VOA慢速英语:NASA Working Toward Mission to Mars

summit - n. a series of meetings

sustainable - adj. able to last for a long time

stimulate – v. to make people excited or interested

propulsion – n. the force that moves something forward

descent – n. moving downwards

solar – adj. having to do with the sun

challenge – n. to invite someone to compete in competition

innovative – adj. new ideas about something

unravel – v. to find the correct explanation for something