The new Lunar shuttles can use solar-power electric propulsion.

"Artist’s rendering of Gateway in its initial configuration, featuring the Habitation and Logistics Outpost (HALO) connected to the Power and Propulsion Element. Credit: NASA" (ScitechDaily, NASA’s Lunar Gateway: Energizing Exploration With Powerful Solar Electric Propulsion)

The lunar shuttles that transport people between the futuristic lunar base and Earth can use solar power to transport people between  Earth orbiter and the Moon. Those shuttles can get their energy from the solar panels, which can give energy to ion thrusters. 

The system can use a regular rocket shuttle that transports people and cargo to the orbiter. There that shuttle can transfer people and cargo to the lunar shuttle. Or it can start to use an ion engine. To make the craft travel the Earth-moon transit trajectory. 

In some other versions, the lunar shuttle can use the electrochemical rocket engines during that transit. In the front of the chamber is the microwave system that vaporizes the propellant. In some models, the system targets microwaves to small particles. And then those particles help to vaporize the propellant. 

"An artist’s rendering of the Gateway space station, which will be humanity’s first space station around the Moon as a vital component of the Artemis missions to return humans to the lunar surface for scientific discovery and chart the path for the first human missions to Mars. Credit: NASA, Alberto Bertolin, Bradley Reynolds" (ScitechDaily, NASA’s Lunar Gateway: Energizing Exploration With Powerful Solar Electric Propulsion)

resting visions, the electrochemical systems can use any propellant. The system can use solar-power lasers to vaporize the dust that the system drives backward using magnetic fields. 

The system can use electric arcs, microwaves, or laser rays to vaporize the propellant, which can be any material from hydrogen to silicone or moondust. The system must create intensive heat that can vaporize the moondust. And then that system ionizes the dust driving it backward using a magnetic accelerator. 

The thing in this kind of ion engine is this. It can use any material, from solid to liquid. That it can vaporize. The system can use hydrogen as well as moon basalt. The system doesn't require vital gas or other things. So the crew can load its tanks on the moon using the dust. The ion engine is a powerful tool, but its thrust is quite weak. There is the possibility that the solar sails can transport at least a small spacecraft between Earth and the Moon. 

Above X-37B

In some visions, the X-37 B-style shuttle can use solar sails to transport it between Earth and the moonbase. The sail is connected at the front of the craft. And the lasers and ion cannons can push it to the trajectory to the moon and back. 

The lasers and ion cannons can make it possible to transport low-weight capsules between the Moon and Earth. The ion beam that the ion cannon aims at the solar sail pushes it to the Earth. The system can use moondust to protect the mylar sail. 

The system can use laser or ion beams to the dust behind the solar sail. And that gives thrust to the system. The purpose of the moondust is that the laser beams do not harm the solar sail. 

https://scitechdaily.com/nasas-lunar-gateway-energizing-exploration-with-powerful-solar-electric-propulsion/