Aerospace and Electronic Systems Magazine August 2016 - 16
Design of Telecommand Software for the Mars Orbiter Mission
Figure 7.
Telemetry EBC logic block diagram.
commands are differential time tagged commands. Both event and
action are programmable.
For example, if one of the star sensors in the loop goes bad, then
the event is generated by AOCE to utilize the redundant star sensor
in the loop. Therefore, if MTcP gets this particular event, then it executes the commands to bring the redundant star sensor into operation.
Programmable Automatic Thermal Control
Thermal management plays an important role in proper functioning of the subsystems. The subsystems generally have a requirement to maintain the temperature within certain limits.
The software continuously monitors the temperature for all of
the subsystems onboard the spacecraft and operates the heaters to
maintain spacecraft temperature within certain temperature limits.
The temperature limits and sensor information are programmable.
The saturation check logic is also incorporated to take care of
the any sensor failure. The programmable automatic thermal control (PATC) logic has an enable/disable feature. Also, each heater
has an enable/disable feature.
Snap Logic
The snap signal gets generated when the spacecraft gets separated
from the launch vehicle. After the snap signal is detected, some predefined operations have to be done. These operations are loaded in the
TT stack at the launch pad. The trigger to these commands is through
the snap signal. The snap logic handles the snap signal and takes the
proper action after the spacecraft is separated from the launch vehicle.
For example, a snap sequence consists of actions like solar
panel deployment, thruster selection, etc. When the spacecraft gets
separated from launch vehicle, the snap sequence is loaded as TT
commands get activated.
Macro
TIME-TAGGED COMMANDING
Differential Time Tagged Command Execution
The differential TT commands belong to the class of time tagged
commands. The TT commands are useful when a particular sequence of action and delay is required between the commands.
16
Each TT command has a differential delay associated with it.
Both command and delay are programmable from the ground station.
The TT command execution is shown in Figure 8. When the TT
execution start is given, a certain number (N) of commands are executed one by one according to differential delays associated with
them. The TT execution start consists of start command number
and number of commands to be executed.
Macro is a block of differential TT commands which can run in
parallel independently. The commands and delays are programmable. The Macro TT is slightly different from the conventional
differential TT as it has two level controls. The Macro TT becomes
active when it is enabled and initiated.
IEEE A&E SYSTEMS MAGAZINE
AUGUST 2016
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