Aerospace & Defense Technology - December 2021 - 9

CubeSat Technology
Functioning of the Model
The controller configures all the systems before the start of a
task. Associated with each task is a schedule time, processing
time, and a deadline. The Modular Space Vehicle (MSV) scheduler
is responsible for scheduling the tasks. The scheduler uses
the Application Sensor Interface Module (ASIM) mapper to
present the task to the corresponding hardware unit.
The ASIM gets triggered by the scheduler based on the orbit
number and the sequence defined in the table. In this dynamic
system simulation, there is a processing module that monitors
and records the latency, power consumption and battery
charging activities. The delay defined for each task is used as
the time that a subsystem will take to complete a task. The subsystem
mapper is responsible for allocating the processes to the
respective subsystems. The ASIM Complete triggers the ASIM
module of the completion of the task. The Plot and Display
modules in the dynamic simulation view of Figure 3 show the
statistics for power, latency, activity and battery charge.
The MSV scheduler has the following tasks defined:
MSV Task in Figure 4 displays a table where four different
events are scheduled to an MSV scheduler. Each event corresponds
to a range of orbits where the same sequence of tasks
is repeated. ID=1 event would be active from orbit number 0
till the 250th orbit. Each orbit has a list of tasks shown in the
Task_ID_Arr column.
Figure 5 contains the description of the tasks listed in the
MSV table and matches the Task ID values. For example, Task
ID=1 corresponds to the Telemetry, Tracking and Control
(TTC) and Task ID=2 corresponds to the Image Capture. The
table also contains the time within each orbit that the task
will be triggered, and by the time in the orbit that the task
might be completed. The duration of the tasks will depend on
multiple factors including the processing time that will be different
during charging and discharging times, availability of
battery power, and access to resources.
Figure 6 shows the list of subsystems that are executed for a
task to complete.
Several observations were made post simulation model. The
tasks were executed at subsystems sequentially. There is another
option to perform a parallel execution of tasks. The statistics for
both sequential and parallel observations are studied.
Conclusion
This article discusses the background and modeling of cubesat
- the overview of satellite operation in space, architectural insights
of the model and how the model functions. The criticality
of modeling lies in the fact that all the tasks should complete
within deadlines. The failure detection and analysis at an early
stage is necessary to eliminate any fault before integration in the
real-life systems. It saves the cost, effort and time of the designer.
Architectural exploration also will give an overall view of how
the system is going to work. Various trade-offs and performance
analysis will allow designers to reach the specified requirements.
This article was written by Deepak Shankar, founder; Tom Jose,
Application Specialist; and Anupurba Mukherjee, Product Market Engineer,
Mirabilis Design Inc. (Sunnyvale, CA and Chennai, India).
For more information, visit http://info.hotims.com/79420-500.
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