83 posts • joined Thursday 14th May 2009 12:38 GMT
Re: Feasible Space Elevators
I haven't ignored it. For a Rotovator design, you hook on and ride half a rotation and then let go. The forces are purely radial in that case. If you are climbing from the tip of rotation to the center, you do see a Coriolis effect, but let's look at the numbers.
Assume you have a maglev-type track that lifts a payload from the tip to center in 3 hours (200 km/s for a ~600 km radius), and the tip velocity is 2400 m/s. Therefore you much transfer 0.22 m/s angular velocity to the structure. The radial tension in the structure is 9.8 m/s at the tip, so you produce 2.2% deflection from purely radial while climbing. This is a manageable deflection of the cable structure.
Re: Feasible Space Elevators
You clearly don't understand orbital mechanics. Of course grabbing a sub-orbital cargo and accelerating it to higher orbit will lower the Rotovator orbit. That I why I mentioned on-board propulsion to make up the kinetic energy lost.
That allows you to substitute low efficiency rocket (on an unassisted rocket) for high efficiency electric thrusters (on the Rotovator), saving you 90% of the propellant consumption, which turns into more payload.
I spent a career in Boeing's space systems division, and am writing a book on the subject ( http://en.wikibooks.org/wiki/Space_Transport_and_Engineering_Methods ) so please credit me with having a clue what I am talking about.
Re: Zero velocity?
Actually, Cayambe in Ecuador ( http://en.wikipedia.org/wiki/Cayambe_%28volcano%29 ) is a better choice. Its the highest point on the Equator and has decent slopes for ground accelerators.
Feasible Space Elevators
Trying to span the depth of the Earth's gravity well with a single structure is terribly non-optimal from an engineering standpoint for a number of reasons. Smaller elevators, however, are quite feasible with off the shelf carbon fiber.
Imagine a rotating cable with a tip velocity of 2400 m/s, and a comfortable 1 gravity at the tip. The radius then works out to 587 km. You don't want the tip to enter the atmosphere, so you set the orbit of the center to 750 km, and the lowest point is then 163 km. The center then orbits at 7.48 km/s, and the tip is moving 2.4 km/s less or 5.08 km/s. Subract the Earth's rotation and you have a velocity of 4.61 km/s relative to the ground.
Your launch vehicle now has a much less challenging job than getting all the way to orbit by itself. It merely needs to reach a landing platform at the tip of the cable. To return to Earth, it has much less velocity to dissipate, so the re-entry heating is much less. Cargo heading to higher orbit merely rides for half a rotation, then lets go. It now is moving at 2.4 km/s above orbit velocity, which puts you in a high transfer orbit.
The load on the cable varies linearly from center to tips, therefore is equal to a cable under 1 g half the length, or 293 km. Good carbon fiber has a breaking length at 1 gravity of 360 km. We want a decent margin of safety, so only load the cable to 40% of ultimate strength. This requires tapering the cable from center to tip, as each point has to support the payload + cable outside that radius, but the taper ratio is not severe, about 7:1 in area.
Because this design is 40 times shorter, it is much less exposed to meteor and debris damage, but they still are a risk. Therefore you build the cable out of something like 21 strands, of which 7 are spares, and cross-connect them every 5 km. So when the inevitable impact happens, you only have to replace the one 5 km segment, which is 0.02% of the total structure. The "single cable" illustrations like the one in this article are just terribly unrealistic from a safety standpoint.
This type of rotating space elevator is called a Rotovator, and can start being useful while under construction, so you don't have to build it all at once. As the length increases, and tip velocity goes up, the launch vehicle needs less velocity, and can therefore carry more payload. If some of the payload is more cable for the Rotovator, the increased cargo on later flights "pays back" the payload spent on launching the cable. This payback time in cargo mass can be relatively short.
You can build a second Rotovator in high orbit, which captures payload sent up by the first one in low orbit, and forwards them to interplanetary trajectories. Since kinetic energy is not free, you need onboard electric thrusters to maintain the Rotovator orbits, but those have ten times higher efficiency than conventional rockets, so you still come out very much ahead on net cargo.
Re: In troubled times...
> I'm not sure I would rank bitcoins as safer than euro stored in a bank backed by a deposit guarantee, the ecb
Cyprus *had* a deposit guarantee, they just threatened to bypass it by taxing deposits. And it was the ECB who was encouraging this theft of depositor funds. The sudden interest in bitcoin is from other people in Europe wondering which other banks might decide to renege on their guarantees.
I agree that shifting your life savings into bitcoin is a bad idea, it is too new and unstable for that. But being inherently transnational, it is a good way to move your money to a safe haven outside the control of the ECB and euro bankers. The risk in using it for funds transfer is much lower, since you would hold them for only a short period of time.
Re: Green Concrete
Concrete can be green if you use a solar furnace to make the cement for it. I plan to prototype such a furnace in the near future.
Background: The reason for concrete being considered not green is the large amount of energy needed to calcine (burn) limestone and shale to make the cement. This energy usually comes from fossil fuels in a cement kiln. The rocks you are heating don't care how they get hot, so a solar furnace works just as well, so long as you can get it hot enough.
360M is still a lot of PC's
90 million PCs per quarter works out to 360 million per year. I already have two of them, so I don't need to buy another until my second one gets so old it's useless, and the new models are enough better than my quad core i7 to be worth an upgrade.
The point is, they are still selling a lot of PCs, and the market is getting saturated. Unless the hardware makes a great leap forward, existing models are good enough for many people.
Re: Google > ITU
What are you talking about? I tried "Naked Boobies" in Google image search, and got a page full of topless women. Works just fine as far as I can tell.
Google > ITU
This is why I would rather have Google as my Internet overlord than the ITU. They at least understand how the darned thing works.
Governments are a local monopoly on force. Since humans are self-interested, they will always try to leverage that monopoly into total control. Therefore you have to provide strong limits on government power, such as constitutional guarantees of certain rights and limits on their ability to meddle in things they should not.
If you want to make certain actions illegal (possession of child porn is the poster child (pun intended) for such actions), make the possession illegal. Don't go breaking use of networks, video cameras, studio rentals, and cash because they *might* be used for that purpose. They have other uses that are perfectly legitimate, so you end up punishing the bystanders and not just the criminals.
Stick to technical standards
The ITU should stick to technical standards for the same reason we set standard voltages on electrical outlets or standard symbols on highway signs. We didn't vote these guys the powers to decide anything political, so they should keep their mitts out of issues like security, public vs private, and what constitutes content and speech.
Re: Surely I am not the only...
Now I understand the origin of the HCF assembler command (Halt and Catch Fire). Thank you.
Re: Cost Benefit
When you air-launch, you never need to go vertical, and that accounts for a large part of the performance gain. When a conventional rocket takes off vertically, gravity opposes thrust and subtracts 1 gee from the net acceleration. When you are horizontal or near horizontal, gravity is perpendicular to thrust and does not slow you down.
Air-launch has an optimal flight angle early-on that is between horizontal and vertical, and the later parts of the flight are pretty much identical to other types of rocket. So it has less losses from fighting gravity in the early flight, and so better performance overall. The other gains you get are less drag loss and higher engine thrust, both from being at lower pressure, plus the actual altitude and velocity of the airplane.
The other part of the cost benefit besides performance is that an airplane has effectively an infinite operating life compared to one-use rocket stages. Thus the cost per flight of the airplane is much reduced. The cost of actual flying time (fuel and maintenance) will be ~$15,000/hr. This will be a tiny part of the total launch cost.
Re: But there is no concept of private property.
Don't forget the Kzinti Lesson (Larry Niven's Known Space series): Every reaction engine is a weapon. Someone wants to mine your asteroid without permission? Point a rocket thruster at them at close range.
This is a math co-processor to assist the CPU to crunch numbers faster. It is not a graphics card, so it does not have monitor outputs. If you want a workstation that can do both heavy duty number crunching and real time graphics, you would need two cards - this one plus a graphics card.
Still pretty good
There are 26.3 million households in the UK. The current sales rate is 10 million per year, which come to a new machine per household every 2.63 years. There are 29.3 million people employed in the UK, so it is one new PC every 5.56 years for every house and job in the nation. I see that as a healthy number, considering not every job requires a PC.
Re: Isn't there [DMCA penalty]
It does not have to be a fine paid to the government. It can be a "processing fee" paid to the content host (YouTube in this case) if it turns out to be a false takedown. That compensates the host for their trouble. You might set up to allow a few mistaken takedowns, but by the third or later, you get charged for wasting everyone's time.
Copyright has a unitary term, all rights expire at the same time. I propose a split term as follows:
* Non-commercial use copyright lasts 20 years.
* Commercial use lasts 40 years.
Thus, after 30 years, anyone can play a song privately, but if your band wants to use someone elses song in a concert, you still have to pay for that.
Consumer Purchase Agreement
Time for us to create a "Consumer Purchase Agreement", whose terms override any manufacturer's EULA. The way to make it enforceable is to tie it to credit card payments. In other words "By accepting payment from this card, you agree to these terms". This can apply to *every* payment, not just to Microsoft. If lots of people use this method it will even the tables with sellers. "Accept these even-handed terms, or we won't buy your stuff."
Re: To quote Top Gear... How Hard Can It Be™
Unlike automobiles, you don't get to crank a rocket engine very many times and take it for a test drive. Boeing does around 2000 test flights on an airplane before it goes to the first customer. The Space Shuttle only flew 135 times ever. By airplane standards, the Shuttle was still in early test when they retired it, and this particular Falcon 9 is attempting it's one and only flight, ever.
So the difficulty isn't that rocketry is harder from an engineering standpoint, it's that you get fewer chances to find design and production defects, and any defects are often catastrophic.
It has the same purpose as any other form of money - to buy things with it. And it's usefulness depends on how easy that is and the range of things you can buy with it. It's still in beta though, the latest version of the bitcoin software is at version 0.62 I think. Unless you like playing with new software, you might want to wait a bit till they get the bugs worked out.
Something to keep handy in an inflatable module is a sticky patch kit. In case of puncture, Hold the patch near the hole, and suction will slap it into place. Then smooth out the edges and probably add a few more layers of patch.
Nextel (TM) is a 3M company ceramic fiber. ( http://www.3m.com/market/industrial/ceramics/misc/tech_notebook.html ). For meteor/debris shields the advantage over Kevlar is the high temperature properties. At orbital speeds, *everything* is moving fast enough to melt or vaporize on impact. So your first layer of Nextel produces a splatter of hot droplets and vapor, including some of the Nextel. Further layers are there to contain the hot splatter.
Another reason to use Nextel over Kevlar, is Kevlar is an organic compound, and low Earth orbits have a significant amount of atomic oxygen ions around, which will eat organics. That's why most everything in orbit is covered with fiberglass or other materials not subject to oxidation.
There is still a major hole in the US economy - Construction. That includes not only the direct labor construction jobs, but all the suppliers of materials for building, and the peripheral jobs in real estate, finance, insurance, etc, and the downstream purchases by construction workers.
Until that hole gets filled, the US will take a long time to reach full employment again.
The bill allows the government to search without a warrant, violating the 4th Amendment of the US Constitution. The US Supreme Court has already that a warrant is required for electronic eavesdropping, pretty much what this is.
Security in the form of password hacks discovered by corporations and disclosed to the government is fine, but the broad searches without warrants allowed by this bill are clearly against already decided law in the US and the congress members who voted for it should be smacked with a wet mackerel for violating their oath to support the Constitution.
Re: It's unlikely but maybe the Private Sector could get there first...
Actually the first steps are more telescopes for finding asteroids, since we only know about 8% of the ones larger than 100 meters. Then prospector missions to visit and get samples back from the candidate ones you find. Looking at these asteroids from millions of km away, like we do from the ground, just does not tell you enough to determine which ones to mine and what you can get out of them. That pretty much follows Earth mining practice, first survey and take mineral samples back to the lab, then decide if you want to mine there.
Re: No gravity well - but asteroids are moving targets
No, you can exploit asteroid resources *in space*. Low orbit satellites need fuel so they don't fall down due to atmospheric drag, and high orbit satellites need fuel to get to high orbit in the first place. So the first mining product will likely be fuel for satellites. Anything else will come later and be gravy. If nothing else, the slag after extracting fuel can become radiation shielding, which you need for anywhere above low orbit.
Even in low orbit, you need some shielding to use modern electronics, because they are sensitive to particles from the radiation belts.
An open source Space Engineering reference book is under construction here:
If you want to find out how all this might be done, it's a starting point.
There is a radiation experiment on that mission to measure what humans would be exposed to on a Mars mission. This will give it some good data.
Self Expanding Factory
What you want eventually is the ability to make things out of local materials on Mars or elsewhere in space, because hauling it all from Earth is just too expensive. So for near term missions, I would send experiments in making simple things, like oxygen or collecting water, to demonstrate those tasks for later missions.
At the same time I would work on Earth and the Space station to prove out the next level of difficulty. An example would be extracting iron from the red rust on the Martian surface, which would later be used as building materials.
The end point would be a self-expanding factory that can make most anything you need on Mars from raw materials, but there are many small steps to take towards that goal. Start with the easiest ones, and work from there
Encrypted File Storage
All this does is encourage online file storage places like Mediafire to add "encrypt on upload" features, so the data is never in un-encrypted form on their machines. Police can raid all they want, they have no way to tell what files are stored there, neither can the storage operator.
It would be easier to pay the embassy of some benighted third world country to host the server. Attacking that *would* be an international incident.
Meanwhile, local pirate boxes (wifi transmitter + data storage) can be located in automobiles parked in busy locations, and solar-powered. By the time the Powers that Be figure out a site is transmitting, they can have moved on. The whole TPB index of magnet links + comments + descriptions can probably fit on a single flash drive these days.
A wll placed SAM?
@sisk - well, no, for two reasons:
* Surface to air missiles fall short by thousands of times in reaching that altitude. A stripped down ballistic missile, or a satellite launcher could get there.
* A 50 meter sphere has a volume of 65,000 cubic meters. Depending on what it is made of, then that asteroid has a mass of 65 to 260 kilotons (1 to 4 large aircraft carriers). A SAM will not do much to it.
The only practical thing to do if you have a few weeks notice is lob a nuclear bomb or three (for redundancy) at it, and try to deflect it sideways. It will almost certainly fragment if you do that, but that does not matter if the fragments miss the Earth. If you have longer lead times (years) you can look at less violent methods of pushing it out of the way.
Make it a feature, not a requirement
I agree with the general trend of the comments - make the Metro UI an option you can turn off, and us desktop users with multiple monitors will not have to mouse all over the place to get simple tasks done.
By the way, I have yet to see a demo of Windows 8 with two or more monitors, how does it handle that situation?
Re: First they came for the copyright infringers-
And they responded by developing the Low Orbit Ion Cannon, Tor, and, for traditionalists, Sneakernet.
Sure, creators should have the right to profit from their work, but non-commercial sharing has always existed. We used to loan DVDs at work to each other in the days before broadband. Before that people made mix tapes on cassette to play in the car.
Staging point in high orbit
We need some sort of staging point in high orbit where we can start producing fuel and other items from asteroid sources. It needs to be a balance of high enough orbit to be easy to reach from NEOs, and close enough to Earth for remote control and sending some human crew.
Instead of sending everything from Earth, send machines tools, and go grab a metal-bearing asteroid. Then you can bootstrap your production and cut the total cost by quite a bit.
Gravity is proportional to mass, which at a fixed density goes as volume. Volume goes as the cube of the radius. Gravity is inversely proportional to the square of the distance from the center of the planet. So combining terms, gravity goes up linearly with radius, or as the cube root of mass.
In the case of a planet with 4.5 times the Earth's mass and the same density, then the surface gravity would be (4.5)^(1/3) = 1.65 times ours. Since the parent star is "metal poor" (astronomers call anything above Helium on the periodic table a metal), this planet is likely to have less iron core and heavy rock mantle, and more lightweight elements, We will have to wait for better telescopes to be sure what it's made of.
MySpace -> Facebook -> ?
@dotdavid - Good point. It's a website, people can move on to another one. When young new companies go public, it's because they need cash to expand. Facebook already serves 40% of the entire internet with the equipment is has now, so it does not need money to expand. Instead, I think it's owners figure it has peaked, so time to cash out before the fall.
Libraries should fund journals themselves
There is obviously *some* administrative work in organizing a journal. University libraries should set up non-profit organizations to do that work, or take it internal to themselves, and then charge actual cost in the subscriptions for other people who want access. Right now they are the ones who are paying most of the journal subscription costs to companies like Elsevier, so they are the ones to see the savings by removing the middlemen.
The key thing a good journal does is filter out crap. Scientists have a limited amount of time to read articles written by others, and they should not spend it reading garbage. The journal editors (who are usually academics themselves) are the first level filter, rejecting submissions not up to some quality standard, and then reviewers who are versed in the field make comments on anything they find wrong in a prospective article. Those comments go back to the author to improve the article. So those levels of filtering ensure some level of quality in what gets published. Any replacement publishing system needs a way to filter out the bad articles, or you risk ending up with garbage being published.
If the operators of Megaupload really made the huge profits claimed, won't that simply attract replacement websites to fill the void? The public's demand for content has not changed, nor has the cost of operating a site. New competitors, assuming they have half a brain, will have a less flashy lifestyle, squirrel away profits somewhere secure, and locate in less extraditable countries.
CNC is not new
The Rep-Rap type plastic extrusion machines are just one example of CNC. They all share a way to position the working head in 3 dimensions relative to the work piece. What is different is what kind of working head: drill bit for cutting metal, plastic extruder, laser for sintering, etc.
Computerized Numerical Control (CNC) machines have been around for decades, working with materials like metal mostly. Like the old mainframe computers, though, they were expensive enough that only businesses used them. There are hobbyists building home CNC machines the way early experimenters built their own PCs. The revolution will be when enough of the machines are cheap enough to make parts for each other at a community or home level. This already happens at the industrial level. The factories that produce CNC machines use more CNC machines to make their parts. It's just been too expensive for ordinary people to do that so far.
Politicians for sale
@ John A Blackley - Oh, we knew they were for sale. The only question is does Hollywood get a discount for buying them in bulk?
Re: Anon Coward at 5:30 GMT
Cnet is in an interesting position to be commenting on SOPA. Their parent company CBS support the bill (as you would expect for a media giant). At the same time, Cnet has distributed over 150 million copies of torrent and other file sharing software, they have a whole section for it in the Downloads tab.
Murdoch is such a hypocrite
Visit the File Sharing section of File Planet powered by IGN:
notice how they have multiple pirating software for download?
Notice how IGN Entertainment is a division of News Corp (Murdoch's company):
Maybe he should clean his own house before complaining about this subject.
Genetically engineered algae are more efficient at using sunlight than trees or grass, and either store oil in their cells, or emit hydrocarbons directly (the way yeast emit alcohol). It depends how you engineer their biology which they do.
If you grow them on land, they don't require good land, just containers to grow in. Alternately you can grow them just off the coast in pens. Australia has plenty of coastline.
@Disco - yes, biofuel is a form of solar energy. They are limited to about 6% efficiency maximum in theory, and a lot lower in unmodified plants, but are cheaper to make since they are self-reproducing.
As an aside, cheap carbon storage would be to grow plants like trees, and then just store the wood in the form of buildings, or put it in deserts or icy locations where it won't decay. Per ton of carbon, that is way less expensive than pumping CO2 down used oil wells or other such methods.
The Obvious Next Step
After getting the carrier aircraft working, the obvious next step is to add some wings, landing gear, and small jet engines to the rocket first stage. Once it is empty of fuel, it will not weigh that much, so it will not need them to be very large. Recovering the rocket stage will dramatically improve the economics.
It makes sense not to tackle that right off the bat, just building the carrier aircraft is a big enough project to start with.
@Eddy Ho - no, gravity goes up linearly with diameter for constant density. Mass goes up as cube of diameter, but gravity decreases as inverse square of diameter, leaving net of linear increase. So surface gravity would be 2.4 time Earth if it had the same density.
Kepler can only find planets whose orbit is edge-on, so that it transits in front of the star and we can notice the light drop when that happens. Assuming planet orbits are randomly oriented, there will be a LOT more of them Kepler will never see. In the case of the Sun and Earth, the odds are 360:1 against it lining up properly. Again, assuming stars with habitable zone planets are randomly distributed, we should expect to find one 7 times closer to Earth for each one Kepler sees, and 360 others at distances in between.
400 ppm CO2
To put it in terms easy to understand, 400 ppm of atmospheric CO2 works out to a layer 2.65 mm thick if it was frozen out. You don't think that a layer of Dry Ice that thick is capable of stopping some light, especially in the infrared, where it is an absorber?
In reality, it's in gas form, so a more accurate model is to take the equivalent thickness of the atmosphere if it was constant pressure all the way up, which is 8400m. 400 ppm of that works out to 3.36 m. Thus a layer of CO2 at one atmosphere 3.36m thick is equivalent to what we have dispersed in the real atmosphere. You can shine light of various wavelengths through that and find out how much has been absorbed. This has been done long ago. Absortion curves for the atmosphere as a whole and it's parts for example are here:
Change the CO2 concentration, and it will absorb more infrared, thus slowing radiation back to space. Change the balance of sunlight in vs infrared out, and you change the temperature, simple as that.
Due Process? Not Any More
The judge seems to have forgotten a few rules of law included in the US Constitution. That includes "due process", the requirement to follow proper procedure, and the right to face your accuser in court.
By all means, if the sites are selling counterfeit goods or infringing trademarks, they should be held accountable. But they should be held accountable following the rule of law, not a system of "punish first, then find if they were guilty".
Less Panic Please
On an annual basis the shortage is 10% of a year's supply. So everyone just delays their purchases by a month, and does some housekeeping to clean up their unneeded files a bit. We can survive.
(mine's the one with the USB hard drive in the left pocket)
Tracking the Satellite
This website has a real-time orbit track, fly-over predictions, and if you click the link in the upper left, details of the current orbit (high and low points):
Because the Earth's atmosphere density is exponential, each 10 km the orbit decays doubles the drag. So the time it takes to fall 10 km times two roughly gives the time to re-entry. Around 120 km is re-entry altitude. At that point drag is so high it will not finish another orbit and heating from atmospheric friction will start to melt parts.
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