Exploring the Solar System

Exploring Asteroids and Comets

How did the NEAR spacecraft orbit asteroid 433 Eros?

Unlike orbiting a planet, which is a very massive round object, orbiting a light, irregularly shaped asteroid like 433 Eros is extremely complicated and cannot be achieved as a simple elliptical path. Instead, the orbital pattern is a complex, spiraling series of ellipses that are constantly changing size and shape. Furthermore, the orbit had to bring the spacecraft very close to the surface—between 3 and 220 miles (5 and 360 kilometers). Flight engineers had to stay constantly vigilant about NEAR-Shoemaker’s position and distance, lest it accidentally strike Eros.


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