1·Rocket propellant has barely changed in the more than 50 years since the launch of the first artificial satellite Sputnik.
自第一颗人造卫星史泼尼克发射以来，火箭推进剂在超过50年的时间内变化不多。
2·Although other electric propulsion systems exist, they require a pressurized container to store the propellant.
尽管其他电力推进系统存在，他们需要一个高压的容器来贮存推进剂。
3·But chemical-based systems are severely limited by the fact that the vehicle mass must be made mostly of propellant, which leaves little room for the payload.
但是基于化学的推进系统被严重限制了，因为机器的质量的大部分用来给了推进剂，结果就是没怎么留下空间给装载量。
4·Russian sources said that much more experimental work and funding would be required to prove that solid propellant could be safely used for a manned landing.
俄罗斯的消息人士称，这将需要更多的试验工作以及资金来证明固体推进剂可以被安全地用于载人着陆。
5·The unmanned supply ship docked with the station Wednesday, bringing propellant, water, experiment hardware, and other items to the three crew members on board.
这艘无人资源供应船在星期三与国际空间站对接，为空间站的三名工作人员带去了推进剂、水、实验硬件和其他物品。