Starfleet declared the entire Mutara sector off limits to all ships after the events of The Wrath of Khan.
Why was the Grissom sent alone to study the Genesis planet in Star Trek 3 : The Search for Spock?
The Grissom was a lightly armed science research vessel of the Oberth class. The wiki page for the Oberth class says it was "more suited for science missions than combat missions, the had minimal defensive systems. They were tactically inferior to such enemy vessels as the Klingon Bird-of-Prey." These vessels also served as transports and supply ships. All in all, clearly not built for battle.
Surely given the security and political issues surrounding the events of the Genesis device detonation, Starfleet should have sent more ships to secure the Mutara sector and defend the science mission there. As moviegoers saw, the Grissom was sent there alone. If it was given escorts, a cloaked Klingon ship would have thought twice about attacking.
Is there anything from the novelization or other canon sources that explain why the Grissom was sent undefended?