The SCaN Testbed flight software resides in the Avionics subsystem and the three Software Defined Radios.

The avionics software runs on the single-board computer to:

process commands
provide thermal monitoring and control
communicate with the radios and ISS
command and configure the radios
control RF subsystem switching
command the APS
collect sensor data
send telemetry to the ground
perform data and file management
Software development for the Avionics subsystem is the responsibility of GRC.

Each of the three SDRs has an Operating Environment (OE), which includes an operating system and provides infrastructure services to applications and waveforms. In addition to the OE, each SDR must run Waveforms, which implement the unique capabilities of the radio to receive and transmit RF signals, provide networking capability, and do navigation and timing. Each radio will have an initial experimental waveform, in addition to test waveforms developed by the radio supplier.

The initial SCaN Testbed software is developed by five organizations:

Glenn Research Center (GRC)
Goddard Space Flight Center (GSFC)
Jet Propulsion Laboratory (JPL)
General Dynamics (GD)
Harris Corporation (HC)
All avionics software that interfaces with ISS is NASA Class C, in accordance with NPR 7150.2 NASA Software Engineering.

Software which will be loaded into the Avionics Subsystem, which directly interfaces with the ISS and which is responsible for safety critical functions, is and will be developed in accordance with NASA Class C. Any reconfigurations/updates to any individual or combination of the SDRs default version will be developed and implemented in accordance with Class E procedural requirements as stated in NPR 7150.2, NASA Software Engineering Requirements, as a minimum, plus selected augmented Class D requirements as supplied by NASA and negotiated between NASA and the Experimenter. Experimenter developed software in the radios will not be Class C, but will require some verification to insure that safety requirements are met.

During the operations phase, radios and the avionics package can be reconfigured from the ground with new software. Software, here, means both that which is running on a processor in the radio, and the configuration of in-flight reconfigurable Field Programmable Gate Arrays (FPGAs). There are no in-flight reconfigurable FPGAs in the Avionics Subsystem.

The Ground System software is developed by GRC in accordance with NPR 7150.2 NASA Software Engineering Requirements and the procedural requirements it specifies for NASA Class C software. Primary path ground software utilizes the NASA Telescience Resource Kit (TReK), a suite of PC-based software applications used by scientists and engineers to monitor and control payloads on-board the International Space Station

Waveform software and firmware defines functionality for most of the SDRs. STRS defines standards for SDRs to maximize waveform firmware and software reuse and reduce porting effort between various radios. All three SCaN Testbed radios will be launched with baseline STRS-compliant waveforms.

Refer to the SCaN Testbed Flight and Ground System Description (in the Candidate Experimenter Info Tab) for more information about waveforms and waveform updates.

The SCaN Testbed software interfaces externally with the ELC via the 1553 interface and the Ethernet interface as shown in Figure 9. The Ground System interfaces with the Enhanced Huntsville Operations Center (EHOSC) through the GRC Telescience Support Center (TSC) and the NASA Integrated Services Network (NISN)/Internet Protocol Operations Network (IONet) as shown in Figure 10.

Figure 9. SCaN Testbed and Ground System Software External Interfaces