Windows and Mac players can use the arrow keys with space bar, or a wired XBox 360 controller to control the ship and navigate the menus if preferred. Mac users will need the "Tattie Bogle" driver to use an XBox 360 controller.
Grades are awarded for completing levels. However the grade awarded is not dependent on your score. The conditions for each grade are as follows:
E Grade: Attempt the mission and get shot down.
D Grade: Clear the mission, taking damage.
C Grade: Clear the mission with full health. You can take damage as long as you charge your health back up by the end.
B Grade: Clear the mission without taking a single hit.
A Grade: Clear the mission without taking a single hit, and with no upgrades active from the shop (you can turn them on or off after purchase from the shop screen).