Your calculation are wrong byl orders of magnitude. The gravitational pull decreases by the inverse square law. The difference in distance is 60 times. the inverse square law gives a difference of 1/3600 between the near side and far side
Come on, this is basic physics.
Gravity at the surface of the moon (1737.1 km from the center) is 1.62 m/s^2 Gravity at 384400 km from the center of the moon is 1.62 * 1737.1^2 / 384400^2 = 33.08 micron per second squared. Gravity at 390771 km from the center of the moon is 1.62 * 1737.1^2 / 390771^2 = 32.01 micron per second squared. Gravity at 378029 km from the center of the moon is 1.62 * 1737.1^2 / 378029^2 = 34.21 micron per second squared.
A difference of 1/60 in the distance does not result in a difference of only 1/3600. Derivatives don't work that way, you are squaring the wrong thing.
Look, I don't have time for this right now. I've got a book about gravity here ("Gravity from the ground up" by Bernard Schutz), which starts from the basics and works up to General Relativity and cosmology in a very scientific, not-dumbed-down way with actual math, and it explains tides exactly like I did. So does the Wikipedia article on tides.
I hate to use authoritative arguments, but I really do have better things to do, sorry. I'm not being paid for this.
Spinning around an axis creates a centrifugal (pseudo-)force, but orbiting by gravity (translation rather than rotation) does not. Otherwise the occupants of the ISS would not feel weightless inside the station but would stick to one side of it like I already explained. The motion of the earth around the center of gravity of the earth-moon system is caused by the attraction of the moon which acts on all of the earth, the only difference between different points being the gravitational gradient. I calculated that tidal gravitational gradient for you in my previous post (about 6% between the two sides, hardly negligible). There's not much more I can do, it really does work that way.
No, I'm sorry, but your theory with centrifugal forces is completely wrong.
First of all, you need to realise that centrifugal forces are not real forces but pseudo-forces that only show up when you are using an accelerating reference frame. If, for example, you take a turn with your car, the tires are making the car turn (providing centripetal force towards the center of the turn) while your body does not receive that force and wants to go straight ahead. This feels like a force that pushes you to the outside of the turn, but that's only because you are using the car as your reference frame. If you take the road as the reference, your body is merely continuing its straight trajectory until it hits the inside wall of the car which is taking a different, curving trajectory.
Now, if the turn is not caused by the friction of the tires but by some sort of gravitational force (like, for example, the ISS orbiting the earth with a centripetal force of almost 1g), you will not feel any centrifugal force. The bodies of the astronauts receive the same gravitational acceleration as the space station so they feel weightless relative to the ISS. If you would spin the ISS at the same distance with a rope instead of the force of gravity, the astronauts would be pinned to the outer side with a centrifugal acceleration of almost 1g.
The earth is indeed orbting the common center of gravity of the moon-earth system (which is inside the earth). If it were orbiting that point because it was attached to it by some fourth-dimensional pin that forcibly made it orbit that point, then yes, you would get centrifugal forces if you took the earth as your reference frame. But this is not the case: it is not orbiting that point because it is attached to it, but rather because the moon is pulling it towards it.
Now here's the contradiction in your theory: IF it were true that the moon was exerting "the same amount of gravity on every cubic mile of the earth with a difference that is completely insignificant", then that would result in no centrifugal force whatsoever. Just like the astronauts feel no centrifugal force in the ISS.
In reality, there IS a significant difference between the moon's attraction on both sides of the earth. A quick back-of-the-envelope calculation, using the moon's average distance of 384400 km, its radius of 1737.1 km, its surface gravity of 1.62 m/s^2 and the earth's radius of 6371 km, gives me about 33 micron/s^2 at the center of the earth, 32 micron/s^2 on the far side of the moon, and 34 micron/s^2 on the near side. That may not seem like much, but since it's a steady force continuously revolving around, it's enough to keep a mass of water moving around the planet.
Of course the water moves horizontally. The water in the tital bulges comes from the sides, where else would it come from? I agree with you on that bit.
And yes, there are local scenarios where particular coastlines and ocean depths change the tides so they happen a bit earlier or later. But that does not change the fact that the major force driving the tides is simply the gradient of the moon's gravitational field.
By the way, gravitational gradients are enough to tear apart asteroids passing too close by Jupiter. You would think that, on an asteroid only a few km across, the difference in attraction to Jupiter on both sides would be completely insignificant. But apparently it's enough to tear rocks apart.
It has nothing to do with the total amount of gravitational pull.
Tidal stress is the difference between the amounts of gravitational pull at different distances. If you are floating in space near a massive object (planet, star, moon), with your feet pointing towards it, your feet will be closer to it and will therefore experience more attraction, while your head will be further away from it and therefore experience less attraction. This will tend to stretch your body a little bit (or a whole lot if you happen to fall into a black hole). If the gravitational gradient is strong enough, it will make your hair stand up. Your entire body is actually accelerating towards the object, but your feet are being pulled harder while your hair gets left behind. Relative to the pull on your gravitational center, it feels like there are two forces pulling at you from opposite sides trying to tear you apart.
On earth, that means there's a high tide on the side of the moon (closer to the moon, therefore attracted more to it) but also on the other side (further from the moon, therefore attracted less and bulging the other way). The effect is the same on both sides because it's not the amount of attraction that matters, but only the difference with the attraction experienced by the earth's center.
The sun also creates a similar effect, though smaller.
When the sun and the moon are either on the same side (new moon) or on opposite sides (full moon), the two effects are added together and you get spring tide. And, apparently, possibly more or stronger earthquakes.
I'm not saying it's impossible. Just that Elon is not necessarily implying that the bang sound was a gun shot. That's just one of many possibilities, and not the most likely one.
The saddest thing is that it's apparently perfectly OK to show an image of people being attacked with napalm, as long as none of them are naked. Because sex is so much worse than killing.
Oh, I'm dead serious, I really think a hypothetical AI designed to randomly take a web company's servers off line is capable of making a rocket explode on the launch pad due to some "must destroy server no matter what it takes" subroutine./sarcasm
I guess that explains why I didn't get the +5 Funny I was aiming for...
The captain entered the wrong coordinates into the Inertial Reference System, which is the airplane's primary reference for position. Normally, there are several ways the system could have detected this:
- It is normally updated by GPS, but if the difference between the two is too large, the sytem considers the GPS to be faulty. Some warning messages were given, but these warnings often occur during normal operation on the ground and then disappear afterwards, so pilots are sort of "trained" by experience to disregard them. - When applying take-off thrust, the system normally realigns to the coordinates of the runway. But, thanks to genius Airbus programming as usual, the system did not perform the update because the error was too large. - If an incorrect latitude is entered, the system can detect the error because it measures the earth's rotation vector and the gravity vector during IRS alignment while the airplane is still parked. In this case the longitude was incorrect, which cannot be detected by the system. The earth rotates the same at any longitude.
After Take-off, two problems arose: 1. The position was way off, the plane actually thought it was somewhere close to South Africa 2. The Enhanced Ground Proximity Warning System activated, yelling "Terrain, terrain!", based on the incorrect position (not a big problem, but confusing as hell and creating extra stress for the pilots). 3. The heading indication was incorrect, because the IRS internally knows only the true heading (relative to true north) while heading indications on aircraft systems are relative to magnetic north for historical reasons. The IRS converts between the two using local magnetic variation (the difference between magnetic north and true north) but, because it thought it was near South Africa, it used the wrong value for the variation and therefore displayed an incorrect magnetic heading. This caused the autopilot to turn the wrong way.
The pilots, fearing that something was wrong with the entire Air Data Reference system, applied a procedure for unreliable airspeed (they did not know which instruments they could trust anymore) and turned off two of the three ADR computers. This resulted in a further loss of information displayed on their screens which was not exactly helpful to their situation. The procedure exists to disable certain safety protections that might accidentally activate based on erroneous data (if two of the three computers say the airplane is stalling, the flight control computers will push the nose down and override the pilots' sidesticks) but in this case this procedure was not necessary and actually made their life harder.
Now, if you've lost half your instruments, you don't know which instruments you can trust and which you can't (with the heading being wrong for certain), it's not a good idea to fly on instruments through clouds at low altitude. Certainly not an approach to a runway without being able to see it. So they needed to go to an airport where the visibility and cloud base allowed a visual landing. The closest suitable airport with good weather was Melbourne, so that's where they went.
If it had been the range safety explosives, I'm pretty sure they would already know. Pretty easy to tell if that's what blew up. From the very first frame of the explosion, it looks like it initiated at the connection on the side of the second stage.
Or some pipe broke with a loud bang, leading to a leak that caused the explosion. Or a bulkhead blew. I seriously doubt their number one most likely scenario right now is someone shot at it.
They shouldn't call it autopilot. Once they give it that name, engineers start to become sloppy because they think the rocket can handle everything itself. They should call it "launching stuff into space assistance" or something like that.
Lots of similar "objects" in the minutes before the event, just birds passing through the picture. Watching frame by frame, the "object" doesn't come anywhere near the ignition point.
It was a FaceBook satellite. FaceBook has a policy of deliberately knocking their own servers off line to test the resilience of the network. At some point someone must have misunderstood what the idea was. Maybe an AI was programmed to randomly take down parts of the network and it somehow figured out how to blow up the rocket.
That treaty is only valid as long as nobody actually has the capability to assert power in space. Once that changes, the treaty will be in the dustbin before you know it. It might still be applicable in theory, as in "we're not claiming ownership of this area, but this is our base, we'll take as many 'scientific samples' as we like, and don't you dare come anywhere near it".
I bet NASA is glad that spacex didn't try to launch it.
That was a Facebook satellite. Facebook has a policy of deliberately knocking their own servers offline to test the resilience of their network, although I think they took things a little too far this time.
Also, AFAIK, there is no indication that autopilot was engaged, quite the contrary. From the pictures this looks like a very high speed crash, probably well above the autopilot speed limit. You can't set the autopilot to drive more than 10 km/h above the speed limit which I would guess at that location would probably be 80 km/h.
It looks like it was being driven manually at a much higher speed and the crash would not have been survivable in any car.
Slashdot Mirror
Your calculation are wrong byl orders of magnitude. The gravitational pull decreases by the inverse square law. The difference in distance is 60 times. the inverse square law gives a difference of 1/3600 between the near side and far side
Come on, this is basic physics.
Gravity at the surface of the moon (1737.1 km from the center) is 1.62 m/s^2
Gravity at 384400 km from the center of the moon is 1.62 * 1737.1^2 / 384400^2 = 33.08 micron per second squared.
Gravity at 390771 km from the center of the moon is 1.62 * 1737.1^2 / 390771^2 = 32.01 micron per second squared.
Gravity at 378029 km from the center of the moon is 1.62 * 1737.1^2 / 378029^2 = 34.21 micron per second squared.
A difference of 1/60 in the distance does not result in a difference of only 1/3600. Derivatives don't work that way, you are squaring the wrong thing.
Look, I don't have time for this right now. I've got a book about gravity here ("Gravity from the ground up" by Bernard Schutz), which starts from the basics and works up to General Relativity and cosmology in a very scientific, not-dumbed-down way with actual math, and it explains tides exactly like I did. So does the Wikipedia article on tides.
I hate to use authoritative arguments, but I really do have better things to do, sorry. I'm not being paid for this.
Spinning around an axis creates a centrifugal (pseudo-)force, but orbiting by gravity (translation rather than rotation) does not. Otherwise the occupants of the ISS would not feel weightless inside the station but would stick to one side of it like I already explained. The motion of the earth around the center of gravity of the earth-moon system is caused by the attraction of the moon which acts on all of the earth, the only difference between different points being the gravitational gradient. I calculated that tidal gravitational gradient for you in my previous post (about 6% between the two sides, hardly negligible). There's not much more I can do, it really does work that way.
Nah, the majority will just go "they came for the nerds, but I was not a nerd, so..."
Well, in that case I'm pretty sure they were awarded three stars for that shot!
No, I'm sorry, but your theory with centrifugal forces is completely wrong.
First of all, you need to realise that centrifugal forces are not real forces but pseudo-forces that only show up when you are using an accelerating reference frame. If, for example, you take a turn with your car, the tires are making the car turn (providing centripetal force towards the center of the turn) while your body does not receive that force and wants to go straight ahead. This feels like a force that pushes you to the outside of the turn, but that's only because you are using the car as your reference frame. If you take the road as the reference, your body is merely continuing its straight trajectory until it hits the inside wall of the car which is taking a different, curving trajectory.
Now, if the turn is not caused by the friction of the tires but by some sort of gravitational force (like, for example, the ISS orbiting the earth with a centripetal force of almost 1g), you will not feel any centrifugal force. The bodies of the astronauts receive the same gravitational acceleration as the space station so they feel weightless relative to the ISS. If you would spin the ISS at the same distance with a rope instead of the force of gravity, the astronauts would be pinned to the outer side with a centrifugal acceleration of almost 1g.
The earth is indeed orbting the common center of gravity of the moon-earth system (which is inside the earth). If it were orbiting that point because it was attached to it by some fourth-dimensional pin that forcibly made it orbit that point, then yes, you would get centrifugal forces if you took the earth as your reference frame. But this is not the case: it is not orbiting that point because it is attached to it, but rather because the moon is pulling it towards it.
Now here's the contradiction in your theory: IF it were true that the moon was exerting "the same amount of gravity on every cubic mile of the earth with a difference that is completely insignificant", then that would result in no centrifugal force whatsoever. Just like the astronauts feel no centrifugal force in the ISS.
In reality, there IS a significant difference between the moon's attraction on both sides of the earth. A quick back-of-the-envelope calculation, using the moon's average distance of 384400 km, its radius of 1737.1 km, its surface gravity of 1.62 m/s^2 and the earth's radius of 6371 km, gives me about 33 micron/s^2 at the center of the earth, 32 micron/s^2 on the far side of the moon, and 34 micron/s^2 on the near side. That may not seem like much, but since it's a steady force continuously revolving around, it's enough to keep a mass of water moving around the planet.
Of course the water moves horizontally. The water in the tital bulges comes from the sides, where else would it come from? I agree with you on that bit.
And yes, there are local scenarios where particular coastlines and ocean depths change the tides so they happen a bit earlier or later. But that does not change the fact that the major force driving the tides is simply the gradient of the moon's gravitational field.
By the way, gravitational gradients are enough to tear apart asteroids passing too close by Jupiter. You would think that, on an asteroid only a few km across, the difference in attraction to Jupiter on both sides would be completely insignificant. But apparently it's enough to tear rocks apart.
It has nothing to do with the total amount of gravitational pull.
Tidal stress is the difference between the amounts of gravitational pull at different distances. If you are floating in space near a massive object (planet, star, moon), with your feet pointing towards it, your feet will be closer to it and will therefore experience more attraction, while your head will be further away from it and therefore experience less attraction. This will tend to stretch your body a little bit (or a whole lot if you happen to fall into a black hole). If the gravitational gradient is strong enough, it will make your hair stand up. Your entire body is actually accelerating towards the object, but your feet are being pulled harder while your hair gets left behind. Relative to the pull on your gravitational center, it feels like there are two forces pulling at you from opposite sides trying to tear you apart.
On earth, that means there's a high tide on the side of the moon (closer to the moon, therefore attracted more to it) but also on the other side (further from the moon, therefore attracted less and bulging the other way). The effect is the same on both sides because it's not the amount of attraction that matters, but only the difference with the attraction experienced by the earth's center.
The sun also creates a similar effect, though smaller.
When the sun and the moon are either on the same side (new moon) or on opposite sides (full moon), the two effects are added together and you get spring tide. And, apparently, possibly more or stronger earthquakes.
And not just in English, but in Mandarin too!
I'm not saying it's impossible. Just that Elon is not necessarily implying that the bang sound was a gun shot. That's just one of many possibilities, and not the most likely one.
It is hard to tell who is awesome and who is a nut.
Thank you :-)
The saddest thing is that it's apparently perfectly OK to show an image of people being attacked with napalm, as long as none of them are naked. Because sex is so much worse than killing.
Oh, I'm dead serious, I really think a hypothetical AI designed to randomly take a web company's servers off line is capable of making a rocket explode on the launch pad due to some "must destroy server no matter what it takes" subroutine. /sarcasm
I guess that explains why I didn't get the +5 Funny I was aiming for...
OK, here's what really happened:
The captain entered the wrong coordinates into the Inertial Reference System, which is the airplane's primary reference for position. Normally, there are several ways the system could have detected this:
- It is normally updated by GPS, but if the difference between the two is too large, the sytem considers the GPS to be faulty. Some warning messages were given, but these warnings often occur during normal operation on the ground and then disappear afterwards, so pilots are sort of "trained" by experience to disregard them.
- When applying take-off thrust, the system normally realigns to the coordinates of the runway. But, thanks to genius Airbus programming as usual, the system did not perform the update because the error was too large.
- If an incorrect latitude is entered, the system can detect the error because it measures the earth's rotation vector and the gravity vector during IRS alignment while the airplane is still parked. In this case the longitude was incorrect, which cannot be detected by the system. The earth rotates the same at any longitude.
After Take-off, two problems arose:
1. The position was way off, the plane actually thought it was somewhere close to South Africa
2. The Enhanced Ground Proximity Warning System activated, yelling "Terrain, terrain!", based on the incorrect position (not a big problem, but confusing as hell and creating extra stress for the pilots).
3. The heading indication was incorrect, because the IRS internally knows only the true heading (relative to true north) while heading indications on aircraft systems are relative to magnetic north for historical reasons. The IRS converts between the two using local magnetic variation (the difference between magnetic north and true north) but, because it thought it was near South Africa, it used the wrong value for the variation and therefore displayed an incorrect magnetic heading. This caused the autopilot to turn the wrong way.
The pilots, fearing that something was wrong with the entire Air Data Reference system, applied a procedure for unreliable airspeed (they did not know which instruments they could trust anymore) and turned off two of the three ADR computers. This resulted in a further loss of information displayed on their screens which was not exactly helpful to their situation. The procedure exists to disable certain safety protections that might accidentally activate based on erroneous data (if two of the three computers say the airplane is stalling, the flight control computers will push the nose down and override the pilots' sidesticks) but in this case this procedure was not necessary and actually made their life harder.
Now, if you've lost half your instruments, you don't know which instruments you can trust and which you can't (with the heading being wrong for certain), it's not a good idea to fly on instruments through clouds at low altitude. Certainly not an approach to a runway without being able to see it. So they needed to go to an airport where the visibility and cloud base allowed a visual landing. The closest suitable airport with good weather was Melbourne, so that's where they went.
If it had been the range safety explosives, I'm pretty sure they would already know. Pretty easy to tell if that's what blew up. From the very first frame of the explosion, it looks like it initiated at the connection on the side of the second stage.
Or some pipe broke with a loud bang, leading to a leak that caused the explosion. Or a bulkhead blew. I seriously doubt their number one most likely scenario right now is someone shot at it.
They shouldn't call it autopilot. Once they give it that name, engineers start to become sloppy because they think the rocket can handle everything itself. They should call it "launching stuff into space assistance" or something like that.
I was wondering the same thing, why would they be expelled from their galaxy? They don't explode asymmetrically, do they?
Yeah, I know, but part of it was going to serve the FaceBook infrastructure, so it was fair game for FaceBook network resilience testing.
I think my theory is at least as likely as some of the UFO theories about that anomaly...
Lots of similar "objects" in the minutes before the event, just birds passing through the picture. Watching frame by frame, the "object" doesn't come anywhere near the ignition point.
It was a FaceBook satellite. FaceBook has a policy of deliberately knocking their own servers off line to test the resilience of the network. At some point someone must have misunderstood what the idea was. Maybe an AI was programmed to randomly take down parts of the network and it somehow figured out how to blow up the rocket.
So they can just go to their local bazar and buy 373248 grapes?
That treaty is only valid as long as nobody actually has the capability to assert power in space. Once that changes, the treaty will be in the dustbin before you know it. It might still be applicable in theory, as in "we're not claiming ownership of this area, but this is our base, we'll take as many 'scientific samples' as we like, and don't you dare come anywhere near it".
2: why didn't they name it OSIRIS-SEX?
That's what SpaceX would have called it.
I bet NASA is glad that spacex didn't try to launch it.
That was a Facebook satellite. Facebook has a policy of deliberately knocking their own servers offline to test the resilience of their network, although I think they took things a little too far this time.
Yeah, they probably would have spotted it at least two weeks ago in that case.
Also, AFAIK, there is no indication that autopilot was engaged, quite the contrary. From the pictures this looks like a very high speed crash, probably well above the autopilot speed limit. You can't set the autopilot to drive more than 10 km/h above the speed limit which I would guess at that location would probably be 80 km/h.
It looks like it was being driven manually at a much higher speed and the crash would not have been survivable in any car.