It would require an international agency for enforcement, you don't need an international agency for notification. > The most technologically advanced is a mat

It would require an international agency for enforcement, you don't need an international agency for notification. > The most technologically advanced is a matter of opinion. How would they block Russia or Chinese lauches? Even India has frequent launches. This is far fetched as either could then do likewise. Well, Russia, China and the US all have demonstrated ASAT capabilities, used to take down their own satellites. Using this capability against satellites owned by another state however would violate the Outer Space Treaty and likely be interpreted as an act of war. To interrupt a launch? All 3 likely could as well. Cyber or physical sabotage would be a great way, even fighter aircraft could potentially be used against a spacecraft at the time of launch, as they have been demonstrated to be effective against ballistic missiles if they are nearby the launch site. Space is an arena where most nations try not to make threats or militarise in the interests of international collaboration, but I'm willing to bet there are some secret contingency plans held by the 3 superpowers you mentioned. India, probably not.