Communications System

How long does it take for transmissions to travel between DS1 and Earth?

The answer to this question depends on where DS1 is at the time. DS1 is getting farther and farther away from Earth, so the transmission time is taking longer and longer. We know how fast radio waves travel and how far away DS1 is. Using those two pieces of information, we can figure out how long a transmission will take at any given time.

Radio waves travel at the speed of light (299,792 kilometers per second) making transmissions almost instantaneous early in the mission. But as the distance between Earth and DS1 gets big, even a signal at the speed of light takes a little while to travel. The time between sending and receiving a signal is called "lag." Keeping track of lag time can be very important because it affects how fast DS1 can respond to ground commands.

For example, if DS1 was to send a signal telling us it has some sort of problem, scientists on Earth would have several solutions available. However, those solutions might need to be applied right away. If the lag is too long, the solution might not work because it will be too late by the time the command message got back up to DS1.

Below is a list of a few distances and the lag times we would experience trying to communicate over that distance.

Light Time Approximate Distance Example
1 second 299,792 km about 0.75 x Earth-Moon distance
8.3 minutes 150,000,000 km Earth-Sun distance
1 hour 1,000,000,000 km about 1.5 x Sun-Jupiter Distance
4 years 4 light years Distance to nearest star