Space Communications and Navigation Testbed (SCAN Testbed) - 01.29.14
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The Space Communications and Navigation Testbed (SCAN Testbed) contains Software Defined Radios that can be reconfigured with new software, which would allow mission planners to change how the radios function after they are in orbit. Software Defined Radios typically have vendor-specific designs that require specific software, but SCaN Testbed radios conform to a common, non-proprietary, NASA standard to allow NASA to change the software and the way they are used. Changing a radio’s software after launch would allow mission operators to adapt to increased data flow, possibly resolve problems with the communications system, and other opportunities.
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United States Department of Defense Space Test Program, Johnson Space Center, Houston, TX, United States
Glenn Research Center, Cleveland, OH, United States
Goddard Space Flight Center, Greenbelt, MD, United States
Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States
Sponsoring Space Agency
National Aeronautics and Space Administration (NASA)
Technology Demonstration Office (TDO)
ISS Expedition Duration
May 2012 - September 2014
Previous ISS Missions
This is the first instance of SCAN Testbed operation in microgravity.
- The Space Communications and Navigation Testbed (SCAN Testbed) offers a new operational capability that advances the readiness of SDR technology for adoption by future space missions. The SCAN Testbed enables different radio vendors to provide software to a radio platform and demonstrate multiple radio implementations of the common architecture standard (Space Telecommunications Radio System (STRS: STRS–AR–00001 through 4, Space Telecommunications Radio System (STRS) Architecture Standard, Release 1.02.1 NASA TM-2010-216809)), eventually providing multiple industry sources of SDRs for future exploration missions. Each radio within the experiment demonstrates the operation and reconfiguration among different signaling formats (e.g., communications with relay satellites, current and future global positioning satellite signal assessments, ect.) and assesses the performance and procedures for Ka-band antenna tracking and performance.
- Currently, Software Designed Radios (SDRs), being a relatively new technology proposed for space missions, are uniquely designed and developed within individual companies. These unique designs only allow the developing company to provide waveform software for the radio and therefore NASA is not able to benefit from lessons learned from one development to another or have the ability to reuse software from one development to another. These limitations increase NASA's cost and dependence on single vendor solutions for communication and navigation radios.
- The SCAN Testbed advances the operational experience with current and emerging reconfigurable radio technologies, and assesses radio and software performance to reduce risk to future missions. This is the first NASA use of communications at Ka-Band using the new constellation of relay satellites. The SCAN Testbed also hosts the first Global Positioning System (GPS) L5 frequency (i.e., a unique aeronautical navigation band) space receiver to study an improved orbit determination capability using multiple GPS frequencies.
NASA's Space Communication and Navigation Office is developing the Space Communications and Navigation Testbed (SCAN Testbed) to investigate the applicability of software defined radios (SDR) to NASA missions. A part of the investigation is an architecture standard for SDRs used in space-based and ground-based platforms to provide commonality among radio developments in an effort to provide enhanced capability and services while reducing mission and programmatic risk by reducing the need for custom, proprietary radio architectures. This radio architecture standard provides value by employing common waveform software interfaces, and methods for instantiation, operation, and testing among different compliant hardware and software products. Such common interfaces within the architecture, mask the underlying hardware through application programming interfaces and other software layers enable independent technology insertion at either the software or hardware layer. This common architecture entitled Space Telecommunications Radio System (STRS) provides the desired software abstraction and flexibility while minimizing developmental and operational resources by tailoring the implementation to functions typically required of NASA radios.
Traditional approaches to radio development have been exemplified by proprietary or custom implementations that only meet a specific set of mission requirements. Presently most requirements can only be satisfied by functions implemented in the hardware (i.e., application-specific integrated circuits (ASIC's)) and thus fixed for a specific mission duration, and historically this was often the only approach, given the available ASIC technology, suitable for space flight. As software defined radios (SDR) begin to infuse deep space, near-Earth, and lunar space applications, a new approach must be considered to best apply the new reprogrammable field programmable gate array (FPGA) technologies for NASA. The advent of software-based radio functionality offers NASA the opportunity to separate the software proliferation and its associated complexities from the underlying and evolving reprogrammable hardware technology by adopting an open architecture standard. Published, well defined interfaces enable different vendors to provide radios that conform to the interface standard, providing commonality among different implementations and enabling interoperability between providers of different hardware and software elements. Standard interfaces provide for software component reuse, and technology insertion through the hardware abstraction. Such a standard also promotes the growth of a large base of domain experts; agency personnel, software and hardware providers, and the user and operations communities, which help reduce the risks of using unique custom architecture implementations.
SCAN Testbed hosts three SDRs based on the STRS Standard. The radios provide different and complimentary capabilities while having the ability to reconfigure their functions based in signal processing hardware (e.g., processors or field programmable gate arrays). The functions performed by the radios include communication with the Tracking and Data Relay Satellite (TDRS) system in both S-Band and Ka-Band, receive Global Positioning Satellite (GPS) signals, and enable proximity communications between the International Space Station (ISS) and approaching vehicles.
The hardware consists of a flight enclosure mounted on a Flight Releaseable Attachment Mechanism (FRAM). There are five main components of the payload: the avionics system, the software defined radios, the radio frequency (RF) subsystem, the antenna pointing system, and heaters. Except for the five externally mounted antennas, most of the subsystems are installed on the inside of the enclosure.
The SCAN Testbed offers different radio hardware providers and various software providers a chance to demonstrate their capability in space, and tests a new communications capability for future space missions. A flexible radio system would allow spacecraft crews and ground teams to recover from unpredicted errors or changes in the system. Using the same hardware platform for various missions, and only changing the software to meet specific mission needs, would also reduce costs and risks .
Radio technology designed for use in space could also be used in ground-based platforms that have limited memory and processing capability. Studying a common, open, software architecture for use in space could spark the development of open technology standards for other radio uses on the ground, such as satellite radio.
SCAN Testbed requires a frequency assignment between the flight system on ISS and TDRS at S-Band and Ka-Band, as well as a command and control interface to/from the ground to the payload system to configure the radios and antenna systems. A data connection, separate from the ISS, provides a bi-directional connection between the radios and ground stations (e.g., White Sands). Individual SCAN Testbed experiments are conducted using the testbed on a regular basis, within operational constraints. Experiments are expected to be conducted on a weekly or bi-weekly basis, ranging from 60 minutes to several days in durations. In order to point antennas, the SCAN Testbed needs ISS position and attitude information.
SCAN Testbed is an external payload which requires no crew interaction. Commands are sent from the GRC Telescience Support Center (TSC) to configure and operate a radio for an experiment. A typical S-Band or Ka-Band experiment involves sending pseudorandom or network traffic experiment data to or from the on-board radios through the Space Network (SN) program satellites, the Near Earth Network (NEN) or various ground stations and the TSC. For GPS experiments, a radio is specifically configured to receive and process GPS signals. GPS data is collected on-board and sent to ground via telemetry. Various parameters and data quality measures are routinely manipulated and examined in order to determine the efficacy of the test software on the radios.
Ground Based Results Publications
Briones JC, Handler LM, Johnson SK, Nappier J, Gnepp S, Kacpura TJ, Reinhart RC, Hall CS, Mortensen D. Space Telecommunications Radio System (STRS) Definitions and Acronyms. NASA Technical Memorandum; 2008.
Briones JC, Handler LM, Hall SC, Reinhart RC, Kacpura TJ. Case Study: Using the OMG SWRADIO Profile and SDR Forum Input for NASA's Space Telecommunications Radio System. NASA Technical Memorandum; 2009.
Reinhart RC, Johnson SK, Kacpura TJ, Hall CS, Smith CR, Liebetreu J. Open Architecture Standard for NASA's Software-Defined Space Telecommunications Radio Systems. Proceedings of the IEEE. 2007; 95(10): 1986-1993. DOI: 10.1109/JPROC.2007.905071.
Communications, Navigation and Networking re-Configurable Testbed
Ground testing and processing of SCAN Testbed hardware (JPL)
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Schematic overview showing SCAN Testbed hardware and components (JPL)
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External image of ISS showing SCAN Testbed installed on ELC 4 nadir side (NASA)
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