My question is why L2 and not L1? L2 is going to be exposed to more meteoric traffic, it will have a hard time communicating through the moon to the earth (yeah you can put a comm satellites at L4 or L5 but that's complicating things and adding cost and new failure modes.)
The sensible plan and undoubted intention would be to put the station not at EML2, but in a Lissajous (or Halo) orbit about it big enough so that it was always in view of Earth. Such orbits exist and are energetically easy to get to, although a little station-keeping may be required (as it would be for the L2 point as well).
The difference in delta-V to L1 and L2 is (for the Moon) pretty small. In fact, if you are willing to take your time, you can get to either with basically no fuel beyond a geostationary transfer orbit injection, using WSB trajectories. (This will take months, so it is not so good for manned voyages, but would save a lot on supply logistics costs, up to doubling the payload delivered per launch.)
By the way, getting a space station from L1 to L2 (or back) is also not energetically hard. The NASA plans on this envision putting a habitat at EML1 and then later move it to EML2, and maybe back after a period. (The station would not be AT EML2, but in a Lissajous orbit about it big enough so that it was always in view of Earth.)
L1, L2 and L3 are pretty easy. The Moon (or whatever secondary body you want, such as the Earth for Earth-Sun Lagrange points) is in some orbit, with some period, about the primary (Earth, in this case). Are there other orbits that have the exact same period ? If the Moon had no mass, the answer would be, no, except for exactly the same mean distance (AKA semi-major axis) from the Earth. With the Moon having a significant mass, things are not quite so simple, but they are not very much harder.
Suppose you are inside the Moon's orbit, on the Earth Moon line. On that line, inside the Moon's orbit, the Moon's gravitational acceleration subtracts from the Earth's, so you feel a little less acceleration towards the Earth, and so your circular orbital period is a little less than it would be in the absence of the Moon. If you go up and down that line, you can find the point where the orbital period (for a circular orbit, with the Moon reducing the Earth's gravity) exactly matches the Moon's original orbital period. That point is the L1 Lagrange point. If you are there, in a circular orbit, you are rotating with the Moon. (It's not stable, but that's another matter.)
Now, suppose you are outside the Moon's orbit on the Earth-Moon line. In that case, the Moon's gravitational acceleration increases the pull of the Earth, so your orbital velocity (for a circular orbit) must be a little faster than it would be without the Moon being present. Again, imagine going up and down the Earth-Moon line until the orbital period (increased by the Moon's gravity) exactly matches that of the Moon. That is the L2 Lagrange point (again, not stable).
L3 is just as easily conceptually - if you are on the opposite side of the Moon, again on the Earth-Moon line, the Moon's gravity again increases the pull of the Earth (by a smidgen, due to its distance), and there is a place on the E-M line, just a smidgen inside the Moon's orbit, where your orbital period is the same as the Moon's. That's the L3 point.
This just accounting for regular own (baryonic) matter. The Halo is still mostly "Dark" matter, which is non-interacting. (It may be WIMPs, i.e., non-baryonic, or it may be quark nuggets, i.e., baryonic, but either way it is non-interacting.)
Exactly. My experience is in the sub-continent is that nothing usable gets thrown out or, if it does, someone grabs it from the trash and makes use of it.
Eclipse : nearer body covers the other body Partial eclipse : the body could cover the other body, but doesn't (i.e., it nicks it). Transits : the nearer body is not big enough to cover the other body. Phobos and Deimos, as seen from the surface of Mars, fall in this category.
The angular size of the Moon is so close to that of the Sun, as seen from the Earth, that a special kind of transit is possible, which has a special term - an annular eclipse, where a thin ring of the Sun's surface is still visible (because the Moon is near apogee, and far enough away to not fully cover the Sun). This is a special case; the term annular eclipse has a long history, and I have never heard it used to describe any other kind of transit.
There is a narrow band, centered on the equator of Mars, within which every point is eclipsed at least once during each semiannual eclipse season. Outside that band, the density of coverage decreases slowly with increasing distance from the equator, until the limiting latitudes are reached.
BTW, a surface transit (that is a more appropriate proper term, as neither moon ever fully eclipses the Sun) was also observed by the VIking Lande 1 in the 1970's.
And for the Earth solar eclipses, over an 18.6 year cycle, are equally likely in either terrestrial hemisphere.
These sequestration cuts will not happen. After the upcoming election, minds will be concentrated, horses will be traded at a furious rate, and this can will be kicked down the road. The details of the can-kicking and horse-trading will depend on the nature of the election results, but the can will be kicked down the road. Of that you can be sure.
That is a good description of classical entanglement - what, in this context, would be called a hidden variable theory (the cards have a certain face value, even if you can't see them).
Let's see if I can expand this analogy. Suppose you had two decks of cards, each with only two cards - say the king of hearts and the king of spades. Off-stage, I shuffle them, so that there is either one deck of 2 hearts, and one of two spades, or one deck of both, and another of both. Say that the chances of either shuffle are the same.
Now, repeat your experiment, except you and your friend only get to pull 1 card each, each from your own deck. Classically, the chances are
- 50%, you pull from 1 spade and 1 heart - 25%, you pull from 2 spades - 25%, you pull from 2 hearts.
And, of course, ditto for your friend.
Now, if you pull a spade, then the classical chances are
2/3 the other card is a heart 1/3 the other card is a spade
and the classical chances for your friend are thus
2/3 he has a spade and a heart 1/3 he has 2 hearts
so his (classical) chances on his card are
2/3 he pulls a heart 1/3 he pulls a spade.
(If you pull a spade, you CANNOT have two hearts, while he can.)
So, if you pull a Spade, you can tell your friend he is likely to have a heart. Do this a lot of times, and you should be correct 2/3 of the time. The cards are indeed entangled, but classically. Experimental error (maybe you can't always see your cards well) will lower this, but (for a long enough term average) cannot raise this.
In Quantum Mechanics, however, you can get correlations that you cannot get in classical physics, i.e., greater than 2/3 in this case. That is the essence of Bell's Theorem - you have correlations that you just can't "get there from here," classically. This is a consequence of having a complex amplitude. Again, it's not just having a correlation, it's that you can get correlations you just can't classically.
I saw a lecture from Dick Feynman once where he showed that you could explain all of this by allowing for negative probabilities for intermediate results, and that this was mathematically the same as the normal (i.e., complex) formulation of QM. (Since you cannot actually measure the intermediate results, you never actually measure a negative probability.) In some ways, I find that helps to grasp the weirdness. YMMV.
The German Autobahn's have no speed limits in rural areas. I have driven at 160 Kph (i.e., 100 mph) and been routinely passed by faster vehicles. In fact, if you are in the left lane at that speed, they may get pretty annoyed with you if you don't get over immediately.
My understanding is that the German Auto Club serves a function much like the US NRA. Touch the speed limit, and your political career will be limited.
My understanding is that they still use the tape drive. When there is no longer enough power to do so, the ability to get data back will take a real hit.
There was the TAU 1000 AU probe, which was to be sold on parallax measurements (i.e., astronomy). I didn't regard that as compelling.
More interesting are the suggestions of a probe to the solar gravitational lens focus, at 688.81 AU (or greater) (for light - it is less than that for gravitational waves or neutrinos, as they pass through the Sun, while light has to go around the Sun).
At that distance or greater, you could use the Sun as a telescope and greatly magnify any remote object at any frequency (and also for gravitational waves and neutrino's). Trouble is, it would be hard to point it at more than one or two targets (as you would have to move the spacecraft 11 AU / deg to do so). You could (I am sure) arrange a trajectory to get 2 or 3 or maybe even 4 objects over time, but that's not many objects for a multi-decade mission.
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L1, L2 and L3 are not stable even in the modified 3-body problem (i.e., where body at L1, L2 or L3 has no mass).
And, there are definitely Lissajous (Halo) orbits of L2 that are always in view of the Earth.
I am not pro-Romney, but it is pretty clear that that was a joke (and, for Romney, a pretty good one).
My question is why L2 and not L1? L2 is going to be exposed to more meteoric traffic, it will have a hard time communicating through the moon to the earth (yeah you can put a comm satellites at L4 or L5 but that's complicating things and adding cost and new failure modes.)
The sensible plan and undoubted intention would be to put the station not at EML2, but in a Lissajous (or Halo) orbit about it big enough so that it was always in view of Earth. Such orbits exist and are energetically easy to get to, although a little station-keeping may be required (as it would be for the L2 point as well).
The difference in delta-V to L1 and L2 is (for the Moon) pretty small. In fact, if you are willing to take your time, you can get to either with basically no fuel beyond a geostationary transfer orbit injection, using WSB trajectories. (This will take months, so it is not so good for manned voyages, but would save a lot on supply logistics costs, up to doubling the payload delivered per launch.)
By the way, getting a space station from L1 to L2 (or back) is also not energetically hard. The NASA plans on this envision putting a habitat at EML1 and then later move it to EML2, and maybe back after a period. (The station would not be AT EML2, but in a Lissajous orbit about it big enough so that it was always in view of Earth.)
L1, L2 and L3 are pretty easy. The Moon (or whatever secondary body you want, such as the Earth for Earth-Sun Lagrange points) is in some orbit, with some period, about the primary (Earth, in this case). Are there other orbits that have the exact same period ? If the Moon had no mass, the answer would be, no, except for exactly the same mean distance (AKA semi-major axis) from the Earth. With the Moon having a significant mass, things are not quite so simple, but they are not very much harder.
Suppose you are inside the Moon's orbit, on the Earth Moon line. On that line, inside the Moon's orbit, the Moon's gravitational acceleration subtracts from the Earth's, so you feel a little less acceleration towards the Earth, and so your circular orbital period is a little less than it would be in the absence of the Moon. If you go up and down that line, you can find the point where the orbital period (for a circular orbit, with the Moon reducing the Earth's gravity) exactly matches the Moon's original orbital period. That point is the L1 Lagrange point. If you are there, in a circular orbit, you are rotating with the Moon. (It's not stable, but that's another matter.)
Now, suppose you are outside the Moon's orbit on the Earth-Moon line. In that case, the Moon's gravitational acceleration increases the pull of the Earth, so your orbital velocity (for a circular orbit) must be a little faster than it would be without the Moon being present. Again, imagine going up and down the Earth-Moon line until the orbital period (increased by the Moon's gravity) exactly matches that of the Moon. That is the L2 Lagrange point (again, not stable).
L3 is just as easily conceptually - if you are on the opposite side of the Moon, again on the Earth-Moon line, the Moon's gravity again increases the pull of the Earth (by a smidgen, due to its distance), and there is a place on the E-M line, just a smidgen inside the Moon's orbit, where your orbital period is the same as the Moon's. That's the L3 point.
it would be a space station at the Earth-Moon L2 Lagrange point about 60000 km from the surface of the dark side of the moon.
Please. It's the far side of the Moon. It goes through day-night cycles just like the near side.
No, no more than the incredibly hot solar corona / wind bothered the Apollo astronauts. The energy density is just way too low.
This just accounting for regular own (baryonic) matter. The Halo is still mostly "Dark" matter, which is non-interacting. (It may be WIMPs, i.e., non-baryonic, or it may be quark nuggets, i.e., baryonic, but either way it is non-interacting.)
Exactly. My experience is in the sub-continent is that nothing usable gets thrown out or, if it does, someone grabs it from the trash and makes use of it.
He is in Bangladesh. Everything local gets reused until it wears out. He can find used typewriters if he looks.
Go to the district in Dhaka in that sells used stuff. Buy some manual typewriters. They, obviously, do not need electricity.
Eclipse : nearer body covers the other body
Partial eclipse : the body could cover the other body, but doesn't (i.e., it nicks it).
Transits : the nearer body is not big enough to cover the other body. Phobos and Deimos, as seen from the surface of Mars, fall in this category.
The angular size of the Moon is so close to that of the Sun, as seen from the Earth, that a special kind of transit is possible, which has a special term - an annular eclipse, where a thin ring of the Sun's surface is still visible (because the Moon is near apogee, and far enough away to not fully cover the Sun). This is a special case; the term annular eclipse has a long history, and I have never heard it used to describe any other kind of transit.
Yes, properly these are transits, not partial eclipses.
Every location on Mars gets an eclipse by both Phobos and Deimos twice a year.
No, only at the equator :
There is a narrow band, centered on the equator of Mars, within which every point is eclipsed at least once during each semiannual eclipse season. Outside that band, the density of coverage decreases slowly with increasing distance from the equator, until the limiting latitudes are reached.
BTW, a surface transit (that is a more appropriate proper term, as neither moon ever fully eclipses the Sun) was also observed by the VIking Lande 1 in the 1970's.
And for the Earth solar eclipses, over an 18.6 year cycle, are equally likely in either terrestrial hemisphere.
These sequestration cuts will not happen. After the upcoming election, minds will be concentrated, horses will be traded at a furious rate, and this can will be kicked down the road. The details of the can-kicking and horse-trading will depend on the nature of the election results, but the can will be kicked down the road. Of that you can be sure.
That is a good description of classical entanglement - what, in this context, would be called a hidden variable theory (the cards have a certain face value, even if you can't see them).
Let's see if I can expand this analogy. Suppose you had two decks of cards, each with only two cards - say the king of hearts and the king of spades. Off-stage, I shuffle them, so that there is either one deck of 2 hearts, and one of two spades, or one deck of both, and another of both. Say that the chances of either shuffle are the same.
Now, repeat your experiment, except you and your friend only get to pull 1 card each, each from your own deck. Classically, the chances are
- 50%, you pull from 1 spade and 1 heart
- 25%, you pull from 2 spades
- 25%, you pull from 2 hearts.
And, of course, ditto for your friend.
Now, if you pull a spade, then the classical chances are
2/3 the other card is a heart
1/3 the other card is a spade
and the classical chances for your friend are thus
2/3 he has a spade and a heart
1/3 he has 2 hearts
so his (classical) chances on his card are
2/3 he pulls a heart
1/3 he pulls a spade.
(If you pull a spade, you CANNOT have two hearts, while he can.)
So, if you pull a Spade, you can tell your friend he is likely to have a heart. Do this a lot of times, and you should be correct 2/3 of the time. The cards are indeed entangled, but classically. Experimental error (maybe you can't always see your cards well) will lower this, but (for a long enough term average) cannot raise this.
In Quantum Mechanics, however, you can get correlations that you cannot get in classical physics, i.e., greater than 2/3 in this case. That is the essence of Bell's Theorem - you have correlations that you just can't "get there from here," classically. This is a consequence of having a complex amplitude. Again, it's not just having a correlation, it's that you can get correlations you just can't classically.
I saw a lecture from Dick Feynman once where he showed that you could explain all of this by allowing for negative probabilities for intermediate results, and that this was mathematically the same as the normal (i.e., complex) formulation of QM. (Since you cannot actually measure the intermediate results, you never actually measure a negative probability.) In some ways, I find that helps to grasp the weirdness. YMMV.
I am from Georgia, and had a tapeworm when I was about 7 or so. And, yes, I was going barefoot a lot that summer.
"We could possibly see drivers going 95 up to 100 miles per hour."
She could buy some peril-sensitive sunglasses.
The German Autobahn's have no speed limits in rural areas. I have driven at 160 Kph (i.e., 100 mph) and been routinely passed by faster vehicles. In fact, if you are in the left lane at that speed, they may get pretty annoyed with you if you don't get over immediately.
My understanding is that the German Auto Club serves a function much like the US NRA. Touch the speed limit, and your political career will be limited.
I was wondering exactly that. I wonder how you would tell ?
That should be good for roughly 700,000 more press releases !
(On a more serious note, they have an elastic definition of "near" - 0.8 light years, IIRC.)
My understanding is that they still use the tape drive. When there is no longer enough power to do so, the ability to get data back will take a real hit.
NP.
You left out
7. Profit !!!!
There was the TAU 1000 AU probe, which was to be sold on parallax measurements (i.e., astronomy). I didn't regard that as compelling.
More interesting are the suggestions of a probe to the solar gravitational lens focus, at 688.81 AU (or greater) (for light - it is less than that for gravitational waves or neutrinos, as they pass through the Sun, while light has to go around the Sun).
At that distance or greater, you could use the Sun as a telescope and greatly magnify any remote object at any frequency (and also for gravitational waves and neutrino's). Trouble is, it would be hard to point it at more than one or two targets (as you would have to move the spacecraft 11 AU / deg to do so). You could (I am sure) arrange a trajectory to get 2 or 3 or maybe even 4 objects over time, but that's not many objects for a multi-decade mission.