Well, it's obvious that there are plenty of ways to fix this problem. However, these kinds of ways are exactly what NASA is trying to avoid.
This was a simplification of earlier landers, which used a radar altimiter to tell the engines when to shut off. A radar altimeter isn't all that complex, nor takes up much space, but it was scrubbed in an attempt to make the craft cheaper and less complex.
To combat these failure modes, you would need additional sensors to detect blow-back and tipping. One possible sensor to detect blow-back could be a series of strips made of a metal with a sufficiently low melting point as to melt under prolonged exposure to exhaust gasses; tipping could be detected via a mechanism similar to a common mercury switch or an aircraft artificial horizon. That's probably a lot more trouble than it's worth. To figure out how to connect all that will take valuable time and money that the space program just doesn't have.
The article pointed out that the craft would only be slowed to 2.4 m/s. That's pretty fast, and the lander must have been fairly durable. Rather than implementing all of these possible fixes, something much easier could have been done.
The article suggests that they had a good idea of exactly where the lander would be, how fast it would be going, and what type of conditions it would be running into. Figuring out whether or not the legs would have been affected by the deceleration due to the parachute is a rather trivial physics problem. Rather than come up with a complex solution a simple delay in the timing of the landing sequence could have been included. Rather than allow the engines to shutdown whenever the switch was activated, only allow the switches to become active after a certain period of time had passed. This would have allowed the engines to operate normally and only be shut-off when the switches could triggered when the engineers would be sure that the lander would be at a realistic height above the surface.
Wigs --The purpose of Physics 7A is to make the engineers realize that they're not perfect, and to make the rest of the people realize that they're not engineers.
I forgot to add: The spamming idiots are sometimes posting 40 idiotic posts that need to be moderated down which does probably screw the setup we had before this became the norm.
I'd definately have to agree with this. I was just reading the AOL Open Access Drop thing and it seems that some AC has decided to post a response to every post. Perhaps moderators should be able to inform the slashdot crew, or someone who could remove these trolls. I think that would definately help that problem. I don't necessarily think this should always apply to all trolls, just the ones that in no way, shape, or form relate to anything.
Wigs --Stupidity got us into this mess - why can't it get us out?
Okay, so the damn (read: damned) program has 65,000+ errors. One of the main reasons that I still dual boot is so I can have some fun. Where is your sense of adventure? I don't know of anything else, where one minute you can be going along fine, and the next blue screens are flashing, your box starts to cough, and you have a good excuse for not turning in that report. (Actually I had a mac go postal on a floppy disk and ate a physics report, but that's another post.)
The way I see it, Windows is like one of those adventure books. You never know where you'll go next. Certain death is almost always inevitable. Microsoft's slogan: "Where do you want to go today?", is perfectly appropriate, because they weren't sure either.
Wigs "Every creature has within him the wild, uncontrollable urge to punt." -- Snoopy
Why didn't you post my story? On a normal day, we can get 150-200 article submissions. Typically we post 8 to 12 of them. Also, Since we post the first submission (unless we screw up- it happens occasionally) yours may have just been 2nd. Or 37th. Or else we posted it a few weeks ago and you're late. Or we may not just have found your article interesting enough. Either way, we've gotta reject 10 times more then we post, so please understand.
I guess the guys at slashdot don't like this one anymore. Perhaps it should say that if you submit it again after waiting a while, one of the guys from the there-are-too-many-author's dept. will post it.
Okay, here's the point: You know, I've been reading slashdot for quite a while now (about 2 years). This sorta thing never used to happen at all, what is it these days? I guess I can understand one or two occasional slip-ups, but it's definately beginning to be noticable.
Wigs Relevant quote/saying/neat sig: As I said before, I never repeat myself!
It's noteworthy that an rock the size of, say, a small car, launched (dropped) from high orbit could and would hit the earth with enough force to generate atomic bomb scale destruction
Uh...sure. Well, that actually would make sense to do, but its practicality, please. First of all you would need to find an asteroid the size of a small car. True, you could probably fit a rock this size in the back of the space shuttle(maybe, I really have no idea if it would fit, but it seems reasonable). Well, considering a rock the size of a car would weigh in at several tons (again, it seems a reasonable enough estimate). Good luck geting a spacecraft up with that much weight attached.
Okay, say you did get it up there, or find a rock that big out in space. How the heck do you propose dropping it throught atmosphere without it burning up? To make much of an impact, you'd need an asteroid a little bigger than that. Good luck finding one out in space that you could some how coax into orbiting earth. Then you'd have to wait until it's orbit was just right so it would fall on the right target. Granted you wouldn't have to be very acurate, but we still have allies all over the planet, wouldn't want to hit them.
I guess this is an interesting thought, maybe even some far fetched science fiction. Really though, the next arms race?
And oh yeah, in visible-light news, microlensing provides strong evidence for stellar-size black holes being numerous.
By "stellar size" they must mean mass. By way of quick calculation (R = 2GM/c^2), we find that these black holes that are "about six times heavier than the Sun", are only 17.74 km(11 mi) in radius. For comparison, the sun has a radius of about 696,000 km(432,474 mi), and the earth 6,370 km(3,958 mi). Keep in mind these are radii. I don't know a whole lot about astronomy, particularly star sizes, but I've heard that the sun is a releativly small star.
The thing that makes me wonder, is if these are so common, what are the chances of coming accross one? It's probably about the same as coming accross an asteroid. I realize that there is a lot of space out there too. Also, the farther away we look, the farther back in time we look as well. Seeing many of these black holes would suggest that there are even more now, and our chances of finding new holes closer to home increase as time passes. I think it will be interesting to see new progress being made in this branch of science. Especially now that the HST is working again and can help out with the workload.
I'm in college, and while the high bandwidth is great, all it means to me is that slashdot and the 5 other sites i visit regularly load up faster. sometimes it also means that downloading that > 10 meg file isn't that big a deal.
I think you are exactly right. This is about the same way I feel. Even though I now have high bandwidth, I only look at a few sites regularly. I think now that I actually have this, I don't spend nearly as much time on the internet. Case in point: Recently, I went home for Christmas break. One day I decided to check my email. Well, I started up the old 486 beast, and connected the 28.8. By the time I looked at my watch, an hour had passed. Granted I have a few different accounts I checked, but still!
At school, I check it about two to three times a day, and it usually takes less than five minutes. The thing I like most, is that I can remain connected all the time. It also allows me to leave things like ICQ open all day. Being 3000 miles from home means I can stay in touch with all my friends that I don't get to see much more easily. I can talk with my parents for free instead of getting a $50 phone bill every month.
Nowdays, a lot more things are going out over the net. Most of my professor's set up email lists for their classes. As the use of computer's and networks become more important the connection will become increasingly important as well.
Also to go along with changing the characteristics of the photon...
When Bob tells Alice which photons he got, he will only tell about some of them. Only telling about some of them will let Alice and Bob know the transmition of photons was a success. This is designed to catch Eve in the act of intercepting photons. If she has intercepted them, and thus changed the characteristics(as mentioned by the other guy), they will know that Eve was listning. Even when Bob and Alice discuss some of the key(and Eve is listning), they should have enough(secret code) left to still encrypt a message.
my four hay-pennys worth (If that's how you spell it.)
I know exactly how you feel. I shiped my computer across the country, coming to school. The monitor ended up broken. The package looked like it fell off the back of the truck. After sending it back accross the country, they finally inspected it after about a month. They finally did admit they were at fault, but gave a false phone number to call to get the claim paid. All of this was insured of course. The moral of the story is even if they are at fault they don't pay. Now I know why. Unfortunately I didn't have a chance to refuse it, because the school signs for it. Their supposed to check it, but whoever did didn't look very closely. Needless to say, a good time was not had by all.
Good point. However I think it has been overlooked that the most likely explanation of why we aren't living on the moon by now, is that the public lost interest. After we beat the USSR to the moon, nobody found space as interesting. It's debatable wether or not we would be living on the moon by now though, if we had continued(with as much vigor)exploring space. That's not the point though. I think there is a reasonable chance that if they think it's possible to produce a GUT, then they can do it. (side note: Who thought it was possible to get to the moon by the end of the decade when Kennedy challenge us?) However, the technology to produce this already exists. Really nothing new is being built. The public doesn't really have any interest (and therefore cannot lose any), because they are uninformed about this. As long as these facilities stay operational, the physcisists will be able to get their work done. Fifty years is a generous estimate as well. A lot of work can be done in fifty years.
I think what you are talking about is the Lawson Criterion. I can't remember much about it, but basically it says that the energy output must exceed the energy required to contain and heat the plasma.(Not the energy input as suggested). There is a relationship between the confinement time, and the density of the plasma. This relationship must exceed some big number. Again I can't remember what it was, but it was big.(i.e 10 to a double digit) Last I heard they were about two orders of magnatude short of this number.
First of all, I doubt that the military has fusion. Really the only product to gain from fusion is energy, not any components for nuclear weapons. Second of all, if the reaction takes place in a vacuum, then not as much heat is required to sustain the reaction as stated in the article. Only about 100,000C is needed before the atoms can become ionized and begin to transfer energy. This only happens if the density is great enough. However this only needs to have a density a little over that of a vacuum. At this stage things get a little fuzzy, because some of the normal laws of physics don't work because the atoms are in a plasma state. The good news is the are electrically charged and can be controlled by magnets(as mentioned in the article). This should help keep the reaction in one spot.
Well, I am a college student so I think I am qualified to respond to this. So what if I take notes in a class and then put them on the internet. I actually took look at 24-7, and they don't charge anything to get the notes. The students are paid to post there notes. Many students are paid by their own universities to do the same thing, in SI sessions. Not only that, but the students are poor and could really use the money. After graduating these students are getting jobs. The university doesn't take anything out of there paychecks. The professors should just pipe down, and let the students fend for themselves.
Slashdot Mirror
This was a simplification of earlier landers, which used a radar altimiter to tell the engines when to shut off.
A radar altimeter isn't all that complex, nor takes up much space, but it was scrubbed in an attempt to make the craft cheaper and less complex.
To combat these failure modes, you would need additional sensors to detect blow-back and tipping. One possible sensor to detect blow-back could be a series of strips made of a metal with a sufficiently low melting point as to melt under prolonged exposure to exhaust gasses; tipping could be detected via a mechanism similar to a common mercury switch or an aircraft artificial horizon.
That's probably a lot more trouble than it's worth. To figure out how to connect all that will take valuable time and money that the space program just doesn't have.
The article pointed out that the craft would only be slowed to 2.4 m/s. That's pretty fast, and the lander must have been fairly durable. Rather than implementing all of these possible fixes, something much easier could have been done.
The article suggests that they had a good idea of exactly where the lander would be, how fast it would be going, and what type of conditions it would be running into. Figuring out whether or not the legs would have been affected by the deceleration due to the parachute is a rather trivial physics problem. Rather than come up with a complex solution a simple delay in the timing of the landing sequence could have been included. Rather than allow the engines to shutdown whenever the switch was activated, only allow the switches to become active after a certain period of time had passed. This would have allowed the engines to operate normally and only be shut-off when the switches could triggered when the engineers would be sure that the lander would be at a realistic height above the surface.
Wigs
--The purpose of Physics 7A is to make the engineers realize that they're not perfect, and to make the rest of the people realize that they're not engineers.
I'd definately have to agree with this. I was just reading the AOL Open Access Drop thing and it seems that some AC has decided to post a response to every post. Perhaps moderators should be able to inform the slashdot crew, or someone who could remove these trolls. I think that would definately help that problem. I don't necessarily think this should always apply to all trolls, just the ones that in no way, shape, or form relate to anything.
Wigs
--Stupidity got us into this mess - why can't it get us out?
The way I see it, Windows is like one of those adventure books. You never know where you'll go next. Certain death is almost always inevitable. Microsoft's slogan: "Where do you want to go today?", is perfectly appropriate, because they weren't sure either.
Wigs
"Every creature has within him the wild, uncontrollable urge to punt." -- Snoopy
As seen in Slashdot FAQ:
I guess the guys at slashdot don't like this one anymore. Perhaps it should say that if you submit it again after waiting a while, one of the guys from the there-are-too-many-author's dept. will post it.Okay, here's the point:
You know, I've been reading slashdot for quite a while now (about 2 years). This sorta thing never used to happen at all, what is it these days? I guess I can understand one or two occasional slip-ups, but it's definately beginning to be noticable.
Wigs
Relevant quote/saying/neat sig: As I said before, I never repeat myself!
Uh...sure. Well, that actually would make sense to do, but its practicality, please. First of all you would need to find an asteroid the size of a small car. True, you could probably fit a rock this size in the back of the space shuttle(maybe, I really have no idea if it would fit, but it seems reasonable). Well, considering a rock the size of a car would weigh in at several tons (again, it seems a reasonable enough estimate). Good luck geting a spacecraft up with that much weight attached.
Okay, say you did get it up there, or find a rock that big out in space. How the heck do you propose dropping it throught atmosphere without it burning up? To make much of an impact, you'd need an asteroid a little bigger than that. Good luck finding one out in space that you could some how coax into orbiting earth. Then you'd have to wait until it's orbit was just right so it would fall on the right target. Granted you wouldn't have to be very acurate, but we still have allies all over the planet, wouldn't want to hit them.
I guess this is an interesting thought, maybe even some far fetched science fiction. Really though, the next arms race?
Wigs
By "stellar size" they must mean mass. By way of quick calculation (R = 2GM/c^2), we find that these black holes that are "about six times heavier than the Sun", are only 17.74 km(11 mi) in radius. For comparison, the sun has a radius of about 696,000 km(432,474 mi), and the earth 6,370 km(3,958 mi). Keep in mind these are radii. I don't know a whole lot about astronomy, particularly star sizes, but I've heard that the sun is a releativly small star.
The thing that makes me wonder, is if these are so common, what are the chances of coming accross one? It's probably about the same as coming accross an asteroid. I realize that there is a lot of space out there too. Also, the farther away we look, the farther back in time we look as well. Seeing many of these black holes would suggest that there are even more now, and our chances of finding new holes closer to home increase as time passes. I think it will be interesting to see new progress being made in this branch of science. Especially now that the HST is working again and can help out with the workload.
Wigs
I think you are exactly right. This is about the same way I feel. Even though I now have high bandwidth, I only look at a few sites regularly. I think now that I actually have this, I don't spend nearly as much time on the internet. Case in point: Recently, I went home for Christmas break. One day I decided to check my email. Well, I started up the old 486 beast, and connected the 28.8. By the time I looked at my watch, an hour had passed. Granted I have a few different accounts I checked, but still!
At school, I check it about two to three times a day, and it usually takes less than five minutes. The thing I like most, is that I can remain connected all the time. It also allows me to leave things like ICQ open all day. Being 3000 miles from home means I can stay in touch with all my friends that I don't get to see much more easily. I can talk with my parents for free instead of getting a $50 phone bill every month.
Nowdays, a lot more things are going out over the net. Most of my professor's set up email lists for their classes. As the use of computer's and networks become more important the connection will become increasingly important as well.
Wigs
Also to go along with changing the characteristics of the photon...
When Bob tells Alice which photons he got, he will only tell about some of them. Only telling about some of them will let Alice and Bob know the transmition of photons was a success. This is designed to catch Eve in the act of intercepting photons. If she has intercepted them, and thus changed the characteristics(as mentioned by the other guy), they will know that Eve was listning. Even when Bob and Alice discuss some of the key(and Eve is listning), they should have enough(secret code) left to still encrypt a message.
my four hay-pennys worth (If that's how you spell it.)
I know exactly how you feel. I shiped my computer across the country, coming to school. The monitor ended up broken. The package looked like it fell off the back of the truck. After sending it back accross the country, they finally inspected it after about a month. They finally did admit they were at fault, but gave a false phone number to call to get the claim paid. All of this was insured of course. The moral of the story is even if they are at fault they don't pay. Now I know why. Unfortunately I didn't have a chance to refuse it, because the school signs for it. Their supposed to check it, but whoever did didn't look very closely. Needless to say, a good time was not had by all.
Good point. However I think it has been overlooked that the most likely explanation of why we aren't living on the moon by now, is that the public lost interest. After we beat the USSR to the moon, nobody found space as interesting. It's debatable wether or not we would be living on the moon by now though, if we had continued(with as much vigor)exploring space. That's not the point though. I think there is a reasonable chance that if they think it's possible to produce a GUT, then they can do it. (side note: Who thought it was possible to get to the moon by the end of the decade when Kennedy challenge us?) However, the technology to produce this already exists. Really nothing new is being built. The public doesn't really have any interest (and therefore cannot lose any), because they are uninformed about this. As long as these facilities stay operational, the physcisists will be able to get their work done. Fifty years is a generous estimate as well. A lot of work can be done in fifty years.
I think what you are talking about is the Lawson Criterion. I can't remember much about it, but basically it says that the energy output must exceed the energy required to contain and heat the plasma.(Not the energy input as suggested). There is a relationship between the confinement time, and the density of the plasma. This relationship must exceed some big number. Again I can't remember what it was, but it was big.(i.e 10 to a double digit) Last I heard they were about two orders of magnatude short of this number.
First of all, I doubt that the military has fusion. Really the only product to gain from fusion is energy, not any components for nuclear weapons. Second of all, if the reaction takes place in a vacuum, then not as much heat is required to sustain the reaction as stated in the article. Only about 100,000C is needed before the atoms can become ionized and begin to transfer energy. This only happens if the density is great enough. However this only needs to have a density a little over that of a vacuum. At this stage things get a little fuzzy, because some of the normal laws of physics don't work because the atoms are in a plasma state. The good news is the are electrically charged and can be controlled by magnets(as mentioned in the article). This should help keep the reaction in one spot.
Well, I am a college student so I think I am qualified to respond to this. So what if I take notes in a class and then put them on the internet. I actually took look at 24-7, and they don't charge anything to get the notes. The students are paid to post there notes. Many students are paid by their own universities to do the same thing, in SI sessions. Not only that, but the students are poor and could really use the money. After graduating these students are getting jobs. The university doesn't take anything out of there paychecks. The professors should just pipe down, and let the students fend for themselves.