More details on the LISA Pathfinder mission

[PB666]

http://www.bbc.com/news/science-environment-34477389

Interesting in here, and somewhat confusing is are they actively keeping the masses at 38 cm or are they letting them freefall and measuring accelerations. Seems like they are arguing both at the same time.

[Hannu]

I do not know but there are two possibilities. One is that feedback system keeps masses at constant distance and wanted information is extracted from feedback data. It is very common technique in measurement electronics. Other is that they let masses fall freely and return them to initial positions when necessary. It may be more accurate but there are breaks in measurement. There may be misunderstandings in that kind of popular articles.