How's this thing powered? Are solar or big RTGs enough? I would think power requirements for these scale lasers, detectors, and transmissions would be pretty large. Isn't it an extraordinary amount of data that needs to be constantly sent back to Earth? I thought LIGO was generating a crazy amount of data per day beyond what I'd think would be possible to stream live back to Earth from so far away.
Also, how can the test masses remain in free fall, while each satellite is undergoing course corrections? Or are corrections infrequent enough for satellites in this earth-following orbit that it wouldn't cause any real amount of downtime? Of course Earth is free-falling.
The 2017 proposal is here: https://web.archive.org/web/20171017043638/https://www.elisa... This information-dense PDF got lost in the shuffle and its contents smeared across a hundred slides on the LISA website, because I guess PR people think only cell phone users exist.
Yes, solar. Laser power is only 5 watts. Total spacecraft power is 760 watts. They're downlinking a mere 334 megabytes a day, sampling at 3.3Hz.
>how can the test masses remain in free fall, while each satellite is undergoing course corrections?
That's the hard part. The test mass floats in the middle of the spacecraft, which maneuvers around it, occasionally firing ultra low-impulse cold gas thrusters to counteract drag. They put up a spacecraft back in 2015 to test that concept: https://en.wikipedia.org/wiki/LISA_Pathfinder
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-interferometr...
The triangle spins as each spacecraft in the constellation travel along their orbits: 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.)
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.
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.
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.
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.
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.
to be fair, i can't imagine that an international group of very smart people with all sorts of PhDs sat around for however many years developing a plan after discussion after discussion would have their idea "bettered" by some rando on the internet. it's just fun to think about and wonder
The funding status of big science collaborations is always a bit opaque, as there are a lot of individual actors with independent funding streams, and there's always a lot of R&D, the cost of which you can only guess in advance.
Formally ESA has moved the LISA project into a "implementation phase", meaning they intend to build it, but no money has been "pledged" as far as I know. However, LISA is a flagship Space Science programme, and the SSPs are part of the ESA budget all member states must contribute to.
Basically there's a fixed, overall budget that is then split for each project adopted. So there is definitely money but I'm not sure there is a public statement that "this particular pile of money belongs to LISA"
My understanding is that ESA has agreed to fund their portion, but other partners haven't finished that process yet - e.g. the UK's science agency has to go to the treasury and make a case for it. Similar with NASA & the other partners involved.
Also, how can the test masses remain in free fall, while each satellite is undergoing course corrections? Or are corrections infrequent enough for satellites in this earth-following orbit that it wouldn't cause any real amount of downtime? Of course Earth is free-falling.