Science Questions

How do space probes send signals to Earth?

Tue, 5th Jul 2016

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Question

Arun asked:

What is the medium that carries the signals from space probes, like Voyager, to receivers on Earth?

Answer

Kat Arney put this cosmic quandary to astronomer Andrew Norton, professor from the Open New Horizons ProbeUniversity...

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To date, most communication to space probes has been with radio waves:

For deep-space probes, you need a directional antenna to maximize transmission speeds.

Given limits on size and weight in a space probe, you usually end up using signals in the microwave band (modern radar systems also use the microwave band)

Usually with a parabolic dish antenna (although the Mars rovers use a phased-array antenna, so they can easily track the orbiter as it moves across the sky)


There have been experiments using lasers for communication in near-Earth orbit; they offer the possibility of very high speed communication (but not on foggy or cloudy days). Lasers are also a natural for communication with submarines (since radio waves penetrate the water even worse than light).

Some satellites have an emergency omnidirectional communication channel using frequencies less than microwave frequencies (similar to those used for TV broadcasts), in case they lose the ability to point their high-gain antenna. This lets ground controllers investigate (and hopefully fix) any problems.


The medium is the electromagnetic field. This field permeates the vacuum of space, and is able to carry both RADAR and LASER signals.

This medium works very well in space - you can easily see the star Betelgeuse with the Naked eye (700 light-years away). And we can still pick up the faint signals from the Voyager probes, on the edge of the Solar System. evan_au, Tue, 8th Mar 2016

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