According to Newton’s first law of motion: A- Once a spacecraft is up to speed no more fuel is required to keep it moving
B- It requires more fuel to go to Mars than to go to Mercury
C- The further a spacecraft gets from the Sun, the more fuel it needs to keep moving
D- To stay in orbit a spacecraft needs a continuous supply of fuel

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.

sheep is a herbivore animal whereas grasshopper belongs to the class chordates but both of them feed on greens.  

if grasshopper and sheep feeding on a pasture land, i do not think both of them will have any impact on each other. however, the number of the species can make difference. since sheep feed on greens, there is a possibility there left no pasture land for the grasshoppers or they may get extinct.