4 ms·

I presume it doesn't capture ripple direction very well. Does the design only capture ripples travelling in the ecliptic?

wanderingstan 3y ago
I wondered about this too. My hunch was that they might be able to use the (comparatively) small detectors on earth to help localize the direction, while using the massive scale of LISA to analyze the details of the waveforms.
- dylan604 3y ago
  What if they added a 4th satellite to form a pyramid to now make it 3D? sure, you're increasing the number of lasers, but so?
  - doormatt 3y ago
    https://en.wikipedia.org/wiki/Big_Bang_Observer https://en.wikipedia.org/wiki/Big_Bang_Observer They're already planning for something like that!
  - genman 3y ago
    Yes, such a relatively low additional cost missed opportunity, if you think about it.
    - Tepix 3y ago
      You would have to add a laser to all satellites and add another one. It probably makes the satellite design a lot more complex and i don't know enough about orbital mechanics but wouldn't be surprised if it would get a lot more complicated as well to fly a 3d formation through space.
      - ragebol 3y ago
        One station would always have to be closer to the sun, which means it should go faster than the other stations. So it gets out of formation.
        ssl232 3y ago
        Indeed, a 4-satellite orbit is probably not a stable one unlike the 3-satellite orbit proposed for LISA. But the 4th satellite already isn't needed due to the conical orbit of the 3-satellite constellation. Fig 5(c) in "On the antenna pattern of an orbiting interferometer" [1] shows the antenna pattern for a LISA-like constellation and it's practically isotropic over a year, and for shorter periods the signals in LISA's sensitive band will be observed for long enough that they will not occupy its less sensitive directions for long and can thus still easily be detected with high SNR. [1] https://academic.oup.com/mnras/article-pdf/289/1/185/18199854/289-1-185.pdf https://academic.oup.com/mnras/article-pdf/289/1/185/1819985...
      - dylan604 3y ago
        even keeping 3 satellites in formation in a single plane, you have to be able to keep station by adjusting in three dimensions.
        genman 3y ago
        I can imagine how all of it adds up but still, it's way less than doing it again in 3D in who know in how many years. But maybe you are all right, it's too much for start.
        ars 3y ago
        https://news.ycombinator.com/item?id=39140232 https://news.ycombinator.com/item?id=39140232 gave you the actual answer why it wouldn't work. Instead they might consider a second formation in orbit 90 degrees away from the first.
        3y ago
- scheme271 3y ago
  They won't be able to do that. LISA will be able to pick up signals with frequencies that can't be detected using LIGO/VIRGO/etc. LISA will be the only detector. However with three arms, it might be possible to localize the signal somewhat.
BrainBacon 3y ago
According to the ESA "As the orientation and direction of motion of the spacecraft triangle changes along the orbit, it will be possible to determine the direction of incoming gravitational wave sources." - From https://sci.esa.int/web/lisa/-/lisa-technology-interferometry-explained https://sci.esa.int/web/lisa/-/lisa-technology-interferometr... Here's a pretty great infographic on how they plan to collaborate with the Athena x-ray observatory to detect black hole mergers ahead of time - https://www.esa.int/ESA_Multimedia/Images/2019/05/How_can_LISA_and_Athena_work_together https://www.esa.int/ESA_Multimedia/Images/2019/05/How_can_LI... It ends up being about 0.4 square degrees in the sky that they're able to narrow in on before the event. That narrowing takes roughly a month.
sbierwagen 3y ago
The triangle spins as each spacecraft in the constellation travel along their orbits: https://en.wikipedia.org/wiki/File:LISA_motion.gif https://en.wikipedia.org/wiki/File:LISA_motion.gif So the dead zone is constantly moving over the course of a year. (In fact, it has to: in order to keep each leg the same length, each spacecraft must be the same distance from the Sun. There's no way to do that in a free falling orbit and have the formation flat to the ecliptic-- the craft closer to the Sun would orbit faster and drift away from its brothers.)

wanderingstan 3y ago

I wondered about this too. My hunch was that they might be able to use the (comparatively) small detectors on earth to help localize the direction, while using the massive scale of LISA to analyze the details of the waveforms.

dylan604 3y ago
What if they added a 4th satellite to form a pyramid to now make it 3D? sure, you're increasing the number of lasers, but so?
- doormatt 3y ago
  https://en.wikipedia.org/wiki/Big_Bang_Observer https://en.wikipedia.org/wiki/Big_Bang_Observer They're already planning for something like that!
- genman 3y ago
  Yes, such a relatively low additional cost missed opportunity, if you think about it.
  - Tepix 3y ago
    You would have to add a laser to all satellites and add another one. It probably makes the satellite design a lot more complex and i don't know enough about orbital mechanics but wouldn't be surprised if it would get a lot more complicated as well to fly a 3d formation through space.
    - ragebol 3y ago
      One station would always have to be closer to the sun, which means it should go faster than the other stations. So it gets out of formation.
      - ssl232 3y ago
        Indeed, a 4-satellite orbit is probably not a stable one unlike the 3-satellite orbit proposed for LISA. But the 4th satellite already isn't needed due to the conical orbit of the 3-satellite constellation. Fig 5(c) in "On the antenna pattern of an orbiting interferometer" [1] shows the antenna pattern for a LISA-like constellation and it's practically isotropic over a year, and for shorter periods the signals in LISA's sensitive band will be observed for long enough that they will not occupy its less sensitive directions for long and can thus still easily be detected with high SNR. [1] https://academic.oup.com/mnras/article-pdf/289/1/185/18199854/289-1-185.pdf https://academic.oup.com/mnras/article-pdf/289/1/185/1819985...
    - dylan604 3y ago
      even keeping 3 satellites in formation in a single plane, you have to be able to keep station by adjusting in three dimensions.
      - genman 3y ago
        I can imagine how all of it adds up but still, it's way less than doing it again in 3D in who know in how many years. But maybe you are all right, it's too much for start.
        ars 3y ago
        https://news.ycombinator.com/item?id=39140232 https://news.ycombinator.com/item?id=39140232 gave you the actual answer why it wouldn't work. Instead they might consider a second formation in orbit 90 degrees away from the first.
        3y ago
scheme271 3y ago
They won't be able to do that. LISA will be able to pick up signals with frequencies that can't be detected using LIGO/VIRGO/etc. LISA will be the only detector. However with three arms, it might be possible to localize the signal somewhat.

BrainBacon 3y ago

According to the ESA "As the orientation and direction of motion of the spacecraft triangle changes along the orbit, it will be possible to determine the direction of incoming gravitational wave sources." - From https://sci.esa.int/web/lisa/-/lisa-technology-interferometry-explained https://sci.esa.int/web/lisa/-/lisa-technology-interferometr... Here's a pretty great infographic on how they plan to collaborate with the Athena x-ray observatory to detect black hole mergers ahead of time - https://www.esa.int/ESA_Multimedia/Images/2019/05/How_can_LISA_and_Athena_work_together https://www.esa.int/ESA_Multimedia/Images/2019/05/How_can_LI... It ends up being about 0.4 square degrees in the sky that they're able to narrow in on before the event. That narrowing takes roughly a month.

sbierwagen 3y ago

The triangle spins as each spacecraft in the constellation travel along their orbits: https://en.wikipedia.org/wiki/File:LISA_motion.gif https://en.wikipedia.org/wiki/File:LISA_motion.gif So the dead zone is constantly moving over the course of a year. (In fact, it has to: in order to keep each leg the same length, each spacecraft must be the same distance from the Sun. There's no way to do that in a free falling orbit and have the formation flat to the ecliptic-- the craft closer to the Sun would orbit faster and drift away from its brothers.)