gravityAssistBody

Given a predicate that represents a relationship or action between entities, generate a one-sentence description explaining its meaning.  
# Instructions
Focus on describing the relationship, not the entities themselves. 
# Response Format
Begin the description with \' Indicates...\'

Predicate: gravityAssistBody

Indicates that one body is used as the primary celestial object providing a gravitational assist to alter the trajectory or velocity of another body or spacecraft.