Question
What is the approximate maximum separation measured along the surface of the Earth between two stations communicating by EME?
Answer Options
- A) 2,000 miles, if the moon is at perigee
- B) 2,000 miles, if the moon is at apogee
- C) 5,000 miles, if the moon is at perigee
- D) 12,000 miles, if the moon is “visible” by both stations
Correct Answer: D
Explanation
EME (Earth-Moon-Earth), or moonbounce, is a propagation mode where radio waves are reflected off the surface of the Moon. This mode allows for communication between any two points on Earth that share a simultaneous line-of-sight view of the Moon. This visibility condition dictates the maximum possible separation between the two stations involved.
The maximum distance between two points on the Earth’s surface that can see the Moon at the same time is very close to the Earth’s diameter. Therefore, the approximate maximum separation measured along the surface of the Earth for EME communication is nearly half the circumference of the globe, which is approximately 12,000 miles, if the moon is ‘visible’ by both stations. This distance is what makes EME a true global communication mode.
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