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

 



Forgot your password?
typodupeerror
DEAL: For $25 - Add A Second Phone Number To Your Smartphone for life! Use promo code SLASHDOT25. Also, Slashdot's Facebook page has a chat bot now. Message it for stories and more. Check out the new SourceForge HTML5 Internet speed test! ×

Submission + - Wikipedia blocked in Turkey (turkeyblocks.org)

Ilgaz writes: The Turkey Blocks monitoring network has verified restrictions affecting the Wikipedia online encyclopaedia in Turkey. A block affecting all language editions of the website detected at 8:00AM local time Saturday 29 April. The loss of availability is consistent with internet filters used to censor content in the country.

Submission + - MIT creates 3D-printing robot that can construct a home off-grid in 14 hours (mit.edu)

Kristine Lofgren writes: Home building hasn't changed much over the years, but leave it to MIT to take things to the next level. A new technology built at MIT can construct a simple dome structure in 14 hours and it's powered by solar panels, so you can take it to remote areas. MIT's 3D-printing robot can construct the entire basic structure of a building and can be customized to fit the local terrain in ways that traditional methods can't do. It even has a built-in scoop so it can prepare the building site and gather its own construction materials.

Submission + - Elon Musk on why he doesn't like flying cars: 'That is not an anxiety-reducing' (yahoo.com)

boley1 writes: Elon Musk on why he doesn't like flying cars: 'That is not an anxiety-reducing situation'.

According to Musk, the main challenges with flying cars are that they'll be noisy and generate lots of wind because of the downward force required to keep them in the air. Plus, there's an anxiety factor.

"Let's just say if something is flying over your head...that is not an anxiety-reducing situation," he said. "You don’t think to yourself 'Well, I feel better about today. You’re thinking'Is it going to come off and guillotine me as it comes flying past?'

Comment Re:Speaking of delays... (Score 1) 106

ULA's track record with the Atlas V: 100%

Yes, let's take one vehicle in its fifth generation (not counting subrevisions), and ignore its track record with all of its earlier versions that led up to this point and all of their failures, and all of Lockheed and Boeings' other launch vehicles over time, with all of their failures. Lets also ignore that they're going to have to switch engines soon, to an engine with zero track record.

Payloads typically launch on schedule or within a few weeks. .... Some payloads have been waiting literally years due to delays.

Let's totally ignore that Atlas V launches once per two months, while SpaceX launches once per month, and that almost all of the wait time was due to investigation backlog. When it comes to hitting launch windows, SpaceX has a higher average success rate than average than Atlas V

And lets entirely fail to mention the point that ULA charges nearly double what SpaceX does per kilogram. Or that SpaceX is doing everything while rapidly evolving its rocket, to the point that they've basically even switched propellants partway through (denisification radically changes their properties). And while at the same time running an aggressive recovery and refurbishment programme and developing a heavy lift vehicle, with a small fraction as much capital.

Comment Re:What governmen brought to the table (Score 1) 106

As if liquid boosters can't fail catastrophically? Check out SpaceX's last failure. Liquids are hardly immune to catastrophic failure.

And actually more to the point, you've got it backwards. The SRB failure on Challenger was slow, more like a blowtorch. The explosion was when it compromised the external tank (which, obviously, stored liquids).

Solid propellants aren't like explosives. More to the point, you have to keep them under pressure to get the sort of burn rate that is desired for a rocket.

Submission + - WikiLeaks Reveals The "Snowden Stopper": CIA Tool To Track Whistleblowers (zerohedge.com)

schwit1 writes: As the latest installment of it's 'Vault 7' series, WikiLeaks has just dropped a user manual describing a CIA project known as ‘Scribbles’ (a.k.a. the "Snowden Stopper"), a piece of software purportedly designed to allow the embedding of ‘web beacon’ tags into documents “likely to be stolen.” The web beacon tags are apparently able to collect information about an end user of a document and relay that information back to the beacon's creator without being detected. Per WikiLeaks' press release

But, the "Scribbles" user guide notes there is just one small problem with the program...it only works with Microsoft Office products. So, if end users use other programs such as OpenOffice of LibreOffice then the CIA's watermarks become visible to the end user and their cover is blown.

Comment Re:Speaking of delays... (Score 2) 106

Could you remind me how many people SpaceX has killed? Boeing and Lockheed have certainly killed people in the past.

If you're referring to the AMOS 6 ground failure, ignoring that part of the whole point of flying a stack unmanned as much as you can before you fly it manned is to shake out any problems, is that a manned mission would have almost certainly survived that. Unless the launch escape system failed, despite the drama, that was an eminently survivable. How do we know this? Because AMOS-6's hypergolic propellant tanks didn't ignite until the satellite hit the ground. AMOS-6 had the fairing as some extra protection, but on the other hand, the satellite itself isn't nearly as durable as a crew dragon.

The launch escape system ignites within milliseconds of a failure being detected and almost immediately reaches full thrust, accelerating away at 10gs. Here's a graphic of Dragon's abort test superimposed over the AMOS-6 failure. Things like this are the very reason that launch escape systems exist. NASA's last manned space vehicle lacked such a system entirely. And while their design for the Shuttle ultimately wasn't chosen, you know what? Lockheed's proposal didn't have one either. And it had a strong impact on influencing the final Shuttle design outcome.

Comment Re:What governmen brought to the table (Score 1) 106

SpaceX and Blue Origin would not use solids, not because there's something wrong with solids per se, but because they're not "fuel and go", which makes them expensive to reuse - and SpaceX and Blue Origin are all about reuse.

A lack of experience with hydrolox surely factors into the picture for SpaceX and Blue Origin; they'd get significantly higher payload fractions by using a hydrolox upper stage. But they're willing to accept lower payloads in order to simplify their manufacture and ground infrastructure, and in particular because the need their propellants to be storable, and storing LH for long periods is a PITA. Storing methalox is quite difficult, but nothing compared to hydrolox.

Comment Re:What governmen brought to the table (Score 2) 106

Solids really aren't that bad when reusability isn't a concern. They're very high thrust, which is exactly what you want out of a booster, and they're structurally very simple. Their low impulse and high structural mass are not particularly important aspects for boosters. Reuse of solids however gains you very little, because there's so much work in refurbishing them.

Comment Re:What governmen brought to the table (Score 3, Informative) 106

That's not the reason you don't use it for a first stage. The disadvantages of hydrolox (which are numerous) are offset by its incredible specific impulse. But for a first stage, specific impulse doesn't matter that much, while thrust matters a lot. Thrust is in large part proportional to fuel density, as a turbopump sweeps out a fixed volume per rotation, so the denser the fuel, the more mass (and generally all else being equal, energy) it pumps per rotation.

Another aspect is that first stages are big, meaning that cost is more important than specific impulse. By contrast, when dealing with an upper stage, a small increase in mass has a huge increase in first stage size, and since first stages are so large and expensive, that's a big cost. So you generally want a higher ISP upper stage. With the caveat that "storability" requirements for engines that need to restart can shift the balance; because hydrogen is so deeply cryogenic it's difficult to store for protracted lengths of time. Also, the longer you plan to have a stage in usage without maintenance, the more you tend to favour simple propellants over high performing ones, particularly when you're dealing with small, light engines. So for example if you have an interplanetary probe you'll tend to favour a self-pressurizing hypergolic system so that you only have to rely on a couple valves working, even though self-pressurizing propellant tanks are heavier and hypergolics tend to be lower specific impulse. Engines that are smaller still are often monoprops for an even greater degree of simplicity.

Submission + - SPAM: Higher sodium intake associated with lower blood pressure. You read that right.

schwit1 writes: In another blow against decades of accepted medical wisdom, one of the most prestigious, long-running studies reports that lowering sodium intake doesn’t reduce blood pressure.

The study also implies that most Americans are consuming a perfectly healthy amount of salt, the main source of sodium. But those who are salt-sensitive, about 20 to 25 percent of the population, still need to restrict salt intake.

Consuming fewer than 2,500 milligrams of sodium daily is actually associated with higher blood pressure, according to the Framingham Offspring Study report, given today. The American Heart Association recommends consuming no more than 2,300 milligrams of sodium daily, equal to a teaspoon of ordinary iodized table salt.

High blood pressure is a known risk factor for heart disease and stroke. Hence, lowering salt intake is supposed to lower blood pressure and thus reduce the risk of cardiovascular disease and stroke. But the study found that supposition to be unfounded.

Moreover, the lowest blood pressure was recorded by those who consumed 4,000 milligrams or more a day — amounts considered dangerously high by medical authorities such as the American Heart Association.

Link to Original Source

Submission + - Spying on Students in the Classroom (eff.org)

schwit1 writes: It seems a day doesn’t go by without another report of a company monitoring what we do on the Internet and selling that data to generate more revenue. And now the Electronic Frontier Foundation (EFF) has examined what happens to the data that's collected from students using technology in the classroom. They released the results of an extensive survey covering students in grades K-12.

What they found was that little work has been done to protect the privacy of the student information that is collected from both the classroom and from using the online software the schools issue for use at home on the students' own devices. They found that while many school districts have embraced technology and all of the benefits it can bring to the schools and students, often little thought has been given to one of the unintended consequences of this: the students' privacy.

The study was very extensive and took two years to complete. Virtually everything was examined, including what's being done along each point from the suppliers of hardware and software and the cloud services, to the schools and the students. They found that lots of data is being collected without permission and that it's easy for outside companies to access the data. They also discovered that there's little to prevent suppliers from sharing data with others, including advertisers.

Slashdot Top Deals

"You need tender loving care once a week - so that I can slap you into shape." - Ellyn Mustard

Working...