Getting to Mars is never going to be cheap. But a couple of mathematicians have figured out how to shave some significant bucks off the price tag. Rather than fly to the red planet when its orbit brings it closest, the craft will “meet” it on the way. The strategy is called ballistic capture and involves launching the ship into a Mars-like orbit, but moving slower than the planet itself. Eventually Mars will catch up and all that fuel that would have been necessary to cruise to the planet suddenly becomes dead weight. Which means there’s no need to carry it, so you can have a smaller, lighter craft. All of this adds up to a significantly cheaper journey. But there is one problem — the journey will take much, much longer. As is, it would take six months to get to there, using ballistic capture would add several more months. It wouldn’t be great for sending humans to Mars, but it could make sending future rovers much more affordable for NASA and other agency.