Follow Slashdot blog updates by subscribing to our blog RSS feed


Forgot your password?
Slashdot Deals: Cyber Monday Sale! Courses ranging from coding to project management - all eLearning deals 25% off with coupon code "CYBERMONDAY25". ×

Comment Re:Sakura Battery (Score 4, Funny) 102

My father has had various top executive roles in oil companies for the past two decades. We often crack jokes with each other about this sort of stuff. "Gee, dad, how was work - suppress any new revolutionary clean energy technologies today?" "Only two... and you know we've only managed to buy off twelve congressmen this month - total? *Sigh*, the business just isn't what it used to be..." "Oh, sorry to hear that dad... maybe you should start a new war, that always works." "Yeah, I'll bring it up at the next Illuminati meeting..." ;)

Comment Re: But (Score 2) 138

Did you RTFA? I'm not normally one to defend /. editors with their crappy proofing and duplicates, but in this case the click bait comes from outside /.

The original article and a few others:

Comment Re: But (Score 1) 138

Science works by peer-review. There's ample peer-review on the topic. If the word "nutter" has any meaning, it's "people who refuse to accept peer-reviewed science."

And obsessing over past interactions with people and following them around (including mentioning them in places where they're not even involved in the conversation) is otherwise known as cyberstalking

Comment Re:How does space elevator save energy? (Score 1) 138

Talking about "energy costs" shows rank amateurism when talking about space flight. Virtually the entire cost is the flight hardware and ground support infrastructure. Energy costs aren't even rounding error on those.

Wow, it's almost as if my original post didn't read:

. So you can see that the fuel costs are just the tiniest fraction, and that it's the engineering challenges of cost-effective production and reuse that are the issue.

The "rank amateurism" here is in your reading comprehension.

Comment Re:How does space elevator save energy? (Score 1) 138

What do you mean "you were using"? Gravitational potential energy at Earth at sea level is 9,81 * ChangeInAltitude * mass. 35,5 m/s * 9,81 * 20000 = 7MJ/s = 7MW. If you "were using" 2,4MW then you were only climbing at 12,2m/s meaning your entire trip takes 41 days - over a month. Which means that your elevator has laughably worthless throughput. And 20k kg climber requires a massive elevator massing millions of tonnes *with* unobtanium. So you're proposing to launch millions of tonnes of unobtanium to GEO in order to send a fraction of 20tonnes up once every 41 days? Good luck with that.

You could expect 60% efficiency

That's exceedingly optimistic even for monochromatic light (which I see we're back to discussing). Have you ever priced the sort of Spectrolab cells you're proposing here? And anyway the highest monochromatic conversion rate ever recorded - lab scale - was 53%.

Remember that PV efficiency goes up as the light gets brighter

Only when you can keep the cells cooled to the same ambient temperature (and it's only a relatively small gain). How exactly do you propose to ditch megawatts of waste heat up there? Heat is a killer to solar cell efficiency. And several megawatts shining on a relatively small area is otherwise known as "vaporizing it".

No comments about the 0,1%-ish efficiency of the sorts of lasers that actually have the coherency and power to beam over such distances, I see. Even over the distances of your "in-orbit" lasers, of which apparently you want there to be hundreds of thousands if you want to ensure that there's one close to the tower at all altitudes at all points in time. Hundreds of thousands of multi-megawatt lasers each consuming a gigawatt or so of power. In order to launch a fraction of 20 tonnes to GEO once every 41 days. Great strategy.

Economically the construction cost will be huge, but once you have one you can build more relatively cheaply because it costs very little to get mass into orbit.

There is nothing "cheap" about what you're proposing. Your capital costs are nonsensically high, and you have to pay interest on capital costs if you want to live in the real world, and interest accrues interest. You will never, ever reach an economically valid argument for it. And for what gain? If you're turning $0,08/kWh industrial-rate grid electricity into climbing power at 0,05% efficiency then you're paying $160/kg to get to orbit, several times the price to orbit of what's possible with a rocket if it can be made reusable with minimal turnaround costs between flights (as mentioned earlier, the Shuttle's propellant cost to orbit was only $80/kg, most of that in the SRBs, which aren't the cheapest of propellants). And of course it's not even close to a Lofstrom loop, which can be made without unobtanium and deliver payloads at an energy cost to orbit of about $1,60/kg, with present tech.

Speed isn't a huge problem if your cable can support multiple climbers.

So you want to make your cable even bigger, heavier, and more expensive. How many times more expensive do you want to make it? 5 times? 10 times? 100 times? Why not just say that your cable is going to be the mass of the moon's worth of unobtanium while you're at it?

And again, we're only talking about the most basic of problems with space elevators here, let alone actually getting into the countless engineering problems, some of which have no known solutions, and none of which you really have a mass safety margin to properly address. The resonance issues are some of my favorite ones: from the climbers, from the atmosphere, from the sun and from the moon. You have a giant cable which has basically zero ability to damp itself, and no mass leeway to install any sort of damping system of the sort of magnitude needed to counter oscillations. On top of the fact that even made of unobtanium it's an ultrathin structure that can barely support itself and has to be able to withstand hypersonic impacts of microscopic debris and long-term exposure to the Van Allen belts at the time time, while in the atmosphere it's going to face wind loading (they call it a ribbon for a reason, and ribbons *blow*), potentially many times higher than that of climbers, potential icing, certain wetting, lighting (which even if the cable itself isn't conductive, the water on it will make for an easier ground path than the air), upper atmospheric (sprite) lightning as well, oxidation (no mass margin for protective coatings), and on and on down the line.

The space elevator concept needs to be consigned to the dustbin. It was a neat thought experiment for a while until the real-world hit. And now we have actually potentially workable structures (the actively suspended ones) that supercede it in every measure, so there's no point to it.

Comment Re:How does space elevator save energy? (Score 1) 138

It's a lot more fundamental than that. Even with 120 GPa unobtanium they still can't support themselves over those sorts of distances - any cable has to have a large taper factor (the lower the breaking strength, the larger the taper factor is needed). Which makes moving cables impossible, because as soon as you rotate it, the taper is structured all wrong - it has to constantly be thickest at the top and thinnest at the bottom or it will break.

Comment Re:How does space elevator save energy? (Score 2) 138

Solar cells may produce - on a clear day - 200W/m^2, if they're sun-tracking and unshadowed. A climber climbing over the course of two weeks (more on that in just a second, you need to climb far faster) has to climb 35,5 meters per second. A small 1 tonne climber with 2 tonnes of cargo requires 1 megawatt of power, meaning 5000 square meters. Think you can fit 5000 square meters of sun-tracking solar cells on a climber that only weighs one tonne?

Speed is important because it defines throughput, and your cables - even if you have some mythical unobtanium 100-120 Gpa diamond filament tether - are still very massive objects with very tiny objects climbing them, meaning you need high throughput to make them economically justifiable.

I don't think most people discussing space elevators realize how tiny the margins on these things have to be even with a cable made of unobtanium. Inside the atmosphere is irrelevant. It's the tiniest fraction of your 43000 kilometer trip, you have no margin to make a special case for in-atmosphere propulsion. It's only relevant for the additional problems it causes your cable, such as wind, lightning, ice, oxidation, etc.

Space elevators really aren't a good design. They're just totally impractical even when made of unobtanium. But science fiction has locked a generation onto this concept when there are far better concepts available.

Comment Re:Violence! (Score 3, Insightful) 469

It was a war. Shit happens.

No, it wasn't a war. It was a series of heavy-handed, ultra-violent overreactions to minor incidents which themselves were responses to systematic oppression. Military action often does kill civilians, the so-called "collateral damage", but herding groups of unarmed women and children into a building and then deliberately shelling that building to kill them all is not collateral damage; the unarmed civilians were the target.

If you want to understand what's really going on in Israel, I highly recommend you read "Goliath: Life and Loathing in Greater Israel", by Max Blumenthal. It's a hard book to read, not because Blumenthal isn't a good writer but because the truth is so horrible. And if you doubt that it is the truth, check the included citations.

Comment Re: But (Score 0) 138

Aww, my stalker is back! Hi, stalker!

Don't you have some nutters over at the USGS to argue with? Damned USGS and their pie-in-the-sky analysis that is pretty much exactly what I wrote a couple weeks ago concerning resource availability and work/uncertainties that remain to be resolved! Given that this is what led you to start stalking me, you might want to split your time with stalking them too.

Comment Re:How does space elevator save energy? (Score 1) 138

No, I mean $18k. From your link:

by 2011, the incremental cost per flight of the Space Shuttle was estimated at $450 million,[3] or $18,000 per kilogram (approximately $8,000 per pound) to low Earth orbit (LEO).

The $60k is when you include the cost of the whole program (including the design/development phase) which no figure in my post included. If you want to compare, you need to compare equivalent situations: the incremental cost per launch. And the incremental cost per launch of the Shuttle was an estimated $18k/kg.

Ocean: A body of water occupying about two-thirds of a world made for man -- who has no gills. -- Ambrose Bierce