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WG3K > ANS 24.06.25 09:04l 73 Lines 4183 Bytes #7 (0) @ AMSAT
BID : ANS173.3
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Subj: The Legacy of AMSAT Flight Software 窶� Part 2
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Burns Fisher, WB1FJ, AMSAT Senior Software Engineer spoke at the 2025
Hamvention AMSAT Forum about his involvement in the development of flight
software for AMSAT satellites. In Part 2, Fisher explains that while Fox
satellites are in Low Earth Orbits between approximately 500 km and 800 km
altitudes, he needs to test newly added functions required for navigation
and propulsion, part of AMSAT窶冱 strategic goals involving highly elliptical
orbits for wide access satellite missions.
Burns explained, 窶廣dding to complexity is the need for fail over
capability. Fail over is a backup operational mode that automatically
switches to a standby system if the primary system fails. We wanted to have
multiple processors that could fail over in a higher altitude radiation
exposure event using processor coordination. One of the newer circuit
boards we are using is the Radiation Tolerant Internal Housekeeping Unit
(RT-IHU). It includes Error Detection And Correction (EDAC) memory that
performs self-tests while in use. We are using higher-quality Automotive
grade components for that purpose.窶�
Burns explained 窶廢ach processor has two redundant cores that cross check
functionality. Each redundant board has these processor chips, non-volatile
memory as well as separate receiver and transmitter. There are bus switches
that disconnect one processor from the main satellite bus if there窶冱 a
failure.窶�
He said, 窶弋he RT-IHU hasn窶冲 flown on an AMSAT satellite. So we wanted to
have something that had flight heritage for more assurance of successful
operation. In addition to the RT-IHU then, we are flying the latest
revision of the legacy IHU 窶� it窶冱 essentially the same board that flew
successfully seven times. The dual IHUs are connected together on the GOLF
bus. Controlling the multiple IHUs is the job of the coordination software
task mentioned above.
窶弋he RT-IHU also has a telemetry transmitter and a command receiver.
Whichever processor is 窶亙n control窶� at a particular time is responsible for
collecting and transmitting telemetry as well as control satellite
subsystems. All the command receivers are active at all times.窶�
窶廬n the photo above, you see my software development bench covered with a
窶彷lat sat窶昶杯he satellite boards all spread out for easy access. You can see
a purple Breakout Board (BoB) that Leandra Mac Lennan, AF1R built, tested
and documented. It has the IHUs, transmitter and receiver boards mounted on
it. The gray ribbon cable connects the BoB to a prototype Central Interface
Unit (CIU). The big green board in front is the GPS evaluation board
system. The GPS system is used to find out where the satellite is and get
our orbital elements out of it as well as getting the exact UTC time.
Toward the back is the ADAC (Attitude Determination and Control System). In
this flat-sat configuration, everything is connected by jumper wires,窶�
Burns explained.
窶弋he BoB is a vital element of the board-level testing of satellite
components. A Hamvention 2025 AMSAT forum presentation by Leandra covered
the BoB in detail and will be available shortly.窶�
Burns continued, 窶弋he photo also shows the test equipment I use. There are
two different power supplies because the actual satellite power supply will
provide multiple voltages. In addition, I use an oscilloscope to help me
understand the electrical signals when a data bus does not operate the way
I expect. Flat-sats like this show how we develop the flight software. Not
in in the photo but to the right of what you see is my Linux computer where
the software is edited and compiled. The software is loaded into the
flat-sat IHUs and tested, often using the console task I mentioned above.窶�
Burns concluded, 窶廣MSAT software development is a continuous and
increasingly complex process We want to get started writing software even
before we have all the correct boards. It requires additional hours of work
and as well as following the development of all of the satellite窶冱
subsystems in order to get an idea of the software that will be required.窶�
[ANS thanks Burns Fisher, WB1FJ, AMSAT Senior Software Engineer for the
above information.]
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