Rocket debris such as boosters and payload fairings are often discarded over bodies of water. If the debris is set to be discarded over waters outside the launching state's territory, do they need to seek permission from the concerned state?
Do launching states need to seek permission for jettisoning rocket stages over waters not counted as international waters?
$\begingroup$ Your title asks about international waters, but the question body asks about "permission from the concerned state". It's my understanding that international waters by definition do not have any concerned states to worry about. Are you asking about jettisoning stages over other countries' waters, not counted as international waters? $\endgroup$– fyrepenguinFeb 8 at 6:23
$\begingroup$ Ah, yes, thank you for pointing that out. I did mean to ask about jettisoning stages over other countries' waters. $\endgroup$– quaoarFeb 8 at 8:27
$\begingroup$ They would need a permission for launching above national waters just like an airplane. So a permission is needed at least while moving through the air. Discarding debris into national waters should therefore require a permission too. $\endgroup$– UweFeb 8 at 10:15
Very few launching states are in a geographic position to do this; almost all have situated their launch sites such that they transit international airspace and over international waters. As you all know, Israel even goes so far as to launch westward to do this.
As far as I know, the only country that this actually comes up for is the United States when launching out of Florida. Even then, launches often use a dog-leg maneuver to avoid (mostly Cuban but also Bahamian) territory and waters. But sometimes, when operating at the edge of payload capabilities, that dog-leg penalty is just too much, so overflight is necessary.
In those very rare instances, practice has been to provide NOTICE of the flight and of the possibility of a staging event in territorial waters, but to very carefully word that notice to avoid any implication that permission is being requested. The legal thinking here is that Article I of the Outer Space Treaty provides "freedom of access" to space and thus, launches headed to space are allowed to transit airspace and stage into waters. This notice provides the state in question time to issue safety notices (NOTAMs, etc.) as necessary.
I'm not aware of any instance when a country has intentionally staged over someone else's land territory. If they did, any damage caused on the ground (same for damage to ships on the ocean actually) would have to be compensated by the launching state regardless of fault, per provisions of the Outer Space Treaty and the Liability Convention.
Tl;dr: notice is given for safety purposes, but permission is not requested.