Iron Star

Far into the future, Earth has used up most of the natural elements and is in need of replenishing them. Scientists have discovered a way of creating and maintaining an artificial star in space, and humans will rely on the natural process of fusion to recreate all of the natural elements. All what they can afford to use is the most abundant element in the universe, Hydrogen, to keep the star alive and grow it to make heavier elements.

The artificial star is very unstable: if not given any Hydrogen, it will collapse on itself, cease to exist, and the mission is failed; if given too much Hydrogen, it will rapidly expand out of control, create a supernova, and incinerate Earth and end life.

It is up to you to properly monitor the rate of Hydrogen given to the star to send elements back to Earth.