Since the beginning of space flight, when the Soviet Union first put Sputnik into orbit, we've needed a way to send and receive data between Earth and whatever we've just flung off Earth.
Surprisingly, as Amy Shira Teitel explains in today's DNews special, we've used the same basic technology since day one – and that's why we can't get a live video stream from Mars. Yet.
Communication between Earth and satellites or other spacecraft is handled exclusively by radio waves, with a few recent exceptions. More on the below. Any kind of data can be encoded into a radio wave – voice transmissions, ship data, pictures, what-have-you. Data from space, orbital or beyond, is sent down to Earth and picked up by terrestrial radio dishes.
Modern spacecraft have digital cameras on board. Images are essentially broken down into a very long sequence of numbers that are beamed back down to Earth via radio waves. So long as there is no large physical impediment to the signal – a moon, say – scientist on the ground simply reassemble the digital image from the numbers.
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The problem with video is that there is a hard limit to the amount of information radio waves can carry. Higher frequency waves can carry more data, but at some point the frequency rises into the range of visible light. At that point, you need optical communications.
But there's a trade-off: While a laser beam can hold a lot more data than a radio wave, the beam needs to be narrow and perfectly aimed at a receiver. At the distances space agencies deal with, that's an issue. But NASA is working on the challenge. In 2013, engineers beamed a picture of the Mona Lisa to the Lunar Reconnaissance Orbiter's LOLA instrument, marking the first optical communication beyond Earth orbit.
Some day, we'll have live video feeds from Mars, but it's going to require significant advances in optical communication technology. Amy has many more specifics in her report, or you can wander over this way and find out why Everything You Know About Planet Colors Is Wrong.
-- Glenn McDonald
Popular Mechanics: How It Works: NASA's Experimental Laser Communication System
Space.com: Live From Mars: Private Red Planet Mission to Beam Video to Earth in 2018
Northwestern University: How Is Data Put On Radio Waves?