Whether it's a good or bad idea depends

There are two ways to get the 300,000 energy required:
1. Slowly build up the sats behind a HUGE defense
2. Build them as fast as possible (usually with a Nanite 5 or 6) behind no defense
With option 1, the sats don't get crashed intentionally - they just sit behind that turtle and you don't have to ever build solar plants

With option 2, you get someone you trust to crash the satellites and you get a few free moonshots (if you sim it right) as well as recover 30% of the crystal you spent.
Thus...
If you're able to do option #2, you can do it almost anywhere (even Galaxy 1) because you can do it in 8 - 12 hours.
If you are doing option #1, you've got to remember that you have enough sats sitting there that someone with a huge fleet could come by anytime and get the 4m crystal DF from ya ...
The most important thing is that you do it on a planet with a high maximum temperature!!!!
There's a gravitron FAQ on the OGame boards under "Guides" if you're interested

All the best!