For its third adventure, the Falcon Heavy will ferry a trove of precious cargo up into space. Around two dozen satellites are going along for the ride this time. But the rocket's most interesting passenger has to be the Orbital Test Bed satellite. Its main payload is an experimental, toaster-sized gizmo called the Deep Space Atomic Clock (DSAC). If the thing works properly, future missions to Mars, Jupiter and beyond could become a whole lot easier — and less expensive.
From HowStuffWorks.com:
https://science.howstuffworks.com/deep- ... -clock.htm
Personally, I do not consider Earth orbit to be "Deep Space" but that was the accurate title of the article...
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