Catch up on stories from the past week (and beyond) at the Slashdot story archive

 



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

Comment Re:Just what the world needed most urgently... (Score 1) 184

Compare programming a 6502 in assembly back in 1980 to programming in Java nowadays.

I see your 1978 and raise you a 1970.

'''Prolog''' is a general-purpose logic programming language associated with artificial intelligence and computational linguistics.

Prolog has its roots in first-order logic, a formal logic, and unlike many other programming languages, Prolog is declarative: the program logic is expressed in terms of relations, represented as facts and rules. A computation is initiated by running a query over these relations.

The language was first conceived by a group around Alain Colmerauer in Marseille, France, in the early 1970s and the first Prolog system was developed in 1972 by Colmerauer with Philippe Roussel.

Prolog was one of the first logic programming languages, and remains the most popular among such languages today, with several free and commercial implementations available.

The language has been used for theorem proving, expert systems, as well as its original intended field of use, natural language processing.

Modern Prolog environments support creating graphical user interfaces, as well as administrative and networked applications.

Prolog is well-suited for specific tasks that benefit from rule-based logical queries such as searching databases, voice control systems, and filling templates.

Prolog did not fail because it was lacking in declarative concision. It failed because there's an annoying layer in between formal description in the problem domain and viable execution strategies in the solution domain.

This layer, too, requires code. Of course, we can just write a formal description of the "annoying layer" as a Prolog program and then let Prolog do all the real work.

Uh, wait a minute, recursion has somehow failed us here. How could that even be? Does not compute. Proceeding to Halt and Catch Fire.

Comment Re:All your jobs are...belong to us! (Score 1) 121

As of yet, there is nothing inherently special about a human being that cannot be reproduced by machines.

What on earth are you smoking?

The present gap, on best available technology, is so staggeringly mind-rending it could serve as the third ring in Dante's Total Enlightenment Vortex.

(Midway through the fifth ring—still reeling in shock from the fourth ring's ascendancy of green slime as fully revealed—the Pilgrim of Total Enlightenment receives a surprising and painful transcranial injection of quantum nanodots, so that the true horrors of rings six—spoiler alert: Chaitin's omega because blindingly intuitive and compulsive to calculate—and seven—HAL hasn't blinked since—can be savoured and swallowed in immense and total abjection.)

Comment Re:Remember kids! (Score 1) 373

I love the politicians who stump for "no invisible tax" and write legislation to ensure that gasoline pumps break out every tax category on the paper receipt (we still have these in Canada, I can't speak for anywhere else).

Everybody knows the deal going in.

I sure wish we'd apply the "no invisible tax" standard to casinos, as well. In this world, every patron is entitled to a printed receipt on the way out (just stick your card into the receipt printer near the main exit) of total $$$ in bets placed and total $ in winnings returned.

Even better if those same receipts enumerate the proportion of your losses that wind up in the government's pocket.

7 Facts about Gambling Winnings in the US

Riddle me this, Batman: how does an activity with a guaranteed amortized loss end up pay tax to Uncle Sam on aggregate negative proceeds?

John, a German national, travels to Las Vegas on holiday. He wins a single $10,000 jackpot on the slot machines while playing at Caesar's Palace, triggering the creation of form W2-G by the casino, a copy of which is given to the player. He also wins $1000 more in various slot machine wins, none of which trigger the creation of form W2-G. When John wins the $10,000 jackpot, he hands the slot attendant his German passport along with Form W8-BEN. The slot attendant processes the form and no withholding is taken from the $10,000 jackpot. At the end of the calendar year, John will need to file Form 1040NR with the IRS and report the $11,000 of gambling winnings. He will attach Form 8833, reporting his use of the treaty position to make the gambling winnings non-taxable in the US, along with a copy of the Form W2-G he received from the casino. John will only need to file Form 1040NR in the years that he has US sourced income.

I understand taxing proceeds in a game of skill like poker, but freaking slot machines? Ludicrous. Beyond insane. Conceptually criminal.

Comment death's excellent extended vacation (Score 2) 462

Are we talking the 'death' when a generational math prodigy turns twenty-five?

Or the 'death' when a the fastest of all fast-living rock stars turns thirty?

Or the 'death' when an formerly fetching actress turns forty?

Or the 'death' when a corner-office executive producer turns fifty.

Or the 'death' when a commercial pilot turns sixty?

Or the 'death' when a professor emeritus turns seventy?

Or the 'death' when a defeated American presidential candidate turns eighty?

Or the 'death' when everyone's favourite preschool teacher turns ninety (on Okinawa)?

Or the mostly-just-resting 'death' when the queen mum turns one hundred?

And we're still not done. George Burns lived an entire Windows 95/98 maximal uptime (49 days) after his one hundredth.

Comment Am I the only one... (Score 5, Interesting) 128

.... who can't help but cheer at my screen when they nail one of those landings? Now I finally understand how sports fans feel when they watch a game and do the same thing ;)

One thing nobody can deny about them is optimism. ;) Seriously, their IPS numbers are, pardon the pun, out of this world. $200k per booster launch. $500k per tanker launch. I mean, really? Good luck with that. No, seriously, good luck with that; I won't be expecting anything close to that, but please by all means prove me wrong ;) ITS would be a great system to have, I've been playing around with some Venus trajectories with it recently. Looks like it can do a low-energy transit with nearly 300 tonnes of payload from LEO and back again with the same, over 400 if starting at a high orbit - but from an economics perspective the high energy transfers actually make more sense.

I noticed a lot of people were confused about why Musk wanted the trips to be so short and was willing to sacrifice so much payload to do so - many assumed it had to do with radiation or something. But the issue is, when your craft costs so much but your launch costs are cheap, you can't have it spending all of its time drifting in deep space, you need to get it back for a new mission as soon as possible. There's a balancing point, in that if you try to go too fast, you reduce useful payload below the point of making up for it with going faster - but a minimum energy trajectory is just not optimal when the ratio between launch costs and transit vehicle cost is so extreme. I come up with the same thing from Venus as they were getting for Mars, although for the Venus case you end up aerobraking to a highly elliptical orbit rather than to the surface for ISRU refill (you need ISRU, but for the ascent stages, so it's not realistic to do so for the return stage in the nearer term). So for Venus they get no refill like on Mars, but they also don't have to do a powered landing nor do an ascent on return - it's six of one, half a dozen of the other. Both are quite accessible with it.

Comment Re:Great strides (Score 1) 128

It depends what you mean by "refurbishing"; each element is different.

The solid rocket boosters, for example, suffered a hard impact into salt water. They then had to be fished out of the water. And of course you don't just "refill" a SRB, they have to be taken apart and recast, then put back together.

The ET is disposable, and had to be rebuilt from scratch.

The orbiter was legitimately reusable, but with design flaws.

I don't blame the shuttle program - they were sort of pigeonholed into this dead end by circumstances. The concept came about during the heyday of the Apollo Programme, when NASA budgets were serious. It was supposed to be a much more reusable, much more maintainable, and somewhat smaller system. It was supposed to then have a huge flight rate supporting all of these big projects that were on NASA's docket, including a permanent moon base and a huge manned orbital station dwarfing ISS, which was supposed to replace Skylab.

But of course, Vietnam and the realities of having soundly trounced the USSR in the space race led to their budgets being slashed, which pushed the program into ever more untenable positions until it was nothing more than a jobs programme. Forget full flyback reusability of all parts. Forget the titanium frame for the shuttle, which would have let it run hot and thus not required so sensitive of a TPS. Go begging for money and be forced to modify the design to meet Air Force requirements, pushing you into an inferior design position. On and on.

If I'd fault them for anything, it'd be for going straight for a full reusable workhorse rather than a small-scale pilot programme first. But those were the days of optimism. Optimism which only recently seems to start being regained.

Either way, the Falcon boosters are a very different beast. A vertical soft landing is hugely different from the SRBs, yet the thermal issues are far easier than with the Shuttle. And the Merlins were designed from the start under the principle of preventing the need for a full teardown. That doesn't mean that they will be cheap to reuse. But it does mean that they have the possibility of it.

I do think SpaceX had a rather clever strategy, in that while their goal was reusable, they made a rocket that in the process was cheap as a disposable. So they could get volume and flight history while working on getting the kinks out. They may have flown too close to the sun with the densified propellants and (externally) unlined COPVs, but obviously, with a company like this, their whole existence is to push the envelope.

Comment Re: Awesome (Score 3, Insightful) 128

Most of Europe agrees with you. And even the US agrees with you up through high school plus with various forms of assistance for college, including state-subsidies, particularly for state colleges, and federal subsidies (direct subsidies, tax credits, and tax breaks), roughly $80B/year each. Pell grants alone cost the government $35B.

Comment Re:No Gut no Glory (Score 1) 66

To be clear:

  * Getting the failure rate down in the lower tenths of a percent or better is what they need to be able to ~10x their launch rate and still be economically viable, since a pad explosion will leave them stuck for just as long and scare off just as high a percentage of their customers whether they're launching 12 a year or 120.
  * SpaceX wants to have reliability like airplanes, and has talked about this frequently.
  * What they want to achieve, and what they need to achieve, are not the same thing. They do not need to achieve airplane-like reliability for the Falcon 9 to be viable.
  * That said, if they ever want to achieve their ultimate IPT plans, they absolutely will need airplane-like reliability. Because they're calling for ~1000 launches per booster on that thing with a turnaround cost of ~200k. They really cannot have anything go wrong with it.

Comment Re:No Gut no Glory (Score 1) 66

It most certainly would be extreme reliability by the standards of the launch industry. The only ones that have better reliability than that that don't have nearly a statistically significant enough number of launches under their belt to assert that. Aka, "they haven't had a failure yet but nowhere near the several hundred launches required to assert a lower fraction of a percent or better failure rate".

We're not talking about airplane reliability here, we're talking about economics (the title of the article is "SpaceX Accident Cost it Hundreds of Millions"). Airplane-like reliability is for the future. We're living in the present.

All COPVs use an inner liner. The problem with SpaceX's COPVs is that they have no outer liner to separate the carbon fibre from the LOX. Outer liners are optional. SpaceX didn't use one. They lost a rocket because of it. They're going to keep trying doing without one. I really hope it doesn't cost them another. CF and LOX aren't fast friends.

Comment Re:Permission? (Score 1) 60

It's hard enough to find affordable LOX dewars. Seems like little ones cost about as much as big SUV-sized tanks. Everyone has LN2 dewars for sale, but you don't put LOX in a LN2 dewar as a general rule unless you're absolutely positive it has no organics (and preferably no silicone) in it, or certain metals. Otherwise it can get a bit... "explodey". The simpler, all-stainless LN2 dewars usually don't have lids, which with LOX would be just plain stupid. You can find used LOX converters online for very cheap, but they generally only will take LOX in, you can only get GOX out.

What I'm saying is if anyone happens to run into an affordable LOX dewar, drop me a line.... ;)

Comment Re:No Gut no Glory (Score 2) 66

It's a somewhat problematic business model.

If they $250M per failure and have a failure 5% of the time on a $62M rocket then the per-rocket cost is $12,5M, or 20% of the rocket's value.

Now they're trying for two things: a big scaleup, and greater safety. So let's say that they get the accident rate down to 2%, and they 10x their value. The cost of a failure should scale proportionally to the size of their market because it means a standstill in launches, the same reputation hit, etc. So now it's a $2,5B failure, occurring 2% of the time, or $50M per launch on a $62M rocket, aka 81% of the rocket's value.

Their business model and scaleup plans appear to be built on a premise of extreme reliability. Whether they can ever actually get that, I don't know. I like to hope so; airplanes have done it, and I know they're thinking, "if we launch enough, like them, we'll have gotten all of the potential kinks out". And there's probably some truth to that. But can they scale reliability at the rate they want to scale their launch rate? I have my doubts, and if so, their expansion plans (and thus business model in general) is erroneous.

A particular aspect that concerns me about them getting failure rates down into the lower tenths of a percent is their use of unlined COPVs. I don't trust them. I don't have some massive level of confidence that simply toying around with their pressurization regimen and getting better at void prevention is going to provide some sort of permanent fix; LOX and composites just plain don't play nice together. Their solution is like (to be hyperbolic here) having a nitroglycerine-fuelled rocket and losing one because during pressurization the tank buckled, and the buckling set off the nitroglycerine, and then announcing that you've got a solution and the tank shouldn't buckle anymore. Well, that's great, return to flight and all, but at the end of the day, you still have a nitroglycerine-fuelled rocket.

I'd feel a lot more comfortable about their business model if they announced plans to switch to lined COPVs, and take the (several dozen?) kilogram mass penalty. But as I always say, I would love to be proven wrong on this!

Slashdot Top Deals

"Well I don't see why I have to make one man miserable when I can make so many men happy." -- Ellyn Mustard, about marriage

Working...