Please create an account to participate in the Slashdot moderation system

 



Forgot your password?
typodupeerror
For the out-of-band Slashdot experience (mostly headlines), follow us on Twitter, or Facebook. ×

Comment: Re:Iran is not trying to save money (Score 1) 229 229

Well, you have to factor in the Iranian cultural mania for disagreeing with each other. The Shah couldn't keep them under his thumb, neither can the mullahs, who have their hands full disagreeing with each other.

From a tyrant's perspective Iran is ungovernable, which doesn't mean elements in the government don't give tyranny a go on a regular basis. It's an ideal setup for producing martyrs. The futility of cracking down means you have a little space to rake some muck before official anger overcomes reason.

Comment: iOS users feel it (Score 1, Insightful) 279 279

I currently have a web radio transceiver front panel application that works on Linux, Windows, MacOS, Android, Amazon Kindle Fire, under Chrome, Firefox, or Opera. No porting, no software installation. See blog.algoram.com for details of what I'm writing.

The one unsupported popular platform? iOS, because Safari doesn't have the function used to acquire the microphone in the web audio API (and perhaps doesn't have other parts of that API), and Apple insists on handicapping other browsers by forcing them to use Apple's rendering engine.

I don't have any answer other than "don't buy iOS until they fix it".

Comment: Re:Big giant scam ... (Score 1) 716 716

I distinctly remember it being promised that the F-35 would beat anything but an F-22 in air-to-air combat, at a fraction of the price. It was not part of the original concept for the system but it was definitely sold politically as being capable of acting as a poor man's F22.

I wonder about the helmet mounted display, whether that's something you'd consider absolutely necessary in an aircraft whose job is to hit surface targets in contested airspace.

Comment: Re:Big giant scam ... (Score 1) 716 716

As a supposed air-superiority platform, this is an utter failure.

To be fair, that was not the original justification for the thing. That was mission creep.

I think the original impetus was to have something stealthy that could do ground strikes in enemy territory. And it makes sense to do a naval version of the same thing. If they'd just focused on that they'd have been done a long time ago with a solid design, which of course in engineering nearly always turns out to be more versatile than you planned for. Adding STOVL and the whizbang helmet (cool as that may be) as necessary elements of the system turned this into an "everything for everyone" project, which almost always turns out less versatile than you hoped.

Comment: Re:Dogfights?! What year is it?! (Score 1) 716 716

Sure you can identify scenarios where the A-10 is useless. But in the last twenty years it's been extremely useful in a number scenarios we've actually faced.

The idea that a system ought to play every role in every conceivable situation is why the F35 performs none of them very well. In hindsight the idea of accommodating the Marines' need for a STOVL aircraft in the same basic design probably dictated too many compromises in the plane's other roles.

Comment: Re:no we can't (Score 2) 75 75

I find this an interesting statement. Running the numbers, I find that you'd have to be using a rocket burning something rather better than H2/O2 (we're talking Isp >500 just to reach escape speed, much less to reach the target rock) to allow two launches of a delta-IV heavy.

Huh?

The fact that a Delta-IV Heavy has a LEO payload of over 27 tonnes is a fact. You don't need to "run the numbers". As for the kick stage, I didn't specify a propulsion system - for all we care (since we haven't established a timeframe), it could be an ion drive and not even take a rocket so large as a Delta IV-Heavy.

Meanwhile, the Falcon Heavy is to make its first launch this year, with double the payload of a Delta IV-Heavy. And as was mentioned, the Tsar Bomba was not optimized to be as lightweight as possible.

And this entirely ignores that noone actually has a Tsar Bomba sized nuke available to be detonated.

Oh, and you didn't allow for a backup

It's almost as if I didn't add "with enough advance warning" for that scenario and leave what "enough advance warning" is unspecified. But if there's another rock the size of the Chicxulub impactor out there and we don't see it until the last second, we deserve to get hit - we're no longer talking about a 50 meter spec (Tunguska-sized), rather a rock with a cross section 30% bigger than the island of Manhattan. We're talking about an impact of a scale that happens once every hundred million years or so.

Comment: OMG - matti makkonen .fi sms pioneer dead (Score 0) 31 31

A more appopriate version of the BBC's article:

---------------
OMG - matti makkonen .fi sms pioneer dead!!!
---------------
WTF - mm just died @63! #txtpioneerdeath was father of sms & dvlped idea of txt msg with phones. @2012 msged BBC that txt would be here "4EVR".
--------------
shoutout 2 Nokia for spreading sms w/Nokia 2010. thought txt good 4 language. was btw mng. director of Finnet ltd and "grand old man" & rly obsessed with tech.
--------------
OMFG people!

Comment: Re:no we can't (Score 2) 75 75

It is not only possible, but the easiest option, to "blow them up Armageddon style" (minus the drilling and the like). There's a lot of simulation work going on right now and the results have been consistently encouraging that even a small nuclear weapon could obliterate quite a large asteroid into little fragments that won't re-coalesce, while simultaneously kicking them out of their current orbit. A few years ago they were just doing 2d calcs, now they've gotten full 3d runs.

Think for a second about what nuclear weapons can do on Earth. Here's the crater of a 100kt nuclear weapon test. It's 100 meters deep and 320 meters wide. You could nearly fit a sizeable asteroid like Itokawa inside the hole. And that thing had Earth's intense gravity field working against it and was only 1/10th the size of weapons being considered here. In space you don't need to "blast out" debris with great force like on Earth, you merely need to give it a fractional meter-per-second kick and it's no longer gravitationally bound. And the ability of a nuclear shockwave to shatter rock is almost unthinkably powerful - just ignoring that many if not most asteroids are rubble piles and thus come already pre-shattered. Look at the "rubble chimneys" kicked up by even small nuclear blasts several kilometers underground (in rock compressed by Earth's gravity). Or the size of the underground cavity created by the wimpy 3kT Gnome blast - 28000 cubic meters. Just ignoring that it had to do that, again, working against Earth's compression deep underground, if you scale that up to a 1MT warhead the cavity would be the size of Itokawa itself.

You of course don't have to destroy an asteroid if you don't want to - nuclear weapons can also gently kick them off their path. Again, you're depositing energy in the form of X-rays into the surface of the asteroid on one side. If it's a tremendous amount of energy, you create a powerful shattering shockwave moving throughout the body of the asteroid. If it's lesser, however, you're simply creating a broad planar gas/plasma/dust jet across the asteroid, turning that whole side into one gigantic thruster that will keep pushing and kicking off matter until it cools down.

The last detail is that nuclear weapons are just so simple of a solution. There's no elaborate spacecraft design and testing program needed - you have an already extant, already-built device which is designed to endure launch G-forces / vibrations and tolerate the vacuum of space, and you simply need to get it "near" your target - the sort of navigation that pretty much every space mission we've launched in the past several decades has managed. In terms of mission design simplicity, pretty much nothing except kinetic impactors (which are far less powerful) comes close, and even then it's a tossup. Assuming roughly linear scaling with the simulations done thusfar, with enough advance warning, even a Chicxulub-scale impactor could be deflected / destroyed with a Tsar Bomba-sized device with a uranium tamper. Even though it was not designed to be light for space operations, its 27-tonne weight could be launched to LEO by a single Delta-IV Heavy and hauled off to intercept by a second launch vehicle.

Comment: Re:Not surprised (Score 5, Insightful) 316 316

Uber drivers are subsidized by everybody else. Taxi drivers have to pay high insurance rates because the act of driving a long distance every day for a ton of strangers is a job that inherently leads to a much higher statistical rate of payouts. If they're driving as a taxi on regular car insurance, it's you that's paying the bill for their swindle of the insurance system.

Comment: Re:What plan? (Score 1) 88 88

How do you come to that assumption?

By linking to a peer-reviewed paper on the subject?

A nuclear warhead has lots of trouble to even "hit" an asteroid.

Essentially every space mission we have launched for the past several decades has had to navigate with a far more precision than that needed to get close to an asteroid and activate a single trigger event when close by.

Comment: Re:What plan? (Score 4, Interesting) 88 88

We send spacecraft on comparable missions all the time. And it doesn't really take a spectacularly large payload to destroy (yes, destroy) an asteroid a few hundred meters in diameter. 1/2-kilometer-wide Itokawa could be blown into tiny bits which would not recoalesce, via a 0,5-1,0 megatonne nuclear warhead, a typical size in modern nuclear arsenals (in addition, the little pieces would be pushed out of their current orbit).

I know it's a common misconception that "nuking" an asteroid would simply create a few large fragments that would hit Earth with even more devastation, but that's not backed by simulation data. And anyway, even if it didn't blow the asteroid to tiny bits (which simulations say it would) and even if it didn't push the remaining pieces off trajectory (which they say it does), anything that spreads an Earth impact out over a larger period of time is a good thing - it means the higher percentage of the energy that's absorbed high in the atmosphere rather than reaching the surface (less ejecta, lower ocean waves, a broader (weaker) distribution of the heat pulse, etc), the weaker the shockwaves, the weaker the total heat at any given point in time, and the more time for Earth to radiate away any imparted energy or precipitate out any ejecta cloud. If the choice is between 15 Chelyabink-sized impactor (most of which will strike places where they won't even be witnessed) or one Meteor Crater-sized impactor (same total mass), pick the Chelyabinsk ones. 50 10-megatonne meteor crater impactors or one 500-megatonne Upheaval Dome impactor? Pick the former. The asteroid impacts calculator shows the former generating a negligible fireball and 270mph wind burst at 2km distance, while the latter creates the same winds 25km away (156 times the area) and a fireball that even 25km away is 50 times brighter than the sun, hot enough to instantly set most materials on fire.

But that's all irrelevant because, quite simply, simulations show that nuclear weapons do work against asteroids.

What we need is enough detection lead time to be able to launch a nuclear strike a few months before the impact date (to give time for the debris to disperse). There is no need to "land" or "drill" for the warhead. There is no pressure wave; instead, an immense burst of X-rays is absorbed through the outer skin of the asteroid on the side of the explosion, causing it to vaporize (unevenly) from within, especially near the ground zero point, and creating powerful shockwaves throughout its body. In addition to ripping it apart, the vaporized material and higher energy ejecta flies off, predominantly on the side where the explosion was detonated, acting a broad planar thruster.

If the facts don't fit the theory, change the facts. -- Albert Einstein

Working...