Become a fan of Slashdot on Facebook

 



Forgot your password?
typodupeerror

Slashdot videos: Now with more Slashdot!

  • View

  • Discuss

  • Share

We've improved Slashdot's video section; now you can view our video interviews, product close-ups and site visits with all the usual Slashdot options to comment, share, etc. No more walled garden! It's a work in progress -- we hope you'll check it out (Learn more about the recent updates).

×

Comment: Re:It is (Score 1) 121

by Rei (#49378241) Attached to: SpaceX's New Combustion Technologies

Wow, this is great to hear - I'd never heard of you guys before. :)

And looking at your site, I like what you're doing even more - direct 3d printed aerospikes? Pretty darn cool. What sort of 3d printing tech are you using? Have you looked into the new hybrid laser spraying / CNC system that's out there (I forget the manufacturer)? The use of high velocity dust as source material gives you almost limitless material flexibility and improved physical properties that you can't get out of plain laser sintering, and the combination with CNC yields fast total part turnaround times.

And you're working on turbopump alternatives? Geez, you're playing with all of my favorite things here.... ;)

What sort of launch are you all looking at - is this ground launched (and if so, do you have a near-equatorial site) or air launched? I'd love to see more details about your rockets, what sort of ISP figures you're getting so far, how you're manufacturing your tanks, and on and on. But I guess I'll have to wait just like everyone else ;)

I wish you lots of success! And even if you don't make it, at the very least you'll have added a ton of practical research to the world :)

Comment: Re:Wrong Focus (Score 1) 121

by Rei (#49378083) Attached to: SpaceX's New Combustion Technologies

Note that it's technically possible to have something like this with a slow reactor; you could for example use steam as a moderator, which will transmit a reasonable proportion of near infrared through it (the hotter you can run your fuel particles, the better transmission you'll get). But not only will you lose some light, but just the simple act of neutron moderation is a very heat-intensive process, meaning big radiators if you want big power (not to mention that the moderator itself for such a slow reactor is also far heavier than the core). The whole point of my variant is to avoid the moderator and avoid the ship having to ever capture anything but incident heat lost due to generation, transmission, reflection, etc losses.

One possibility for a slow reactor, albeit only directly applicable to the rocket mode above, is to have your propellant be your moderator, absorbing both IR and moderating fast neutrons. The fact that it's heating then becomes irrelevant (actually an advantage), since you're dumping it out the nozzle for thrust. If one wanted mission flexibility in such a scenario you could have such a moderator-ejecting rocket mode used to get to orbit, and then switch to retaining the moderator once in orbit and cooling it instead in order to make use of the fission fragment operating mode.

But a fast reactor would obviously be highly preferable so you don't have to worry about a moderator at all. :) I'm just pointing the above out because slow reactor versions have already been simulated.

Comment: Re:Wrong Focus (Score 1) 121

by Rei (#49378039) Attached to: SpaceX's New Combustion Technologies

Wait a minute, no, I entered it right into the calculator the first time around. Argh, this interface is confusing. Radiative equilibrium for Tunsten at its melting point 3300C according to the calculator is 92MW/m. A "cool" 1200C radiative temperature according to the calculator 2,6MW/m. According to the calculator, 10kW/m is about 380C.

Comment: Re:So What (Score 1) 249

by hey! (#49376609) Attached to: Poverty May Affect the Growth of Children's Brains

It is your choice to make your eventual obliteration the focus of your life. That's something you can either try to change (good luck with that), or it's something you can choose to accept. But choosing to accept that doesn't mean you have to sit around being miserable and resentful while you wait for the Grim Reaper. The world is only as cold and hard as the things in it you choose to focus on. There's also more wondrous and amazing and even funny things in the world than you an get around to thinking about in a lifetime.

It's like summer vacation when you're in school. You only get ten weeks or so of it, not nearly enough to get to all the things you want to do. And there are some people who will react to that by spending the whole time from day 1 unhappy about going back to school. What a waste of existence! But that's definitely a choice open to you.

Imagine your last few seconds of consciousness before you die. How would you like to spend them? Being angry? Sad? I think that's a waste of precious time. I'd like to have someone I love very much tell me a very funny joke.

Comment: Re:So What (Score 1) 249

by hey! (#49376541) Attached to: Poverty May Affect the Growth of Children's Brains

No, we all make the choice of the kind of world we want -- or maybe it'd be better to say the kind of world we can live with. It just so happens that some people can live with a world that they don't like very much, so long as that doesn't demand very much of them.

Anyone can by choice have an immense effect on the world around them. Maybe they can't change the *whole* world very noticeably, but they can transform their own neighborhood.

Comment: Re:Not sure, if this is "news for nerds" (Score 1) 97

Sorry, but Amazon took over the market by operating at a deficit for decades. I've heard that they are still operating at a deficit, which, if true, is frankly amazing. How *do* they stay in business.

When most companies use this policy (pricing below the cost of service) the governments put them out of business. Somehow Amazon is allowed to "prosper". (I'm not sure that proper is the right term if they're actually still operating at a deficit. I know they did for over a decade, as there used to be many financial people commenting about it.)

Comment: Re:Proof (Score 1) 128

While that's reasonable circumstantial evidence, I don't know that it couldn't have been done by someone else, and the balance of the opinion seems to be that it, indeed, could be done by someone else.

OTOH, it's not clear who else would have a motive. And, governments not being any more monolithic that corporations, it could quite well have been some department (or actor within a department) acting without any knowledge by the official spokesman, and either with, or without, approval by higher organizational figures. And you can't tell. And that's *assuming* (without proof) that China, in some meaning of the term, was behind the attack.

So were I to guess, I'd guess that it was probably China behind the attack, and the spokesman for China didn't know. But please note that this is a guess with a lot of unverifiable assumptions, and I wouldn't even want to guess how much probability to assign it.

Comment: Re:Plausible Deniability (Score 2) 128

Well, it's actually quite plausible. That doesn't mean you should believe it. Lots of things are believable that aren't true.

The interesting thing is, I can't think of how they could either make it believable that they did it or that they didn't do it. In some things there are no good grounds for having a belief in either (any) direction.

The thing is, all the governments I've paid any attention to lie so often that you would do well to use a roulette wheel to decide HOW they are lying in any particular statement. And "They're telling the truth" would be the 00 slot of the wheel. But belief should occur only when there is reasonably grounded evidence...and then it shouldn't be committed belief, because governments are quite able to fabricate evidence when they find it worth the effort.

Comment: Re: Wasted Energy? (Score 1) 195

Math:

Ameliorating $4/month waste:

$1000 / 4 = 250 months until positive ROI. Your $1000 estimate is way high, though -- what he proposed is about $300 at most, at the scale he indicated. Probably not even that. It mostly depends on the wiring. Long is costly. Short and efficient, you're way down in costs. The rest is relatively constant. Solar panels, charge regulator, inverter. I show the closer numbers along with yours in square brackets: [$300 / 4 = 75 months until +ROI]

That's 20 years. [6 years]

After that, it's a constant ~$48 / year win.

Over the working and retired lifetime, figuring age 30 is when this is done in deference to slashdot's basic demographic as I perceive it, 40 years remain, so 20 [6] of that is payment, which means the ROI is 20 x $48 = $960 [34 x $48 = $1632]

There's also the social benefit of not drawing that power. It all adds up.

There's also the benefit of not losing functionality when power goes out.

And it's fun and personally rewarding.

And it's affordable, much more so that typically larger solar projects.

So, no, no stupidity. You're not thinking clearly, and to top that off, your data is bad.

Comment: Why pay for family planning? (Score 1) 930

but why should anyone but the individual pay for said options???

We have to start from the premise that said individual may well not be able to afford these options.

Then, we pay for the same reason that we as group pay for other things that benefit society over the long term, like roads, fire departments, public education, defense, sewers, sidewalks, dikes, rain gutters. We know certain needs are going to come up, and/or certain events will actually happen, so we prepare for them in some way that optimizes the outcome.

Unwanted children are very often a serious burden both on society at large, and often upon the parents, and often even to themselves. The workforce is diminished and damaged, and people grow up under conditions that start out with a fairly strong negative impetus.

We benefit directly by stronger parent-child relations; by prepared parents as opposed to "oh crap, I/we didn't plan on THIS!" parents; By better educated and happier citizens.

It's the future we're investing in. That's one of the best things society can do.

Lastly, the evaluation should, at least in my estimation, be based upon this criteria:

Which is worse? Unwanted children, loss of productivity, social turmoil and misery, or a very reasonable levy upon the citizens in general?

All family planning services taken together ca. 2010 account for 2.37B out of the total of 3.55 trillion spent, or .06%, or 6/10,000ths of the total expenditure. That means for every $1000.00 you paid in taxes, that 60 cents of that went to cover family planning. Not too harsh, I'm thinking.

To me, if that is the question (and I think it is), the answer is pretty much a foregone conclusion.

Fools ignore complexity. Pragmatists suffer it. Some can avoid it. Geniuses remove it. -- Perlis's Programming Proverb #58, SIGPLAN Notices, Sept. 1982

Working...