What is the primary difference between a prograde and a retrograde orbit?

What is the primary difference between a prograde and a retrograde orbit?

• A. Prograde orbits move opposite to Earth's rotation.
• B. Prograde orbits travel with Earth's rotation; retrograde orbits travel opposite.
• C. Prograde orbits alternate between high and low altitudes.
• D. Prograde orbits are only used for satellites.

Answer: (B)

Prograde and retrograde describe the direction of the orbit relative to Earth's rotation. Prograde means the satellite moves with Earth's rotation, typically eastward around the planet. Retrograde means it moves opposite Earth's rotation, westward. This directional difference explains why launches are often timed to go eastward to gain the rotational speed of Earth, while retrograde orbits require more energy since you’re moving against that rotation. The other options don’t capture this fundamental directional distinction.