It might be hard to fathom now, but the human exploration of the solar system isn't going to stop at the moon and Mars. Eventually, our descendants will spread throughout the solar system—for those interested in space exploration, the question is only of when rather than if. Answering that question is the focus of a new paper released on arXiv by a group of researchers from the U.S., China, and the Netherlands. Their approach is highly theoretical, but it is likely more accurate than previous estimates, and it gives a reasonable idea of when we could expect to see humans in the outer solar system. The latest they think we could reach the Saturnian system is 2153.

How to even start such a calculation is complicated, so it's best to start at the basics, which in this case involves a bit of calculus. To understand when humans will reach further out in the solar system, the authors needed two variables—distance and time. In this case, distance is defined as the distance from Earth that humans have traveled, and time is defined as having started at the beginning of the space race in 1957 when no human had yet left Earth.

NASA is planning a mission to demonstrate the ability to repair and upgrade satellites in Earth orbit. The mission, called OSAM-1 (On-orbit Servicing, Assembly, and Manufacturing-1), will send a robotic spacecraft equipped with robotic arms and all the tools and equipment needed to fix, refuel or extend satellites' lifespans, even if those satellites were not designed to be serviced on orbit.

The first test flight of OSAM-1 is scheduled for launch no earlier than 2026 and will go to low Earth orbit to rendezvous, grapple and dock with Landsat 7, an Earth observing satellite that has been in orbit since 1999. The mission will conduct a first-of-its-kind refueling demonstration test, then relocate the satellite to a new orbit. While some parts of the mission are autonomous, human tele-operators will conduct much of the procedures and maneuvers remotely from Earth.

NASA says that repairing satellites—instead of just letting defunct spacecraft drift in Earth orbit—helps decrease space debris to create a more sustainable future for space exploration.