Slashdot is powered by your submissions, so send in your scoop

 



Forgot your password?
typodupeerror
×

Comment Re:Use a space elevator? (Score 1) 545

That's a common misconception.
In fact, pulling an object upwards the elevator will enact a specific impulse of about 5km/s, westwards, onto the elevator, felt as coriolis force.
However, that impulse can simply be transferred to the earth by anchoring it (think some kind of swimming oil rig in the ocean.
You just need to put the elevator's center of gravity slightly above geostationary altitude and the constant pull will keep the cable tense.
Pulling stuff up and down the elevator will then put the cable into oscillations, which can even be controlled to avoid space debris.

Comment Re:Use a space elevator? (Score 1) 545

Unfortunately, my source is only a german-language podcast by ESA (http://raumzeit-podcast.de/2013/07/05/rz054-space-elevator/); however, all my following statements are backed by it.
You can spin a rope of carbon-nanotubes; once you manage to create single molecules that are a few centimeters long, the rope's strength will be in the same order of a single molecule.
Centimeter-long nanotubes can very well be created with current technology; however, no reasearch team has real interest in it, because they are rather focused on the electronics applications (imagine an even flatter iphone as opposed to a lousy space elevator!)
However, with such a spun carbon-nanotube rope, the required diameter-at-geostationary-altitude-to-diameter-at-end ratio would be 4:1.
With this rope, a 1-ton payload elevator rope would weigh only 30 tons, well within the launch capacity of the Falcon Heavy.
From then on, the elevator could be used to construct itself, until capable of thousands of tons of payload.

Comment Re:Wrong question. (Score 1) 545

Definitely. Even with today's technology, it's possible to shoot down a satellite. There are few things more vulnerable than spacecraft. You don't even need orbital velocity; hell, with more modern electronics/software, even a german 1942 V2 rocket could destroy the International Space Station (or any spacecrat in low orbit for that matter).
Due to radiation constraints, elysium would most certainly be built in low orbit.

Comment Use a space elevator? (Score 1) 545

Using a space elevator, enormous structures in space would not only be a lot cheaper to launch (in the range of a few dollars per kg), but also a lot easier to build - no longer would spacecraft need to instantly work when launched, nor would they need to absorb the launch vehicle's g-forces.
All fundamental issues are solved (carbon nanotubes of the required length have been created, the orbital mechanics math works out etc.). If we had the will, like we had when we landed on the mun, we could probably finish an 100-ton-per-day elevator by the end of the decade, for maybe $1 trillion.

Comment Re:Self-replicating technology can make it faster (Score 2) 545

Self-replicating technology is incredibly hard to build. Self-replicating technology needs to be at least able to build computers, for which it requires a semi-conductor factory, requiring extremely precise optics, all kinds of lasers, etc, which in turn require dozens of different elements, some of them rare-earth, which in turn need to be chemically extracted from the asteroid or even bred in nuclear reactors if too scarce.

Take a look at this paper http://www.rfreitas.com/Astro/ReproJBISJuly1980.htm for a 440-ton machine (or rather swarm of machines) capable of reproducing once every 500 years under the conditions of a gas giant moon such as Ganymede, under the assumption that He3-Deuterium fusion technology is available for power.

Comment Re:first world problems (Score 1) 532

PWM frequencies are usually chosen as a trade-off: Too low frequencies mean flickering, audible noises, and, depending on the application, larger caps/coils. Too high frequencies mean higher CMOS switching losses, and RF signals emissions which may violate regulations.
The WLAN frequency was chosen as the resonance frequency of water because due to absorption that frequency is basically useless, so nobody really wanted it.

Comment Re:Bogus argument (Score 1) 311

For this reason, building instructions are usally provided, e.g. in the form of a Makefile.
Furthermore, almost every distribution provides you with all dependencies and the full packaging script which was used to create the distribution's binary in the first place.
Source-based distributions such as Gentoo even go as far as to do the actual creation of the binary on your local machine.
On Windows, however, this is admittedly a problem, since _everybody_ simply downloads an exe file from somewhere, without even checking the md5 hash that is usually provided (however, in most cases, in vain because the website is not even SSL secured). Most software probably can't even be compiled on Windows.

Slashdot Top Deals

A morsel of genuine history is a thing so rare as to be always valuable. -- Thomas Jefferson

Working...