There actually is a docking adapter, but its utility is limited for a few reasons * If you're futzing with hydrazone, you want to avoid sending humans to mess

There actually is a docking adapter, but its utility is limited for a few reasons * If you're futzing with hydrazone, you want to avoid sending humans to mess with it * Any mission to repair it risks damaging the sensors just from the reaction mass that it takes to rendezvous * There is currently no path forward to actually doing this servicing mission, in terms of equipment and vehicles. The technology will almost definitely exist in the future, but by the time it does why not just send a new mission? * Designing the spacecraft to make it serviceable imposes new limitations on it