Moon and Planets

Talking to spacecraft that are far from Earth isn’t easy. It takes powerful transmitters to beam signals to other worlds, and giant radio dishes to hear the replies.

There’s also the matter of time. Radio signals travel at the speed of light — 670 million miles an hour. Even so, it takes minutes or hours for a signal to travel between Earth and a spacecraft at another planet.

For some examples, consider three brilliant objects in tomorrow’s early morning sky: the Moon and the planets Venus and Jupiter. Venus is the “morning star,” to the upper right of the Moon. Jupiter is farther to the lower left of the Moon.

Spacecraft are operating at all three worlds right now. The Moon is our satellite world, less than a quarter of a million miles away. So it takes only a bit more than a second for a radio signal to travel between it and Earth. If any problems develop on a lunar satellite, then, flight controllers know about it almost instantly.

That’s not the case for Venus and Jupiter, though.

Venus is about 60 million miles away right now. It takes radio signals about five and a half minutes to cross that gulf. And Jupiter is almost 10 times farther — more than 50 minutes by radio.

If anything goes wrong with a spacecraft at either planet, Earth won’t know about it for a while. So spacecraft are designed to shut down many of their systems when there’s a problem and wait to hear from home — however long that takes.

Script by Damond Benningfield