Methods and apparatus of adding propellant to a thruster assembly are described. A first end of a beaker is disposed in an opening of the tank, where the beaker contains propellant and the first end of the beaker includes a breakaway bottom. The thruster assembly and beaker are placed in a first environment, where the first environment is substantially a vacuum and/or an environment composed substantially of gases that can be absorbed by the propellant. A plunger in the beaker is depressed to cause the breakaway bottom of the beaker to break and the propellant to flow into the tank of the thruster assembly. The thruster assembly is removed from the first environment and the beaker is removed from the opening. A cap is added to complete the assembly. The assembly contains a vent to allow gases to escape the interior of the tank.