Communications System

How does NASA communicate with spacecraft?

How is lag dealt with?

Even though there are ground teams that constantly monitor and control spacecraft, the ever-increasing lag time between when a message is sent and when it is received limits their ability to respond to conditions on the spacecraft in a timely manner. Basically there are two options when dealing with this lag time. Simply waiting for messages or sending them in time to get to a craft may be sufficient.. However, certain problems that arise might not allow for waiting time. If this is the case, then the spacecraft needs to be able to figure out on its own what to do. These instructions that the spacecraft has are called "fault-protection routines."

One example of a common fault-protection routine is the Command-Loss Timer. This is a software timer running in the spacecraft's computer which is reset every time the spacecraft receives a command from Earth. If enough time has gone by that the timer can get all the way to zero, the computer assumes that the spacecraft failed to receive a message because of a problem with its receiver, command decoder, or some other hardware in the command string. The fault-protection routine takes actions such as swapping to back-up hardware in an attempt to reestablish the ability to receive commands.

The test of a new computer program called Remote Agent in DS1 is taking independence even one step past fault-protection. During a two week period in which DS1 is testing Remote Agent, DS1 will figure out what to do for itself. Remote Agent will be giving commands to fire rockets, take pictures, as well as the usual fault-protection.

What are uplink and downlink?
How long does it take for transmissions to get between DS1 and Earth?
What is a remote agent?
How does a remote agent work?
How are remote agents used?

How are gaps in data dealt with?
What new communications features is DS1 using?
How do AutoNav and the remote agent work together?

How is lag time kept track of?