Viking Time System
SOL is the length of a Mars solar day. The latest value is 88,775.244 seconds (24h 39m 35.244s) .
The Viking missions used 88,775.25 seconds (24h 39m 35.25s).
Therefore, all calculations of this website adopts the old value: 88,775.25 seconds.
On Viking 2 Lander mission, SOL is used to express the elapsed time from the epoch.
SOL/Earth-day Conversions are defined as follows:
||Epoch (Earth Time)
||Seconds of year
|Viking Lander 1
||1976 201 19:39:54.04
|Viking Lander 2
||1976 247 12:48:45.07
(See reference )
Each epoch time is midnight at each landing site, which means the Sun direction is opposite to the landing site.
GCSC Count is an integer count kept by the GCSC (Guidance Command and Sequencing Computer) for timing.
Normally, one bit in this count represents 160 milliseconds.
This number cycles through 0 approximately every 31 days.
See reference  for more details.
The data of EDR-2 Tape and VUS Tape include this GCSC count in each data buffer.
To analyze the data, GCSC count must be converted to the Lander Local Time (LLT).
Lander Local Time (LLT)
Lander Local Time (LLT) is the time at the location of the landing point.
The unit of LLT is SOL, and LLT runs from 00:00:00 to 24:39:35 LLT, where hours, minutes, and seconds are equivalent to those of Earth.
00:00:00 LLT is corresponding to the midnight and 12:19:47 is corresponding to noon.
SEISMIC EDR-2 tapes include GMT in each data buffer,
which is the time in milliseconds of earth receipt of the first bit of the buffer .
This time is used for the reference to convert from GCSC Count to LLT.