In case anyone else was wondering, at today's prices the materials in the test mass would be worth $177,365.77. And you need three of them, so that's $532,097.31.
I only skimmed the paper but didn't find a clear explanation why AuPt is the best choice of materials. It seems like the surface shape and balance needs to be perfect, density is important, and magnetic susceptance is also somehow relevant?
Given the overall cost estimate, material costs are probably not their primary concern though ("LAGRANGE cost is estimated in the medium range of $600M to $1B.")
Edit: I completely missed this part, described on the LISA page (similar experiment, someone linked it below) - "shooting laser beams from one spacecraft to the other and then superimposing their signal to determine changes in the masses’ distances down to a few billionths of a millimetre." - so they're pointing laser beams from one spacecraft at one lagrange point to another spacecraft at another lagrange point. That's crazy.
Unlike gold, platinum is quite stiff. I suspect they're using it because they don't want to have to compensate for the effect of gravity on the shape when it's being machined. At a guess the properties they're going for in the alloy are:
- Easy to shape
- Very shiny
- Won't oxidise in atmosphere prior to launch
- Very susceptible to gravity (because dense)
- Not susceptible to magnetism (because not ferromagnetic)
- Strong enough not to sag under gravity (because Pt)
At this precision I have no gut feel as to whether tidal losses might be important, but that might be a factor too. Platinum would help attenuate them, I suspect. Pure gold would be squidgy where AuPt will be (comparatively) springy.
"“LISA is an endeavour that has never been tried before. Using laser beams over distances of several kilometres, ground-based instrumentation can detect gravitational waves coming from events involving star-sized objects – such as supernova explosions or merging of hyper-dense stars and stellar-mass black holes. To expand the frontier of gravitational studies we must go to space,” explains LISA lead project scientist Nora Lützgendorf."
Using three satellites in equilateral formation. The project sounds incredibly cool.-
As history has shown, there a significant difference between project deadlines mentioned at the start of the project and the actual date of when it's launched. 2035 become 2037 becomes 2040 becomes 2045 very easily
