Jul 18, 2016 00:39 curryd1@udayton.edu Posted on: Breakthrough Initiatives

Could you use a chemical processes of perhaps a clever coating on the sail that would react with the lasers and create an added thrust? This would require this material to also dissipate at the same time so that the added weight wouldn't make the process negligable. But I could see this reducing some of the power needed if done well. Just a thought.

Also on another note couldn't we have more than one power source or laser. This would increase stability and would reduce the issues of having such incredibly high power systems. Or we could have a power source on earth and in space. If we had multiple stages of lasers to propel the sail we may even be able to reduce the structural concerns of the high acceleration. I know this was discussed in comments above but it would need to be down in close increments due to the speed of the spacecraft it would actually take more power because we would need more and more powerful lasers the farther it got away. Therefore, using a different power site for example each day would be somewhat redundant. This process would still need to be in quick succession but could possible reduce the acceleration large percent, which even a 25% reduction would make the design of the sail structure more bareable.

Jul 23, 2016 21:19 Breakthrough Initiatives Posted on: Breakthrough Initiatives

Excellent questions. Thank you.

The Starshot program is fortunate to be developed in a time when battery costs are dropping and performance is rising dramatically due to electric vehicle development and the need for grid level storage for solar and wind power.
The current cost of Li batteries is about $100/kw-hr. Note this is cost per energy (kw-hr) NOT cost per unit power.
In the timescale of the development of the Starshot program we expect dramatic reductions in the costs of batteries as well as in super capacitors or a hybrid. This is an extremely active area of development and one that the Starshot program will gain from without likely having to develop a custom battery or super capacitor.

For technical details see section in the paper “A Roadmap to Interstellar Flight”:
http://arxiv.org/abs/1604.01356
It will often be referred to as the “roadmap” paper.

You can find a photon propulsion calculator to design your own mission and see the trades between the various system parameters such as energy and energy storage costs here:
http://www.deepspace.ucsb.edu/projects/starshot
This calculator implements the equations in the above “roadmap” from sections 2, 2.1 and 2.2.

– Prof. Philip Lubin, Breakthrough Starshot

Jul 25, 2016 10:55 michael.million@sky.com Posted on: Centauri Dreams

I doubt batteries, fuel cells or supercaps would be cost effective, a MHD would generate ample power.

Aug 01, 2016 11:45 michael.million@sky.com Posted on: Centauri Dreams

These MHD's can be made very powerful and compact, a set of these MHD's arranged in a simple configuration allows us to share the superconducting magnets in a torus shape reducing costs of the structures and the size of the construction foot print. A common turbine set could also be used to pump H2/O2 into the rocket chambers significantly reducing the cost due to the very expensive turbines.

Aug 13, 2016 10:04 michael.million@sky.com Posted on: Centauri Dreams

We should look at having MHD's giving a large block of power due to their compact size and then having solid or liquid fuel cells arranged down the exhaust channel to use the waste heat to good effect. Some solid state fuel cells operate around 1000 C which is the point where the thermal plasma effect of a MHD gives way. Solar cell and/or solar concentrator farms can then be used to reform the H2/O2 fuel for the next launch over time.

Aug 28, 2016 08:55 Markus Hlusiak Posted on: Breakthrough Initiatives

In this discussion it is important to distinguish between POWER and ENERGY requirements.

ENERGY is no problem at all. A single launch would need about 20 GWh of electricity, which can be sourced for a couple of million dollars from just about any currently used electricity source (PV, wind, hydro, coal, gas, nuclear all cost about 0.1 $/kWh – give or take half an order of magnitude).

POWER is totally different. All electricity generating technologies mentioned above cost around 1000 $/kW to build, so setting up a dedicated system and then using it only once for 10 minutes is obviously a bit pricey (100 billion dollars).

100 GW is somewhere in the range of a tenth of the combined electricity generation of North America and Europe. Even if you distributed all lasers over a whole hemisphere of Earth you couldn’t just flick a switch and get those 100 GW without significantly affecting the power grid.

Even if this were not the problem, the cost of drawing 100 GW from a high voltage AC supply system seems prohibitive. Transforming power down to the few volts DC needed for the lasers would cost somewhere around 100 $/kW, or 10 billion dollars in total.

So obviously some kind of storage is needed. And to keep the cost of having to transmit 100 GW as low as possible it should be very close to the lasers. If the system was designed to be charged within a week external power supply needs reduce to 100 MW, which seems manageable.

At this level, the only near-team feasible options seem to be high-power batteries and supercaps. Current prices for Li, as mentioned by Philip and Karen, are 100 $/kWh or 10 $/kW. Last time I checked supercaps were around 10 000 $/kWh, which would mean around 1700 $/W in the case of a 10 min launch. This still leaves us with a multi-billion dollar bill, which might be stretching the budget.

The only hope I see is a strongly integrated modular option with laser diodes and caps/batteries in close proximity, preferably on the same chip or at least on the same voltage level. I don’t think that anything that can’t be miniaturised would be an option, e.g. flywheels, MHD, superconducting magnets, pumped hydro etc.

Aug 31, 2016 09:54 michael.million@sky.com Posted on: Centauri Dreams

'The only hope I see is a strongly integrated modular option with laser diodes and caps/batteries in close proximity, preferably on the same chip or at least on the same voltage level. I don’t think that anything that can’t be miniaturised would be an option, e.g. flywheels, MHD, superconducting magnets, pumped hydro etc.'

MHD’s are very powerful, powers 100's of MW per cubic meter and therefore can be made very compact! they are not to be ignored and there is room for much improvement.

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19760066328.pdf

Sep 11, 2016 05:57 michael.million@sky.com Posted on: Centauri Dreams

What is also interesting is that once we get into space we can use variable short UV and X-ray FEL's with their narrow emissions and wide emission wavelength variations to resolve the Doppler/reflectivity issue for dielectric mirrors or prisms and allow for a much longer powered phase. They are large and heavy but will allow much greater energy and accelerations to produce much higher velocities. If they are packed in a multi barrel design for X-ray configurations it would allow electron recycling over the whole system substantially improving efficiencies...but first little steps.

http://xfel.desy.de/localfsExplorer_read?currentPath=/afs/desy.de/group/xfel/wof/EPT/TDR/XFEL-TDR-final.pdf

On Earth we have an opportunity to use the visible part of the spectrum to just inside the UV part of the spectrum which has more energy than in the infrared part of the spectrum, for instance UV 0.4 micron would have around 3.5 times the energy of a 1.5 micron window and the atmosphere is more transparent over a larger range, so it could be better.

Oct 23, 2016 07:57 michael.million@sky.com Posted on: Centauri Dreams

We could make the MHD unit very compact and powerful if we say used one rocket chamber and turbine set and then a series of nozzles leading from it each into a channel. The superconducting magnets are then arranged in a torus shape between each channel which would fully contain the magnetic field reducing stray field losses and reduce the distance over which the magnetic field has to jump a channel.

The MHD conducting plates could also be made thermionic which could emit charged particles just through heating, this could be achieved by having a vacuum space at the back of the channel plate where the charged particles can jump to the polished collector plate. Now if we had the cryogenic fuel running over the collector plates before it gets pumped into rocket motor it would improve the design efficiency significantly by reducing heat losses and improve charged particle collection. By combining thermionic and MHD concepts into the package the overall design would become quite efficient.

http://phys.org/news/2016-03-scientists-thermionic-energy-conversion-efficient.html

And

http://www.nanowerk.com/spotlight/spotid=39283.php

Nov 05, 2016 03:22 Breakthrough Initiatives Posted on: Breakthrough Initiatives

RE:
"Jul 25, 2016 10:55michael.million@sky.comPosted on: Centauri Dreams
I doubt batteries, fuel cells or supercaps would be cost effective, a MHD would generate ample power."

RE:
"Aug 01, 2016 11:45michael.million@sky.comPosted on: Centauri Dreams
These MHD's can be made very powerful and compact, a set of these MHD's arranged in a simple configuration allows us to share the superconducting magnets in a torus shape reducing costs of the structures and the size of the construction foot print. A common turbine set could also be used to pump H2/O2 into the rocket chambers significantly reducing the cost due to the very expensive turbines."

RE
"Aug 13, 2016 10:04michael.million@sky.comPosted on: Centauri Dreams
We should look at having MHD's giving a large block of power due to their compact size and then having solid or liquid fuel cells arranged down the exhaust channel to use the waste heat to good effect. Some solid state fuel cells operate around 1000 C which is the point where the thermal plasma effect of a MHD gives way. Solar cell and/or solar concentrator farms can then be used to reform the H2/O2 fuel for the next launch over time."

Answer:
Great idea. We wish we could find a supplier of a magnetohydrodynamic generator that could be cost competitive to gas or coal power plants. The current state of the industry is gas fired plants are at about $0.07 kw/hr that is really tough to beat. Although I am concerned about the byproducts of combustion and just having that much methane around for the gas fired power plants. It turns out that when hit with 1064 laser light the CH4 may glow. This is something we need to investigate.

- Avi Loeb, Breakthrough Starshot