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Comment: Re:WIMPs (Score 1) 223

by Rei (#49366735) Attached to: Dark Matter Is Even More of a Mystery Than Expected

In fact all forces should get weaker with distance faster in an expanding space than in flat space.

That seems like quite an assumption on your part, if I'm understanding you correctly. We can't just assume that all properties of spacetime are scaling evenly - if they did, then we'd perceive no effect at all.

But perhaps I'm misunderstanding you.

Comment: Re:Still photos (Score 1) 358

by Rei (#49366707) Attached to: Why the Final Moments Inside a Cockpit Are Heard But Not Seen

Some pilots would probably still want the ability to override the limits in an emergency if they feel that they can handle the situation better than the autopilot (for example, if the plane is crashing and the pilot wants better control over where/how to bring it down). If so, then you should make it a possibility to disable the limits, have it such that only *ground* can disable the limits. This would of course impose a delay, but at least overriding the limits would remain a possibility.

Of course, a pilot may try to trick ground into disabling limits (such as pretending to be going down or pretending to have a malfunction), so ground would need as much data as possible to assess whether the situation is legit. Might be tricky... best would be to err on the side of caution and only remove limits if everyone is absolutely sure that this is appropriate, if there's any doubt the answer should be "no".

Comment: Re:Wrong Focus (Score 1) 95

by Rei (#49366605) Attached to: SpaceX's New Combustion Technologies

Not today. But maybe in the future. If you can develop a crazy-power-dense energy source and cooling system, you could probably do it with a MPD thruster. The research I've seen on MPD thrusters operating in pulsed mode yields crazy output relative to the mass of the thruster. But you can't run it continuously because it'd overhead and take way too much power. But who knows about the future? There's the potential for extreme heat conductors like isotopically pure diamond, maybe a some kind of fission fragment reactor with a deceleration grid for power...

(of course, if you have a fission fragment reactor, at least when you're in space itd be best just to jet your fragments rather than use them to power a MPD thruster...)

Comment: Re:It is (Score 2) 95

by Rei (#49366565) Attached to: SpaceX's New Combustion Technologies

I hope they simulate propane too, not just methane. Propane has some really interesting properties as rocket fuel but have (like methane) never gotten much research. But now there's a big rush to research methane as fuel based on the concept of generating it on Mars - so propane still gets left in the dark.

Methane's ISP is only very slightly better than propane's - 364,6 vs. 368,3 at a 100:1 expansion into vacuum and 20MPa chamber pressure. But propane at around 100K (note: not at its boiling point, 230K) has far higher density (782 kg/m^3), closer to that of room temperature RP-1 (820 kg/m) then that of boiling point methane (423 kg/m^3), which reduces tankage mass and cost. 100K propane's ISP is of course better than RP-1's 354.6 in the same conditions as above. Plus, its temperature is similar enough to your LOX that they can share a common bulkhead, which reduces mass further and simplifies construction.

Hydrogen generally is the easiest fuel to synthesize offworld. Methane is generally second, and propane third. Hydrogen is often rejected as a martian fuel because of the tankage and cooling requirements. Methane can be kept as liquid on Mars with little cooling in properly designed reflective / insulated containers - but so can 100K propane, in similar conditions, but with significantly smaller tankage requirements.

It seriously warrants more research, I tell you what.

Comment: Quote (Score 1) 146

by Rei (#49363093) Attached to: Russia Wants To Work With NASA On a New Space Station

"We are pleased Roscomos wants to continue full use of the International Space Station through 2024 -- a priority of ours -- and expressed interest in continuing international cooperation for human space exploration beyond that. The United States is planning to lead a human mission to Mars in the 2030s, and we have advanced that effort farther than at any point in NASA's history. We welcome international support for this ambitious undertaking.

Yeah, that's basically "Go F* yourselves" in diplomatic speech.

And as it should be.

Comment: Re:WIMPs (Score 1) 223

by Rei (#49360117) Attached to: Dark Matter Is Even More of a Mystery Than Expected

One thing that dark energy can't be is *all* fundamental constants, plus position, velocity, etc scaling up evenly. Because if such was the case then there would be no perceptible change.

If youe saying that for example what is ground state would change too then it seems like you're arguing that things at the quantum level *aren't* moving into higher energy states. But things at the macroscopic level absolutely are moving into a higher energy state. So are you arguing that dark energy doesn't act on the quantum scale? I find that difficult to accept if so.

Comment: Re:WIMPs (Score 4, Interesting) 223

by Rei (#49358535) Attached to: Dark Matter Is Even More of a Mystery Than Expected

That the thing about dark matter... it has a perfectly reasonable explanation (WIMPs). It's not that weird of a "thing".

Dark energy on the other hand, that's just WEIRD ;) It doesn't act like any "energy" as we know it, even though everything is clearly moving into a higher energy state. A question I've had for a while... if space itself is being inflated (or any sort of mathematically equivalent scenario) - everything inflating in all directions at all scales - wouldn't there be some sort of weak radiation signal from electrons expanding into a higher energy state due to dark energy and then collapsing back down? But I have trouble picturing how to reconcile an absolute, varying distance at the atomic scale with quantization of energy states, positions, etc...

Comment: Re:Ummmm ... duh? (Score 1) 370

by Rei (#49358149) Attached to: Modern Cockpits: Harder To Invade But Easier To Lock Up

Sure there is: add this to the CPDLC standard and make all of the hardware modifications needed to support it:

----
Message type: Revert flight plan and lock
Message arguments: TIME: the time of the flight plan to use
Message description: Revert to the flight plan that was active at TIME that had been approved by both ground control and the pilot; engage autopilot; and disable all pilot / copilot access to all systems. If there is no approved flight plan then the flight plan is to return to the nearest suitable airport in the most direct route possible.
----

Additional modifications: Make sure that the pilot can never disable datalink communications with ground by any means that ground wouldn't have time to respond to.

Result: Nobody is ever "remote controlling" the plane from the ground. A murderous / terrorist ground controller can't crash the plane, only make it autopilot itself on a previously approved or otherwise reasonable flight plan. A pilot behaving suspiciously can't crash the plane, as ground control will just engage the autopilot and lock them out. To abuse the system both ground and the pilot would have to agree on a suicidal flight plan.

Comment: Re:Memorizing site-unique passwords isn't possible (Score 2) 257

by Rei (#49350175) Attached to: Generate Memorizable Passphrases That Even the NSA Can't Guess

Yeah, the suggested method for generating passwords generates needlessly long passwords. The total entropy is good, but the entropy per character is pretty poor. You get much better entropy per character with abbreviation passwords, where you have a sentence or group of random words and you use the first letter from each, or second, or last, or alternating, or whatever suits you. It's still not as much entropy per character as a random pattern, but it's much better than writing out full words - and pops into your head just as fast (because it is, in essence, the same).

Comment: Re:what will be more interesting (Score 5, Insightful) 637

by Rei (#49345311) Attached to: Jeremy Clarkson Dismissed From Top Gear

Are people really going to miss yet another totally fake show pretending to be reality? Is it just because this one combined cars and Daily Mail-style politics?

Sorry, but I have no sympathy for a primadonna for whom curses at an employee for 20 minutes and then physically assaults him up for half a minute (without any resistance from his victim) before someone pulled him off, all because the Clarkson's food wasn't warm. And this is hardly the first time Clarkson has behaved like this, he was already on "final warning" after a string of other incidents. What befalls him is his own bloody fault. And all of the abuse that the victim got over this whole thing... my favorite tweet on the subject was:

"Man assaults another man and victim receives abuse because people can’t watch a TV show about cars. Bravo society. "

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