I'm not even sure if it's even possible to successfully manage panic on impossible difficulty. Everyone starts at 3 panic, the countries you don't chose on panic mission get more 2 panic (and everyone else on that continent 1 more panic), making them maxed out immediately. There's no way to get satellites up in time (especially since you have to build more power factories on impossible) to prevent countries from pulling out and forget about what will happen if you fail a mission...
It is. Your early build order is completely railroaded though.
0) Live through the first mission. Not as easy as it sounds.
1) Accept the first abduction mission, take the engineer reward regardless of location or difficultly. If it is in South America and the other two are in Asia and Europe, too bad.
2) Finish the second mission. Enjoy aggroing three packs of sectoids at once with rooks and five health squaddies. This is even harder than the first mission, unless you get a heavy w/o hosptial time out of the first mission.
3) Build a sat as soon as the mission is over.
4) Try to get a sergeant in the first month, either as a reward for the 2nd abduction mission or out of repeated success. Start building the OTS. Hope you can start carrying a sniper.
5) Launch sat in an engineer-producting terrirtory to protect a country before the council meeting.
6) You now have money from the council and 10 engineers after the first of the month,build a power generator and 2nd nexus when done. On the 9th of the month or so build two or even three sats. Sell damn near everything except alloys to do it.
7)Do OK on the 2nd month terrior mission.
8) Launch sats at the end of the month. Keep interceptor coverage so they don't get shot down. Build a workshop if you need more engineers to build your third nexus on month 3.
There's not a lot of variation but you can control panic on Impossible. It just involves not losing missions, and early on that is really more luck than skill (which is what people who play impossible hate).