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understanding how the moon has developed

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would really help us in understanding

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how the other plants in the inner part

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of the solar system the rocky planets

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have also developed the purpose of the

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ground mission is to investigate the

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interior structure of the moon to

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achieve that we have to measure the

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gravitational field of the moon so we're

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all familiar with with tides on the

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earth that are that are caused by the

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moon the moon actually has similar title

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response and when the moon changes its

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shape a little bit due to those tides

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just like the earth does we can actually

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measure that that affects the gravity

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field there's a lunar shape varies his

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gravity field changes and we're able to

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observe that we are using a very simple

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measurement which is gravity it's a

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little bit like taking the cat scan of

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the moon but using the gravity waves

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instead of acoustic waves to unlock the

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secrets of the interior of the moon we

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have two spacecraft that are in a polar

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orbit around the moon want essentially

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chasing each other around the moon

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there's a part of the Earth's moon a

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very significant part at the far side of

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the moon that is that does not present

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its face to the earth so we can never

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directly observe the spacecraft as it

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goes across the forest of the moon using

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earth-based tracking antennas so the

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solution to that was rather than track

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the motion of the spacecraft as it's

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orbiting a moon from the earth track it

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with another spacecraft also orbiting

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the moon it's essentially the same

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technology as the GPS in your mobile

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phone and in fact the two orbiters

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together form sort of a mini GPS and

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receiver constellation except using

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different frequencies from normal GPS

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the first thing we do actually once the

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map is in our hands is compare it with

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the topography map hopefully of

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comparable resolution and from there we

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can look at specific features such as

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mountains and basin craters

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and compare the gravity on the

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topography this is where it gets really

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interesting you would normally think

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that if there is a mountain present on

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the planet there's additional mass and

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additional gravitational signal as the

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spacecraft flies over it but if it does

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and there is no additional gravity

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signal then something on the inside is

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going on that is particularly

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interesting and that's what we want to

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know when I was just getting into middle

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school I had to rely on my information

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on the moon watching the Apollo missions

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on television we wondered students to

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have a hands-on role in exploring the

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moon it's an experiment called moon cam

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we will have up to four cameras on each

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Grail spacecraft students will be able

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to look at the ground track of where

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Grail will be at going around the moon

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on a daily basis and to propose images

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that will be taken it's going to go a

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long way towards helping students