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First ever image from Moon's far side revealed

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Vox

Would love to see greater investment in this area but without cutting corners that might put lives at (more) risk.

 

For those in the know, is there anyway that the moon might be militarised? Particularly the far side insofar as China goes?  Also, do nations have the ability to claim a territory for its own like Antartica or far flung islands?

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Susanc241

Showing my ignorance, but how do they get a signal back to Earth with the bulk of the moon in the way? Have they got a satellite in orbit round the moon to bounce a signal off?

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Buzz_Light_Year

They sent a lunar orbiter along with the moon lander.

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Susanc241

Simple when you know! Thanks.

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Derek Willis
Posted (edited)

Interestingly - depending on your point of view - the first probe to land on the dark side of the Moon was Luna 16, on September 24th 1970 - almost half a century ago.

https://en.wikipedia.org/wiki/Luna_16

Luna 16 was a Soviet "sample return" mission, and landed 60 hours after local sunset. The probe had to land at that time in order to align the trajectory of the capsule which would bring the sample back to the Earth.

What the Chinese have done is commendable. I do, though, feel the media are over doing it. Almost fifty years ago, men were walking on the Moon. Had America continued the Apollo Moon program there would have been men walking on the far side of the Moon at least forty years ago. But I am sure we all wish the Chinese well. Their achievement may well stimulate a desire to once more start exploring space beyond low Earth orbit.

Edited by Derek Willis
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Noteverythingisaconspiracy
2 hours ago, Vox said:

For those in the know, is there anyway that the moon might be militarised? Particularly the far side insofar as China goes?  

There really isn't any conceivable reason to militarise the Moon. 

2 hours ago, Vox said:

 Also, do nations have the ability to claim a territory for its own like Antartica or far flung islands?

No. There are treaties that makes it clear that you can't claim territory in space.

Space is best compared to the seas, you can own ships on the sea, but you can't own the sea itself. 

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Waspie_Dwarf
1 hour ago, Buzz_Light_Year said:

They sent a lunar orbiter along with the moon lander.

It's not actually orbiting the moon, if it did it would be out of contact with the lander for at least half it's orbit and, worse still, would be out of contact with the Earth when it was in contact with Chang'è 4.

In fact the relay satellite, know as Queqiao, is in a Earth-Moon L2 halo orbit. L points (short for Lagrangian points) are stable areas where the gravitational effects of two bodies, in this case the Earth and Moon, effectively cancel each other out (it's a bit more complicated than that but I don't understand it sufficiently well enough to give a better explanation). L2 is in a direct line between the Earth and Moon but 60,000 Km from the Moon and 450,000 Km from the Earth. From this point Queqiao can always stay in contact with both the lander and Earth.

Queqiao was not carried along with Chang'e 4. It was launched separately on 20th May last year and reached the L2 halo orbit 24 days later.

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L.A.T.1961
56 minutes ago, Derek Willis said:

I do, though, feel the media are over doing it. Almost fifty years ago, men were walking on the Moon. Had America continued the Apollo Moon program there would have been men walking on the far side of the Moon at least forty years ago. But I am sure we all wish the Chinese well. Their achievement may well stimulate a desire to once more start exploring space beyond low Earth orbit.

I think the media are more interested in the Chinese angle than the technicality's of landing a spacecraft on the moon. The mission appears to be doing well so far, hopefully we will see some more science results from their efforts. 

 

 

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Derek Willis
40 minutes ago, Noteverythingisaconspiracy said:

There really isn't any conceivable reason to militarise the Moon. 

No. There are treaties that makes it clear that you can't claim territory in space.

Space is best compared to the seas, you can own ships on the sea, but you can't own the sea itself. 

I wonder if any legal eagles out there can properly explain the effectiveness of the Outer Space Treaty. Nations such the UK, the USA, Russia, and Denmark are ratified to the treaty, meaning they have agreed to be bound to the terms by the actions of other signatories. A number of nations - China being one - have only agreed to accession, meaning they agree to bind themselves to the terms, but will not be bound to them by other signatories. I think there may soon be pressure put on China by the UN (or nation states) to become ratified, or explain why they won't do so. When a nation is not space-faring, the difference is academic. But China is space-faring, so it is somewhat worrying that they are yet to go all the way.   

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AstralHorus

Still no cheese, fake!

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ChrLzs

The following is only for those who wish to know *everything* and complicate their lives and overload their brains.. :D

11 hours ago, Waspie_Dwarf said:

It's not actually orbiting the moon, if it did it would be out of contact with the lander for at least half it's orbit and, worse still, would be out of contact with the Earth when it was in contact with Chang'è 4.

In fact the relay satellite, know as Queqiao, is in a Earth-Moon L2 halo orbit. L points (short for Lagrangian points) are stable areas where the gravitational effects of two bodies, in this case the Earth and Moon, effectively cancel each other out (it's a bit more complicated than that but I don't understand it sufficiently well enough to give a better explanation). L2 is in a direct line between the Earth and Moon but 60,000 Km from the Moon and 450,000 Km from the Earth.

Just to clarify - the L2 Lagrange point is actually directly behind the Moon..  But wait, you cry - then yes, the relay spacecraft would receive signals from the lander, but the Moon would still be in the way and communications with earth wouldn't be possible!!  And you'd be right, except..  The relay craft is actually *orbiting* the L2 point, and its 'halo orbit' is just wide enough for it to be able to see earth at all times..  So -

11 hours ago, Waspie_Dwarf said:

From this point Queqiao can always stay in contact with both the lander and Earth.

Queqiao was not carried along with Chang'e 4. It was launched separately on 20th May last year and reached the L2 halo orbit 24 days later.

 

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OverSword
Posted (edited)

Anyone notice the Chinese Space Agency logo looks like Star Fleet? Sorry can’t post example from phone.

Paramount Pictures: Hey China, did you realize that Star Trek and it’s logo are our intellectual property?

China: That logo looks nothing like the copyrighted Star Trek logo imperialist dog! 

Edited by OverSword
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Susanc241
2 hours ago, ChrLzs said:

The following is only for those who wish to know *everything* and complicate their lives and overload their brains.. :D

Just to clarify - the L2 Lagrange point is actually directly behind the Moon..  But wait, you cry - then yes, the relay spacecraft would receive signals from the lander, but the Moon would still be in the way and communications with earth wouldn't be possible!!  And you'd be right, except..  The relay craft is actually *orbiting* the L2 point, and its 'halo orbit' is just wide enough for it to be able to see earth at all times..  So -

 

I now don’t feel so daft for not understanding how they get a signal back to Earth from the far side of the moon.  Not so simple after all, but ingenious to those of us who aren’t scientists or astrophysicists.  Thanks for all the clarification guys.

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Jon the frog
17 hours ago, OverSword said:

Anyone notice the Chinese Space Agency logo looks like Star Fleet? Sorry can’t post example from phone.

Paramount Pictures: Hey China, did you realize that Star Trek and it’s logo are our intellectual property?

China: That logo looks nothing like the copyrighted Star Trek logo imperialist dog! 

And Roscosmos, Jaxa and ISRO have all the same Star trek element into their logo, quite strange !

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Noteverythingisaconspiracy
15 hours ago, Susanc241 said:

I now don’t feel so daft for not understanding how they get a signal back to Earth from the far side of the moon.  Not so simple after all, but ingenious to those of us who aren’t scientists or astrophysicists.  Thanks for all the clarification guys.

It was never a daft question at all. Asking questions is how we learn new things. :tu:

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OverSword
1 hour ago, Jon the frog said:

And Roscosmos, Jaxa and ISRO have all the same Star trek element into their logo, quite strange !

I don’t think it’s strange. Star Trek is just so iconic that it can’t help but be an influence.

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Derek Willis
10 hours ago, Noteverythingisaconspiracy said:

It was never a daft question at all. Asking questions is how we learn new things. :tu:

But there are daft questions, such as "Were the Moon landings faked?"

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Noteverythingisaconspiracy
49 minutes ago, Derek Willis said:

But there are daft questions, such as "Were the Moon landings faked?"

As someone that have worked in retail I can assure you that when people say "There are no stupid questions" they are wrong.:P

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Peter B
On 1/4/2019 at 7:41 PM, Susanc241 said:

I now don’t feel so daft for not understanding how they get a signal back to Earth from the far side of the moon.  Not so simple after all, but ingenious to those of us who aren’t scientists or astrophysicists.  Thanks for all the clarification guys.

Don't worry. The concept of a halo orbit is, to me at least, spectacularly unintuitive.

However, the interesting thing for me is that someone proposed using a halo orbit to NASA back in 1968 in exactly this way to allow an Apollo mission to land on the far side of the Moon. I already knew that once he'd been selected as Lunar Module Pilot for Apollo 17, geologist Jack Schmitt proposed a landing on the far side, most likely completely aware of the 1968 proposal. Part of the reason for his proposal was to try to re-ignite public interest in Apollo - sadly it seems he was a couple of decades ahead of his time...

In the end, the first use of a halo orbit wasn't until a few years after Apollo.

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Waspie_Dwarf
10 minutes ago, Peter B said:

Don't worry. The concept of a halo orbit is, to me at least, spectacularly unintuitive.

Indeed the idea that a satellite is orbiting a mathematical point in space rather than a real object is not an easy to grasp concept.

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Derek Willis
1 hour ago, Waspie_Dwarf said:

Indeed the idea that a satellite is orbiting a mathematical point in space rather than a real object is not an easy to grasp concept.

Well, it is isn't really a "mathematical point in space". It is a point in space with particular gravitational conditions.

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Peter B
9 hours ago, Derek Willis said:

Well, it is isn't really a "mathematical point in space". It is a point in space with particular gravitational conditions.

That's true, but the intuitive description of an orbit means something in regular motion around a Thing - a star, a planet, a moon or an asteroid/comet - not an empty point in space.

After all, think of the SOHO spacecraft: it's located at the Sun-Earth L1 point, but it's still very clearly orbiting the Sun. In the case of Queqiao, sure, it's orbiting the Earth like the Moon does, but it's not located at the Earth-Moon L2 point. Even as I explain it, and understand it intellectually, it's still strange.

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Derek Willis
10 hours ago, Peter B said:

That's true, but the intuitive description of an orbit means something in regular motion around a Thing - a star, a planet, a moon or an asteroid/comet - not an empty point in space.

After all, think of the SOHO spacecraft: it's located at the Sun-Earth L1 point, but it's still very clearly orbiting the Sun. In the case of Queqiao, sure, it's orbiting the Earth like the Moon does, but it's not located at the Earth-Moon L2 point. Even as I explain it, and understand it intellectually, it's still strange.

An "orbit" is the behavior of an object within a gravitational field. For instance, not all orbits are "closed" - i.e. elliptical. Some are "open" - i.e. parabolic or hyperbolic, depending on the velocity of the object in relation to the strength of the gravitational field.

It may be that more than one gravitational field is at play, which is the case with the Lagrangian points in the Earth-Moon system. It is the net value of the gravitational fields that matter. So, there can be a location in "empty space" around which an object can move in a closed orbit. However, the space is not "empty" - there is a net gravitational field at play. Imagine a ball bearing suspended from a string. Two identical magnets could be arranged so that the ball bearing is pulled in a direction between the directions of the magnets. Would you say the ball bearing is pointing towards a point in "empty space", or to a point where the net magnetic field is at a maximum?

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