Take control of the spacecraft Vaus and prevents energy ball reach the earth, if you do know the destruction the planet. To stop it you must put your ship in the middle of the path of collision and let it bounce with your shield strength into space, but there is a problem as there are hundreds of enemy ships waiting to descend upon impact.
So the best strategy is to bounce the ball of energy with its rectangular ships and destroy them one by one. Only when you destroy all the ships that generate energy to keep this ball of active energy disappear, something difficult and you have to bounce the ball at the right angle to destroy the ships.
In addition the difficulty and pressure adds that if only we were wrong once Vaus move the ship to another place on Earth be destroyed. So we must take risks to the maximum in each movement to destroy our enemy, since the Vaus is the only Earth ship ready to bounce this type of attack.