The distance from earth to the center of our galaxy is about 23 000 ly (1 ly = 1 light-year = 9.47 × 1015 m), as measured by an earth-based observer. A spaceship is to make this journey at a speed of 0.9990c. According to a clock on board the spaceship, how long will it take to make the trip? Express your answer in years (1 yr = 3.16 × 107 s).