Talk-Polywell.org

NASA Ames’ Worden reveals DARPA-funded ‘Hundred Year Starship’ program


October 18, 2010

By Amara D. Angelica

Read More: http://www.kurzweilai.net/nasa-ames-wor ... ip-program






“The microwave thermal thruster using beamed propulsion is an excellent idea,” said Dr. Narayanan M. Komerath, a professor at Georgia Tech College of Engineering and a NASA Institute of Advanced Concepts Fellow. “[Kevin Parker] picks the 140 GHz window, which apparently offers strong advantages in absorption by the materials that he uses in the propulsion system.”

I saw that.

Kinda like tokamak fusion though. If you put the goal out far enough, you don't have to accomplish it on your watch.

But Worden kind of a neat guy. I met him at an asteroid deflection conference a couple of years back. He'll tell you what he really thinks, straight up, and says he does not mind being fired for it.

This microwave beam launch concept is similar to others such as Myrabo's Lightcraft concept. This is probably what Earth to orbit space launch will become if we do not get anything like polywell fusion and the like.

Here's the thesis from the Principle Investigator. Note, there's no cost analysis.

http://thesis.library.caltech.edu/2405/ ... Thesis.pdf

Very nice thesis, but am I wrong to think this would cost trillions to build and an army to maintain? Can't be anything like cheaper than Falcon or Zenit.

The microwave launch system seems like a good idea. But why Hydrogen?

There does not appear to be any chemistry involved in the propulsion process. The Hydrogen is heated up by the microwaves and then expelled out the rear of the craft. Perhaps the Hydrogen reacts with the Oxygen in the atmosphere to propel the space craft. If this is not the case, why use Hydrogen?

Hydrogen is a pain in the ass to work with. You have to keep it near absolute zero, which means lots of engineering plus a high boil-off rate. Also, Hydrogen leaks like crazy because its a small molecule, which means even more engineering. Why not Nitrogen instead? It is cheap and easy to handle. It can be kept at 77K rather than near absolute zero and its a much bigger molecule. Since its not reactive, its much safer to work with as well.

If there is chemistry involved in the propulsion, why not use kerosene instead?

If there's no chemistry involved, the thrust and specific impulse of the space craft will be a function of the propellant mass and the velocity it's expelled at. Perhaps Hydrogen, being a light molecule, gets expelled at a higher velocity than anything else and, therefor, gives you a higher specific impulse than anything else. Then, the issue is the trade off between increased specific impulse and the increased engineering and other costs of using Hydrogen rather than anything else.

The selection of hydrogen would be for the same reason Dr. Bussard specified it for the top end of the flight of his Polywell-powered QED scramjet craft. Due to the low molecular weight, a given amount of kinetic energy applied to the molecule results in a higher exhaust velocity. High exhaust velocity is essentially high specific impulse. It is the most efficient use of the available energy.

Of course, that's at the cost of low density of the stored propellant, and all the other downside of hydrogen.

I tend to lean towards water as the working propellant, and Dr. Bussard did too on anything that had to re-fuel from in-situ resources or be stored for long trips. I'd put that as choice 2.

The selection of hydrogen would be for the same reason Dr. Bussard specified it for the top end of the flight of his Polywell-powered QED scramjet craft. Due to the low molecular weight, a given amount of kinetic energy applied to the molecule results in a higher exhaust velocity. High exhaust velocity is essentially high specific impulse. It is the most efficient use of the available energy.

That's what I figured.

Yeah, I would prefer water as well, due to its cheapness and ease of handling.

Speaking of Bussard's QED scramjet, does anyone have the estimated cost to orbit for it?

Ugh, had to walk all the way over to the computer that has PowerPoint.

From tomorrow's Pecha Kucha talk, about $27 per kg. At some point I looked up the cost of a ticket to Europe on the Concord, and it worked out to a being cheaper than the Concord.

Let's see if the footnotes will paste ...

System Technical and Economic Features of QED-Engine-Driven Space Transportation, Robert W. Bussard

Inertial-Electrostatic-Fusion Propulsion Spectrum: Air-Breathing to Interstellar Flight, R. W. Bussard and L. W. Jameson, Journal of Propulsion and Power, v. 11, no. 2, pps 365-372.

It should be in one or both of those, found in the bowels of the Askmar.com fusion page.

Thanks, I found the powerpoint on my computer. I suspect $27/Kg is optimistic. There are considerable engineering issues in developing an air-breathing SSTO. The polywell power-plant is a small part of the package. Materials with long lifetimes that can handle the heat generated by hypersonic atmospheric speeds is one major issue. However, even if it is $50-75/Kg, thats still better than any beamed propulsion system, which is predicted to be around $250/Kg to LEO.

If that is my old 2007 presentation, the most recent versions follow that slide with one of the X-51. The air-breathing QED is a tad less speculative now that they have a scramjet that will actually burn for 200-300 seconds.

Plus the artists' depiction of the X-51 in flight makes a stunning slide.

But you are absolutely right ... the air-breathing SSTO is the ship that will take the most development. The rest are tin cans with a power source and a thruster. His price estimates supposedly account for life cycle costs and a specific fleet size, I think without the development costs, but in truth if he got within an order of magnitude of the real value it would be good work.

Yes, its your old 2007 presentation.

Developing an air-breathing SSTO is a horrendous engineering challenge. The materials used for the scramjets, especially the inlets, seems to be the most difficult challenge. The other is the re-entry materials. The NASA guys have never come with a practical solution that is low-maintenance (e.g. does not require extensive refurbishment following each flight). I don't know if Fullerine materials have this kind of high-temperature stability.

The good news about an air-breathing SSTO is that it can be flown and tested and developed incrementally, just like any airplane. You fly a little higher and faster each time until you make it into orbit.

The microwave beam system paper mentions a $5 billion development price tag. I think development of a scramjet will be similar to this.

This is not out of the ballpark for private financing. Iridium was financed to the tune of $6.6 billion before it tanked. Boeing has spent $2-3 billion developing its 787 "dreamliner". Its a matter of convincing investors there is a market for cheap launch services and the first mover advantage.

From the game Simcity 2000 disaster scenarios:

Silicon Valley: The high-tech society of the 2010 Silicon valley is hit hard when its futuristic power source goes awry - microwave beams transferring solar energy from an orbital satellite miss their intended receiver and instead incinerate many businesses and people in the area.

http://en.wikipedia.org/wiki/SimCity_20 ... _Disasters

Couldn't help but think of that.

You could make a killing selling chicken wire!

DavidWillard wrote:
What if early surveys of the Martian satellites and nearby asteroid belt reveal worthwhile mining interests of rare earths and somewhat pure veins of solid metals? Densities of ore never unheard of before?

Recent complaints were made by the US about China possibly limiting export of the 19 top rare earth elements, which China has the lions' share of the market for green technology use.
http://www.bbc.co.uk/news/world-asia-pacific-11581288

There's some motivation for a market that is constrained, but committed to reducing CO2 production. Those who have to buy those metals from a captured market will either have to acquire new cheaper sources, or pay the prevailing rising price of the market. Worse yet, some countries might game and capitalize ruthlessly on a hard to acquire source like this.

So play the game, and spend extra billions in the near future, or explore and maintain a steady price with the possibility of reducing the cost of acquisition to provide growth?

Rare Earth's are not that rare. They are a byproduct of Phosphate mining as well as Aluminum refining. The reason why the Chinese dominate the market is that they are the low cost producer of Rare Earths. All of their rare earths come from a single huge mine near Mongolia with essentially no worker safety or control over the environmental effects of the extraction of Rare Earths. Once other producers get in the game (with mines with better safety and environmental management), the prices will probably increase 50-100%, but the "known reserves" will probably increase 10 times. This price increase can easily be absorbed by the semiconductor industry, given that it has coped with a 1000% price increase in semiconductor grade Silicon in the past with little ill effect.

The only materials worth the cost and expense of asteroid mining as Platinum Group Metals (PGM) and maybe Hafnium.

I have a friend who knew a mining engineer who analyzed meteorites for the purposes of determining the feasibility of mining asteroids. He said the best asteroids are Carbonaceous types that have metal phases in them. These phases can be separated by grinding and sifting (meaning no chemistry has to be done on the asteroid) and the resultant phases sent back to Earth.

The difficult part is prospecting. Since the phases are mostly inside the asteroid, identifying the ideal asteroid cannot be done with spectroscopy using telescopes on Earth. A prospecting probe has to be sent out to the target asteroid to prospect. 10 or more such probes may have to be sent before the motherlode asteroid is identified. This is costly and time consuming.

Perhaps the probes can be made small (micro-satellite sized) such that a bunch of them can be sent up with a single rocket launch, then each of them independently target to a unique asteroid. Each micro-satellite probe would need its only propulsion system. However, since they are small, this may not be a problem and the probes can be mass produced.

The motherlode asteroid can probably be grinded and sifted, with the recovered PGM phases packaged and sent back to Earth by a fully-automated system. No people needed to be sent into space. If a maintenance/mining crew has to be sent, add another billion or so to the price tag.

An asteroid prospecting and mining venture would be a multi-billion dollar venture and would take probably 10 years before final payoff. Of course the payoff could be worth a $100 billion or more.

Its a highly speculative venture that is unlikely to happen in the next 2 decades.