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Comment: Re:Not so fast (Score 2) 131

by Rei (#49385153) Attached to: World's Largest Aircraft Seeks Investors To Begin Operation

Most people's perception of how airships should behave from holes is wrong, and it's based on their experience with party balloons. The reason for the differences are:

* Party balloons are pressurized - the skin is stretched taught. The skin on airships are loose.
* Skin area (and thus leak rate) scales proportional to the radius squared, while the volume scales proportional to the radius cubed. Airships are many, many orders of magnitude larger than party balloons. Consequently the rate in which gas can leak out of a hope is drastically lower.

Even large holes in airships don't take them down quickly. Even a moderate sized airship can generally continue flying to its destination and then fix the damage and refill there.

Comment: ROI depends on investment as well as return (Score 1) 139

by billstewart (#49384253) Attached to: IT Jobs With the Best (and Worst) ROI

The original material talked about salaries and job titles; it didn't say how much investment it took to develop the skills to get those titles. Some of those skills are things you can add quickly; others take a long time or access to appropriate work environments. (For instance, learning PHP is quick, and Ruby on Rails isn't that hard either. But while you can learn SQL and MySQL pretty quickly, becoming a DBA really needs access to real-world databases and workloads that you're involved in administering.)

Comment: Re:THIS is a "golden age"? Yikes. (Score 1) 66

by hawk (#49383705) Attached to: We're In a Golden Age of Star Trek Webseries Right Now

I'm sorry, the fan-made "Star Trek" stuff is terrible, because the actors are terrible. It's as simple as that. They get pretty much everything right, otherwise, but without decent actors, it doesn't matter. I mean, the acting is high-school-level bad.

Err . . . how would this make it any different than Star Trek???

hawk

Comment: Re:It is (Score 1) 124

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) 124

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) 124

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:Wrong Focus (Score 1) 124

by Rei (#49375327) Attached to: SpaceX's New Combustion Technologies

The cornerstone of it is the dusty fission fragment rocket, so I'd start there. Another key aspect is the use of a accelerator-driven subcritical fast reactor rather than a critical slow reactor. Lastly it's a variant of a nuclear lightbulb, albeit (as mentioned) without the primary drawbacks of them (containment and radiation blackening of the chamber blocking the light). This latter aspect is due to the spectrum changes of fused silica (I can't find a paper on short notice that shows the IR spectrum, but you can see that for most types of fused silica / fused quartz, there's little loss of transmission on the red side of the spectrum; this holds true but is even more pronounced in the IR range).

Adding features does not necessarily increase functionality -- it just makes the manuals thicker.

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