Interplanetary spacecraft have some immense challenges as they reach the neighborhood of Jupiter, and some such as Pioneer 10 and 11 have left the solar system! After crossing the asteroid belt, which is between Mars and Jupiter, they have achieved one big hurdle. Then the powerful gravitational pull of Jupiter begins to work it's magic.
Jupiter is what is called a gas giant. This planet is so big that over one hundred Earths could fit inside it! That's big, but not only big, it's very far away. Jupiter is the next planet you would see after Mars if you were venturing to the outer solar system. It stands to reason that it is not an easy planet to get to, but even though there are the distance drawbacks, there are some spacecraft that have already traveled there.
The Voyager spacecraft comes to mind immediately. Voyager was launched back in the late seventies, on a course called "the grand tour". If you were alive back then, you might recall many magazines raving about the fact that the outer planets of Jupiter, Saturn, Uranus and Neptune were coming into alignment like they do every 150 years. So the brilliant engineers at the Jet Propulsion Laboratory, known simply as JPL, decided to take advantage of this fact and send the Voyager spacecraft to capitalize on it.
Sending a spacecraft to Jupiter was about the limit of travel back then, due to weight and power constraints. However, there is something called the "gravitational slingshot effect" that can be harnessed to send spacecraft all the way to Neptune. How it works is that the Voyager craft would arrive at Jupiter on a certain angle, take advantage of the gravitational field, then slingshot it's way to the next planet which is Saturn. No additional rocket fuel was required because the power of gravity is being harnessed. Brilliant indeed!
So for the very first time we would have stunning pictures of all the outer planets. Not only that but Voyager is still on its way out of the solar system. There is a fascinating picture that Voyager took of Earth from very, very far out on the edges of our solar system. Earth looks just like another star from that distance, and it's mind-boggling to think that we are living and breathing on that tiny speck in the Cosmos. Check it out by going to the Space.com website and do a search on Voyager if you want to be blown away.
With the advent of more powerful rockets and the huge advances of technology, no doubt we will see more spacecraft heading to Jupiter and beyond. In fact, right now the Horizon mission is on it's way to Pluto. The last planetoid in our solar system. It is so far out there that even with the Horizon craft traveling at over 60,000 miles per hour it is still going to take over ten years to arrive, sometime in 2015.