QUESTION:
Can you tell me which error correcting codes are being used on the
communications between Mars and Earth? Do you use a Reed Solomon code and a
convolutional code, and if so, which ones?

ANSWER from Charles Whetsel on July 11, 1997:
All deep space missions these days use error correcting codes both to
correct the effects of data "glitches" in tranmitting our images and data
across space, and also to allow us to transmit at higher data rates than if
we sent uncoded data (Although the higher data rates are more susceptible to
data hits, the number of errors encountered are still within the ability of
the coding schemes to reconstruct the original stream of data which was sent
before the errors were introduced).

The specific coding schemes used for the Mars Missions (Mars Global Surveyor
and Mars Pathfinder) involve first using a standard Reed-Solomon coding
scheme, and then passing the Reed-Solomon data symbols through a
convolutional Vitterbi encoder prior to transmit.  On MGS, the Vitterbi
parameters are r=7, k=1/2, while Pathfinder can select between k=7, r=1/2
and k=15, r=1/6.

Charles Whetsel
Chief Engineer
Mars Surveyor Operations