Just think about that for a minute. Can you imagine not only putting a rover on the surface of Mars, but also putting satellites in orbit around the planet to handle communications to and from Earth by shuttling data to and from the rover as they pass over it in the Martian sky?
Not only designing this system, but building it and sending it through space 50 million miles away--and getting it to work perfectly?
I am in awe of what the NASA engineers have pulled off.
Mars is rotating on its own axis so Mars often "turns its back" to Earth, taking the rover with it. The rover is turned out of the field of view of Earth and goes "dark," just like nighttime on Earth, when the sun goes out of the field of view of Earth at a certain location when the Earth turns its "back" to the sun. The orbiters can see Earth for about 2/3 of each orbit, or about 16 hours a day. They can send much more data direct-to-Earth than the rovers, not only because they can see Earth longer, but because they can operate their radio for much longer since their solar panels get light most of the time, and they have bigger antennas than the rovers. (Cont`d)
Thursday, January 30, 2014 6:54:31 PM
More info for the curious:
The process of getting these Mars images to Earth isn't easy or simple, to say the least. Here`s now NASA describes it:
The data rate direct-to-Earth varies from about 12,000 bits per second to 3,500 bits per second (roughly a third as fast as a standard home modem). The data rate to the orbiters is a constant 128,000 bits per second (4 times faster than a home modem). An orbiter passes over the rover and is in the vicinity of the sky to communicate with the rovers for about eight minutes at a time, per sol. In that time, about 60 megabits of data (about 1/100 of a CD) can be transmitted to an orbiter. That same 60 megabits would take between 1.5 and 5 hours to transmit direct to Earth. The rovers can only transmit direct-to-Earth for at most three hours a day due to power and thermal limitations, even though Earth may be in view much longer. (Cont`d)