The SCaN Testbed, radios and infrastructure components are shown in Figure 1.
Figure 1. SCaN Testbed, Radios and Infrastructure Components (viewed from Ram/Zenith Angle)
SCaN Testbed System Statistics:
Mass: 800 lb
Power: 500 W
Speed: 733 MHz
Flash Memory: 64 GB
Software Lines of Code: >100,000
GD/JPL S-Band: 10 Mbps data rate class
Harris Ka-Band: > 100 Mbps data rate class
JPL GPS: Tracking and navigation performance at GPS L1, L2, and future L5 frequencies.
Operating Frequencies: (see Figure 2 for other NASA missions)
GD/JPL S-Band: 2.0-2.3 GHz
Harris Ka-Band: 22-26 GHz
JPL GPS Receiver: L1, L2, and L5 frequencies, 0.4-16 GHz
Figure 2. Representative NASA Spectrum Use (300 MHz-30 GHz) (Source: NASA’s Space Flight Enterprise Strategy; November, 2003.)
By comparison, here are some common items and their operating frequency:
AM Radio: 1 kHz or 0.000001 GHz
FM Radio, Television, and GPS: 0.05-1.6 GHz
Cell phones: 0.8-2 GHz
3G/4G Data Networks: 1.7-2.7 GHz
Microwave: 3-30 GHz (ovens at 2.5 GHz)
SCaN Testbed Subsystems
The SCaN Testbed provides infrastructure to support operations of the three software defined radios:
General Dynamics (GD) Corporation
Jet Propulsion Lab (JPL)
The infrastructure is comprised of:
Mechanical Subsystem, includes Structural and Thermal
Avionics Subsystem, includes Command & Data Handling (C&DH), Electrical and Analog
Antenna Pointing Subsystem (APS)
These subsystems provide interface to the carriers and environments, structural support, environmental control, commanding, data transfer, data processing, data storage, data routing, power control/distribution, RF signal switching, amplification, transmission and reception, and satellite pointing and tracking.
The SCaN Testbed system consists of four primary subsystems:
Flight System: SCaN Testbed located on the Express Pallet on the ISS
SCaN Testbed Support Equipment located at various ground stations,
SCaN Testbed Control Center (STCC)
SCaN Testbed Ground Testbed both located at the Glenn Research Center.
The overall functional interfaces are shown in figure 3.
Figure 3. SCaN Testbed System Simplified Functional Diagram
Both the SCaN Testbed and Ground System:
send and receive commands and data ;
manipulate (stores, routes, and processes) data;
interface with external systems to send and receive RF signals to and from space as shown in Figure 4.
Figure 4. Simplified Functional Diagram of the SCaN Testbed System
The SCaN Testbed interacts with the carriers and radios as shown in Figure 5.
Figure 5. SCaN Testbed Subsystems & Functional Interactions
The Mechanical Subsystem is comprised of:
Traveling Wave Tube Amplifier (TWTA) Power Supply Unit (PSU) housing
The mechanical subsystem interfaces with the ExPA, Radios, Avionics Subsystem, Integrated Gimbal Assembly, and RF Subsystem as shown in Figure 6.
Figure 6. Mechanical Subsystem
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 controlled
Operational heaters are supplied by ELC operational power, Avionics controlled
The Avionics Subsystem is responsible for:
Command and Control of the payload
Gathering health and status data from all subsystems for downlink via the primary data path.
Running experiment software to support networking and other experiments
Controlling the radios
Controlling the antenna pointing for MGA and HGA
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.
Figure 7. Avionics Subsystem
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.