posted on Aug, 5 2012 @ 07:55 AM
Originally posted by QuantumDisciple
...So it takes some 48 hours for images to make it to Earth?
I think it has to do with bandwidth. The speed-of-light delay between Mars and earth is about 13 1/2 minutes, but that is NOT the reason why it
sometimes takes long to get videos and pictures. It has more to do with bandwidth and the stems they use to relay the information.
Images do bot get sent directly from the Rover to earth. Images are first sent to an orbiting satellite (the primary satellites are the Mars Odyssey
and the Mars Reconnaissance Orbiter, and the secondary is ESA's Mars Express). These satellites are used as a relay point, receiving the information
from Curiosity, then transmitting that information to Earth.
There could be several reasons why that information from Curiosity does go to earth immediately. First, there needs to be a line of sight between
Curiosity and the orbiter. If the Orbiters are over the horizon from Curiosity's location, then Curiosity would need to hold the images and video in
its own memory until one of the satellites is in position to receive information. Then that satellite itself needs to be in a position to relay the
information back to Earth.
For the landing procedure, NASA took the time to move a satellite (the Mars Odyssey) in the right orbit to be able to transit landing telemetry data
back to earth in real time (well, with the 13 minute speed of light delay), but that won't always be the case. Sometimes it may take hours between
Curiosity acquiring data, and that data being sent to earth.
And then there's bandwidth. The amount of bits per second being received by the earth is not enough to stream "live-as-it-happens" video. They
would need to download the video first before it can be viewed. It may take a few hours to download a few minutes of video, due to bandwidth. Even
photos are received slowly -- just think how long it would take to get a video that requires six images for every second of video. I can tell you
that the bandwidth does not allow for the download of six images every second of real time.