Piezoelectric actuator still relies on a mechanical motion. It has to be - the idea of nitrogen nozzle is to have a storage of nitrogen under some pressure in a

Piezoelectric actuator still relies on a mechanical motion. It has to be - the idea of nitrogen nozzle is to have a storage of nitrogen under some pressure in a closed volume, and to be able to open that volume to let some gas out. That opening has to be mechanical - unless they use some exotic force fields to keep nitrogen from escaping, in which case it's hardly a (regular) nitrogen thruster anymore. Flexing is still a motion. That, however, can be compensated with an opposite motion in another gas channel. If other parts of satellite can bend on demand, they'd need an actuator or, alternatively, one can use Earth magnetic fields to reorient the spacecraft and let external forces affect it unevenly, thus providing bending. This, however, is outside of the scope of the article. So, to summarize - either secondary subsystems on Gaia are quite unconventional, or the article isn't quite precise.