Search found 114 matches

by cjameshuff
Sun Jul 01, 2018 4:09 am UTC
Forum: Science
Topic: Cooling gas by expansion
Replies: 17
Views: 5503

Re: Cooling gas by expansion

There's several basic issues with the hydrogen steamer. Rocket exhaust expansion is isentropic. You need an expansion ratio of about 230000 for the exhaust to reach 20 K, not the author's estimated 45000. The serpentine nozzle is also far from an ideal de Laval nozzle, and you'd have thermal signatu...
by cjameshuff
Sun May 15, 2016 5:21 pm UTC
Forum: Science
Topic: Which planet?
Replies: 28
Views: 5431

Re: Which planet?

Mars: top of the list purely for practical reasons: large deposits of water and CO2 and some atmospheric nitrogen, which can be used as feedstock for rocket propellant and other chemical industry. A long history of liquid water, possibly extending to the present, meaning lots of familiar mineral dep...
by cjameshuff
Sun Jan 17, 2016 1:34 pm UTC
Forum: Science
Topic: SpaceX manned moon landing: Falcon Heavy/Dragon V2
Replies: 9
Views: 4132

Re: SpaceX manned moon landing: Falcon Heavy/Dragon V2

To get the return fuel, you would need to put a separate fuel tank in lunar orbit beforehand for the Dragon to rendezvous with. More or less true. Judging from historical examples (i.e. I don't think any rocket has discarded a fuel tank (i.e. a non-pendulum fallacy example of what KSPers call "...
by cjameshuff
Tue Jan 05, 2016 12:41 pm UTC
Forum: Science
Topic: SpaceX manned moon landing: Falcon Heavy/Dragon V2
Replies: 9
Views: 4132

Re: SpaceX manned moon landing: Falcon Heavy/Dragon V2

Not that it entirely changes your reasoning, but the Merlin Vacuum has a wider throttle range, down to 360 kN (39%) according to this:
http://www.spacex.com/sites/spacex/file ... ev_2.0.pdf
by cjameshuff
Sun Jul 12, 2015 2:02 pm UTC
Forum: Science
Topic: Conductors and Motors/Generators
Replies: 7
Views: 1846

Re: Conductors and Motors/Generators

Could you use water rather than wire in a motor (or generator) for the winding? What about carbon? Assuming not, are there any non-metallic conductors you can use? Any conductor will work, including water (though note that pure water is a decent insulator, it only becomes conductive when it contain...
by cjameshuff
Thu Jun 11, 2015 11:08 pm UTC
Forum: Science
Topic: Ion thrusters v.s fusion thrusters
Replies: 12
Views: 4152

Re: Ion thrusters v.s fusion thrusters

If you wanted to go from New York to Toronto, would you fly or drive? Fusion is more expensive, but faster. Ion is cheaper, but slower. First of, I would fly, and second that leads me another point. I think ion thrusters would be better for space probes, while fusion thrusters would be a lot better...
by cjameshuff
Thu Jun 11, 2015 12:38 am UTC
Forum: Science
Topic: Ion thrusters v.s fusion thrusters
Replies: 12
Views: 4152

Re: Ion thrusters v.s fusion thrusters

I know that we currently don't have fusion thrusters already, but I'm talking about when we do. Also lets say they both have the same amount of fuel. Would the fusion thruster have more delta-v m/s than the ion thruster? That question isn't answerable. Higher delta-v with the same propellant mass w...
by cjameshuff
Sun May 24, 2015 4:09 pm UTC
Forum: Science
Topic: Bladeless Wind Turbine: Do joints look better than fans?
Replies: 17
Views: 3502

Re: Bladeless Wind Turbine: Do joints look better than fans?

Looking at their website, i'm as sceptical about this as about those solar road ways. Call me old fashioned, but flashy websites and crowdfunding don't induce trust in me when it's about an energy company. Also, they have estimates with single digit precision percentages about savings in large scal...
by cjameshuff
Wed Apr 22, 2015 12:02 pm UTC
Forum: Science
Topic: Is the 3 body problem particularly hard?
Replies: 4
Views: 1949

Re: Is the 3 body problem particularly hard?

I remember hearing that the 3 Body Problem (find a stable orbit for three shperes) was one of the most difficult problems in physics. It had only 3 answers until these guys came along http://phys.org/news/2013-03-physics-duo-solutions-newtonian-three-body.html . I was wondering if there was whole g...
by cjameshuff
Mon Apr 13, 2015 12:39 pm UTC
Forum: Science
Topic: Earth's trajectory if the sun disappeared...?
Replies: 48
Views: 10327

Re: Earth's trajectory if the sun disappeared...?

If the Sun disappears, Jupiter's Hill Sphere will admittedly expand quite dramatically. But the escape velocity of 1 Jupiter mass at a distance of 596,109 km is 20.61 km/s. Inside, it is smaller; outside, it is larger. That's backwards, escape velocity is lower at greater distances. You say, "...
by cjameshuff
Wed Apr 01, 2015 1:22 pm UTC
Forum: Science
Topic: Ad Astra takes on SPAAAAAAAAACE
Replies: 6
Views: 1990

Re: Ad Astra takes on SPAAAAAAAAACE

Exciting? Certainly. Probes to the far reaches of the solar system get there a lot faster with this kind of specific impulse. VASIMIR isn't bullshit. It has been tested extensively and openly, together with NASA. On earth bound tests it displayed the massive specific impulse quoted in the wiki page...
by cjameshuff
Mon Mar 30, 2015 3:45 pm UTC
Forum: Science
Topic: Extension cord question. Is Jimmy right?
Replies: 21
Views: 5625

Re: Extension cord question. Is Jimmy right?

But extension cords are safe... I'd go with precaution as background for Jimmy's qualm. The last cable should be the weakest link in the chain, so people can see how much amps the cable chain can handle. The reverse argument could be made as well...the last cable should be the one most able to take...
by cjameshuff
Sat Mar 28, 2015 5:42 pm UTC
Forum: Science
Topic: Deadlifter
Replies: 17
Views: 4300

Re: Deadlifter

There are also hybrid rockets , which, like many liquid rockets, have separate fuels and oxidizers, except one's liquid and the other's solid (usually the fuel). They can be relatively simple, like a big dumb booster, or more complex, more like a liquid rocket with turbopumps. Solid rockets can be ...
by cjameshuff
Sun Nov 09, 2014 5:17 am UTC
Forum: Science
Topic: Gravity vs Conservation of energy
Replies: 12
Views: 4078

Re: Gravity vs Conservation of energy

You need to expend energy, but you most certainly don't want to speed up if your plan is to de-orbit. You want to brake against your motion, but the result is that you do speed up...at least until you reach atmosphere. Start in a circular orbit and brake. You end up with an elliptical orbit with ap...
by cjameshuff
Thu Oct 23, 2014 4:49 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

Apparently D-D and D-T fusion aren't hard to do at room temperature using an ion beam aimed at metal deuterides/tritirides, so that's good. But yeah, it looks like the emission direction is random, so if you want a directed beam you just block all other directions. Not terribly helpful. The only wa...
by cjameshuff
Tue Oct 21, 2014 7:53 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

If this actually works, do we think Lockheed Martin will Lobby for a carbon tax? That's the reaction with Li-6. With neutrons of sufficient energy (>5 MeV), Li-7 produces the same products, plus another neutron. You're not the first to overlook this reaction: http://en.wikipedia.org/wiki/Castle_Bra...
by cjameshuff
Mon Oct 20, 2014 11:16 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

You could also use D-T fusion to provide the neutrons. As a bonus, it'll also produce useful power, and probably do so more cheaply than the aneutronic reactor it's making fuel for. D-T fusion only produces one neutron per Tritium atom consumed. Tritium requires one neutron bombardment to be produc...
by cjameshuff
Fri Oct 17, 2014 10:51 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

relevant Nukees comic , it seems a little harsh to me, but as I understand it nothing much has been accomplished scientifically here, just financially. It hits at the big problem with all their talk: virtually no details about how it works. Just lots of claims about its small size, and a cartoonish...
by cjameshuff
Thu Oct 16, 2014 6:12 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

MHD generation requires a fusion reaction that produces little or no neutrons, and the required reactions are quite a bit more difficult to achieve. Why exactly? Neutrons are neutral, and don't interact strongly with magnetic fields. Energy released in the form of neutrons goes into heating the lit...
by cjameshuff
Thu Oct 16, 2014 3:02 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

MHD generation requires a fusion reaction that produces little or no neutrons, and the required reactions are quite a bit more difficult to achieve. Why exactly? Neutrons are neutral, and don't interact strongly with magnetic fields. Energy released in the form of neutrons goes into heating the lit...
by cjameshuff
Thu Oct 16, 2014 2:17 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

and with frozen hydrogen fuel carefully deposited inside. I was wondering about this; they basically assembled a tiny cage to hold a... small piece of liquid hydrogen? Frozen hydrogen. The hohlraum contains a hollow capsule with a film of solid hydrogen deposited inside. http://www.nature.com/natur...
by cjameshuff
Thu Oct 16, 2014 1:16 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

To achieve more electrical power out than in with 60% efficient thermoelectrical efficiency, 30% efficient lasers (current CO2 lasers) and achieved 20% efficiency in laser to fuel compression a gain of 27.78 must be achieved. It's even worse than that. The 20% laser to fuel compression efficiency i...
by cjameshuff
Wed Oct 15, 2014 11:25 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

I remember reading somewhere that magnetic mirrors themselves where nothing but handwavium. Is that incorrect? Pretty thoroughly incorrect. They even occur in nature: the poles of planetary magnetic fields act as magnetic mirrors, trapping charged particles into radiation belts. Ones suitable for f...
by cjameshuff
Wed Oct 15, 2014 10:55 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

The neutral beam injectors function both for adding material and igniting. The "neutral" refers to the flow of deuterium/tritium being electromagnetically neutral, that is, non-ionized. I'm guessing that the injection point is a magnetic/pressure minimum in the device and so anything inje...
by cjameshuff
Wed Oct 15, 2014 9:55 pm UTC
Forum: Science
Topic: Skunk Works reveals compact fusion reactor?
Replies: 47
Views: 8738

Re: Skunk Works reveals compact fusion reactor?

The NIF design is inertial/thermal confinement, where a zillion lasers all focus on a single pellet, which implodes inward to produce a spherical inmoving shockwave with enough inertia to trigger fusion. This has given good results in terms of energy output, but it's necessarily a pulsed design, wh...
by cjameshuff
Sat Oct 11, 2014 1:33 pm UTC
Forum: Science
Topic: Let's terraform Jupiter!
Replies: 26
Views: 8809

Re: Let's terraform Jupiter!

Apart from the hydrogen excess, "stocking up on helium" is biologically improbable, it's an inert gas that diffuses readily through many materials. Attempts to sequester the atmosphere in place also just make the surface gravity issue worse. But, I persist anyway. Does anybody have any oth...
by cjameshuff
Fri Oct 03, 2014 12:22 pm UTC
Forum: Fictional Science
Topic: RF Resonant Cavity thruster-based spacecraft
Replies: 13
Views: 10232

Re: RF Resonant Cavity thruster-based spacecraft

This gives an absolute minimum required power of just over 9 MW (111*81.4e3), at least initially. The EMDrive already violates conservation of momentum as we know it. It might work itself around conservation of energy as well. It does. Check page 6 of http://www.emdrive.com/2Gupdate.pdf, where Shaw...
by cjameshuff
Sat Aug 16, 2014 1:30 pm UTC
Forum: Science
Topic: Aerogel
Replies: 28
Views: 10154

Re: Aerogel

I mean the deflated, storage volume of the balloon. e.g. Most balloons are transported in the basket in a horse float sized trailer which is towed by a pickup. No one will want a balloon that needs a semi truck for transport, no matter how much they'll save on balloon fuel. If it can carry a decent...
by cjameshuff
Wed Aug 13, 2014 10:52 pm UTC
Forum: Science
Topic: Aerogel
Replies: 28
Views: 10154

Re: Aerogel

Yes indeed. However if I line the conventional hot air balloon, it will just add weight. If I use the insulator as the envelope itself, it will save weight. Not if it's not structurally suitable for an envelope. This pyrogel is just an unwoven fiberglass mat to give an aerogel based insulating laye...
by cjameshuff
Tue Aug 12, 2014 11:10 pm UTC
Forum: Science
Topic: Aerogel
Replies: 28
Views: 10154

Re: Aerogel

You're overcomplicating things. The reason you want aerogel is as an insulator, you don't need it to have any tensile strength or to be airtight...just line a relatively conventional hot air balloon with insulating material. No no, not Silicia aerogel. Other types of aerogel are better suited. Pyrog...
by cjameshuff
Sat Jul 19, 2014 3:32 pm UTC
Forum: Science
Topic: nuclear power and disaster movies
Replies: 5
Views: 2042

Re: nuclear power and disaster movies

Regards number 3: that would be similar to a sunk submarine. Nothing much happens to the fuel, assuming its shutdown rods are inserted in time. The golden rule of nuclear accidents is 'keep the core covered with liquid water'. If you can supply water faster than it can boil away you're golden. Afte...
by cjameshuff
Sun Jun 22, 2014 4:00 pm UTC
Forum: Science
Topic: Speed of Propagation of a Magnetic Field.
Replies: 116
Views: 28121

Re: Speed of Propagation of a Magnetic Field.

i'd count "different enough" as relativistic, though. If a DeLorean zipping down the road is fast enough to get the job done, and you use that fact to define 88 mph as "relativistic", where does that leave your original objection? You've just removed all meaning from the term &q...
by cjameshuff
Sun Jun 22, 2014 12:40 pm UTC
Forum: Science
Topic: Speed of Propagation of a Magnetic Field.
Replies: 116
Views: 28121

Re: Speed of Propagation of a Magnetic Field.

i'd count "different enough" as relativistic, though. If a DeLorean zipping down the road is fast enough to get the job done, and you use that fact to define 88 mph as "relativistic", where does that leave your original objection? You've just removed all meaning from the term &q...
by cjameshuff
Sat Jun 21, 2014 11:19 pm UTC
Forum: Science
Topic: Speed of Propagation of a Magnetic Field.
Replies: 116
Views: 28121

Re: Speed of Propagation of a Magnetic Field.

If magnetic fields travel faster than light, send a message back in time to last week and post it then. that's unfair. you'd still need two reference frames at relativistic speeds to each other. That's not necessary. Sure, you may not be able to send information very far back in time in one go, but...
by cjameshuff
Sun Jun 01, 2014 11:35 am UTC
Forum: Science
Topic: Solar Road Ways
Replies: 82
Views: 14277

Re: Solar Road Ways

stoppedcaring wrote:
gmalivuk wrote:If it's not wet, then so what?

Moisture will still make it in, no?


There's no shortage of examples of semi-enclosed areas that are very effective at reducing rain, snow, and ice. It isn't necessary to maintain a cleanroom environment.
by cjameshuff
Thu May 29, 2014 4:27 pm UTC
Forum: Science
Topic: Highest purity water and materials
Replies: 15
Views: 4368

Re: Highest purity water and materials

I do mean macroscopic objects. The molecular-scale objects you are describing aren't exactly "pure," we can just distinguish them from their surroundings. Any reaction that produces antimatter produces tons of other stuff too, but we can identify the antimatter in it. We can do more than ...
by cjameshuff
Wed May 28, 2014 11:32 pm UTC
Forum: Science
Topic: Highest purity water and materials
Replies: 15
Views: 4368

Re: Highest purity water and materials

What is the highest purity substance ever achieved? I know some metals and gases can be purified beyond 99.9999%, but I don't know how far beyond. It is hard to find purity measurements in parts-per notation. For instance, ultrapure water is measured in terms of resistivity, not parts-per notation....
by cjameshuff
Tue May 27, 2014 9:56 pm UTC
Forum: Science
Topic: Solar Road Ways
Replies: 82
Views: 14277

Re: Solar Road Ways

It would have to melt the same quantity of snow regardless, so that doesn't change the energy requirement. Well, it actually does, since it means you have to constantly heat the air as well as the ice. Looks like about 25 W/m^2/K is a reasonable ballpark value for free convection in air. For the gi...
by cjameshuff
Tue May 27, 2014 4:08 pm UTC
Forum: Science
Topic: Solar Road Ways
Replies: 82
Views: 14277

Re: Solar Road Ways

except that one goal of surfacing material design is to reduce resistance and noise. And their textured surface turns out to be a grid of large bumps which looks like it'd be quite noisy. btw, t can't imagine a road made of hexagonal tiles to provide for a very smooth ride. one of the advantages of...
by cjameshuff
Tue May 27, 2014 3:58 pm UTC
Forum: Science
Topic: Solar Road Ways
Replies: 82
Views: 14277

Re: Solar Road Ways

No one expects kilowatts from piezoelectric generators, Which was my point. They wouldn't be worth installing. and they could be used in cities where rolling resistance isn't as big a part of the energy the car exerts. Cities, with their traffic density and existing pollution problems, are precisel...

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