Want to read Slashdot from your mobile device? Point it at m.slashdot.org and keep reading!


Forgot your password?
Check out the new SourceForge HTML5 internet speed test! No Flash necessary and runs on all devices. ×

Comment Re:Seriously...music off YouTube...? (Score 1) 176

Hell, when I was about 12yrs, I went into a high end audio shop at the time, and heard my first pair of Klipschorns hooked to a McIntosh tube amp...and was hooked.

When I was 12, I was doing well enough just to hit "record" on the boombox when BBC Radio 1 started playing something I wanted to keep.

(Two years later: substitute "AFN Kaiserslautern" for "BBC Radio 1," but since they were both on AM, audio quality on either of them would've been dismal by modern standards.)

Comment Re:Liberals and their insults (Score 1) 115

Eight successful years as Secretary of State.

Chris Stevens was not available for comment.

What has Trump ever done that benefited the American people?

Created who knows how many jobs, which puts money in the hands of those who earned it. People like Trump sign the fronts of checks. People like Hillary have only ever signed the backs of checks.

Comment Re:Pretty cool (Score 1) 158

In California, it's almost $50 a month for a 380W server.

Your server most likely isn't pulling 380W 24/7 unless it's running on an ancient power hog like a Pentium 4 and/or has a shit-ton more disks than usual. Mine uses an AMD A4-3300 and has four hard drives (a Seagate Barracuda LP, two WD Greens, and one 5400-rpm WD Blue...10.5 TB total) for media storage. I haven't measured it lately, but I would be surprised if it pulled as much as 100W at idle (CPU idle, drives still spinning). Even at full tilt, the CPU's only going to add another 60-65W at most.

Comment Re:Pretty cool (Score 1) 158

That ties up your phone while it's playing video, though. I bring a Chromecast with me, pre-configured for the travel router I also bring. Plug it in, connect the router to the local WiFi, fire up Plex, get access to everything I have at home. A 5-port USB charger runs everything off of one outlet (though the Chromecast can often steal power from the TV) and can still charge my phone and tablet.

Comment Re: Powerful indeed! (Score 1) 96

The F-1 was actually optimised for reliability and not-killing-the-passengers hence its abysmal performance by today's standards.

I believe GP was referring to aerostatic nozzle optimization, which every rocket needs to have. This type of optimization applies only to the nozzle, and not the rest of the rocket engine. (pumps, combustion chamber, etc.) A rocket with a nozzle designed for space will not perform well compared to the same rocket with a nozzle optimized for earth at sea level. This is because Earth's atmosphere plays a role in how the gases expand from the engine.

This phenomenon can be observed particularly well on the SpaceX webcasts. The exhaust gases from the engine are expelled directly behind the engine when the rocket is leaving the launch pad. Just before stage separation though, a significant portion of the exhaust gasses can be seen to the sides of the rocket. This is another of the many reasons multiple stages are used in rocketry.

Other trade offs are made between safety and performance, mainly in the combustion chamber and pumps. Experienced scientists and engineers can do some calculations to factor out nozzle optimization and get a more accurate comparison between different types of rockets.

Comment Re: Impressive spec (Score 1) 96

Why compare apples with oranges?

Why show how much sea level and vacuum ISPs vary in other hydrocarbon engines? Because they vary that much in all engine, even non-hydrocarbons (same sort of difference in LOX/LH and solids). Methane is not some sort of magical exception to the rule.

The RD-0162 is the closest unit you can compare the Raptor with. It pushes all its propellant mass through the chamber. It uses the same propellant mixture. Therefore the real world vacuum performance of the sea-level version Raptor can be best guesstimated from the RD-0162 figures rather than by comparing it with dissimilar units.

No, they cannot. You have no clue whatsoever how the efficiency of the RD-0162 compares to Raptor. Not in the slightest. Which makes it a pointless comparison.

Comment Re:So how is it supposed to communicate? (Score 4, Insightful) 74

I think you're confused. Plumes means "in space". The whole benefit of plumes is that you don't need to go under the ice at all, you can do flybies to collect ice particles, or have a lander observe and sample the plumes at the surface. The key is that it means a recent connection between the depths and the surface, and that would be huge for simplifying exploration.

We're nowhere near to being able to launching an ice boring / swimming probe. If I recall correctly the last thing I read on the subject, however, the most promising means for communicating with such a probe on an affordable mass budget was.... not communicating with it. Aka, having it fully autonomous - melting its way down, sampling/observing the ocean, then re-melting its way back to the surface - then and only then transmitting. The waiting period with no data would be stressful (as if it failed you'd never know why), but it could potentially be used on almost any icy solid body regardless of the ice thickness.

It's also possible that there's liquid water much closer to the surface than the global ocean. There are some inferred lakes at a depth of only a few kilometers, which is potentially short enough for a probe to maintain a fiber connection with the surface. And after JUICE and Clipper, we may well have found locations that are even shallower.

Comment Re:Wat (Score 3, Insightful) 74

Right. Because brief observations from an already present spacecraft that could help make critical design decisions about an upcoming multibillion dollar mission are an absurdity.

Look, we know Juno wasn't designed for this sort of mission and is not well equipped or positioned for it. But if researchers determine that its observations could help pinpoint more details of the plumes, then yes, they damn well should regardless of whether "tomhath at slashdot" considers that to be "real science" (apparently some vague category that he doesn't even feel the need to expand upon -- apparently planetary scientists have been working on "fake science" all these years, who knew?).

Comment Re: Impressive spec (Score 1) 96

Look, I'm sorry but what sea-level Merlin does or doesn't achieve is totally irrelevant for Raptor - even for sea-level Raptor.

Because pointing out the typical difference between vacuum and sea level performance in hydrocarbon engines is "totally irrelevant" in a discussion about the difference in vacuum and sea level performance in hydrocarbon engines?

The fact is that the 17 MPa LCH4/LOX sea-level RD-0162 is rated for 356 s of vacuum Isp, so the 30 MPa (+76%!) LCH4/LOX sea-level Raptor is definitely going to be in the 360+ s vacuum Isp territory.

I see your argument - all engines for a given propellant mixture are identical except for only one varying parameter (pressure). Why it's so simple, why didn't I think of that? ;) *snicker*

Meanwhile, back in the real world, performance varies widely between different engine families, and there are many factors that affect them. What you're doing is equivalent to saying "Because my gasoline hybrid engine is super efficient, then your non-hybrid gasoline pickup truck engine should be too!" If you want to compare the performance of vacuum engines to sea level engines, you need to compare for the same engine.

There is nothing magical about methane that makes it somehow, unlike all other fuels, have a tiny difference between ISPs in optimal vacuum vs. optimal sea level designs.

Comment Re: Impressive spec (Score 1) 96

The sea level version of the aforementioned Merlin 1D is 311. Not "~340". We're comparing different nozzle versions of an otherwise identical engine. You don't lose a mere 15-25 sec ISP when losing your nozzle extension and operating at sea level. Period. That's just not reality. If you think for some reason that the Merlin-1D is a bad comparison, pick another engine with otherwise identical vacuum and sea level versions, and cite the vacuum ISP for the vacuum version and the sea level ISP for the sea level version. The sea level ISP will always be vastly lower, not a mere 15-25 sec. I strongly challege you to find a single engine where the difference even remotely approaches your figures.

And to be clear, Merlin 1D is already a fairly high pressure engine, 100 bar is no slouch. And it's not some sort of linear relation with pressure because a lot of the heat is from the internal energy difference between the high-pressure and low-pressure exhaust; it's not simple thermal expansion, as there's a change in the reaction equilibria and in some cases release of the latent heat of vaporization. Chamber pressure has a positive but fairly weak correlation with ISP; most people overestimate its influence.

Slashdot Top Deals

You're at Witt's End.