Artist's impression of NASA's Space Launch System during takeoff, with the Orion spacecraft riding on top. A test flight of SLS, which will send Orion around the moon and back, is expected to take place in 2019.
As NASA considers sending astronauts deeper into the solar system, one major barrier will be cost. Launching cargo from Earth is expensive, which is why the Apollo program that brought crews to the moon in the 1960s and 1970s cost the equivalent of $109 billion in 2010 dollars.
To make moon flights cheaper, a new paper proposes using an electrically powered lunar space tug that would operate between Earth and the moon, carrying logistics modules with supplies for a lunar space station. The research was recently published in Acta Astronautica.
This is a different vision from NASA's present plans for lunar exploration. The space agency is hoping to resume missions to the moon in the near future using its new Space Launch System, a rocket that is capable of bringing humans to the moon or other places outside of Earth orbit. (The rocket hasn't been tested yet, but is expected to send an uncrewed Orion spacecraft around the moon in 2019.) In later decades, NASA tentatively proposes developing a Deep Space Gateway — a space station around the moon that could serve as a base for missions to the moon, Mars, or other distant destinations.