I believe the idea was that they were able to custom fit higher energy-storage batteries. The latches and casings to include a removable battery aren't insignificant in terms of weight and volume, so there is a certain argument for eliminating them. With an 8-hour battery life, it seems fair to expect that most people won't be itching to change it all the time.
I've never really made use of the fact that my laptops have removable batteries, except for replacement after years of use (which 16 screws isn't terribly difficult for long-term replacement). At the same time, with a 17" laptop I have trouble believing the extra weight and volume would make much difference... doing it for the air makes more sense to me.
If it is an important feature to you, there's the 15" MBP (which is probably better for travelling anyway). And I guess the small part of the market that really wants a 17" with a removable battery isn't a large concern for Apple... if they wanted to fill every niche we'd see the xMac, a netbook, a tablet, and everything else people have been asking for for a long time.
While I agree with the sentiment, the one serious counter-argument I'd give is that you need to ensure that people are able to receive public safety announcements. TV is much better than radio for dealing with severe weather, because being able to see the weather maps and storm tracks gives you a much better idea of what's going on. Going into tornado season in Oklahoma (where I grew up) without TV would make me a little uncomfortable.
Recall that we (the people) give the broadcasters the right to use the airwaves in exchange for them providing public services: news, weather, and emergency announcements. We decided these things are important, so its important to make sure their accessible.
But at the same time, this has been coming for a long time, people should have been able to figure it out by now.
In a certain respect, it is related to the focal length, if you consider the eyepiece or sensor fixed. If you have a fixed pixel size on your CCD, then changing the focal length will change the angular size of each pixel, and thus change the resolution, although I think this kind of result is usually called magnification. Similarly, when using an eyepiece, the magnification is related to the ratio of the focal lengths, so a longer focal length will change the magnification
When the CCD pixels get small enough though, that size is no longer the limit on the resolution. Instead (neglecting atmospheric effects) you run into the fact that photon impacts are defined by probability densities that behave like waves, and you get a certain 'spreading' around the nominal impact location. The diameter of this spreading (the Airy disk) means that two sources that are too close together cannot be distinguished from each other, and this is called the diffraction limit. (There are other equally valid explanations for this effect, particularly coming from a wave perspective, this is just the one that I started typing.)
Now, in order to reduce this you want to bring in more photons from further seperated distances, meaning you want a larger aperture in order to improve the diffraction limited resolution. Generally the limiting angular resolution is given by theta_r = 1.4 lambda/D. Of course, if you have too strong of aberrations in the optical system, have to deal with atmospheric 'seeing' effects, the system is not diffraction limited, and the point spread function spreads out more.
Of course, its dangerous to compare the capabilities of telescopes at different wavelengths (Hubble is visible, Herschel is infrared to millimeter wave), because the total amount of light available changes, the angular resolution changes, and the engineering requirements change. Really, Hubble is about the maximum size optical space telescope you can make with current launch vehicles without moving to a completely new kind of telescope (active feedback with wavefront sensing like JWST). Herschel is able to be bigger easily because it requires significantly lower precision, due to the larger wavelengths.
The problem isn't the red light cameras in general*, but the fact that they are tied to a lowering of the time for yellow lights. What I was taught is that a yellow light indicates "clear the intersection". If that means to brake, you brake; if that means to keep moving or possibly accelerate because you can't brake in time for whatever reason (tailgater, simply not enough space, etc.), you go on through. Obviously for a typical vehicle there will be a certain zone where one or the other is the right choice.
Since people aren't perfect and cars aren't all the same, there should be some margin in the middle so that if its close either choice is an acceptable one. You create and expand this margin by throwing a couple of seconds in to the yellow period. The problem with many of the red camera light systems, including the one in the town I live in, is that the cameras are seen not only as a way to improve safety, but also to generate more revenue. Many installations operate where the manufacturer of the system actually gets a cut of the fines generated from the system, and they tend to say they won't install a system unless the light time is shortened to the minimum allowed by the state. The police departments themeselves get additional funding from the additional fines as well, so its not especially hard to twist their arm into doing so.
To a certain extent I do appreciate the systems, because I live in a college town and we have some of the worst drivers I've ever seen. However, by shortening the light times, you end up with a system that is safer than the original case, but still not especially good. Because there is very little margin, and a guaranteed fine, people are much more likely to slam on the brakes to stop. While you reduce the number of dangerous cross-traffic accidents, you increase the number of rear-end collisions, a situation that could be avoided by installing the systems responsibly.
*aside from possible privacy issues, which isn't the point here.
The problem isn't the red light cameras in general*, but the fact that they are tied to a lowering of the time for yellow lights. What I was taught is that a yellow light indicates "clear the intersection". If that means to brake, you brake; if that means to keep moving or possibly accelerate because you can't brake in time for whatever reason (tailgater, simply not enough space, etc.), you go on through. Obviously for a typical vehicle there will be a certain zone where one or the other is the right choice.
Since people aren't perfect and cars aren't all the same, there should be some margin in the middle so that if its close either choice is an acceptable one. You create and expand this margin by throwing a couple of seconds in to the yellow period. The problem with many of the red camera light systems, including the one in the town I live in, is that the cameras are seen not only as a way to improve safety, but also to generate more revenue. Many installations operate where the manufacturer of the system actually gets a cut of the fines generated from the system, and they tend to say they won't install a system unless the light time is shortened to the minimum allowed by the state. The police departments themeselves get additional funding from the additional fines as well, so its not especially hard to twist their arm into doing so.
To a certain extent I do appreciate the systems, because I live in a college town and we have some of the worst drivers I've ever seen. However, by shortening the light times, you end up with a system that is safer than the original case, but still not especially good. Because there is very little margin, and a guaranteed fine, people are much more likely to slam on the brakes to stop. While you reduce the number of dangerous cross-traffic accidents, you increase the number of rear-end collisions, a situation that could be avoided by installing the systems responsibly.
*aside from possible privacy issues, which isn't the point here.
I saw on the Ars thread on this that the Cox and Comcast have divvied up Tucson, so the reason it only affected some customers is probably because the others are on Cox.
Given Diamandis' involvement, I'm guessing its modeled on the International Space University, which seems to do well enough. However, I am skeptical since the 'space community' is a little bit more well-defined than the 'singularity community'.
As an American, I must say, we need to take a look at this nomenclature: Shadow Minister sounds so much cooler than Senate Minority Leader or the like.
It helps when the guy has an ounce of sense too...
Although I do enjoy the West Wing, sci-fi has the great advantage of being able to touch issues in a harsher way and reach a broader audience, because its not attached to any real-world events that people are attached to. Also, I'd really say, from what little I've seen of 24, it really hits a lot of the issues a lot more directly, but it also assumes a correct answer.
However, what BSG is able to do is reproduce analogs to current events, placing us on the side we dont normally associate ourselves with (i.e. the resistance on New Caprica), and leave it to you to judge what is right our wrong. In doing so, in this way, you can bring up the issues without alienating as many people.
I personally think this is one of the key factors of science fiction/fantasy as art as opposed to just entertainment.
Interesting, thanks for pointing out that article. Bandwidth synthesis actually looks like something I was about to start looking for, although I was hoping to use the varying frequency to induce phase diversity to help with phase-reconstruction methods.
Also, I know there have been a few papers written on using Cherenkov arrays (sorry, don't have my resources with me), although I'm not sure if any have actually been implemented. In the same vein, I've idly wondered if the big mirror-farm style solar plants could be pointed well enough to use. Although I'm guessing the answer is no, but it would be very interesting to be able to use something that large, placing a sensor at the focus of the plant.
Absolutely right, although we have some advantages now that we didn't when the Narrabi experiments were run. First, detectors have improved: higher response speed and higher quantum efficiency do make things easier. This might be able to double the sensitivity at most though (I'd have to find hard data and run numbers, and I need to do other things today).
However, there are some other ways to improve the SNR. By using a splitting up the incoming light into multiple spectral bands and correlating the signals from each band separately, you can increase the SNR by a factor of N_b (number of bands) or sqrt(N_b), I can't recall exactly. Another method (actually what I should be writing about right now for my thesis) is to use multiple telescopes simultaneously to get more baselines, and have a sufficient number of extra measurements than parameters that you want to calculate, and then perform a least squares analysis. This also allows you to find more than stellar radii and limb darkening, since you can include more parameters; none of this could be done at the time of the Narrabri experiments because the computational capability wasn't up to the challenge.
Also, for anyone else reading the thread (I'm sure the parent knows), the 10-meter dishes weren't imaging quality telescopes, since those would be horrendously expensive. They were built of spherical hex-shaped pieces and assembled against a parabolic backing. The original experiments imaging Sirius were actually done with surplus spotlight reflectors. The biggest advantage of intensity interferometers is that they can use crude light buckets and metrology only has to be ~1 cm accurate.
While I'm cautious to be too optimistic about what we can do with new technology applied to intensity interferometers, its definitely worth looking at again.
While you're absolutely correct, I would point out that you can get some useful data from intensity interferometry in the optical wavelengths. The mechanics of the process means that you get the square magnitude of the mutual coherence, which means a direct reconstruction of an image is impossible. But, this is a problem faced in other areas, particularly x-ray crystallography, so there are ways to reconstruct the image based on some known information about the scene. In imaging a star or planet, you know the background is black and your target is close to circular, etc.
Certainly not as straightforward as radio interferometry, and SNR levels are troublesome, because quantum noise imposes a harsh limit, but its certainly an interesting alternative at any rate.
Really, it all comes down to what's known as Fourier optics. In the far field from a distant source, the mutual coherence (cross-correlation) of the light is the 2-D Fourier transform of the original image, through the van Cittert-Zernike theorem. If you're at all familiar with FTs, the components further from the origin correspond to the highest frequencies. So a larger telescope (essentially an analog IFT in this way of thinking, simulating propogating the wave pattern back to the source) is able to cross-correlate the light between the two furthest points on the aperture, allowing you to take into account higher frequency ranges, and get higher resolution.(1)
Therefore, there are two reasons for increasing a telescopes size: 1. You collect more photons, improving signal quality 2. You increase the resolution as you're able to gather more components of the Fourier band. This is limited on Earth due to the seeing effects of the atmosphere, unless you start dealing with adaptive optics.
This kind of work, using multiple apertures to synthesize a much larger one, gets you the second result without much help on the first, but at a much cheaper price. By manually taking the cross-correlations(2), you can get a map of the Fourier field of the image and computationally compute the original image from it.
(1) This is also why blockages over parts of the aperture don't have an obvious effect. (2) which is why this only works with radio, optical frequencies are much too high to record the actual waveform, so physical beam transmission is necessary over carefully controlled (to 10 nanometers) path lengths.
Actually, I understood exactly what you were saying, but as far as I know its incorrect. A Jupiter-based lunar mission would require two launches as well. A simple comparison of launch capabilities between Ares V and Jupiter-232 shows why. The Ares V will be able to launch 188,000 kg to LEO, while the Jupiter-232 can only launch 111,000 kg.
So, basically, two Jupiter-232 rockets are slightly more capable than an Ares I+V combination (which is slightly underpowered), and thus two Jupiter-232 vehicles would be required to launch a successful lunar mission of similar scale to those planned with the Constellation program.
Also, putting it all in a single stack was ideal for the Apollo goal of getting there first in a blaze of glory. However, the current mission goals, trying to do it in a sustainable way, and in a way that paves the way for further human exploration, means that learning to use smaller rockets and handle on-orbit rendezvous and construction (clearly a necessity for Mars) is important, and trying to avoid it is self-defeating.
Actually, the Jupiter plan uses two rockets as well. The difference is that in Jupiter its two of the same rockets, making design and construction work more efficient. Instead of having everything but the Orion/CM vehicle on board the Ares V, you launch only the Earth departure stage on one rocket, and launch the entire CM/SM/LM setup on the second.
The ultimate goal, to me and most people I know involved in the industry/movement, is permanent, sustainable, and eventually self-sufficient human life beyond Earth. Of course, this is to improve the odds of the survival of our species in the long run (so Hawking says).
At a lecture by Rick Tumlinson at ISDC 2007, he was talking about being in the working group defining what Bush's Vision for Space Exploration meant. The conclusion they came to is that the ultimate goal of any moon/Mars/etc. plan has to be permanent settlement. Now whether or not the current Constellation mission architecture fulfills this goal is a matter for some debate, I can't really argue effectively either way.
I do think that a lot of work up till now has gone that direction. The Mercury/Gemini/Apollo program developed the fundamental technologies to keep a human alive. The space shuttle/ISS science program has always had a strong focus on life sciences and determining the effects of life in space on humans. A well-developed lunar or martian mission would build on these, develop technology to facilitate life on another planet's surface, and study the effects of long-term presence in reduced gravity fields. Of course, having the people present does make the planetary science goals a bit easier.
I'd also say that the purer sciences of planetary and solar studies are important, and not particularly controversial since they are cheaper and safer. And one can't forget the Earth science objectives that are especially important right now with the potential of global climate change and demographic changes forcing food and water issues.
All of these do compete for resources, and it is necessary to allocate resources between the goals. However its not unreasonable to have three missions (four actually, remember aviation), since one doesn't preclude another, and in fact they are intricately linked. Earth-science and planetary exploration share many instruments and technology; understanding the environment of the solar system and the planets is necessary to keep people in space alive. The hard part is deciding the proper allocation: I imagine the Obama administration is going to build up earth-science, leave planetary exploration as is, and attempt to focus the manned program on more immediate goals by decreasing the manned gap while pushing back eventual moon and Mars missions, which makes sense to me since climate issues are more immediately critical, while the long-term goals of planetary settlement are important but can be delayed.
While, as a US national, I do agree a reduction there would be nice, there is something I appreciate about having a distinct civilian space program whose primary purpose is scientific discovery and exploration. Also, it separates the budgets more. We already have a constant tug-of-war between manned flight, aviation, earth science, and unmanned exploration for funding; placing it in the same arena as national security needs would probably reduce all of these, as the Air Force administrators would be pushing for the military-needs projects, since they are more immediately practical. By congress setting aside a certain amount for NASA specifically, we are able to keep going on these invaluable, but less tangible goals.
Of course, I also think that improving communication channels and reminding them that they have the same resources (and discouraging NIH syndrome) would be a great thing. For instance, look at the debate over EELVs to launch the Orion capsule. However, the different mission requirements do introduce some fundamental differences in designs, and the need of the military to classify programs also may cause problems. So I'd imagine a lot of this is already done, but stubbornness and bureaucracy I expect still cause large inefficiencies in sharing resources.
There not saying they're qualified to make the decision themeselves, that's why they're trying to ask around from people who are qualified. Unfortunately Griffin is being so overprotective of his pet project that its making a mockery of the transition process, which on all other fronts seems to be the most graceful thing Bush has ever done.
I've ranted a few times about why I think cutting Ares (particularly Ares 1) is a good idea... put simply its a mishmash that ignored the actual purpose of the Vision that was laid out, and it is designed to look shuttle-derived while almost all of it is having to be reengineered. I'm not sure about the EELV option, but Ares looks like its going to be over-cost and will under-perform... if the Falcon 9 tests go better than the Falcon 1, that *may* be our best bet.
My semi-informed opinion is that scrapping Ares, going to something like Jupiter and giving COTS a chance is a more responsible choice. And I think that all the concern over the transition team is overblown, they're simply practicing due diligence and studying all the options... the two that I know much about on the team are strong proponents of continued manned flight.
I don't know if it was luck or a really good understanding of where the industry was going, but the iPod popularity is significantly different than the MacBook or iPhone.
The MacBook took the existing Mac product line, improved it, and grew more popular for a number of reasons... the Intel switch, the improvements in OSX and the recent developments that have made the OS less and less critical are the first things that occur to me. While popular, it doesn't absolutely dominate the market. Its simply a healthy growth of one of Apple's oldest product lines.
The iPhone was a new move into an already well-established market. It has generated new interest in smartphones and helped to push other vendors to improve their products; however, it hasn't ridden the boom of a new market to complete dominance in the same way that the iPod has. iPhone is not (yet?) synonymous with smartphones, and despite strong sales doesn't have the absurdly high installed base.
However, the iPod came out when MP3 players were a niche product for techno-geeks, and rode the growth of the market to have a 70%(?) market share. I can't say whether it led to the growth of the market or simply rode a trend that would have occurred anyway, but needless to say, the iPod's place in the market is stronger than either the MacBook or the iPhone. They are synonymous with the market as a whole, have dozens of companies making accessories... iPod compatibility is even listed as a selling feature on cars.
The supposition of Apple getting lucky makes sense to me. If they're product hadn't been so well developed (at 3rd gen) by the time of the boom, or if some other companies had had better developed products at the time, with well-developed music stores, I can see the iPod being a 20%-30% market share product, that while still successful wouldn't be the cultural phenomenon it is now. And note that I type this on a Macbook Air with my iPhone beside me and my iPod in the car, so believe me when I say I have nothing against the company.
If it goes to a jury trial then yes. A person upholding an oath to protect and defend the Constitution comes off a lot better than someone using their privileges to change elections (which sounds an awful lot like corruption). Even if it doesn't, political pressure form public opinion is important, particularly with a new administration coming up. If the investigation comes out with him acting in good faith it would be a lot easier for Obama to issue a pardon than if he comes out looking like a bitter political hack who was trying to bring Bush down.
Which also brings me to the point that it is an investigation... the result isn't out yet, and its not necessarily going to be a kangaroo court.
If you look at it differently, assuming it as primarily politically motivated (not that I'm saying it was), then although the results were different, the means were no different than Cheney's revealing the identity of Valerie Plame... of course he faced no real consequences for that...
That is, if Tamm wished to have Bush voted out because he didn't like his other policies, he released classified information for his own political gain, which in my mind is not legal (disregarding the question of whether the actual activity he disclosed was illegal, which is important). Even beyond the releasing of classified information, civil servants aren't supposed to be involved politically beyond voting and belonging to political organizations, so trying to influence an election goes beyond the spirit of those laws, which were intended as anti-corruption laws.
I'm not trying to say that the investigation is correct, or that this alternative scenario is either; all I'm saying is that there is another argument that no one else seems to have articulated, and I like to try and see all sides of an argument. It does seem to me though, that without knowing more myself, the investigation could be less of a sinister Big Brother-esque nightmare and more of simple due diligence.
From reading the article, there is a question as to his motivations. Apparently he had been very uncomfortable with the administrations push for capital punishment, and so its supposed that he may have had a political axe to grind, and that this may have muddied his judgement on how to proceed.
Basically my interpretation is that if he hadn't had other motivations as well, he may have tried more to go through legal means to do something about the program before contacting the press. The fact that he was very frustrated that the Times didn't publish immediately (and thus break Bush's chance for re-election) could be interpreted as implying he had a personal vendetta against the administration rather than being solely motivated by stopping an unconstitutional program. Of course, I'll grant you that that frustration could be just as likely to come from a desire to see the program stopped. But trying to affect the results of an election rather than just putting a stop to a program that he couldn't get stopped any other way puts it in a different light.
Of course, I think the 'Protect and defend the Constitution of the United States' phrase in the oath probably had the most to do with it, but as with most things in life there are some uncomfortable shades of gray.
You get some free energy from the spin, yes, but the main reason you try and launch from lower latitudes is that you want to have the option to get a near equatorial orbit inclination. Basically, you can't launch to an inclination lower than your latitude; if you think about it, launching due east (or west, but that would be going against the spin) would put you in an orbit thats the same inclination. If you aim a little north or south you end being inclined a little bit more... whether its north or south changes the position of the ascending node, but not the overall inclination. If you aim due north or south you get into a polar orbit. As far as the additional altitude... its such a miniscule amount that its not worth worrying about.
The reason you may want to have a low as inclination as possible is because if you're going to GEO or lunar or planetary missions, you want to be near zero inclination. In order to get there, you have to do an expensive plane change maneuver, which has a delta-v=sin(i)*V, so getting that inclination lower means big fuel savings.
As far as calculating the fuel savings, just consider the difference between the rotational speed of the point on the surface (sin(lat2)-sin(lat1))*r_earth*(2*pi/24 hrs) to get the additional velocity you get (and thus less delta-v you need to apply on orbit). Running that between the Russian Star City (45 degrees) and the cape (21 degrees) shows that we get ~150 m/s difference, which is nice but not game changing.
As far as sky launch or mountain launch, I learned a great little rule of thumb here a few weeks ago, the 666 rule. Launching from Mach 6 at 60000 feet (probably much higher than any reasonable air launch system), gives you only a 6% energy savings for orbital systems. So, it really doesn't give you a whole lot for the added complexity, which is why as far as i know theres only one air-launched system, an Orbital Sciences rocket that launches off an L1011. The reason why it works for Virgin/Scaled Composites is that it gives you probably 30% of the energy needed to reach the altitude, but not the orbital velocity.
As far as equations... the atmospheric drag models make launch hard to judge, but what is cleverly called the "Rocket Equation" is a really easy way to look at fuel usage with impulsive delta-vs... usually a more valuable quantity than energy since it directly applies to the amount of fuel needed and used.
Actually, on any airplane, the wing has to be able to support the full mass of the aircraft, albeit spread over the entire surface of the wing. If you think about it, it has to have the aerodynamic pressure be at least equal to the mass of the aircraft. And then all that load gets transferred to the spars, so on a normal single-wing aircraft, the central spar is carrying the entire aircraft mass, if its the type of design that carries through the middle of the aircraft.
Also, in order to strengthen it to support the weight of SpaceShipTwo, you can do it without any visible change, just make the spars in the wing heftier.
As far as having to make it look cool, of course they do... its supposed to appeal to people who want to spend $200k going to (suborbital) space. And given that the methods to check the structural soundness of such a set-up are well established, and that Rutan isn't an idiot, I'd imagine it can handle worst case scenario loads with a safety factor of 1.2 or 1.3, as is common for any aerospace application.
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I believe the idea was that they were able to custom fit higher energy-storage batteries. The latches and casings to include a removable battery aren't insignificant in terms of weight and volume, so there is a certain argument for eliminating them. With an 8-hour battery life, it seems fair to expect that most people won't be itching to change it all the time.
I've never really made use of the fact that my laptops have removable batteries, except for replacement after years of use (which 16 screws isn't terribly difficult for long-term replacement). At the same time, with a 17" laptop I have trouble believing the extra weight and volume would make much difference... doing it for the air makes more sense to me.
If it is an important feature to you, there's the 15" MBP (which is probably better for travelling anyway). And I guess the small part of the market that really wants a 17" with a removable battery isn't a large concern for Apple... if they wanted to fill every niche we'd see the xMac, a netbook, a tablet, and everything else people have been asking for for a long time.
While I agree with the sentiment, the one serious counter-argument I'd give is that you need to ensure that people are able to receive public safety announcements. TV is much better than radio for dealing with severe weather, because being able to see the weather maps and storm tracks gives you a much better idea of what's going on. Going into tornado season in Oklahoma (where I grew up) without TV would make me a little uncomfortable.
Recall that we (the people) give the broadcasters the right to use the airwaves in exchange for them providing public services: news, weather, and emergency announcements. We decided these things are important, so its important to make sure their accessible.
But at the same time, this has been coming for a long time, people should have been able to figure it out by now.
In a certain respect, it is related to the focal length, if you consider the eyepiece or sensor fixed. If you have a fixed pixel size on your CCD, then changing the focal length will change the angular size of each pixel, and thus change the resolution, although I think this kind of result is usually called magnification. Similarly, when using an eyepiece, the magnification is related to the ratio of the focal lengths, so a longer focal length will change the magnification
When the CCD pixels get small enough though, that size is no longer the limit on the resolution. Instead (neglecting atmospheric effects) you run into the fact that photon impacts are defined by probability densities that behave like waves, and you get a certain 'spreading' around the nominal impact location. The diameter of this spreading (the Airy disk) means that two sources that are too close together cannot be distinguished from each other, and this is called the diffraction limit. (There are other equally valid explanations for this effect, particularly coming from a wave perspective, this is just the one that I started typing.)
Now, in order to reduce this you want to bring in more photons from further seperated distances, meaning you want a larger aperture in order to improve the diffraction limited resolution. Generally the limiting angular resolution is given by theta_r = 1.4 lambda/D. Of course, if you have too strong of aberrations in the optical system, have to deal with atmospheric 'seeing' effects, the system is not diffraction limited, and the point spread function spreads out more.
Of course, its dangerous to compare the capabilities of telescopes at different wavelengths (Hubble is visible, Herschel is infrared to millimeter wave), because the total amount of light available changes, the angular resolution changes, and the engineering requirements change. Really, Hubble is about the maximum size optical space telescope you can make with current launch vehicles without moving to a completely new kind of telescope (active feedback with wavefront sensing like JWST). Herschel is able to be bigger easily because it requires significantly lower precision, due to the larger wavelengths.
(Sorry, forgot to set paragraph breaks)
The problem isn't the red light cameras in general*, but the fact that they are tied to a lowering of the time for yellow lights. What I was taught is that a yellow light indicates "clear the intersection". If that means to brake, you brake; if that means to keep moving or possibly accelerate because you can't brake in time for whatever reason (tailgater, simply not enough space, etc.), you go on through. Obviously for a typical vehicle there will be a certain zone where one or the other is the right choice.
Since people aren't perfect and cars aren't all the same, there should be some margin in the middle so that if its close either choice is an acceptable one. You create and expand this margin by throwing a couple of seconds in to the yellow period. The problem with many of the red camera light systems, including the one in the town I live in, is that the cameras are seen not only as a way to improve safety, but also to generate more revenue. Many installations operate where the manufacturer of the system actually gets a cut of the fines generated from the system, and they tend to say they won't install a system unless the light time is shortened to the minimum allowed by the state. The police departments themeselves get additional funding from the additional fines as well, so its not especially hard to twist their arm into doing so.
To a certain extent I do appreciate the systems, because I live in a college town and we have some of the worst drivers I've ever seen. However, by shortening the light times, you end up with a system that is safer than the original case, but still not especially good. Because there is very little margin, and a guaranteed fine, people are much more likely to slam on the brakes to stop. While you reduce the number of dangerous cross-traffic accidents, you increase the number of rear-end collisions, a situation that could be avoided by installing the systems responsibly.
*aside from possible privacy issues, which isn't the point here.
The problem isn't the red light cameras in general*, but the fact that they are tied to a lowering of the time for yellow lights. What I was taught is that a yellow light indicates "clear the intersection". If that means to brake, you brake; if that means to keep moving or possibly accelerate because you can't brake in time for whatever reason (tailgater, simply not enough space, etc.), you go on through. Obviously for a typical vehicle there will be a certain zone where one or the other is the right choice. Since people aren't perfect and cars aren't all the same, there should be some margin in the middle so that if its close either choice is an acceptable one. You create and expand this margin by throwing a couple of seconds in to the yellow period. The problem with many of the red camera light systems, including the one in the town I live in, is that the cameras are seen not only as a way to improve safety, but also to generate more revenue. Many installations operate where the manufacturer of the system actually gets a cut of the fines generated from the system, and they tend to say they won't install a system unless the light time is shortened to the minimum allowed by the state. The police departments themeselves get additional funding from the additional fines as well, so its not especially hard to twist their arm into doing so. To a certain extent I do appreciate the systems, because I live in a college town and we have some of the worst drivers I've ever seen. However, by shortening the light times, you end up with a system that is safer than the original case, but still not especially good. Because there is very little margin, and a guaranteed fine, people are much more likely to slam on the brakes to stop. While you reduce the number of dangerous cross-traffic accidents, you increase the number of rear-end collisions, a situation that could be avoided by installing the systems responsibly. *aside from possible privacy issues, which isn't the point here.
I saw on the Ars thread on this that the Cox and Comcast have divvied up Tucson, so the reason it only affected some customers is probably because the others are on Cox.
Given Diamandis' involvement, I'm guessing its modeled on the International Space University, which seems to do well enough. However, I am skeptical since the 'space community' is a little bit more well-defined than the 'singularity community'.
As an American, I must say, we need to take a look at this nomenclature: Shadow Minister sounds so much cooler than Senate Minority Leader or the like.
It helps when the guy has an ounce of sense too...
What, are you a rocket scientist or something? Remember, alcohol and aerospace don't mix.
Although I do enjoy the West Wing, sci-fi has the great advantage of being able to touch issues in a harsher way and reach a broader audience, because its not attached to any real-world events that people are attached to. Also, I'd really say, from what little I've seen of 24, it really hits a lot of the issues a lot more directly, but it also assumes a correct answer.
However, what BSG is able to do is reproduce analogs to current events, placing us on the side we dont normally associate ourselves with (i.e. the resistance on New Caprica), and leave it to you to judge what is right our wrong. In doing so, in this way, you can bring up the issues without alienating as many people.
I personally think this is one of the key factors of science fiction/fantasy as art as opposed to just entertainment.
Interesting, thanks for pointing out that article. Bandwidth synthesis actually looks like something I was about to start looking for, although I was hoping to use the varying frequency to induce phase diversity to help with phase-reconstruction methods.
Also, I know there have been a few papers written on using Cherenkov arrays (sorry, don't have my resources with me), although I'm not sure if any have actually been implemented. In the same vein, I've idly wondered if the big mirror-farm style solar plants could be pointed well enough to use. Although I'm guessing the answer is no, but it would be very interesting to be able to use something that large, placing a sensor at the focus of the plant.
Absolutely right, although we have some advantages now that we didn't when the Narrabi experiments were run. First, detectors have improved: higher response speed and higher quantum efficiency do make things easier. This might be able to double the sensitivity at most though (I'd have to find hard data and run numbers, and I need to do other things today).
However, there are some other ways to improve the SNR. By using a splitting up the incoming light into multiple spectral bands and correlating the signals from each band separately, you can increase the SNR by a factor of N_b (number of bands) or sqrt(N_b), I can't recall exactly. Another method (actually what I should be writing about right now for my thesis) is to use multiple telescopes simultaneously to get more baselines, and have a sufficient number of extra measurements than parameters that you want to calculate, and then perform a least squares analysis. This also allows you to find more than stellar radii and limb darkening, since you can include more parameters; none of this could be done at the time of the Narrabri experiments because the computational capability wasn't up to the challenge.
Also, for anyone else reading the thread (I'm sure the parent knows), the 10-meter dishes weren't imaging quality telescopes, since those would be horrendously expensive. They were built of spherical hex-shaped pieces and assembled against a parabolic backing. The original experiments imaging Sirius were actually done with surplus spotlight reflectors. The biggest advantage of intensity interferometers is that they can use crude light buckets and metrology only has to be ~1 cm accurate.
While I'm cautious to be too optimistic about what we can do with new technology applied to intensity interferometers, its definitely worth looking at again.
While you're absolutely correct, I would point out that you can get some useful data from intensity interferometry in the optical wavelengths. The mechanics of the process means that you get the square magnitude of the mutual coherence, which means a direct reconstruction of an image is impossible. But, this is a problem faced in other areas, particularly x-ray crystallography, so there are ways to reconstruct the image based on some known information about the scene. In imaging a star or planet, you know the background is black and your target is close to circular, etc.
Certainly not as straightforward as radio interferometry, and SNR levels are troublesome, because quantum noise imposes a harsh limit, but its certainly an interesting alternative at any rate.
Really, it all comes down to what's known as Fourier optics. In the far field from a distant source, the mutual coherence (cross-correlation) of the light is the 2-D Fourier transform of the original image, through the van Cittert-Zernike theorem. If you're at all familiar with FTs, the components further from the origin correspond to the highest frequencies. So a larger telescope (essentially an analog IFT in this way of thinking, simulating propogating the wave pattern back to the source) is able to cross-correlate the light between the two furthest points on the aperture, allowing you to take into account higher frequency ranges, and get higher resolution.(1)
Therefore, there are two reasons for increasing a telescopes size:
1. You collect more photons, improving signal quality
2. You increase the resolution as you're able to gather more components of the Fourier band. This is limited on Earth due to the seeing effects of the atmosphere, unless you start dealing with adaptive optics.
This kind of work, using multiple apertures to synthesize a much larger one, gets you the second result without much help on the first, but at a much cheaper price. By manually taking the cross-correlations(2), you can get a map of the Fourier field of the image and computationally compute the original image from it.
(1) This is also why blockages over parts of the aperture don't have an obvious effect.
(2) which is why this only works with radio, optical frequencies are much too high to record the actual waveform, so physical beam transmission is necessary over carefully controlled (to 10 nanometers) path lengths.
Actually, I understood exactly what you were saying, but as far as I know its incorrect. A Jupiter-based lunar mission would require two launches as well. A simple comparison of launch capabilities between Ares V and Jupiter-232 shows why. The Ares V will be able to launch 188,000 kg to LEO, while the Jupiter-232 can only launch 111,000 kg.
So, basically, two Jupiter-232 rockets are slightly more capable than an Ares I+V combination (which is slightly underpowered), and thus two Jupiter-232 vehicles would be required to launch a successful lunar mission of similar scale to those planned with the Constellation program.
Also, putting it all in a single stack was ideal for the Apollo goal of getting there first in a blaze of glory. However, the current mission goals, trying to do it in a sustainable way, and in a way that paves the way for further human exploration, means that learning to use smaller rockets and handle on-orbit rendezvous and construction (clearly a necessity for Mars) is important, and trying to avoid it is self-defeating.
Actually, the Jupiter plan uses two rockets as well. The difference is that in Jupiter its two of the same rockets, making design and construction work more efficient. Instead of having everything but the Orion/CM vehicle on board the Ares V, you launch only the Earth departure stage on one rocket, and launch the entire CM/SM/LM setup on the second.
The ultimate goal, to me and most people I know involved in the industry/movement, is permanent, sustainable, and eventually self-sufficient human life beyond Earth. Of course, this is to improve the odds of the survival of our species in the long run (so Hawking says).
At a lecture by Rick Tumlinson at ISDC 2007, he was talking about being in the working group defining what Bush's Vision for Space Exploration meant. The conclusion they came to is that the ultimate goal of any moon/Mars/etc. plan has to be permanent settlement. Now whether or not the current Constellation mission architecture fulfills this goal is a matter for some debate, I can't really argue effectively either way.
I do think that a lot of work up till now has gone that direction. The Mercury/Gemini/Apollo program developed the fundamental technologies to keep a human alive. The space shuttle/ISS science program has always had a strong focus on life sciences and determining the effects of life in space on humans. A well-developed lunar or martian mission would build on these, develop technology to facilitate life on another planet's surface, and study the effects of long-term presence in reduced gravity fields. Of course, having the people present does make the planetary science goals a bit easier.
I'd also say that the purer sciences of planetary and solar studies are important, and not particularly controversial since they are cheaper and safer. And one can't forget the Earth science objectives that are especially important right now with the potential of global climate change and demographic changes forcing food and water issues.
All of these do compete for resources, and it is necessary to allocate resources between the goals. However its not unreasonable to have three missions (four actually, remember aviation), since one doesn't preclude another, and in fact they are intricately linked. Earth-science and planetary exploration share many instruments and technology; understanding the environment of the solar system and the planets is necessary to keep people in space alive. The hard part is deciding the proper allocation: I imagine the Obama administration is going to build up earth-science, leave planetary exploration as is, and attempt to focus the manned program on more immediate goals by decreasing the manned gap while pushing back eventual moon and Mars missions, which makes sense to me since climate issues are more immediately critical, while the long-term goals of planetary settlement are important but can be delayed.
While, as a US national, I do agree a reduction there would be nice, there is something I appreciate about having a distinct civilian space program whose primary purpose is scientific discovery and exploration. Also, it separates the budgets more. We already have a constant tug-of-war between manned flight, aviation, earth science, and unmanned exploration for funding; placing it in the same arena as national security needs would probably reduce all of these, as the Air Force administrators would be pushing for the military-needs projects, since they are more immediately practical. By congress setting aside a certain amount for NASA specifically, we are able to keep going on these invaluable, but less tangible goals.
Of course, I also think that improving communication channels and reminding them that they have the same resources (and discouraging NIH syndrome) would be a great thing. For instance, look at the debate over EELVs to launch the Orion capsule. However, the different mission requirements do introduce some fundamental differences in designs, and the need of the military to classify programs also may cause problems. So I'd imagine a lot of this is already done, but stubbornness and bureaucracy I expect still cause large inefficiencies in sharing resources.
There not saying they're qualified to make the decision themeselves, that's why they're trying to ask around from people who are qualified. Unfortunately Griffin is being so overprotective of his pet project that its making a mockery of the transition process, which on all other fronts seems to be the most graceful thing Bush has ever done.
I've ranted a few times about why I think cutting Ares (particularly Ares 1) is a good idea... put simply its a mishmash that ignored the actual purpose of the Vision that was laid out, and it is designed to look shuttle-derived while almost all of it is having to be reengineered. I'm not sure about the EELV option, but Ares looks like its going to be over-cost and will under-perform... if the Falcon 9 tests go better than the Falcon 1, that *may* be our best bet.
My semi-informed opinion is that scrapping Ares, going to something like Jupiter and giving COTS a chance is a more responsible choice. And I think that all the concern over the transition team is overblown, they're simply practicing due diligence and studying all the options... the two that I know much about on the team are strong proponents of continued manned flight.
I don't know if it was luck or a really good understanding of where the industry was going, but the iPod popularity is significantly different than the MacBook or iPhone.
The MacBook took the existing Mac product line, improved it, and grew more popular for a number of reasons... the Intel switch, the improvements in OSX and the recent developments that have made the OS less and less critical are the first things that occur to me. While popular, it doesn't absolutely dominate the market. Its simply a healthy growth of one of Apple's oldest product lines.
The iPhone was a new move into an already well-established market. It has generated new interest in smartphones and helped to push other vendors to improve their products; however, it hasn't ridden the boom of a new market to complete dominance in the same way that the iPod has. iPhone is not (yet?) synonymous with smartphones, and despite strong sales doesn't have the absurdly high installed base.
However, the iPod came out when MP3 players were a niche product for techno-geeks, and rode the growth of the market to have a 70%(?) market share. I can't say whether it led to the growth of the market or simply rode a trend that would have occurred anyway, but needless to say, the iPod's place in the market is stronger than either the MacBook or the iPhone. They are synonymous with the market as a whole, have dozens of companies making accessories... iPod compatibility is even listed as a selling feature on cars.
The supposition of Apple getting lucky makes sense to me. If they're product hadn't been so well developed (at 3rd gen) by the time of the boom, or if some other companies had had better developed products at the time, with well-developed music stores, I can see the iPod being a 20%-30% market share product, that while still successful wouldn't be the cultural phenomenon it is now. And note that I type this on a Macbook Air with my iPhone beside me and my iPod in the car, so believe me when I say I have nothing against the company.
If it goes to a jury trial then yes. A person upholding an oath to protect and defend the Constitution comes off a lot better than someone using their privileges to change elections (which sounds an awful lot like corruption). Even if it doesn't, political pressure form public opinion is important, particularly with a new administration coming up. If the investigation comes out with him acting in good faith it would be a lot easier for Obama to issue a pardon than if he comes out looking like a bitter political hack who was trying to bring Bush down.
Which also brings me to the point that it is an investigation... the result isn't out yet, and its not necessarily going to be a kangaroo court.
If you look at it differently, assuming it as primarily politically motivated (not that I'm saying it was), then although the results were different, the means were no different than Cheney's revealing the identity of Valerie Plame... of course he faced no real consequences for that...
That is, if Tamm wished to have Bush voted out because he didn't like his other policies, he released classified information for his own political gain, which in my mind is not legal (disregarding the question of whether the actual activity he disclosed was illegal, which is important). Even beyond the releasing of classified information, civil servants aren't supposed to be involved politically beyond voting and belonging to political organizations, so trying to influence an election goes beyond the spirit of those laws, which were intended as anti-corruption laws.
I'm not trying to say that the investigation is correct, or that this alternative scenario is either; all I'm saying is that there is another argument that no one else seems to have articulated, and I like to try and see all sides of an argument. It does seem to me though, that without knowing more myself, the investigation could be less of a sinister Big Brother-esque nightmare and more of simple due diligence.
From reading the article, there is a question as to his motivations. Apparently he had been very uncomfortable with the administrations push for capital punishment, and so its supposed that he may have had a political axe to grind, and that this may have muddied his judgement on how to proceed.
Basically my interpretation is that if he hadn't had other motivations as well, he may have tried more to go through legal means to do something about the program before contacting the press. The fact that he was very frustrated that the Times didn't publish immediately (and thus break Bush's chance for re-election) could be interpreted as implying he had a personal vendetta against the administration rather than being solely motivated by stopping an unconstitutional program. Of course, I'll grant you that that frustration could be just as likely to come from a desire to see the program stopped. But trying to affect the results of an election rather than just putting a stop to a program that he couldn't get stopped any other way puts it in a different light.
Of course, I think the 'Protect and defend the Constitution of the United States' phrase in the oath probably had the most to do with it, but as with most things in life there are some uncomfortable shades of gray.
You get some free energy from the spin, yes, but the main reason you try and launch from lower latitudes is that you want to have the option to get a near equatorial orbit inclination. Basically, you can't launch to an inclination lower than your latitude; if you think about it, launching due east (or west, but that would be going against the spin) would put you in an orbit thats the same inclination. If you aim a little north or south you end being inclined a little bit more... whether its north or south changes the position of the ascending node, but not the overall inclination. If you aim due north or south you get into a polar orbit. As far as the additional altitude... its such a miniscule amount that its not worth worrying about.
The reason you may want to have a low as inclination as possible is because if you're going to GEO or lunar or planetary missions, you want to be near zero inclination. In order to get there, you have to do an expensive plane change maneuver, which has a delta-v=sin(i)*V, so getting that inclination lower means big fuel savings.
As far as calculating the fuel savings, just consider the difference between the rotational speed of the point on the surface (sin(lat2)-sin(lat1))*r_earth*(2*pi/24 hrs) to get the additional velocity you get (and thus less delta-v you need to apply on orbit). Running that between the Russian Star City (45 degrees) and the cape (21 degrees) shows that we get ~150 m/s difference, which is nice but not game changing.
As far as sky launch or mountain launch, I learned a great little rule of thumb here a few weeks ago, the 666 rule. Launching from Mach 6 at 60000 feet (probably much higher than any reasonable air launch system), gives you only a 6% energy savings for orbital systems. So, it really doesn't give you a whole lot for the added complexity, which is why as far as i know theres only one air-launched system, an Orbital Sciences rocket that launches off an L1011. The reason why it works for Virgin/Scaled Composites is that it gives you probably 30% of the energy needed to reach the altitude, but not the orbital velocity.
As far as equations... the atmospheric drag models make launch hard to judge, but what is cleverly called the "Rocket Equation" is a really easy way to look at fuel usage with impulsive delta-vs... usually a more valuable quantity than energy since it directly applies to the amount of fuel needed and used.
Actually, on any airplane, the wing has to be able to support the full mass of the aircraft, albeit spread over the entire surface of the wing. If you think about it, it has to have the aerodynamic pressure be at least equal to the mass of the aircraft. And then all that load gets transferred to the spars, so on a normal single-wing aircraft, the central spar is carrying the entire aircraft mass, if its the type of design that carries through the middle of the aircraft.
Also, in order to strengthen it to support the weight of SpaceShipTwo, you can do it without any visible change, just make the spars in the wing heftier.
As far as having to make it look cool, of course they do... its supposed to appeal to people who want to spend $200k going to (suborbital) space. And given that the methods to check the structural soundness of such a set-up are well established, and that Rutan isn't an idiot, I'd imagine it can handle worst case scenario loads with a safety factor of 1.2 or 1.3, as is common for any aerospace application.