I've read the deflector dish is to "deflect particles that might tear the ship apart at warp speed".
But if the ship is at warp speed, the na-cells are moving space around the ship and the ship isn't moving at all, so there would be no need for a deflector shield at warp speed.
It just for impulse/sublight speeds, then?
"Can you keep a secret? Can you know something and never speak of it again?"
I just want to point out that this not actually a technical question, but a lore one.
shareI believe the main deflector dish actually helps with moving space around the ship ("deflecting and bending space"), so in essence aiding the nacelles to form a warp bubble. It also is the main navigational device on the Enterprise so it probably has a system of all-range sensors as well, which would aid it in manoeuvring the ship through space (or space around the ship).
Like you I never thought it was for deflecting damaging particles or debris as I assumed that's what the shields were for. Also as you say the nacelles can gobble up particles as the Enterprise moves through space, and converts some of them (hydrogen I imagine) into energy as a secondary fuel source.
The ship may not be moving in relation to the warp field, but it is moving in relation to everything else.
Object A is traveling at warp speed, at rest within it's own inertial frame of reference within the warp field.
Object B is floating in space, at rest within the universal inertial frame of reference.
The two reference frames intersect, and both A and B find themselves being impacted by a fast moving object. Physics does its thing and a large amount of energy is released, also known as an explosion.
This is not good. So the deflector works to project ahead of the ship and move objects out of the ship's path.
Then there's the whole deal with the bussard collectors...
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"Old Man" of the BSG (RDM) boards.