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Old April 22nd 17, 02:42 PM posted to sci.space.policy
William Mook[_2_]
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Default Reusable Laser Launcher

On Saturday, April 22, 2017 at 7:50:49 AM UTC+12, Robert Clark wrote:
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"0something0" wrote in message
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Lets say that a laser(and other equipment that needs to be replaced every so
often) can be used 10 years before needing to be replaced, there are 2
launches every day, and that all of the cost is from the 472 million dollar
laser array.(probably can get better info from Atomic Rockets but I don't
have time for that). Each launch consumes a megawatt and takes 1 hour, so it
takes $120 per launch if we are drawing power from a US grid(12 cents per
kw-hour). Each launch can lift 10kg.


Diode lasers have exceptionally long life if used within certain parameters.. So, in this instance, other factors, such as power supplies, and so forth give life span. However, those lives can be shortened by increasing their power output. In fact, they can be used like old-style flash bulbs, that put out a helluva lot of power and are replaced after each use. Why shorten the life? Because it gains in power per dollar at the cost of energy per dollar.

Now the metric, or calculus, of the relationship, for lowest cost, given near unity efficiencies and ignoring weight considerations, is power output per dollar versus number of hours of use.

According to DOD studies, modern high efficiency diode lasers purchased at above gigawatt scale cost under $0.10 per watt, with virtually unlimited use - 10 years or more. However, by over-amping the diode, lifetimes can be shortened. With a 57% utilisation over a year, each watt of capacity consumes 5 kWh. At $0.12 per kWh that's $0.60 per year. A 10 year life span consumes $6.00 per watt, and with $0.10 per watt of capacity, its clear the energy costs dominate.

What if the cost of the laser was say $10 per watt and not $0.10? 100x more. Then the trick of overamping the diodes and making them disposable parts of the system, pays dividends.

Typically, by running at over the rated power, you shorten life cycle. Running at 1000x the rated power shortens life time from 10 years to 10 hours. So, $10 per watt becomes $0.01 per watt as you overpower the diode by 1000x (1 kW) and the 10 kWh cost $1.20 -

If your laser cost $10,000 per watt - and you over amp it 1 million times rated power shortening its life to 10 minutes - then you consume $20 worth of power for every $0.01 worth of expensive laser.


10 years = 3650 days * 2 =service life: 7300 launches
$472,000,000/7300 launches =(around) $64657.5+$120(electricity
cost)/launch(10kg) = $6477.75 per kilogram. According to Atomic Rockets, the
1966 Proton has $5000/kg launch cost.


Your figure is dominated by low utilisation rate. You assume 2 launches per day of 10 kg - a total of 20 kg per day for a $400 million investment. It takes 10 minutes to launch a vehicle to orbit. So, you're assuming 20 minutes of use of a very expensive item out of 1,440 minutes (24 hours) each day. That's 1.4% capital utilisation. If you applied 57% utilisation as I've done above, with no other changes in your assumption, you'd have $1,575 per launch and $157.50 per kg for the hardware and $120.00 per kg for the power.

However, you haven't really taken modern reportage from the DOD as it relates to current costs of laser systems into account. When you do that the cost of power dominates, and the cost of capital is a correction factor.

Now, having a steady state power source big enough to blast a payload into space, that drives a steady state laser source big enough to accept all the power at its peak, and using it only a few minutes a day, is not efficient.. Clearly it pays dividends if you understand the engineering and physics of diode life cycle and power output, and if you organise your use of these to increase their capital utilisation.

So, consider the following material

https://www.extremetech.com/extreme/...-later-as-heat

Adapted for use inside a Fabrey-Perot interfometer. That is, a material that sits in a large open pond absorbing sunlight, and designed to flash all of its power over a 10 minute period to produce a powerful laser pulse!

Here, we are dealing with pumps, tanks, and optics - only! The cost of energy is zero, the cost of power is zero. The cost of pumps and tanks and optics is about 5% of total system cost (for the steady state) or $0.005 per watt. So a Giga-watt scale laser under these circumstances would cost $5 million - and with a 10+ year life, and 57% utilisation, would be far less than the fuel cost of modern airliners. So, such systems would not only be capable of launching stuff into space, but also of powering passing aircraft and even powering a city via optical fiber.

http://lasermotive.com/markets/uav-power-links/

https://www.theguardian.com/technolo...es-world-debut

The same pulse power trick that can be used to minimise cost of diodes, can also be used to minimise cost of materials, so energy costs dominate,

https://www.google.com/patents/US3662280

However, if the energy source is the sun, and you have a thin layer of material laying in the sun, costs of energy drops toward zero as well.






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Likely, the cost for the 1,000 lasers at 10 kW each will be less than
$472,000,000 since they would be bought in large quantity. And the quoted
price was for the entire laser cutting system. The cost would be less for
the bare laser.


The DOD has declassified literature from early 2000s that show at the GW scale, large diode lasers cost $0.10 per peak watt. At these prices, even CW lasers have energy cost over their life cycle dominating. There are pulsed power tricks that reduce even expensive laser systems - like chemical lasers - to where the cost of energy dominates again. Finally, combining ideas to create chemical lasers that gather energy from sunlight very cheaply, we can reduce cost of power to zero. Even with terrestrial systems. In space costs can be lowered even more using thin film reflectors to concentrate sunlight reliably to create compact chemical processing systems on orbit, that provide power where its needed on demand.

The cost in your system is high because you're building a continuous system with off-the-shelf (less than optimal) technology and using it less than 2% of the time. If you built a more reasonable system, using current technology (and why the hell if you're spending half a billion dollars wouldn't you use best practices?) - costs for space travel can be brought to lower than air travel, and even air travel can be reduced in cost.


Also, the flight time to orbit is expected to be about the same as for usual
rockets about 10 minutes. So you could then have many more flights to
amortize the cost of the lasers.


That's right! Now you're getting it! Using your approach you can get prices down to $250 per kg. Using best practices with diode lasers, that can be reduced to $12 per kg, and combining best practices with current tech, gets you to $0.60 per kg and less.

https://www.youtube.com/watch?v=33_-teBjZ4w

With this technology you not only open up the world to the cosmos, but you make travel from any point on Earth to any other, easy.

In the future people will live in the Andes, work in New York, have lunch in Paris, and pick up their kids in China, before going home. This capacity to travel anywhere in minutes, in less time than it takes someone living in Malibu to travel to LAX to board a private jet.

Facilities on orbit that accept small craft and are capable of travel deeper into space, across the solar system, will one day provide seamless travel from the surface of the Earth to the surface of any world or space colony.

The ability to deliver energy at very low cost and very high power levels, to run these propulsion systems, also gives us the ability to run our industrial economy at very low cost, and zero environmental impact. Combine these capacities with artificial intelligence and smart materials, like utility fog, and you see that a world of great wealth and adventure awaits us.



Bob Clark
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