It followed efforts in the 1970s by san francisco , where a small fleet of cars known as the air pollution patrol roved the streets in search of dirty vehicles .

这是仿效旧金山20世纪70年代的做法，当时旧金山组建了一支人数不多的空气污染巡防队（airpollutionpatrol），在街头各处游走，寻找污染车辆。

Better , say the doubters , to spend the money on scientific missions , such as hubble 's successors , and leave exploration to the kind of robotic missions that have successfully roved about on the surfaces of mars and titan , one of saturn 's moons .

质疑者认为应该将资金花在更科学的任务上，比如哈勃望远镜的成功；或者自动探索，比如火星和泰坦（土星一颗卫星）表面的成功探索。