.. but where is a gravitation center around which it can orbit?
There isn't one, at least not in the typical sense. It's probably easiest to think of the Pathfinder as primarily orbiting the Sun but using the Earth's gravity to modulate it's position. The main gravity gradient in the solar system is due to the Sun of course, a large 'bowl' around which all the planets etc run around. But locally near each planet there is a significant dimple, however that is a moving dimple because of the movement of the planet. So the craft can be set up to periodically dip further into or out of that dimple. This can be stable for a while. There will always be perturbations eg. the Moon which is another travelling dimple again.
FWIW this also a good way to think of the gravity assist manoeuvres so beloved of probes that want to get to the outer solar system without a massive launch vehicle. What happens here - and timing is crucial - is rather like Michael J Fox in Back To The Future hanging on to the tailgate of a passing vehicle while on his skateboard. So the probe pinches a bit of some planet's momentum and can thus kick further outward in the solar system. With other timings you can get the opposite effect.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
In the final report now delivered to ESA, the Gravitational Observatory Advisory Team concludes that the L3 mission in gravitational waves is technically feasible. Laser interferometry between free-falling test masses is a well-established technical baseline.
This great news happened at April 18th 2016
Hopefully the NASA will come back on board of this project to close the third leg with an additional interferometer arm, which will increas the sensitivity to its formely projected value.
Lisa Pathfinder arrived it's orbit ..
)
Something called a Lissajous orbit around the Earth–Sun L1 according to wiki
Hallo! Since Tuesday 16th the
)
Hallo!
Since Tuesday 16th the test cubes floating freely inside LISA Pathfinder.
Kind regards and happy crunching
Martin
RE: .. but where is a
)
There isn't one, at least not in the typical sense. It's probably easiest to think of the Pathfinder as primarily orbiting the Sun but using the Earth's gravity to modulate it's position. The main gravity gradient in the solar system is due to the Sun of course, a large 'bowl' around which all the planets etc run around. But locally near each planet there is a significant dimple, however that is a moving dimple because of the movement of the planet. So the craft can be set up to periodically dip further into or out of that dimple. This can be stable for a while. There will always be perturbations eg. the Moon which is another travelling dimple again.
FWIW this also a good way to think of the gravity assist manoeuvres so beloved of probes that want to get to the outer solar system without a massive launch vehicle. What happens here - and timing is crucial - is rather like Michael J Fox in Back To The Future hanging on to the tailgate of a passing vehicle while on his skateboard. So the probe pinches a bit of some planet's momentum and can thus kick further outward in the solar system. With other timings you can get the opposite effect.
Cheers, Mike.
I have made this letter longer than usual because I lack the time to make it shorter ...
... and my other CPU is a Ryzen 5950X :-) Blaise Pascal
Hallo! Unexpected early this
)
Hallo!
Unexpected early this realy nice news :
This great news happened at April 18th 2016
Hopefully the NASA will come back on board of this project to close the third leg with an additional interferometer arm, which will increas the sensitivity to its formely projected value.
Kind regards and happy crunching
Martin