Reusable rockets are key to making space travel more accessible. This is because if a rocket can be used more than once, the cost of spaceflight can be brought significantly down.
SpaceX and Blue Origin are leading the effort in making rockets reusable.
Amazon CEO Jeff Bezos, who founded Blue Origin, said he even envisions "millions of people living and working in space." Blue Origin has launched and landed its reusable rocket, called New Shepard, four times so far.
Elon Musk's company SpaceX has also made significant progress in developing its reusable rockets, which travel much faster and further than Blue Origin's rockets.
SpaceX has launched and successfully landed four separate rockets. Three of the rockets landed on a drone ship in the middle of the sea and one landed on land.
Musk said SpaceX could reuse one of these retrieved rockets as soon as September and according to Musk, the company could be sending people to live in space within the decade.
Speaking at a tech conference earlier this month, Musk said that he wants to land people on Mars in just nine years, by 2025.
"We're establishing cargo flights to Mars that people can count on," Musk said at the conference. "The Earth-Mars orbital rendezvous is only every 26 months, so there 'll be one in 2018; there 'll be another one in 2020. And I think if things go according to plan, we should be able to launch people probably in 2024 with arrival in 2025."