Based on this article.
Cislunar spaceflight is a trip that passes behind the moon, but does not land on it. The early Apollo missions were all cislunar, as are some of the probes we have sent in that direction. Now, the ISS countries are looking at the feasibility of launching pieces of a spacecraft to orbit, then using the astronauts at the ISS to assemble those pieces into a fully functioning spacecraft for Cislunar flight.
Doing this would be a major step forward for human spaceflight. It would be the first time that anything has been assembled in orbit with the purpose of going somewhere. Currently, the best we have done is build the ISS, which floats in a nice orbit around Earth.
Space assembly of a craft would require the propellant be shipped up separately to the main components, and would force the ISS countries into creating the first propellant depot in space. Once a propellant depot is established, it can be used by other parties, commercial or governmental, and thus used to lower the cost of more than a single space flight. Likewise, if the costs are acceptable, it would show the feasibility of space-based construction of spacecraft.
That might not sound like much, but it makes a great deal of distance. The reason is the atmosphere that surrounds Earth. For you or me, that atmosphere is incredibly important. For a spacecraft, it’s a pain in the ass. It limits the shape, capability, and materials. But if the craft is built in orbit, those limits disappear. A vessel can then be designed that is reusable, designed to garner energy from the solar wind, and one that uses a far higher percentage of its mass for crew and crew support.
Given this, I hope that the ISS countries decide to push ahead with implementing this plan. However, given the nature of politics and the world’s current financial limitations, I believe that this will remain on the drawing board for many years to come.