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Comment Re:Wat (Score 1) 52

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...

But they can't. Juno isn't a mission to look at Jupiter's moons, it's not in the right orbit to look at Jupiter's moons, it doesn't have instruments to look at Jupiter's moons. It's designed for looking at Jupiter and Jupiter's plasma and field environment.

There's already a mission planned to investigate Europa: Europa clipper.

Comment ice particles AND water vapour (Score 1) 52

Isn't vacuum always cold? I fail to see how it could have a temperature above 0K.

Vacuum in itself has no temperature at all. "No temperature" is not the same as 0 Kelvin.

The temperature of something IN a vacuum is determined by the sources heating it and the infrared radiation outward from it. Initially, water exposed to vacuum will start to boil; the boiling will reduce the temperature (losing the heat of vaporization), and the lower temperature will freeze the water. So, in fact, it will boil and freeze at the same time, resulting in ice particles AND an expanding cloud of water vapor.

I got cooled to absolute zero, but I'm 0K now.


Comment How to solve the problem (Score 1) 120

...then massive, costly, and punitive CO2 mitigation schemes become pointless and wasteful.

It is a political talking point that doing anything to address the production of CO2 will be "massive, costly, and punitive". Since the response of the fossil fuel industry has been "do everything possible to cast doubt on the fact that a problem even exists, and divert all attention away from realistic thinking about possible ways to address the problem", though, this has never been thought through.

The problem being that a non-existent 'climate crisis' allows governments, politicians, and their bureaucracies unprecedented powers and control that they will never willingly give up.

It is a right wing talking point that if climate change is real, then the only possible way to address it is to give "governments, politicians, and their bureaucracies unprecedented powers and control."

I find it amusing that the right wing's only approach to the problem is to say that if the problem is real we need to give governments more power. It's as if their political philosophies don't have any tools to solve problems other than "give the government more power."

Comment Million year time scale (Score 2) 120

I think you have that backwards. Snyder is saying that the historical record shows that the sensitivity of temperature to carbon dioxide is much HIGHER than the GISS estimates. Gavin Schmidt's comment is, basically, that her data shows correlation, not causation.

I took away from her study that, as far as she could extrapolate from the available data on climate/temperature cycles going back 2 million years, that we were pretty much smack at the point of the two curves one would expect during this point in time, so to speak, on both CO2 and temperature and from that lack of deviation from expected norms then suggesting that humans have had little if any significant effect on global temperature averages

In that case, you are misled by a misinterpretation of her results.

She looked at temperature and carbon dioxide with five thousand year averaging. Five thousand year averaging says absolutely nothing about the effects of industrialization-- we don't even show up in her data. With averaging on five-thousand year bins, you only see effects on time scales that are long compared to five thousand years.

, and that the warming that is occurring and will continue for a long time at pretty much the same average rate is pretty well inevitable given past history with or without human industrialization.

A more accurate statement of that : "The activities of humans over the last 100 years have not had an effect that is yet visible on a graph plotted over million-year time scales."

To which one could accurately add: "yet".

Seeing as how industrialization in it's entirety has failed to have been shown to appreciably affect global temperature changes

..enough to be evident over million-year time scales.

Comment Re: Impressive spec (Score 1) 81

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 3, Informative) 52

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) 52

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) 81

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) 81

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.

Comment Re:coal???? (Score 1) 81

A coal-LOX hybrid rocket would work, and the ISP wouldn't be too bad (though hydrogen-rich fuels would be better). It'd be an interesting challenge.. normally with hybrids you want the fuel to melt and whip up into droplets at the surface to increase their surface area, but I imagine with a coal hybrid you'd want it to break up into a dust. So maybe fine coal dust with a paraffin or polyethylene binder.... that'd actually probably have excellent thrust performance.

Comment Re:True and false - billion$ moving the wrong way (Score 1) 81

To be fair, we don't know that it was a COPV failure (although that would be most likely) - all we know at this point is that the failure was in the helium system and was unrelated to the strut failure in CRS-7.

While technically you can also produce other fuels off-world methane is indeed the highest throughput and efficiency, as sabatier synthesis yield by far the highest mass fraction as methane, so you don't have to do a lot of recycling of the methane to try to get your desired fraction as an output. Yet the mass is still mostly carbon, which is much easier to get than hydrogen (to the point that even a lot of in-situ production concepts have still called for bringing the needed hydrogen from Earth (reliable/sustainable fuel cell decomposition of CO2 to CO and O2 is pretty much a solved problem; reliable/sustainable permafrost brine mining and purification in Mars conditions, not so much). Methane is also cleaner burning, aka less likely to clog up your injectors and the like. Its disadvantages compared to RP-1 are its cryogenic nature and much lower density (increasing rocket bulk/cross section/mass and decreasing thrust). The lower density does however have its advantages as well - by virtue of requiring bulkier launch vehicles, you inherently increase fairing diameters, which allows for bulkier payloads.

Comment Re: Impressive spec (Score 1) 81

Chances are that even the sea-level version of Raptor will have its vacuum Isp in the 360-370 range anyway

"Chances are" in no way that a sea-level version of a vacuum-optimized rocket with an Isp of 384 will have an Isp of 360-370. Merlin-1D vacuum has a vacuum ISP of 348, but the nearly identical Merlin-1D designed for atmospheric use (same thing, just without the nozzle extension) has a sea level Isp of 282 sec.

Comment Re:Haha no. (Score 3, Insightful) 81

Indeed. Part of the reason that satellites are so expensive is how light you have to make everything; there's a huge amount of engineering that has to be done in order to achieve mass goals, as well as make use of the most expensive materials on the planet. An example is the use of things like top-end Spectrolab multi-junction solar cells, which get the highest efficiencies, but since they're basically lab-scale production hardware they cost two orders of magnitude more than what slightly less efficient panels on Earth cost (about $400/W).

Beyond the simple cost effect on engineering, there's the size effect. Look at James Webb and the massive expense they had to try to make it "origami" itself to fit into smaller launch vehicles. Or how many parts ISS had to be built out of in space, dramatically escalating both ground engineering / production costs and in-space assembly costs (the latter costing nearly $10m per man-day). There are serious expenses to trying to compensate for a lack of space or payload capacity when you really need it.

Then there's the size of the market. As launch costs have been dropping, the number of companies looking to launch payloads has skyrocketed. The skyrocketing launch demand has been reducing average payload development costs, as designs get more reuse. Both of these trends will continue as costs continue to decline. Meanwhile, new markets will continue to open up. Space tourism has always been hindered by the absurdly high launch costs, limiting it to only the wealthiest individuals. While it will remain a "small" market for the forseeable future, it can expand by orders of magnitude with reduced launch costs. Which again makes more demand..

Lastly, there's economies of scale. It's generally recognized in the rocketry world that - at least up to a point - larger rockets get a better cost per kilogram than smaller rockets. So wherein you can launch a lot at once - multi-satellite launches, large geo launches, large interplanetary probes, fuel depots for tugs/boost stages, shielding mass for manned missions, etc - you tend to save a lot of money by going big rather than using multiple smaller launches. The caveat is that just simply going big is no guarantee of a price reduction. Just like you can make an absurdly-expensive smaller craft, you can also make an absurdly expensive large craft. And even a "moderately priced" large craft isn't generally a "win" - if you can sell payload space for $5k/kg on a 10 tonne payload rocket and for the same price per kilogram on a 100 tonne payload, the vast majority of customers will choose the former. But if you're a company like SpaceX that's been delivering cost reductions on the small scale, and you can carry it over to the large scale, it gives you the potential to take the cost reductions even further.

If you can pull it off.

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