After comet Sliding Spring's Oct. 19, 2014 close flyby of Mars, NASA reports that
All three NASA orbiters around Mars confirmed their healthy status Sunday after each took shelter behind Mars during a period of risk from dust [from the comet's tail].
"Took shelter behind Mars"? These spacecraft are in orbit around Mars, constantly in motion, so they can't very well just pack up and move to the other side of Mars to avoid getting hit with the dust.
So my questions are: What exactly qualifies as taking shelter behind Mars? Does it simply mean being on the other side of the planet from the tail of the comet as dust from the tail passed Mars?
How did NASA get the (constantly in motion) spacecraft to hide behind Mars? I assume that the orbits had to be modified in advance of the comet's arrival. I picture some orbital modifications that changed the phase of the orbits of the satellites so that they would be on the other side of Mars as the dust flew by, perhaps also making the orbits more elliptical with the apsis behind Mars, allowing the satellites to spend additional time in Mars' protection.
Will these orbital modifications affect the ability of the spacecraft to fulfil their primary missions as they relate to Mars? I am not asking whether dust from the comet will affect the quality of the instruments on the spacecraft (indeed, this whole question focuses on steps NASA is taking to prevent that from happening) but whether the altered orbits the spacecraft have after their orbital modifications will affect their ability to pursue their primary missions (such as flying over different parts of Mars than was originally intended, which may or may not be beneficial to answering the questions the spacecraft were originally launched to answer. Although scientists are nothing if not resourceful and I'm sure any data that come from the spacecraft, whether intended or not, will lead to important discoveries).