Experts suggest that extended expeditions to the moon and Mars will need some form of atom electrical power. Such systems are now being developed by NASA. The agency is also working on an electric-ion rocket engine that could accelerate the months-long journey between the Earth and Mars. For an extended stay on the moon and Mars, NASA will also need to develop shelters that could be transported, landed and installed. Extended stays also may require a system to protect astronauts from exposure to cosmic and solar radiation.