(1) Installation on the ground is less expensive than on rooftops.
(2) If you put them on rooftops, all the houses would have to point in the same direction and have the same roof angles to get best efficiency
(3) In hurricane country, you might want to reset the panels horizontal in a storm to avoid damage
I assume they will be tied to the rest of the grid as backup, and to cover cloudy days, ie the city will generate its own power on average, but not necessarily at any given moment.
Therefore the output will be 175kW per square meter. To get 350MW will require 2000 square meters of cells, or a square that's 45m on a side. Thats a bit bigger than one wing of the space station's solar panels. I assume 350MW at the cells, since to deliver 200MW to the utility, you will need to convert the cell output to something, probably microwaves, then convert it back to electricity at the ground.
Now, to get 350 suns focussed on the cells, you will need a big set of mirrors, but those can be just reflectorized plastic sheets. You will also need to cool the cells. The input sunlight is on the same order as the power that modern cpu chips take (50W/cm^2), so that's doable, certainly.
I expect the issues with this system will be (1) can you unfold the very large reflectors needed, and (2) can you keep the heat removal system a reasonable weight.
In economics, let us assume they can sell the power at $0.10/kWh. That comes to $20,000 an hour or about $170 million a year. Assuming something like $5,000/kg launch cost to low orbit, and that it uses ion thrusters to carry itself to high orbit, it takes about 4 years to pay off the launch.
I assume it can use ion thrusters cause its got lots of power onboard, and they are more weight efficient than chemical rockets by a factor of 10.
All microwave solar power systems use a phase control signal sent up from the ground. That signal is sent from the center of the receiver field, and is *powered by the down beam*. So if for some reason the beam wanders, it loses focus and spreads over the entire earth.
Whatever name is announced to the public, The engineers, mission controllers, and astronauts will call it "Node 3". That's what we have been calling it all through the design stage. For example, in this photo, you can see the hatch is labeled "To LAB", short for US Laboratory Module, not "Destiny".
30 seconds of googling reports that dye cells currently produce around 6-10%. If you can triple that, it makes a really good solar cell. If you can do that and keep costs low, it makes a great solar cell.
I kid you not, but once upon a time the requirements for a "snap freezer" for the space station required impossible physics.
The point of a "snap freezer" is to quickly freeze a biological sample from an experiment in space, so it can be analyzed later on the ground.
Unfortunately, the requirements as given could not be satisfied even if the freezer was at absolute zero. Biological samples tend to be mostly water, and it has a finite thermal conductivity and amount of energy required to remove during freezing, so there is a minimum time to freeze a given size sample, no matter how cold the freezer is. And the requirements wanted it *faster*.
So, yeah, been there, and long before Homer Simpson said it, we more or less replied "At this company we obey the laws of thermodynamics".
A major problem with electric vehicles is the weight of batteries. My suggestion is to build "electric lanes" on major highways. These would supply power to electric cars as they drive along, and so give them more range. Locally in cities, or at the home end of trips, you would use internal batteries.
If you can supply more power than the car is using, you can "charge while driving" and top off the internal batteries.
The way to transfer power to the cars (sliding contacts, induction coils buried in the road, etc), safety, and payment features are left as jobs for smart engineers.
The atmosphere absorbs around 25% of sunlight on a sunny day, and you have nighttime and clouds. So a solar collector in space produces around 5 times as much raw power as one on the ground. Space solar power makes sense if *ALL THE OTHER COSTS OF GETTING THE POWER DOWN TO THE UTILITY GRID* are less than 5 times as high. Otherwise ground based solar power is cheaper.
Right now, the cost equation says it does not make sense. Some combination of cheaper launch methods, robotic construction, and supply of 99% of the power satellite parts from space-based sources *MIGHT* change that answer.
(I am a rocket scientist, in fact I got paid to help figure out that 99% number in considerable detail. Most of a solar power satellite can be sourced from space. A small part it makes more sense to get from earth, computer parts for example)
I invite the whole of Slashdot to think of a way to absolutely block piracy that will work short of yanking your cable out of the wall. I propose that it cannot be done.
Even yanking the cable out of the wall won't work, just slow it down a bit. Think burned discs and portable drives and laptops.
Exactly two years ago I paid $72 for an annual premium account on SL, my first out of pocket expense. Within three months I had broken even, and by next month I expect to have total profits of $10,000 accumulated. That includes partnering in a failed club and generally losing money on land transactions.
I've learned enough what not to do, so I don't make those mistakes any more, and now provide services that people pay me for. Electronic goods, being copiable, tend to zero price. Services, being custom for each client, hold their price better, so that's what I do.
Yes, people with unrealistic plans will lose money in SL, just like in real life. And Linden Labs is happy to collect money from them, mostly in the form of land fees.
I calculated the energy density from Toshiba's specs for a module containing multiple cells plus some charging electronics. This works out to about twice the figure for a deep-cycle lead-acid car battery.
Note: I worked on the ISS project from 1988 to 2005, and while I didn't work on the debris shield directly, I knew the guys who did.
At the typical speed objects colliding in low Earth orbit hit each other, which is around 7 km/sec, the kinetic energy of impact (~25 MJ/kg) exceeds the energy required to melt structures (600 kJ/kg for Aluminum, what the ISS modules are made of) by a wide margin. So when things collide, they generally melt or vaporize each other. The ISS has debris shields that consist of aluminum sheets mounted several inches away from the pressure shell. When a small (~1 cm or less) object impacts the debris sheild, the object melts or vaporizes itself and a small portion of the debris sheild. This stuff now splatters over a fairly wide area (~1 ft across). It's still moving fast, but the ~1 cm thick pressure wall of the module can take the impact if it is spread over a large area.
I would assume that the Bigelow engineers are smart enough to have designed a similar strategy in their module by having multiple layers in the design. The first layer vaporizes the incoming object, and the second, 3rd, etc. layers soak up the impact over a larger area. The key is to have enough separation between the layers to allow the splatter to spread over a larger area, which is easier to do with an inflatable module than a rigid one like the ISS has.
If your orbital debris is larger than ~3 cm, it won't necessarily melt when hitting the ISS debris sheild. In that case it can continue on to punch a hole in the pressure wall, and then get stopped somewhere in the equipment inside the module. Essentially all of the surface inside the module is covered with equipment racks. The result, depending on size of the debris, would be like firing a shotgun or hand grenade inside the equipment rack - not fun.
The ISS strategy is to track objects in this size range via ground radar, and if they look like they might get in the way, dodge them by moving the Station. If you have a day's warning, and you have to move ~1 mile to dodge, you only have to change speed by 0.04 mph.
When I worked at Boeing, I was in charge of a fuel-depot study. The method we looked at was a BFG to launch the fuel into orbit. The big gun used hydrogen gas that is quickly heated in a heat exchanger, then pushes a 600 kg projectile to 2/3 of orbital speed. The projectile uses some onboard fuel to go the rest of the way to orbit, then delivers the remaining 100 kg of fuel to the orbital gas station. The projectile de-orbits and is recovered to be reused. The projectile is rugged enough that it can land on anything without damage.
The big gun is very cheap ($100M) compared to electromagnetic launchers, because it is basically a length of pipe, compared to a series of coils, switches, and big power supplies. On the other hand, it is more expensive to operate.
The velocity split between the gun and the projectile depends on the size of the projectile and how much traffic there is to orbit. For the case we were studying, delivering fuel to carry comsats to GEO, we were launching 100 kg a day, or 30 tons/yr (allowing for downtime).
First of all, technology has improved a lot since the 1960s. There are cell phones with more computer processing power than all of NASA during the Apollo program.
Second, to bring the cost down, we should use techniques that have great leverage on reducing costs. These are advanced automation and use of local materials.
Advanced automation means instead of sending robots to a place, you send a robot factory. Instead of sending structural beams to the moon, you send a magnetic sifter to separate the 0.2% iron-nickel particles. These come from asteroids that have rained down on the moon over time and blasted themselves to bits and gotten mixed in with the surface material. A focusing mirror or lens can heat the steel to melting, and for a casting mold, just smooth out the lunar surface and draw a groove.
The point is that automated equipment can have payback of many times in less weight you have to bring from earth, thus reducing costs.
There are also ways to vastly reduce the cost to get to space. The Shuttle-derived launchers that NASA is pursuing now aren't it. They are merely optimization of a fundamentally poor technology - chemical rockets.
The way to price the renewal fee is to have the copyright holder self-assess the value of the copyright, and then have the fee be a fixed percentage of the value, just like real estate is assessed for property taxes.
The catch would be that works could be freed to the public domain at the self-assessed value. This would prevent holders from setting a low assessment just to lower their fees.
IAARRS (I am a retired rocket scientist, and have participated in a NASA Space Elevator workshop, and been on a science panel with one of the Liftport guys - I guess that makes me a relative expert)
A tower going up from the ground meeting a cable coming down from orbit is more efficent than a cable going all the way to the ground, if, and this is important, the strength of the cable is substantially less than the depth of the earth's gravity well.
Here's why: As you build a longer cable or a taller column of constant area under gravity, the stress gets higher. In a column the maximum stress is at the bottom, and in a cable it is at the top. Eventually you exceed the strength of the material.
The Earth's gravity well is equal to one gee times the radius of the planet = 6,378 km. A space elevator is centered at GEO, which is 97% of the way out of the Earth's gravity well, so we need to span 6,167 km at one gee.
The strongest readily available carbon fiber that is not made of nanotubes is about 1 million psi in strength. It has a density of 0.067 lb/in^3, so if you had a cable 15 million inches long under one gee, it would be at the limit of it's strength. 15 megainches = 381 km, which is a factor of 15 below what we need.
You can build towers or cables longer than the strength limit if you make them progressively wider to keep the stress below the limit of the material. Each 15 inches of length in the cable above adds one millionth to the stress, therefore the area has to increase by one millionth. Over a 381 km length, the area of the cable increases by a factor of e (2.718...). This length, found by dividing strength by the density of the material, is called the scale length. If you have 16.2 scale length to cover (6167/381), your cable area increases by e^16.2 = ~10 million.
A graphite/epoxy composite is needed for a tower. Bare fibers are okay in tension, but you need to stiffen them for a compression structure. Typically using the same fibers, the composite will be 30% as strong in compression as the bare fibers are in tension. Now assume you build a tower up and a cable down with the same area ratios from bottom to top. The tower's scale height is 114 km, so the combined scale heights for the tower + cable = 495 km. Now you need 6167/495 = 12.5 scale heights. e^12.5 = ~250,000, which is a factor of 40 improvement.
If you have carbon nanotube cable which has, say a 10 million psi strength, your scale length is 3810 km, and your area only needs to grow by a factor of 5 from bottom to top, so the reduction possible by using a tower is much less helpful. Of course, we are not making 10 million psi cable in useful quantities yet.
A slot-car type power source would have too many problems with debris or rain in the slot, lane changing, etc. So you need a non- contact way to get power into the car.
To extend the range of electric cars you can build inductive chargers into roads. The car can transmit an identifying signal (think RFID) that would do two things: identify who to bill for the electricity used, and limit the time the inductor is running to only when a car that can use it is present.
The inductors would be spaced along roads so that cars could get a charge while in motion. Since the efficiency of an induction coupling depends on the two sets of wires being close to each other, the power transfer will happen in short pulses as a car passes over each coil. If the batteries can't handle the high pulses, you would need to supplement with a capacitor to smooth out the power transfer.
Note that an inductive coupling means you will be operating an electric motor if the road coil and car coil are offset. So you can get an actual push or pull on the car (linear motor), as well as transferring power to the car's batteries.
Clay County, AL, where I own land, only has Health Department rules for septic systems, but no building department that you have to get a construction permit from.
Having said that, it would be wise to get plans for a house reviewed by an engineer and inspected when built. The government may not stop you from building, but an insurance company may decline to insure it if it is not built to some standard.
If you look at Mr Gates' sales of MSFT stock, it looks like he doesn't have a lot of confidence in it's future. He's been steadily selling his stake in the company. It's down to 10% now, and at the rate he was selling in 2004, will be down to nothing in about 7 years.
Now, Bill may be many things, but he's not stupid. If he's selling his stake in Microsoft, then he believes it's future prospects are below average. Anything he says publicly is likely affected by his desire for the stock price to stay up until he is done selling.
Communications satellites do the same job as cell phone towers - they receive and send radio signals, usually on multiple channels.
When you design a comm sat, you want to maximize earnings, which comes from maximizing number of channels (transmitter/receivers) you have and lifetime of the satellite. For each of the component parts of the satellite, you usually have a choice of cheaper, heavier parts, such as aluminum structure and single junction solar cells, vs more expensive, lighter parts: graphite structure and triple junction solar cells.
When you lower the cost per pound of launch, the optimal design, measured in transponder- years per megabuck, will shift to heavier, cheaper components.
Note that Boeing has not one, but two semi- commercial launch systems: Sea Launch and Delta IV. In both there was some government development and some private investment.
In the case of Sea Launch, a Zenit rocket (developed by pre-breakup Soviet Gov't) is launched from a converted drilling platform in the Pacific. Boeing paid for the home port in Long Beach, CA, and builds satellites that ride on the rocket. The Sea Launch program is actually a partnership between Boeing, Kvaerner AG, who is a Norwegian ship and drilling platform builder, and privatized Russian and Ukrainian companies that build the rocket.
The Delta IV, despite it's name, is basically an all-new launcher built partly with Air Force funding an partly with Boeing money. The first and second stages are built here in Alabama in one of the world's largest buildings - 30+ acres.
As I write, I'm in the computer lab where we're testing the software for the "Centrifuge Module", which is in the queue to be attached to the station eventually. The centrifuge will be able to spin lab animals at various levels of gravity so that we can learn what happens to them beween 0 and 1 gee.
So far we know that at 1 gee, everything is normal, and at zero gee your body figures it doesn't need bones anymore, so they atrophy. What we need to find out is what happens at 1/6 gee (Moon), 0.38 gee (Mars), and various levels of gravity up to 1 gee spinning (because that might be different in its effects than 1 gee not spinning here on Earth).
With this knowledge we will have some idea how to design for lunar bases, mars bases, and long duration travel (mars and asteroids).
Daniel
ISPs should charge each other for email delivery
on
Another Whack at Spam
·
· Score: 1
ISPs should charge each other for transporting email. AOL provides Earthlink a service by delivering Earthlink customer's emails to the recipient using AOL's equipment. So they are justified in charging Earthlink for that service.
Now if traffic flow is balanced, no actual money is exchanged. How you affect spammers is when traffic flow is imbalanced. An Isp sending more email than it receives ends up paying the other Isps. Then the spammer who creates the excess email will be billed by his Isp, and the Isp on the receiving end has a new source of revenue to defray it's costs, leading hopefully to lower charges for normal customers.
It would take a handful of the larger Isps to agree among each other to do this, and to declare that after a certain date they will no longer accept traffic from senders who do not agree to the deal.
Slashdot Mirror
As in the device in the X-Men movies?
Several reasons:
(1) Installation on the ground is less expensive than on rooftops.
(2) If you put them on rooftops, all the houses would have to point in the same direction and have the same roof angles to get best efficiency
(3) In hurricane country, you might want to reset the panels horizontal in a storm to avoid damage
I assume they will be tied to the rest of the grid as backup, and to cover cloudy days, ie the city will generate its own power on average, but not necessarily at any given moment.
These cells work at 35% efficiency at 500kW (350 suns) input light:
http://www.spectrolab.com/DataSheets/TerCel/C1MJ_CDO-225-IC.pdf
Therefore the output will be 175kW per square meter. To get 350MW will require 2000 square meters of cells, or a square that's 45m on a side. Thats a bit bigger than one wing of the space station's solar panels. I assume 350MW at the cells, since to deliver 200MW to the utility, you will need to convert the cell output to something, probably microwaves, then convert it back to electricity at the ground.
Now, to get 350 suns focussed on the cells, you will need a big set of mirrors, but those can be just reflectorized plastic sheets. You will also need to cool the cells. The input sunlight is on the same order as the power that modern cpu chips take (50W/cm^2), so that's doable, certainly.
I expect the issues with this system will be (1) can you unfold the very large reflectors needed, and (2) can you keep the heat removal system a reasonable weight.
In economics, let us assume they can sell the power at $0.10/kWh. That comes to $20,000 an hour or about $170 million a year. Assuming something like $5,000/kg launch cost to low orbit, and that it uses ion thrusters to carry itself to high orbit, it takes about 4 years to pay off the launch.
I assume it can use ion thrusters cause its got lots of power onboard, and they are more weight efficient than chemical rockets by a factor of 10.
All microwave solar power systems use a phase control signal sent up from the ground. That signal is sent from the center of the receiver field, and is *powered by the down beam*. So if for some reason the beam wanders, it loses focus and spreads over the entire earth.
Whatever name is announced to the public, The engineers, mission controllers, and astronauts will call it "Node 3". That's what we have been calling it all through the design stage. For example, in this photo, you can see the hatch is labeled "To LAB", short for US Laboratory Module, not "Destiny".
http://msnbcmedia3.msn.com/j/msnbc/Components/Photos/060707/060707_last-hatch_hmed_1p.hmedium.jpg
30 seconds of googling reports that dye cells currently produce around 6-10%. If you can triple that, it makes a really good solar cell. If you can do that and keep costs low, it makes a great solar cell.
I kid you not, but once upon a time the requirements for a "snap freezer" for the space station required impossible physics.
The point of a "snap freezer" is to quickly freeze a biological sample from an experiment in space, so it can be analyzed later on the ground.
Unfortunately, the requirements as given could not be satisfied even if the freezer was at absolute zero. Biological samples tend to be mostly water, and it has a finite thermal conductivity and amount of energy required to remove during freezing, so there is a minimum time to freeze a given size sample, no matter how cold the freezer is. And the requirements wanted it *faster*.
So, yeah, been there, and long before Homer Simpson said it, we more or less replied "At this company we obey the laws of thermodynamics".
A major problem with electric vehicles is the weight of batteries. My suggestion is to build "electric lanes" on major highways. These would supply power to electric cars as they drive along, and so give them more range. Locally in cities, or at the home end of trips, you would use internal batteries.
If you can supply more power than the car is using, you can "charge while driving" and top off the internal batteries.
The way to transfer power to the cars (sliding contacts, induction coils buried in the road, etc), safety, and payment features are left as jobs for smart engineers.
The atmosphere absorbs around 25% of sunlight on a sunny day, and you have nighttime and clouds. So a solar collector in space produces around 5 times as much raw power as one on the ground. Space solar power makes sense if *ALL THE OTHER COSTS OF GETTING THE POWER DOWN TO THE UTILITY GRID* are less than 5 times as high. Otherwise ground based solar power is cheaper.
Right now, the cost equation says it does not make sense. Some combination of cheaper launch methods, robotic construction, and supply of 99% of the power satellite parts from space-based sources *MIGHT* change that answer.
(I am a rocket scientist, in fact I got paid to help figure out that 99% number in considerable detail. Most of a solar power satellite can be sourced from space. A small part it makes more sense to get from earth, computer parts for example)
I invite the whole of Slashdot to think of a way to absolutely block piracy that will work short of yanking your cable out of the wall. I propose that it cannot be done.
Even yanking the cable out of the wall won't work, just slow it down a bit. Think burned discs and portable drives and laptops.
Exactly two years ago I paid $72 for an annual premium account on SL, my first out of pocket expense. Within three months I had broken even, and by next month I expect to have total profits of $10,000 accumulated. That includes partnering in a failed club and generally losing money on land transactions.
I've learned enough what not to do, so I don't make those mistakes any more, and now provide services that people pay me for. Electronic goods, being copiable, tend to zero price. Services, being custom for each client, hold their price better, so that's what I do.
Yes, people with unrealistic plans will lose money in SL, just like in real life. And Linden Labs is happy to collect money from them, mostly in the form of land fees.
I calculated the energy density from Toshiba's specs for a module containing multiple cells plus some charging electronics. This works out to about twice the figure for a deep-cycle lead-acid car battery.
Note: I worked on the ISS project from 1988 to 2005, and while I didn't work on the debris shield
directly, I knew the guys who did.
At the typical speed objects colliding in low Earth orbit hit each other, which is around 7 km/sec,
the kinetic energy of impact (~25 MJ/kg) exceeds the energy required to melt structures (600 kJ/kg
for Aluminum, what the ISS modules are made of) by a wide margin. So when things collide, they
generally melt or vaporize each other. The ISS has debris shields that consist of aluminum sheets
mounted several inches away from the pressure shell. When a small (~1 cm or less) object impacts
the debris sheild, the object melts or vaporizes itself and a small portion of the debris sheild.
This stuff now splatters over a fairly wide area (~1 ft across). It's still moving fast, but the
~1 cm thick pressure wall of the module can take the impact if it is spread over a large area.
I would assume that the Bigelow engineers are smart enough to have designed a similar strategy
in their module by having multiple layers in the design. The first layer vaporizes the incoming
object, and the second, 3rd, etc. layers soak up the impact over a larger area. The key is to
have enough separation between the layers to allow the splatter to spread over a larger area,
which is easier to do with an inflatable module than a rigid one like the ISS has.
If your orbital debris is larger than ~3 cm, it won't necessarily melt when hitting the ISS debris
sheild. In that case it can continue on to punch a hole in the pressure wall, and then get stopped
somewhere in the equipment inside the module. Essentially all of the surface inside the module
is covered with equipment racks. The result, depending on size of the debris, would be like
firing a shotgun or hand grenade inside the equipment rack - not fun.
The ISS strategy is to track objects in this size range via ground radar, and if they look like
they might get in the way, dodge them by moving the Station. If you have a day's warning, and
you have to move ~1 mile to dodge, you only have to change speed by 0.04 mph.
DRN
When I worked at Boeing, I was in charge of a fuel-depot study.
The method we looked at was a BFG to launch the fuel into orbit.
The big gun used hydrogen gas that is quickly heated in a heat
exchanger, then pushes a 600 kg projectile to 2/3 of orbital
speed. The projectile uses some onboard fuel to go the rest
of the way to orbit, then delivers the remaining 100 kg of fuel
to the orbital gas station. The projectile de-orbits and is
recovered to be reused. The projectile is rugged enough that
it can land on anything without damage.
The big gun is very cheap ($100M) compared to electromagnetic
launchers, because it is basically a length of pipe, compared
to a series of coils, switches, and big power supplies. On the
other hand, it is more expensive to operate.
The velocity split between the gun and the projectile depends
on the size of the projectile and how much traffic there is to
orbit. For the case we were studying, delivering fuel to
carry comsats to GEO, we were launching 100 kg a day, or 30 tons/yr
(allowing for downtime).
DRN
DLT tape cartridge was 0.5 in x 1700 ft, or 10,000 square inches.
At 0.75 Gbyte/sq in, that's 7.5 Tbyte per tape. That's a lot.
Daniel
First of all, technology has improved a lot since the 1960s.
There are cell phones with more computer processing power
than all of NASA during the Apollo program.
Second, to bring the cost down, we should use techniques
that have great leverage on reducing costs. These are
advanced automation and use of local materials.
Advanced automation means instead of sending robots to a
place, you send a robot factory. Instead of sending
structural beams to the moon, you send a magnetic sifter
to separate the 0.2% iron-nickel particles. These come
from asteroids that have rained down on the moon over time
and blasted themselves to bits and gotten mixed in with
the surface material. A focusing mirror or lens can heat
the steel to melting, and for a casting mold, just smooth
out the lunar surface and draw a groove.
The point is that automated equipment can have payback of
many times in less weight you have to bring from earth,
thus reducing costs.
There are also ways to vastly reduce the cost to get to
space. The Shuttle-derived launchers that NASA is pursuing
now aren't it. They are merely optimization of a fundamentally
poor technology - chemical rockets.
Daniel
The way to price the renewal fee is to have the copyright holder
self-assess the value of the copyright, and then have the fee be
a fixed percentage of the value, just like real estate is assessed
for property taxes.
The catch would be that works could be freed to the public domain
at the self-assessed value. This would prevent holders from setting
a low assessment just to lower their fees.
Daniel
IAARRS (I am a retired rocket scientist, and have participated in a NASA
Space Elevator workshop, and been on a science panel with one of the Liftport
guys - I guess that makes me a relative expert)
A tower going up from the ground meeting a cable coming down from orbit is
more efficent than a cable going all the way to the ground, if, and this is
important, the strength of the cable is substantially less than the depth
of the earth's gravity well.
Here's why: As you build a longer cable or a taller column of constant area
under gravity, the stress gets higher. In a column the maximum stress is at
the bottom, and in a cable it is at the top. Eventually you exceed the
strength of the material.
The Earth's gravity well is equal to one gee times the radius of the planet
= 6,378 km. A space elevator is centered at GEO, which is 97% of the way out
of the Earth's gravity well, so we need to span 6,167 km at one gee.
The strongest readily available carbon fiber that is not made of nanotubes
is about 1 million psi in strength. It has a density of 0.067 lb/in^3, so
if you had a cable 15 million inches long under one gee, it would be at the
limit of it's strength. 15 megainches = 381 km, which is a factor of 15
below what we need.
You can build towers or cables longer than the strength limit if you make
them progressively wider to keep the stress below the limit of the material.
Each 15 inches of length in the cable above adds one millionth to the stress,
therefore the area has to increase by one millionth. Over a 381 km length,
the area of the cable increases by a factor of e (2.718...). This length,
found by dividing strength by the density of the material, is called the
scale length. If you have 16.2 scale length to cover (6167/381), your
cable area increases by e^16.2 = ~10 million.
A graphite/epoxy composite is needed for a tower. Bare fibers are okay in
tension, but you need to stiffen them for a compression structure. Typically
using the same fibers, the composite will be 30% as strong in compression as
the bare fibers are in tension. Now assume you build a tower up and a cable
down with the same area ratios from bottom to top. The tower's scale height
is 114 km, so the combined scale heights for the tower + cable = 495 km.
Now you need 6167/495 = 12.5 scale heights. e^12.5 = ~250,000, which is
a factor of 40 improvement.
If you have carbon nanotube cable which has, say a 10 million psi strength,
your scale length is 3810 km, and your area only needs to grow by a factor
of 5 from bottom to top, so the reduction possible by using a tower is much
less helpful. Of course, we are not making 10 million psi cable in useful
quantities yet.
Daniel
A slot-car type power source would have too
many problems with debris or rain in the
slot, lane changing, etc. So you need a non-
contact way to get power into the car.
To extend the range of electric cars you can
build inductive chargers into roads. The car
can transmit an identifying signal (think RFID)
that would do two things: identify who to bill
for the electricity used, and limit the time
the inductor is running to only when a car that
can use it is present.
The inductors would be spaced along roads so that
cars could get a charge while in motion. Since
the efficiency of an induction coupling depends
on the two sets of wires being close to each
other, the power transfer will happen in short
pulses as a car passes over each coil. If the
batteries can't handle the high pulses, you
would need to supplement with a capacitor to
smooth out the power transfer.
Note that an inductive coupling means you
will be operating an electric motor if the
road coil and car coil are offset. So you
can get an actual push or pull on the car
(linear motor), as well as transferring power
to the car's batteries.
Not everywhere in the US has building codes.
Clay County, AL, where I own land, only has
Health Department rules for septic systems,
but no building department that you have to
get a construction permit from.
Having said that, it would be wise to get
plans for a house reviewed by an engineer
and inspected when built. The government may
not stop you from building, but an insurance
company may decline to insure it if it is
not built to some standard.
Daniel
If you look at Mr Gates' sales of MSFT stock, it looks like he doesn't have a lot of confidence in it's future. He's been steadily selling his stake in the company. It's down to 10% now, and at the rate he was selling in 2004, will be down to nothing in about 7 years.
Now, Bill may be many things, but he's not stupid. If he's selling his stake in Microsoft, then he believes it's future prospects are below average. Anything he says publicly is likely
affected by his desire for the stock price to
stay up until he is done selling.
Daniel
Communications satellites do the same job as
cell phone towers - they receive and send
radio signals, usually on multiple channels.
When you design a comm sat, you want to maximize
earnings, which comes from maximizing number
of channels (transmitter/receivers) you have
and lifetime of the satellite. For each of
the component parts of the satellite, you
usually have a choice of cheaper, heavier
parts, such as aluminum structure and single
junction solar cells, vs more expensive, lighter
parts: graphite structure and triple junction
solar cells.
When you lower the cost per pound of launch,
the optimal design, measured in transponder-
years per megabuck, will shift to heavier,
cheaper components.
Daniel
(who is a rocket scientist)
Note that Boeing has not one, but two semi-
commercial launch systems: Sea Launch and
Delta IV. In both there was some government
development and some private investment.
In the case of Sea Launch, a Zenit rocket
(developed by pre-breakup Soviet Gov't) is
launched from a converted drilling platform
in the Pacific. Boeing paid for the home
port in Long Beach, CA, and builds satellites
that ride on the rocket. The Sea Launch
program is actually a partnership between
Boeing, Kvaerner AG, who is a Norwegian
ship and drilling platform builder, and
privatized Russian and Ukrainian companies
that build the rocket.
The Delta IV, despite it's name, is basically
an all-new launcher built partly with Air
Force funding an partly with Boeing money.
The first and second stages are built here
in Alabama in one of the world's largest
buildings - 30+ acres.
Daniel
As I write, I'm in the computer lab where we're
testing the software for the "Centrifuge Module",
which is in the queue to be attached to the
station eventually. The centrifuge will be
able to spin lab animals at various levels of
gravity so that we can learn what happens to
them beween 0 and 1 gee.
So far we know that at 1 gee, everything is
normal, and at zero gee your body figures it
doesn't need bones anymore, so they atrophy.
What we need to find out is what happens at
1/6 gee (Moon), 0.38 gee (Mars), and various
levels of gravity up to 1 gee spinning (because
that might be different in its effects than
1 gee not spinning here on Earth).
With this knowledge we will have some idea
how to design for lunar bases, mars bases,
and long duration travel (mars and asteroids).
Daniel
ISPs should charge each other for transporting
email. AOL provides Earthlink a service by
delivering Earthlink customer's emails to the
recipient using AOL's equipment. So they are
justified in charging Earthlink for that service.
Now if traffic flow is balanced, no actual money
is exchanged. How you affect spammers is when
traffic flow is imbalanced. An Isp sending more
email than it receives ends up paying the other
Isps. Then the spammer who creates the excess
email will be billed by his Isp, and the Isp
on the receiving end has a new source of revenue
to defray it's costs, leading hopefully to lower
charges for normal customers.
It would take a handful of the larger Isps to
agree among each other to do this, and to
declare that after a certain date they will
no longer accept traffic from senders who do
not agree to the deal.
Daniel