해석 좀 부탁드려요......

1. starting in the late 1970s, the giant outer planets - jupiter, saturn, urans, and neptune - would line up in a way that the gravity of one would be able to pull a spacecraft to the next one.

2. to take advantage of this line-up which occurs only once every 175 years, nasa planned the voyager project - twin spacecrafts to the outer solar system.