• Ion engines: Ion engines are a type of electric propulsion that uses ions to generate thrust. They are very fuel-efficient, but they also produce very little thrust. This makes them ideal for long-duration missions, such as sending probes to distant planets.
• Rotating detonation rocket engines: Rotating detonation rocket engines are a new type of rocket engine that uses a rotating detonation wave to generate thrust. They are much more efficient than traditional rocket engines, and they could potentially reduce the cost of space travel.
• Nuclear thermal rockets: Nuclear thermal rockets use the heat from a nuclear reactor to heat a propellant, which is then expelled through a nozzle to generate thrust. They are very powerful, but they also produce a lot of radiation. This makes them unsuitable for human spaceflight, but they could be used for unmanned missions to distant planets.

These are just a few of the latest advancements in rocket propulsion technology. As research continues, we can expect to see even more innovative and efficient propulsion systems in the future. This could lead to new possibilities for space exploration, such as sending humans to Mars or even beyond.