Sun collector that can focus a beam can be used as a laser. Just don't turn it towards the Earth this time!
No - just joking, you can use it for:
a) moving asteroids from their trajectory, preferably farther from Earth! (plan has been made with NASA, so you can also collaborate on that research to make a powerful enough laser). Maybe NASA would like to fund such lasers for a protection of the Earth?!
b) power up the probe to Alpha centauri
You certainly wont get out of power soon, by using electrical power to power up lasers...nor will you have problem with power delivery! Just design the Sun-collector to be Solar storm proof...

2. If you manage to design such a laser, than a solar sail will have to absorb the wavelength of the Sun from the laser. It would also have the additional power from the Sun (at least up to Jupiter orbit), depending on the scale of the Solar sail. But, as the Alpha centauri 1 is similar in wavelength of our Sun, the Solar sail can be used as a:
a) Solar parachute into the Alpha centauri system - maybe not to slow down the probe much to enter the system (but why not, maybe even that trajectory can be obtained?!), but at least to slow it down to get more time for observation & more time to get pictures from another star system.
b) Can also be used to steer the probe around some objects in inner Alpha centauri system. Because it would be bad if a probe comes to Alpha centauri & crashes on planet similar to Uranus or Neptune...

Hope that the ideas interest you...

Apr 16, 2016 20:56 Karen Pease Posted on: Breakthrough Initiatives

"In essence, a big enough Sun collector that can focus a beam can be used as a laser"

No, it can't. The sun is not a point source of light; photons come to you at varying angles, and you cannot reduce this variation when you reflect it; it's a basic limit of optics. The reflected sunbeam is not a "column" but a cone that rapidly increases in size with distance, quickly weakening to irrelevance when dealing with how fast this craft would be moving as it accelerates.

Orbital mirrors for power generation - we're talking, things directly over the Earth, aiming at the Earth - have spot sizes on the order of hundreds or thousands of square kilometers.

The sun is not a laser. The reflected sun is not a laser. Stop calling it a laser. ;) It does not have a single wavelength, it has a spectrum roughly approximating a blackbody curve. It is not coherent light. It is not collimated. It is not what is required for this task.

No, you cannot "solar parachute" the probe to decelerate it on the other end. The amount of force is vastly insufficient, by many orders of magnitude.

Apr 17, 2016 21:53 Gary Camp Posted on: Breakthrough Initiatives

I agree with Pease but dissagree too. To space based I say we can overcome the Killer Laser in orbit problem. We cooperate with everyone on the ISS and we can do it under UN for this laser. The cost of "to orbit" is about to drop significantly. See SpaceX and Orbital for very rapid improvements in efficiency. SpaceX is already the cheapest to orbit and is about to get 30% cheaper shortly. And in theory, might approach 90% cheaper in a few years. Especially with competition. Musk is strongly interested in getting to the stars (Mars is just a practicle 1st step) so he might be open to providing freebies or at least "Cost only" launch.

Apr 21, 2016 11:18 Giulio Prisco Posted on: Breakthrough Initiatives

@Theodore Re "Okay, this is going to INCREASE costs substantially but I think for good reason: Put it on the FAR side of the moon!..."

I think this option should be considered. It's likely to more than double the overall cost of the project, but the establishment of a moonbase on the far side - which could double as an astronomical observatory and other uses - is a worthy goal in itself and could attract its own funding.

NASA, ESA and other space agencies have preliminary plans for a farside moonbase. While unlikely to significantly contribute to Starshot itself, the space agencies could be persuaded to contribute to the establishment of the moonbase, including transportation. Perhaps Starshot could be the catalyst that makes a moonbase happen.

Apr 24, 2016 14:02 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/

Apr 25, 2016 14:30 Mike Gorman Posted on: Breakthrough Initiatives

"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 is where we run into policy questions regarding weaponization of the technology. Some consider that the only safe location for the phased array would be the far side of the moon, where it could not be used as a weapon against cities or satellites near earth.

We need some clear policy decisions to direct the solution and its implementation otherwise we will end up with something not at all like we expect.

Apr 26, 2016 07:48 Mihai Ionescu Posted on: Breakthrough Initiatives

"Some consider that the only safe location for the phased array would be the far side of the moon, where it could not be used as a weapon against cities or satellites near earth."

There is a huge difference in cost between building a high-power laser facility on the moon and using those in operation today, used for research purposes by universities in various countries, plus one or more geo-stationary satellites equipped with nanocraft beaming optics.

Whoever might want to use this combination for other purposes, would need to control both components of the proposed solution. If the satellite(s) would be controlled by an international consortium (similar to the International Space Station) and the ground lasers are controlled by the respective universities that operate them, I don't see any more reasons to discuss James Bond movies scenarios.