Escape speed from Earth is 11 km/sec and you end up barely moving relative to the Earth once you're reasonably far away (say past the Moon). So you share the 30 km/sec orbital speed with the Earth. That means that you're moving *sideways* to the direction of the Sun at that gawdawful speed. If you try to move toward the Sun, you'll still slip to the side and miss it. You've got to kill your sideways orbital speed first, and then you (automatically) drop down closer to the Sun. (Irony of it is, you then speed back up. Common orbital mechanics quip is that you hit the brakes to speed up.) It's not issue of how fast you are going when you hit the Sun, it's a matter of not being able to hit the Sun at all from those initial conditions unless you kill that forward speed.
You're assuming that they *do* work. In some situations, I'm sure that this is true. However, in a grocery store I worked at in high school and college, they tried a similar tactic with little screens at the checkout that ran ads. People complained a lot and the screens disappeared after a few months. If the profits had really been good for the screens, I'm sure they would still be in place, but I'm pretty sure that the complaining and diversion of business elsewhere worked in this case.
Note that grocery stores are at one extreme of the options-continuum for most people: we have *lots* of choice as to where we want to shop in most residential areas. It doesn't take much to push customers from one store to another, in my experience, so something as annoying as talking ads on the shopping carts could definitely seriously cut into business. (On the other hand, more specialized stores or locations can get away with more obnoxiousness because the customers have little or no choice.)
I'd wouldn't call the space shuttles "robotic" and I certainly wouldn't use the term of, say, the Mercury capsules. The term "robotic", which is very commonly used for *all* unmanned spacecraft, is meant to differentiate those missions from the manned ones. It's not a buzz-word, it's standard parlance.
The answer is easiest to see in terms of angular momentum. (Orbits are really all about angular momentum, more so than energy.) If you break free of Earth's immediate gravity, you're still in pretty much the same orbit as the Earth going around the Sun. You have to dump a lot of that angular momentum to reach Mercury or the Sun, and that takes quite a bit of work. Remember, escape speed from the Earth's surface is around 11 km/sec, but the Earth's orbital speed is around 30 km/sec. You have to dump about 7 km/sec to go into a sufficiently elliptical orbit to reach Mercury and then you need to dump another 20-something km/sec to circularize the orbit. You have to dump almost all your orbital velocity it to reach the Sun at all (even on an elliptical orbit that reaches the Earth, I figure you need to drop down to 3 km/sec at Earth's orbit to reach the surface of the Sun). On the other hand, escaping completely from a circular orbit requires less than 45% more speed, so escaping the solar system completely requires less delta-v than going to Mercury. (It takes about 15 km/sec to reach Pluto's orbit, making yours ultimately circular.)
You can't exactly put a base on the "unlit side", though. All sides get sunlight at some point. It's like saying that the humans have built Washington DC on the night-side of Earth: possibly technically true when said, but not very descriptive since that changes.
Well, it'll go into orbit eventually, so yes. Hopefully.
And even without getting a lot closer, this is *huge*. Fully 55% of Mercury's surface has never been imaged by spacecraft (and cannot really be imaged well from the ground), so we don't have a very good idea what more than half the planet looks like. This flyby, I'm told, well see about half of the un-imaged area.
It's a "Gee-Whiz" statistic meant to get the public excited. I don't think it's really meaningful in any formal sense. (Certainly not as-written: "90 times more powerful".) This particular improvement is aimed at one area of research, I don't think it generally helps others (at least not as much). To really be "90 times more powerful" as a generic statement, I think you need to make an improvement in the light-gathering power/quantum efficiency of the chip/resolution, something that affects nearly everyone's observations.
Actually, that's not entirely shocking: Mercury is in a 3:2 spin-orbit resonance, so if the spacecraft always hit the planet in essentially the same solar-system longitude, there's a fair chance that the geometry would be exactly the same. (One chance in four, I'd say.)
Luckily, you can still do radar mapping and other experiments on the unlit face. And, if you wait awhile, the planet will turn for you and you can image it then.
There exists a considerable body of literature on the topic of orbital mechanics for spacecraft trajectories, which helps a lot. The spacecraft navigation folks are taught huge tracts of this as students (and probably pick up tons more as needed on the job). Of course, computers are also heavily employed to test and optimize trajectories.
However, from what I've seen (working on a NASA mission), a lot of how trajectories get discovered is pure skill and creativity on the parts of the navigation team. As with any such job, an element of instinct and lateral-thinking is always required, and they do it very well.
Right, but a flyby is far, far less valuable than an orbiter. Look at how much more we've learned from Galileo and Cassini about Jupiter and Saturn (respectively) than several flyby missions combined.
In this case, the situation is even better: we've never imaged 55% of the surface of Mercury with any kind of resolution to speak of. (It's difficult to image from the ground, what with having to catch it near the horizon, and Mariner, due to a resonance, caught the same side of the planet all three times.)
As noted already, no: the problem is that the s/c will be going too fast when it gets there. A better way to look at these problems is (specific) angular momentum (which is conserved between orbital maneuvers/close encounters). Angular momentum increases as you move away from the Sun (as sqrt(a)), so the spacecraft, with a larger semi-major axis (in order to reach beyond Mercury's orbit at aphelion) has too much angular momentum when it's near Mercury. That means it's going too fast when it arrives. Shedding angular momentum is tricky business, but inverting the usual gravity assist geometry to ditch the excess angular momentum works. (Before MESSENGER, I had wondered a few times to myself whether you might ever want to do that. Maybe I should have patented it or something.:-)
Actually, it's looking for fruit in a fruit tree where the fruits are *high*. Europa, while the best extra-terrestrial candidate for bearing life at present, requires some serious radiation shielding on any spacecraft going there, a fairly expensive landing, and a *lot* of work to bore through 1-10 km of literally-rock-hard ice. The probability of finding a viable ecosystem is balanced against the great difficulty to get to it.
As I recall, a recent NASA study said that they can't do it for under $1 billion (US); actually, I think that they found that they couldn't even do a decent orbiter for under $1.5 billion, let alone a lander or a submarine probe. (Warning! This is only my recollection from presentations 6 months ago.)
Sadly, I'm fast losing hope in print media as well. I'm watching newspapers attempt to reclaim their audience be essentially becoming printed TV news. Our local paper, which I recall being pretty good a decade ago, is eschewing real reporting for quoting people and calling it a day. Real reporting includes quotes, but it also requires checking the speakers' facts when possible. They've cited Wikipedia several times in the past few weeks (just what I've seen), and they crib their weather stories from a Denver paper -- in spite of the fact that we have a NOAA center literally down the road a couple miles from them. (It's a local call!) The stories they run as big news seem to often be geared towards creating a furor where none legitimately exists or pandering to idiocy: we've had stories recently about "Indigo children" and "the world will end in 2012... the Mayans said so."
Honestly, it's hard to not lose hope in the face of this.
Click the title of the movie (not the movie itself). This will open the page with the caption and (typically) three formats of the movie, including QuickTime -- which your Mac should surely play.
They upload three formats because there really isn't just one that works for everyone.
Oddly, that image didn't make it into the options for the voting. (Candidates were largely nominated by visitors to the site, incidentally.) The black and white version of that image *was* in the voting, but only got 6% of the BW vote. Pity, because I agree that it's a really amazing view.
Re:Are these images from an explorer spacecraft?
on
Cassini's Best Images
·
· Score: 4, Informative
The images are real (and as unaltered as humanly possible). Then again, the accuracy of the figures should be an indication that this is so: the best ellipse you can draw (even with a computer) is no match for the shape of the Sun or any of the gas-giant planets, for example. (Also, most of the rings are really darned circular, especially at this level.)
Right. The assumption is that if we started Earth off at the same location, we'd end up in the same state. (We're roughly the same size and, it's assumed -- with some evidence, that we had the same composition.) Basically, Venus got to evaporating lots of its water, driving up its greenhouse effect. At some point, this cycle goes past a tipping point and it runs away. Eventually, all the water is gone from the surface and you can no long scrub CO2 out of the air, so that also builds up to insane levels.
Ironically, if you neglected the greenhouse effect, you'd expect Venus to be a lot cooler than the Earth. (Very high albedo = very little solar energy is absorbed.) Earth's greenhouse, while a around 10 times smaller, does push us up to a mean temperature above freezing, so we're sort of lucky.
The greenhouse effect isn't the point at all, here. In the nuclear winter scenario, you've merely reflected more sunlight (or kept it from the ground, at any rate). No greenhouse effect is required, only an atmosphere that isn't *so* thick that high deck of clouds or dust are irrelevant. (You're correct, this *is* the case at Venus.) Not only is Mars susceptible to this same effect, it was the global Martian dust storm in 1971 (which caused surface cooling on that planet) that led Sagan, Pollock, and Toon to apply the principles to Earth in the first place.
Also, Mars's albedo is 0.15, significantly lower than Earth's. I'm not sure what you mean by "Its surface reflects most of the sunlight already," but I have a hard time seeing Mars's surface as being very reflective.
We might argue that we've come this far *because* our lives are short. If we lived a long, long time, I think we'd stagnate, set in our ways. New ideas would be almost always rejected or suppressed. (There's an old half-true joke that new theories aren't accepted, the resistance just dies -- and not figuratively.)
Our lifespans mean that there's always a fresh crop of people with new ideas and wanting to find better ways to do things ready to replace us and it also makes sure we feel some healthy pressure to accomplish our goals now rather than later. That's a gift, not an obstacle.
I don't think that the water can be that much colder than 273 K. That's sort of the point, here. Sure, you can lower the freezing point with salts (which goes against this recent finding) or with ammonia (possible and long-posited, but I don't think any ammonia has been detected yet), but I'm pretty sure that the models are suggesting water around 273 K. So the solubility of sodium should be pretty easy to determine.
On the other hand, all bets are off if this water isn't in contact with a significant rock deposit. Ice tends to get salts out of itself, so if this is ice-melt, there could still be a significant water reservoir I think. It would mean, however, that you don't have the undersea vent situation going on.
Did you read? The 0.5% is *not* all spent on astronomy. It's spent on *NASA*, most of which goes to manned missions (no astronomy there), aviation research (which benefits industry, the economy, and ultimately you), and Earth-observing science (like your climatology). About $2 billion are spent a year on solar system exploration (and a large chunk of *that* is explicitly dedicated to only Mars). That's 0.07%, or less than $7 per person in this country.
Slashdot Mirror
Think of it like this:
Escape speed from Earth is 11 km/sec and you end up barely moving relative to the Earth once you're reasonably far away (say past the Moon). So you share the 30 km/sec orbital speed with the Earth. That means that you're moving *sideways* to the direction of the Sun at that gawdawful speed. If you try to move toward the Sun, you'll still slip to the side and miss it. You've got to kill your sideways orbital speed first, and then you (automatically) drop down closer to the Sun. (Irony of it is, you then speed back up. Common orbital mechanics quip is that you hit the brakes to speed up.) It's not issue of how fast you are going when you hit the Sun, it's a matter of not being able to hit the Sun at all from those initial conditions unless you kill that forward speed.
You're assuming that they *do* work. In some situations, I'm sure that this is true. However, in a grocery store I worked at in high school and college, they tried a similar tactic with little screens at the checkout that ran ads. People complained a lot and the screens disappeared after a few months. If the profits had really been good for the screens, I'm sure they would still be in place, but I'm pretty sure that the complaining and diversion of business elsewhere worked in this case.
Note that grocery stores are at one extreme of the options-continuum for most people: we have *lots* of choice as to where we want to shop in most residential areas. It doesn't take much to push customers from one store to another, in my experience, so something as annoying as talking ads on the shopping carts could definitely seriously cut into business. (On the other hand, more specialized stores or locations can get away with more obnoxiousness because the customers have little or no choice.)
I'd wouldn't call the space shuttles "robotic" and I certainly wouldn't use the term of, say, the Mercury capsules. The term "robotic", which is very commonly used for *all* unmanned spacecraft, is meant to differentiate those missions from the manned ones. It's not a buzz-word, it's standard parlance.
How about we all just use day-of-year notation? 2008-015 (time unknown).
Or, better suggestion, write the month's name: 15 Jan. 2008.
The answer is easiest to see in terms of angular momentum. (Orbits are really all about angular momentum, more so than energy.) If you break free of Earth's immediate gravity, you're still in pretty much the same orbit as the Earth going around the Sun. You have to dump a lot of that angular momentum to reach Mercury or the Sun, and that takes quite a bit of work. Remember, escape speed from the Earth's surface is around 11 km/sec, but the Earth's orbital speed is around 30 km/sec. You have to dump about 7 km/sec to go into a sufficiently elliptical orbit to reach Mercury and then you need to dump another 20-something km/sec to circularize the orbit. You have to dump almost all your orbital velocity it to reach the Sun at all (even on an elliptical orbit that reaches the Earth, I figure you need to drop down to 3 km/sec at Earth's orbit to reach the surface of the Sun). On the other hand, escaping completely from a circular orbit requires less than 45% more speed, so escaping the solar system completely requires less delta-v than going to Mercury. (It takes about 15 km/sec to reach Pluto's orbit, making yours ultimately circular.)
You can't exactly put a base on the "unlit side", though. All sides get sunlight at some point. It's like saying that the humans have built Washington DC on the night-side of Earth: possibly technically true when said, but not very descriptive since that changes.
Yes, I know. The question was asked rhetorically.
Well, it'll go into orbit eventually, so yes. Hopefully.
And even without getting a lot closer, this is *huge*. Fully 55% of Mercury's surface has never been imaged by spacecraft (and cannot really be imaged well from the ground), so we don't have a very good idea what more than half the planet looks like. This flyby, I'm told, well see about half of the un-imaged area.
Mercury has a dark side?
It's a "Gee-Whiz" statistic meant to get the public excited. I don't think it's really meaningful in any formal sense. (Certainly not as-written: "90 times more powerful".) This particular improvement is aimed at one area of research, I don't think it generally helps others (at least not as much). To really be "90 times more powerful" as a generic statement, I think you need to make an improvement in the light-gathering power/quantum efficiency of the chip/resolution, something that affects nearly everyone's observations.
Actually, that's not entirely shocking: Mercury is in a 3:2 spin-orbit resonance, so if the spacecraft always hit the planet in essentially the same solar-system longitude, there's a fair chance that the geometry would be exactly the same. (One chance in four, I'd say.)
Luckily, you can still do radar mapping and other experiments on the unlit face. And, if you wait awhile, the planet will turn for you and you can image it then.
There exists a considerable body of literature on the topic of orbital mechanics for spacecraft trajectories, which helps a lot. The spacecraft navigation folks are taught huge tracts of this as students (and probably pick up tons more as needed on the job). Of course, computers are also heavily employed to test and optimize trajectories.
However, from what I've seen (working on a NASA mission), a lot of how trajectories get discovered is pure skill and creativity on the parts of the navigation team. As with any such job, an element of instinct and lateral-thinking is always required, and they do it very well.
Right, but a flyby is far, far less valuable than an orbiter. Look at how much more we've learned from Galileo and Cassini about Jupiter and Saturn (respectively) than several flyby missions combined.
In this case, the situation is even better: we've never imaged 55% of the surface of Mercury with any kind of resolution to speak of. (It's difficult to image from the ground, what with having to catch it near the horizon, and Mariner, due to a resonance, caught the same side of the planet all three times.)
As noted already, no: the problem is that the s/c will be going too fast when it gets there. A better way to look at these problems is (specific) angular momentum (which is conserved between orbital maneuvers/close encounters). Angular momentum increases as you move away from the Sun (as sqrt(a)), so the spacecraft, with a larger semi-major axis (in order to reach beyond Mercury's orbit at aphelion) has too much angular momentum when it's near Mercury. That means it's going too fast when it arrives. Shedding angular momentum is tricky business, but inverting the usual gravity assist geometry to ditch the excess angular momentum works. (Before MESSENGER, I had wondered a few times to myself whether you might ever want to do that. Maybe I should have patented it or something. :-)
Actually, it's looking for fruit in a fruit tree where the fruits are *high*. Europa, while the best extra-terrestrial candidate for bearing life at present, requires some serious radiation shielding on any spacecraft going there, a fairly expensive landing, and a *lot* of work to bore through 1-10 km of literally-rock-hard ice. The probability of finding a viable ecosystem is balanced against the great difficulty to get to it.
As I recall, a recent NASA study said that they can't do it for under $1 billion (US); actually, I think that they found that they couldn't even do a decent orbiter for under $1.5 billion, let alone a lander or a submarine probe. (Warning! This is only my recollection from presentations 6 months ago.)
Sadly, I'm fast losing hope in print media as well. I'm watching newspapers attempt to reclaim their audience be essentially becoming printed TV news. Our local paper, which I recall being pretty good a decade ago, is eschewing real reporting for quoting people and calling it a day. Real reporting includes quotes, but it also requires checking the speakers' facts when possible. They've cited Wikipedia several times in the past few weeks (just what I've seen), and they crib their weather stories from a Denver paper -- in spite of the fact that we have a NOAA center literally down the road a couple miles from them. (It's a local call!) The stories they run as big news seem to often be geared towards creating a furor where none legitimately exists or pandering to idiocy: we've had stories recently about "Indigo children" and "the world will end in 2012... the Mayans said so."
Honestly, it's hard to not lose hope in the face of this.
Click the title of the movie (not the movie itself). This will open the page with the caption and (typically) three formats of the movie, including QuickTime -- which your Mac should surely play.
They upload three formats because there really isn't just one that works for everyone.
With caption at http://ciclops.org/view.php?id=1507.
Oddly, that image didn't make it into the options for the voting. (Candidates were largely nominated by visitors to the site, incidentally.) The black and white version of that image *was* in the voting, but only got 6% of the BW vote. Pity, because I agree that it's a really amazing view.
The images are real (and as unaltered as humanly possible). Then again, the accuracy of the figures should be an indication that this is so: the best ellipse you can draw (even with a computer) is no match for the shape of the Sun or any of the gas-giant planets, for example. (Also, most of the rings are really darned circular, especially at this level.)
Right. The assumption is that if we started Earth off at the same location, we'd end up in the same state. (We're roughly the same size and, it's assumed -- with some evidence, that we had the same composition.) Basically, Venus got to evaporating lots of its water, driving up its greenhouse effect. At some point, this cycle goes past a tipping point and it runs away. Eventually, all the water is gone from the surface and you can no long scrub CO2 out of the air, so that also builds up to insane levels.
Ironically, if you neglected the greenhouse effect, you'd expect Venus to be a lot cooler than the Earth. (Very high albedo = very little solar energy is absorbed.) Earth's greenhouse, while a around 10 times smaller, does push us up to a mean temperature above freezing, so we're sort of lucky.
The greenhouse effect isn't the point at all, here. In the nuclear winter scenario, you've merely reflected more sunlight (or kept it from the ground, at any rate). No greenhouse effect is required, only an atmosphere that isn't *so* thick that high deck of clouds or dust are irrelevant. (You're correct, this *is* the case at Venus.) Not only is Mars susceptible to this same effect, it was the global Martian dust storm in 1971 (which caused surface cooling on that planet) that led Sagan, Pollock, and Toon to apply the principles to Earth in the first place.
Also, Mars's albedo is 0.15, significantly lower than Earth's. I'm not sure what you mean by "Its surface reflects most of the sunlight already," but I have a hard time seeing Mars's surface as being very reflective.
We might argue that we've come this far *because* our lives are short. If we lived a long, long time, I think we'd stagnate, set in our ways. New ideas would be almost always rejected or suppressed. (There's an old half-true joke that new theories aren't accepted, the resistance just dies -- and not figuratively.)
Our lifespans mean that there's always a fresh crop of people with new ideas and wanting to find better ways to do things ready to replace us and it also makes sure we feel some healthy pressure to accomplish our goals now rather than later. That's a gift, not an obstacle.
I don't think that the water can be that much colder than 273 K. That's sort of the point, here. Sure, you can lower the freezing point with salts (which goes against this recent finding) or with ammonia (possible and long-posited, but I don't think any ammonia has been detected yet), but I'm pretty sure that the models are suggesting water around 273 K. So the solubility of sodium should be pretty easy to determine.
On the other hand, all bets are off if this water isn't in contact with a significant rock deposit. Ice tends to get salts out of itself, so if this is ice-melt, there could still be a significant water reservoir I think. It would mean, however, that you don't have the undersea vent situation going on.
Did you read? The 0.5% is *not* all spent on astronomy. It's spent on *NASA*, most of which goes to manned missions (no astronomy there), aviation research (which benefits industry, the economy, and ultimately you), and Earth-observing science (like your climatology). About $2 billion are spent a year on solar system exploration (and a large chunk of *that* is explicitly dedicated to only Mars). That's 0.07%, or less than $7 per person in this country.