Talk-Polywell.org

hanelyp wrote:

GIThruster wrote:

williatw wrote:... A nuclear thermal like Nerva, add O2 to the H2 exhaust for extra thrust, and finally nuclear electric when the reactor is ratcheted back.

... High temp O2 is very corrosive. I have heard though, the P&W people have solved that already. Would be great if true.

The systems like that I've read about inject the O2 downstream of the reactor. Only the post combustion chamber and expansion nozzle have to deal with hot oxygen.

Actually, the corrosion concern was posed in a paper published by Sandia in the 90's. P&W responded to it directly by saying they had some sort of beryllium cladding that would thwart the trouble, IIRC.

Sorry I can't site the $1B figure but it's a couple years since I've researched this issue.

GIThruster wrote:I'd be curious to see this $500k to the Moon estimate of Musks. You're sure that's not urban legend? Right now he's hoping to get $50M/ 7-man flight to LEO, or $700k@, just to go round trip to ISS or Bigelow's Space Bed 'n Breakfast. I can't see how he'll ever get the savings to go to Mars for less. I'd think given the infrastructure needed, he'd need at least 2+ orders magnitude increase or more. . closer to $70B@. And that's on a budget. Virgin galactic gets $200,000@ for suborbital flight and that's literally 1/10 the energy needed for orbit.

It is from a talk he gave here: http://www.hobbyspace.com/nucleus/index ... emid=32777
The gist of it is he thinks he could send people to Mars at 500K a ticket one way(he is assuming they are permanent colonist) if launch vehicles to orbit were re-usable. That's what he is shooting for. My idea is how to make money off of a mars colony straightaway. No mining/powersats or anything that would require years/decades of capital investment. 500K a ticket for lets say 500 colonist + supplies & equipment at $3000/lb you could set up a colony for around 5 billion initially private investment. Get that back very quickly with a few 10's or 100's of billions of deposits in the bank of mars. No taxes few regs very competitive interest would be very attractive.

First thing would simply be colonists. The profit comes off sending them there with all their equipment. If you can send them, everything they need to get going, etc., then you have a product/service to sell. If the $500,000 includes the corporate profit, then just start sending people, they'll figure out how to live there.

Plenty of people would be willing to get off earth, even at $1 million.

Then you send the bankers, and then the industry.

GIThruster wrote: I'd be curious to see this $500k to the Moon estimate of Musks. You're sure that's not urban legend? Right now he's hoping to get $50M/ 7-man flight to LEO, or $700k@, just to go round trip to ISS or Bigelow's Space Bed 'n Breakfast.

err..hate to correct someone else's math but, $50M/7= about 7mill, not 700k. So assuming he is figuring on allot of cost reduction from reusability, not an unreasonable assumption if he pulls it off. Course 7mill is far less that than the current going rate of 24mill to go to the International space station.

kunkmiester wrote:First thing would simply be colonists. The profit comes off sending them there with all their equipment. If you can send them, everything they need to get going, etc., then you have a product/service to sell. If the $500,000 includes the corporate profit, then just start sending people, they'll figure out how to live there.

Plenty of people would be willing to get off earth, even at $1 million.

Then you send the bankers, and then the industry.

And of course the 8000 that Musk estimates would be able to pay is assuming each colonist has to pay his own way. If an investment group set up the Mars colony with the idea of making their money back(plus profit) from the bank of mars, they might foot the bill to send carefully screened/vetted people who were qualified and willing to be permanent colonists.

16 km/s (or more) delta V budgets plus Tsiolkovsky's rocket equation preclude profitable extraterrestrial mining ventures.

With chemical rockets.

MSimon wrote:

16 km/s (or more) delta V budgets plus Tsiolkovsky's rocket equation preclude profitable extraterrestrial mining ventures.

With chemical rockets.

That 16 includes 9 or 10 to rise from earth's surface and achieve orbit.

NTR doesn't have the thrust to weight ratio needed to make the ascent.

And, as I mentioned, given propellant sources high on the slopes of earth's gravity well, you no longer have 16 km/s delta V budgets. With lunar volatiles, the picture changes.

HopDavid wrote:That 16 includes 9 or 10 to rise from earth's surface and achieve orbit. NTR doesn't have the thrust to weight ratio needed to make the ascent. And, as I mentioned, given propellant sources high on the slopes of earth's gravity well, you no longer have 16 km/s delta V budgets. With lunar volatiles, the picture changes.

No NTR don't but I think a variant called "Timberwind" http://en.wikipedia.org/wiki/Project_Timberwind was supposed to but was never developed. The key is to reduce the cost to orbit by a couple orders of magnitude by some means. Once your in orbit you are half way to anywhere as Heinlein said. Reusable rockets like Musk wants may be the best near term solution. Nuclear thermal rockets use propellant too, they could use your lunar propellant stations as well. And with a SI of 800-1000seconds, compared to perhaps 450 for chemical rocket go with greater delta V. Long term if we are serious about colonizing developing the solar system with millions of people living various places in space we need nuclear power/propulsion.

williatw wrote: No NTR don't but I think a variant called "Timberwind" http://en.wikipedia.org/wiki/Project_Timberwind was supposed to but was never developed.

Here is a thread where various forms of nuclear propulsion are discussed.

williatw wrote:The key is to reduce the cost to orbit by a couple orders of magnitude by some means. Once your in orbit you are half way to anywhere as Heinlein said.

An oft repeated meme. But wrong.

(Start Mass/Final Mass) = e^(dV/Ve)

Where e is Euler's number, about 2.72.
dV is delta velocity, the change in speed needed.
Ve is exhaust velocity.

With hydrolox, the above doubles every 3 km/s you add to the delta V budget.


Each 3 km/s is a square on the above chess board. Getting to LEO is about 9 km/s. Adding another 6 to that quadruples your initial mass. So if you go by initial mass, LEO is 1/4 of the way. Possibly even more as you would likely need to add stages.

If trip times are 8 months, you need more robust radiation shielding and life support more reliable and trouble free than the ISS (remember, a Mars Transfer vehicle can't enjoy supply and maintenance trips as does the I.S.S.)

williatw wrote:Reusable rockets like Musk wants may be the best near term solution.

Here we agree. But the reusable rockets to LEO must be chemical for a number of reasons.

Recovering a working stage after 8 km/s re-entry is a problem.

Presently SpaceX is working on the Grasshopper. SpaceX videos depict the two stages using reaction mass to propulsively shed mass as well as using aerobraking. Can Musk et al pull this off? They need to achieve some difficult mass fractions -- I given them less than even odds.

But if Musk's upper stage could refuel in LEO, I would give a reusable Grasshopper much better than even odds.

HopDavid, I think you are missing the key reason/assumption why LEO is half way to anywhere in the system -- Once in LEO everything takes significantly less delta v (which I know you are aware of). If you only bring enough fuel to get to LEO, and then meet up with a refueling station, your range is greatly increased without also increasing your starting mass.

Establish refueling points in LEO, LLO, LMO, etc and your mass requirements to get between Earth, Luna and Mars go down quite a bit. Thus, once in LEO you are halfway to anywhere in the system.

krenshala wrote:HopDavid, I think you are missing the key reason/assumption why LEO is half way to anywhere in the system -- Once in LEO everything takes significantly less delta v (which I know you are aware of). If you only bring enough fuel to get to LEO, and then meet up with a refueling station, your range is greatly increased without also increasing your starting mass.

Establish refueling points in LEO, LLO, LMO, etc and your mass requirements to get between Earth, Luna and Mars go down quite a bit. Thus, once in LEO you are halfway to anywhere in the system.

Well, yes. Each time you have access to a propellant source you get to start over at 1 grain of rice. Given propellant depots, the chessboard above looks like this:



But sadly the propellants depots pictured above don't exist.

HopDavid wrote:Well, yes. Each time you have access to a propellant source you get to start over at 1 grain of rice. Given propellant depots, the chessboard above looks like this:



But sadly the propellants depots pictured above don't exist.

And if they did exist nuclear thermal rockets like Triton could use them far better than could chemical rockets. You want to stick with technology of "covered wagons" rather than going to railroads. We didn't develop nuclear rockets for reason political, (anti-nuclear movement) in the States, not for reasons technical(or even financial) Another way my private mars colony could make money: be a test bed for perceived risky technological development. Even if polywell works out..even it could not match the power/SI/high trust of a nuclear pulse rocket. No reactor can match the power output of a series of nuclear explosions. I like anti-matter catalyzed designs like the ICAN-II: http://www.engr.psu.edu/antimatter/documents.html
Fat chance of the necessary experiments to bring it to fruition ever being done on earth especially the United States...but say there was some place beyond earth law/regs where a group of people could do research out in the desert with nary a soul around for 100's or even a thousand miles around in every direction.

It might be me, but the artistic embellishment on those graphics drown out the actual meaning. I can't see what they're supposed to communicate.

Betruger wrote:It might be me, but the artistic embellishment on those graphics drown out the actual meaning. I can't see what they're supposed to communicate.

An interest in art.

Betruger wrote:It might be me, but the artistic embellishment on those graphics drown out the actual meaning. I can't see what they're supposed to communicate.

In addition to the illustrations I include a verbal explanation and math.

I suspect the math is beyond your reach.