what happens if a spaceship launches and just travels down?

"South" and "down" aren't the same thing in space. In fact, there is no "down"in space. "Up" and "down" only have meaning in the gravity field of a planet, and down is always under your feet, towards the centre of Earth, no matter where on the planet you are standing. Because of the way the Solar System was formed, nearly everything of interest is confined to a plane called the ecliptic. If you travel out of the ecliptic plane, you get nothing but empty space, unless you travel many light years, when you might encounter a star, if you were lucky. But since space is mostly empty, the chances of encountering are star are virtually zero, unless you aim for a particular star. With our current technology, it would take thousands of years to reach a star.

May be gangga maii ne darshan kardo jaa rhio hoogo

If a space ship took off from the North or South pole and kept going in a straight line it wouldn't run into very much of anything until it reached the Oort cloud. Most of the stuff in the solar system lies on a plane called the ecliptic.

Look south tonight. That's where.