ssimmons - Slashdot User

Comment Re:Cable? Why? (Score 5, Informative) 165

by ssimmons on Tuesday June 02, 2009 @11:56PM (#28191605) Attached to: Research Vehicle Reaches the Bottom of the Ocean

... the ocean might simply be good at blocking transmissions.

The ocean isn't just good at blocking transmissions. It's ridiculously good at blocking radio waves. If you work the math on this page, you can see that your basic WiFi transmission (at 2.4 GHz) will experience an attenuation of almost 1700 dB/meter! At that rate you'd get far less than a millimeter of penetration.

Even the lowest frequency short wave bands (1.8 MHz) get 46 dB/meter attenuation. It starts to get possible to receive RF when you get down in the kHz range but of course, your data rate goes to hell.

For underwater communications under a couple hundred meters or so you can use an acoustic modem. Even then, your best data rate is going to be on the order 2400 baud or less.

If you want high speed underwater communications, you gotta use a cable.

Difficult Times For SF Magazines 218

Posted by kdawson on Saturday January 31, 2009 @11:11PM from the genre-you-save-may-be-your-own dept.

Lawrence Person writes "Another speculative fiction magazine folds: Realms of Fantasy is ceasing publication. This comes hot on the heels of the announcement that the venerable Fantasy and Science Fiction will be moving from a monthly to a bimonthly schedule, and underscores what a tough environment this is for science fiction and fantasy magazines, all of which have suffered declining circulation for quite some time. This is a real problem, since short fiction is generally where new writers cut their teeth, appearing in print alongside their more famous peers. Given that a one-year subscription costs less than the average video game, those with an interest in science fiction might want to consider buying subscriptions to Asimov's, Fantasy and Science Fiction, and Analog. (Those in the UK might want to add Interzone and/or Black Static and Postscripts as well.)"

Submission + - Thank an Engineer (ti.com)

Submitted by ssimmons on Tuesday November 11, 2008 @01:15PM

ssimmons writes: TI has some videos up that try to imagine a world without some of the things that most people take for granted and then ask people to 'Thank an Engineer' for the world we live in. OK, so they're not really funny. Still, as an engineer, it's nice to get a little love for the work I do.

Comment Re:That isn't gps working underwater (Score 1) 99

by ssimmons on Monday August 11, 2008 @04:04PM (#24559621) Attached to: Robot Submarine To Dive Deep In the Caribbean

The sub uses GPS for positioning on and near the surface. The rest of the way it's using inertial navigation.

USL@NOC is also working on multibeam sonar so that the robot can assess its position using geologic features on the bottom (up to about 200m away I expect) for position keeping in a current.

I'm not sure why they'd use a multi-beam for station keeping when they already have an ADCP (Acoustic Doppler Current Profiler) on board. The particular ADCP they're using here was made by a company I used to work for (in fact, I wrote a lot of the firmware in that sucker) and is accurate to within a few tenths of a percent and can track the bottom out to 200m.

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