Personal space distances vary dramatically across cultures; what's considered comfortable in one culture might be intrusive in another. elaborate
Some satellites use a type of propulsion called "ion thrusters," which are incredibly fuel-efficient but produce very low thrust, meaning they accelerate slowly over long periods. elaborate
The first object launched into space by humans was a German V-2 rocket in 1944, though it wasn't intended for peaceful space exploration. elaborate
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a fact elaborate