Communications System

How does NASA communicate with spacecraft?

Why does the data transfer rate have to drop with distance?

A spacecraft's radio signal strength gets weaker very quickly as distance between it and Earth increases. But even as a ship's signal gets weaker, the amount of noise (other kinds of energy that can obscure the signal) stays the same. This means that the signal-to-noise ratio gets worse as distance increases. This makes it harder for people on the ground to pick out important data from any spacecraft's signals, and increases the likelihood of making an error.

Space probes send back information coded as bytes, or 8-bit hunks of information a computer can "read." The probability of a successful transmission of a bit equals the strength of the signal multiplied by the time it takes to send the bit. At high power levels, the "bit rate" (or number of bits sent per unit time) is fairly high.

As the signal strength drops, to keep the successful transmission probability the same (low enough to be useful), then the bit rate has to go down proportionally to the loss in signal strength. Its a little like speaking slowly and clearly to communicate in a noisy room.

What interferes with communications?
How long does it take for transmissions to get between DS1 and Earth?
What could go wrong with communications?
How is data put on radio waves?

What kind of data is DS1 sending back?
How are gaps in data dealt with?
What problems are there besides noise?
Why does communication get harder at greater distances?
How much data is DS1 able to transfer?

How is data processing managed?