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

 



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

Comment Re:His analysis is wrong (Score 1) 208

Exactly correct! An article claiming to explain how to answer questions involving run-time complexity shouldn't have such obvious mistakes in its analysis of run-time complexity.

(Yes, constant-time can be achieved by preallocating a fixed hash table, but that's not the same as using an arbitrary set insert/retrieve and since it permits collisions and is inherently bounded. It solves only a subset of the described problems.)

Mostly the dice article illustrates how the author is a poor person to look to for advice in that type of interview.

Comment Re:Not looking at microsatellites (Score 2) 117

I was also going to recommend cubesat.org and smallsat.org. The mailing list at cubesat@cubesat.org is active with numerous ongoing projects, mostly university-based. There are ITAR issues with American citizens participating in open projects, but there is a one-man korean satellite/art project at http://opensat.cc/about.html that has scheduled a launch.

Another collaborative effort is the GENSO organization, attempting to coordinate a federation of volunteer ground stations to expand telemetry coverage.

It's true that small satellites are built from off-the-shelf components and that a 500km orbit is generally self-cleaning due to atmospheric drag, but there are still some significant engineering challenges involved.

I'm a hobbyist-level engineer with an MS CS; my thesis focused on methods of software reliability for satellites in low-Earth orbit. Here are a few of the things that I consider to be "difficult" parts of a cubesat:
- RF communication on a very small power budget. Expensive (for a hobbyist) commercial solutions exist.
- Power management and design. Expensive (for a hobbyist) commercial solutions exist.
- Attitude determination and control.
- Passing the specific thermal/vibration testing requirements for a specific launch provider
- Surviving radiation-induced errors. A significant fraction of student-built failed satellites are lumped into "Command and Data Handling Failure" that could be attributed to the wrong bit flipped at the wrong time

There are a few happy coincidences that make it easier:
- most orbits result in alternating sun/shadow exposure, every 90 minutes. This just happens to make the temperature of the typical picosatellite oscillate between -20-80F-ish (very, very -ish) such that electronic components keep working with a minimum of thermal engineering.
- low-earth orbit has enough atmospheric drag that you don't have to build an active deorbit mechanism to avoid becoming hazardous space junk
- the radiation energy levels at low-earth orbit are enough to cause single-event-upsets (flipped bits) in RAM, but NOT enough to damage typical FLASH memory, so an appropriate reset mechanism is usually sufficient. (A NASA engineer summarized it as "Restarting from a known good state")

Also, WOW, there's a lot of ignorant posts here on slashdot. I don't remember the signal-to-noise being this bad, but I could be biased by nostalgia.

Image

10 Worst Evolutionary Designs 232

JamJam writes "Besides my beer gut, which I'm sure has some purpose, Wired is running a story on the 10 Worst Evolutionary Designs. Ranging from baby giraffes being dropped 5-foot during birth to Goliath bird-eating spiders that practically explode when they fall from trees."

Slashdot Top Deals

Memory fault -- brain fried

Working...