The SCaN Testbed, radios and infrastructure components are shown
in Figure 1.
SCaN Testbed System Statistics:
Mass: 800 lb
AM Radio: 1 kHz or 0.000001 GHz
SCaN Testbed Subsystems
The SCaN Testbed provides infrastructure to support operations of the three software defined radios:
General Dynamics (GD) Corporation
Mechanical Subsystem, includes Structural and Thermal
Flight System: SCaN Testbed located on the Express Pallet
on the ISS
send and receive commands and data ;
The Mechanical Subsystem is comprised of:
The SCaN Testbed is passively cooled. Three of its five sides (Starboard, Zenith and Ram) are effective radiators coated with 10-mil Silver Teflon. All heat generated by the SCaN Testbed electronics is radiated to space through these 3 radiators. The Wake and Nadir sides (toward other ORUs on the ELC) are not radiating (through coatings and/or MLI). The sixth Enclosure side, the ExPA will be covered with Multi-Layer Insulation (MLI – i.e. Beta Cloth) to minimize heat transfer to it.
There are two sets of heaters which provide thermal control post-installation on ELC-3
Survival heaters are supplied by ELC contingency power, thermostat
The Avionics Subsystem is responsible for:
Command and Control of the payload
It provides the electrical interface between ISS systems and
the SCaN Testbed systems. More specifically, the Avionics subsystem
provides the electrical interface to the EP-MP and ELC (through
the ExPA), SCaN Testbed power distribution and control, grounding
and isolation, communications (commanding and data) interfaces
with the ELC, Flight System health and status, and the various
subsystem communications and control as shown in Figure 7.
Avionics Electrical System
The Avionics system provides power distribution, grounding, and isolation. Power distribution for the 28VDC operational and 120VDC operational power is performed within the Avionics subsystem for the three software defined radios, RF subsystem, APS, and the SCaN Testbed heaters.
While installed onto the ELC, the SCaN Testbed has two sets of heaters. The first set of heaters is powered from the ELC 120VDC contingency power feed. These are resistance type with electro-mechanical thermostat control. The second set of heaters is operational heaters powered from the ELC 120VDC operational power feed and controlled by solid-state MOSFET switches internal to the avionics subsystem.
When operating on the ELC, power is distributed through the
avionics unit. ELC 28VDC operational power is used to power
the avionics unit. A digital power card internal to the avionics
unit is used to control (on/off) power to the SDRs. It also
controls a latching relay internal to the TWTA to start power,
inhibit lines to the TWTA PSU, and pulses power to the coax
switches. The digital power card uses optically isolated high
side power mosfets to control power. The avionics monitors
power to “primary” power feeds used to power the major sub-systems.
“Secondary” power feeds are not monitored. Each power line
is also fused. Power for heaters is controlled with low side
switches located on the input filter card.