Here we go again. At least, that’s the hope.

Today, Elon Musk tweeted out a picture of SpaceX’s used rockets hanging out in a giant hanger, itching to be re-used. There are now four lucky rockets that have landed successfully. According to the tweet, one of them might get that chance in September or October of this year.

We know that the rocket that gets to launch a second time won’t be the rocket that SpaceX first successfully landed in December. As the first, it will likely be preserved for posterity. But the other three rockets are all contenders.

Reusable rockets could cut costs of rocket launches by 30 percent — a big deal when it comes to making space travel more affordable and attainable.