I'm disappointed. I followed the link in your sig in the hope of seeing a cat/goatse/Rick Astley but all I got was an ad that matches its description. Congratulations, you invented the reverse rickrolling. That or I spend too much time on the web.
I realize I should have just said that a flyby and an orbit are two different things, and that the article is therefore correct. Explaining why it is easier to get close to an object when you are orbiting around it than when you are flying past it is irrelevant.
P.S. I hope that the reason/. doesn't have an edit button is because Bezos patented it. Seriously guys, it is 2012.
In a flyby the probe is moving really fast relative to the asteroid. It thus can't produce enough delta-v for a last minute avoidance maneuver. The trajectory is determined well before the encounter. How close you can safely get depends on how accurately you can predict the asteroid path. A few kilometers at close approach with a reasonably low risk of collision is pretty good.
If you enter orbit first the situation is completely different. You can gradually lower the orbit and get as close as you want. You can also take all the time you need to accurately map the gravity field. And if there is a risk a collision the gravity is so low that you can quickly raise the orbit. The main difficulty in a low gravity environment is landing without bouncing back into space.
I don't understand where you got the idea that solar impulse cannot climb on its own. It is not a sailplane. It has solar panels and engines. They allow it to climb during the day and charge the battery. This energy (chemical and gravitational) is then available for the night. That it can gain more energy during the day than it consumes at night has been proven during their first 24h flight. Although of course it is only true around the summer solstice.
You are missing the point. Their objective is not to to develop a practical solar aircraft but to circumnavigate the globe with one.
Thus their plane only has to be good enough for that purpose. In particular it doesn't matter if it can't fly during the winter solstice or if it is slow.
Note also that aggressively exploiting currents and thermals was already a key part of the strategy of Breitling Orbiter 3, from some of the same people.
Reserving exceptions for error handling is a convention that makes it easy to distinguish error handling code from normal code and therefore improves readability.
This rule is mainly intended to discourage this kind of monstrosity: int find (int val, char *t, int n) {
try {
for (int i = 0; i n; i++) {
if (t[i] == val)
throw i;
}
}
catch (int i) {
return i;
}
return -1; }
If however you had to return across multiple function calls you would have to choose between exceptions and longjmp. Non-purists wouldn't object to exceptions in that case as they are safer.
In other news, some people are wrong. The right to be forgotten is the obligation, for providers of web services, to provide an option to delete you account and erase the personal information they have about you. No more no less.
It depends. Hurd itself is an implementation of the unix api as servers running on top of a microkernel. Drivers are not its concern.
The way drivers are handled on a Hurd system depends on the choice of microkernel. Mach includes drivers, so they run in kernel space. L4 doesn't have drivers, so they will have to be written separately and run in user space.
Pu-238 is not used in nuclear explosives proper but some nuclear weapons use a Pu-238 fueled RTG as a power source (see RCED-97-52, section "ELECTRICAL POWER SOURCES").
Historically most Pu-238 was produced for security applications. The space program was a minor user. The end of the cold war caused a dramatic reduction in the number of weapons. Thus the existing stockpile plus the Pu-238 recovered from dismantled weapons constituted a more than adequate reserve that rendered continued production unnecessary.
Today they are comparatively few weapons and most have migrated to different power sources. Hence the space program can no longer count on the nuclear weapons program to "subsidize" production. If it wants more Pu-238 it will have to cover a large portion of the cost of restarting production. We can thus expect RTGs to be used less often than in the past.
But if you put a camera behind the building looking away from it and connect it to a large screen in front of the building then someone located in front of the screen won't see the building.
My understanding is that these devices work similarly. They don't block radiation, but bend it.
What they did here is integrate a secure terminal like this one directly on the card.
These terminals are used for online banking. Every time you log in, you receive a different challenge. You then insert the card into the terminal and enter both the pin and the challenge and get the response back. Then you enter the response in the browser.
The goal of the system is to provide two-factors authentication. You need both something you have (the card) and something you know (the PIN).
The reason you need a secure terminal is that typing the PIN directly on the computer would allow a keylogger to steal it.
The first half of the trajectory should match the real thing quite well.
The second half is indeed slightly steeper than in reality. The final altitude is about half what it should be. This is due to some simplifying assumptions (in particular that of a constant drag coefficient).
However note that local terminal velocity decreases with altitude (due to an increase in air density), so the real curve is not as flat as you might think.
Slashdot Mirror
I drive a Ford nucleon, you insensitive clod.
Errors in the comments (s/increment/decrement/) would have been a nice touch.
This is comment on a single line of code taken from qemu/hw/ds1338.c:
Would you say that it is useless ?
I'm disappointed. I followed the link in your sig in the hope of seeing a cat/goatse/Rick Astley but all I got was an ad that matches its description. Congratulations, you invented the reverse rickrolling. That or I spend too much time on the web.
I realize I should have just said that a flyby and an orbit are two different things, and that the article is therefore correct. Explaining why it is easier to get close to an object when you are orbiting around it than when you are flying past it is irrelevant.
P.S. /. doesn't have an edit button is because Bezos patented it. Seriously guys, it is 2012.
I hope that the reason
You can't compare the two scenarios.
In a flyby the probe is moving really fast relative to the asteroid. It thus can't produce enough delta-v for a last minute avoidance maneuver. The trajectory is determined well before the encounter. How close you can safely get depends on how accurately you can predict the asteroid path. A few kilometers at close approach with a reasonably low risk of collision is pretty good.
If you enter orbit first the situation is completely different. You can gradually lower the orbit and get as close as you want. You can also take all the time you need to accurately map the gravity field. And if there is a risk a collision the gravity is so low that you can quickly raise the orbit. The main difficulty in a low gravity environment is landing without bouncing back into space.
I don't understand where you got the idea that solar impulse cannot climb on its own. It is not a sailplane. It has solar panels and engines. They allow it to climb during the day and charge the battery. This energy (chemical and gravitational) is then available for the night. That it can gain more energy during the day than it consumes at night has been proven during their first 24h flight. Although of course it is only true around the summer solstice.
You are missing the point. Their objective is not to to develop a practical solar aircraft but to circumnavigate the globe with one.
Thus their plane only has to be good enough for that purpose. In particular it doesn't matter if it can't fly during the winter solstice or if it is slow.
Note also that aggressively exploiting currents and thermals was already a key part of the strategy of Breitling Orbiter 3, from some of the same people.
Where is -1 offensive when you need it ? Seriously.
penultimate: that word doesn't mean what you think it does.
Who cares if modern stuff is not durable. I can buy 10 modern keyboards for the price of one of these dinosaurs.
Reserving exceptions for error handling is a convention that makes it easy to distinguish error handling code from normal code and therefore improves readability.
This rule is mainly intended to discourage this kind of monstrosity:
int find (int val, char *t, int n)
{
try {
for (int i = 0; i n; i++) {
if (t[i] == val)
throw i;
}
}
catch (int i) {
return i;
}
return -1;
}
If however you had to return across multiple function calls you would have to choose between exceptions and longjmp. Non-purists wouldn't object to exceptions in that case as they are safer.
It wasn't a pure U-233 weapon though, but a U-233/Pu-239 one.
In other news, some people are wrong. The right to be forgotten is the obligation, for providers of web services, to provide an option to delete you account and erase the personal information they have about you. No more no less.
I agree that this right is poorly named though.
It depends. Hurd itself is an implementation of the unix api as servers running on top of a microkernel. Drivers are not its concern.
The way drivers are handled on a Hurd system depends on the choice of microkernel. Mach includes drivers, so they run in kernel space. L4 doesn't have drivers, so they will have to be written separately and run in user space.
Pu-238 is not used in nuclear explosives proper but some nuclear weapons use a Pu-238 fueled RTG as a power source (see RCED-97-52, section "ELECTRICAL POWER SOURCES").
Historically most Pu-238 was produced for security applications. The space program was a minor user. The end of the cold war caused a dramatic reduction in the number of weapons. Thus the existing stockpile plus the Pu-238 recovered from dismantled weapons constituted a more than adequate reserve that rendered continued production unnecessary.
Today they are comparatively few weapons and most have migrated to different power sources. Hence the space program can no longer count on the nuclear weapons program to "subsidize" production. If it wants more Pu-238 it will have to cover a large portion of the cost of restarting production. We can thus expect RTGs to be used less often than in the past.
I meant that Sandia technology has a higher potential to impact his life than he thinks.
You will after a nuclear war.
But if you put a camera behind the building looking away from it and connect it to a large screen in front of the building then someone located in front of the screen won't see the building.
My understanding is that these devices work similarly. They don't block radiation, but bend it.
Pics or it didn't happen.
What they did here is integrate a secure terminal like this one directly on the card.
These terminals are used for online banking. Every time you log in, you receive a different challenge. You then insert the card into the terminal and enter both the pin and the challenge and get the response back. Then you enter the response in the browser.
The goal of the system is to provide two-factors authentication. You need both something you have (the card) and something you know (the PIN).
The reason you need a secure terminal is that typing the PIN directly on the computer would allow a keylogger to steal it.
Overall it is a pretty solid system.
Except that there are not trying to build a bomb. Do you yourself a favor and read The Complete Idiot’s Guide to Iran and the Bomb.
Sanctions, like war, are a form of coercion. And they kill, too, just more slowly. They have nothing to do with diplomacy (i.e. negotiations).
This is a simulation that I coded myself.
The first half of the trajectory should match the real thing quite well.
The second half is indeed slightly steeper than in reality. The final altitude is about half what it should be. This is due to some simplifying assumptions (in particular that of a constant drag coefficient).
However note that local terminal velocity decreases with altitude (due to an increase in air density), so the real curve is not as flat as you might think.
The previous plot was based on old data. Here is a revised plot based on actual flight data (start height: 39045m, max speed: 373m/s).