The Iridium communication satellites utilize K-Band (RF) communication links
in delivering hundreds of channels of digital voice data between satellites of
the constellation. These links are designated
as Cross-links since some of these communicate
accross orbital planes (picture).
(There are 66 satellites in 6 orbital planes.) My responsibility was to design
and code the real-time control software manipulating the RF
aboard the satellites. The software essentially maintains the physical
communication link as the orbital characteristics of the constellation are
The resulting software can be considered as a complex device driver that higher level subsystems utilize for communication. There were a number of ASICs that implemented hardware functionality which in turn had to be controlled in a real-time fashion. Performance was a paramount consideration that has been achieved in the implementation.
After the links have been qualified I have taken responsibility for several subsystems. Namely: Crosslink Management, the subsystem responsible for all of the high level control of the cross links; Feederlink Management, the subsystem used to command the links that communicate with the gateways on Earth; Secondary Link Management and receiver/transmitter control which is the backup link to the Iridium satellite (possibly the only link in some cases); Payload Instruction Management, the subsystem responsible for handling large volumes of commands and data for such functions as routing and link scheduling and management.
Development has been done on Sun Sparc workstations running SunOS. A great deal of attention was paid to the development process which resulted in a Software Engineering Institute Level 3 process maturity valuation. The development process included Detail Level Design using Shlaer/Mellor Object Oriented Design coupled with simulation via the ObjectBench CASE tool. The judicious use of this paradigm has been valuable. Subsequent source code has been held to an internal standard via both informal and formal code inspections. Unit testing has been aided by a simulation environment that supported execution of the code on the Sun workstation, thus by the time the code was ready for integration in the software laboratory a high degree of confidence has been attained. Those issues that were hardware specific have been addressed by the use of sophisticated digital analysis systems. The final integration on actual flight hardware was also an important step that marked the point of handoff from Payload Software to System Integration and Test. I have been involved in all phases of this process.
Laszlo Kiss — (602) 418-9922