NASA spacecraft typically rely on human-controlled radio systems to communicate with Earth. As collection of space data increases, NASA looks to alternative radio technologies to meet demand and increase efficiency.
The growth of Software Defined Radios (SDRs), such as cognitive radio, offers NASA the opportunity to improve the way space missions develop and operate space transceivers for communications, networking, and navigation.
Reconfigurable SDRs provide the capability to change the functionality of the radio during a mission and optimize the data capabilities (e.g. video, telemetry, voice, etc.). The ability to change the operating characteristics of a radio through software once deployed to space offers the flexibility to adapt to new science opportunities, recover from anomalies within the science payload or communication system, and potentially reduce development cost and risk through reuse of common space platforms to meet specific mission requirements. SDRs can be used on space-based missions to almost any destination.
According to Janette C. Briones, principal investigator in the cognitive communication project at NASA’s Glenn Research Center (Cleveland, OH), “Modern space communications systems use complex software to support science and exploration missions. By applying artificial intelligence and machine learning, satellites control these systems seamlessly, making real-time decisions without awaiting instruction.”
To understand cognitive radio, it’s easiest to start with ground-based applications. In the U.S., the Federal Communications Commission (FCC) allocates portions of the electromagnetic spectrum used for communications to various users; for example, the FCC allocates spectrum to cell service, satellite radio, Bluetooth, Wi-Fi, etc. Imagine the spectrum divided into a limited number of taps connected to a water main. What happens when no faucets are left? How could a device access the electromagnetic spectrum when all the taps are taken?
SDRs such as cognitive radio use artificial intelligence to employ underutilized portions of the electromagnetic spectrum without human intervention. These “white spaces” are currently unused, but already licensed segments of the spectrum. The FCC permits a cognitive radio to use the frequency while unused by its primary user until the user becomes active again.
Cognitive radio draws on “water” from the water main that would otherwise be wasted. The cognitive radio can use many faucets, no matter the frequency of that faucet. When a licensed device stops using its frequency, cognitive radio draws from that customer’s faucet until the primary user needs it again. Cognitive radio switches from one white space to another, using electromagnetic spigots as they become available.
“The recent development of cognitive technologies is a new thrust in the architecture of communications systems,” said Briones. “We envision these technologies will make our communications networks more efficient and resilient for missions exploring the depths of space. By integrating artificial intelligence and cognitive radios into our networks, we will increase the efficiency, autonomy, and reliability of space communications systems.”
NASA has developed an architecture standard for SDRs used in space and ground-based platforms to provide commonality among radio developments to provide enhanced capability and services while reducing mission and programmatic risk. The Space Telecommunications Radio System (STRS) architecture standard defines common waveform software interfaces, methods of instantiation, operation, and testing among different compliant hardware and software products. These common interfaces within the architecture abstract, or remove, the application software from the underlying hardware to enable technology insertion independently at either the software or hardware layer.
For NASA, the space environment presents unique challenges that cognitive radio could mitigate. Space weather, electromagnetic radiation emitted by the Sun, and other celestial bodies fill space with noise that can interrupt certain frequencies.
“Glenn Research Center is experimenting in creating cognitive radio applications capable of identifying and adapting to space weather,” said Rigoberto Roche, a NASA cognitive engine development lead at Glenn. “They would transmit outside the range of the interference or cancel distortions within the range using machine learning.”
In the future, a NASA cognitive radio could even learn to shut itself down temporarily to mitigate radiation damage during severe space weather events. Adaptive radio software could circumvent the harmful effects of space weather, increasing science and exploration data returns.
A cognitive radio network could also suggest alternate data paths to the ground. These processes could prioritize and route data through multiple paths simultaneously to avoid interference. The cognitive radio’s artificial intelligence could also allocate ground station downlinks just hours in advance, as opposed to weeks, leading to more efficient scheduling.
Additionally, cognitive radio may make communications network operations more efficient by decreasing the need for human intervention. An intelligent radio could adapt to new electromagnetic landscapes without human help and predict common operational settings for different environments, automating time-consuming processes previously handled by humans.
Testing Cognitive Radio
The Space Communications and Navigation (SCaN) Testbed aboard the International Space Station (ISS) provides engineers and researchers with tools to test cognitive radio in the space environment.
“The testbed keeps us honest about the environment in orbit,” said Dave Chelmins, project manager for the SCaN Testbed and cognitive communications at Glenn. “While it can be simulated on the ground, there is an element of unpredictability to space. The testbed provides this environment — a setting that requires the resiliency of technology advancements like cognitive radio.”
Chelmins, Rioche, and Briones are a few of the many NASA engineers adapting cognitive radio technologies to space. As with most terrestrial technologies, cognitive techniques can be more challenging to implement in space due to orbital mechanics, the electromagnetic environment, and interactions with legacy instruments. In spite of these challenges, integrating machine learning into existing space communications infrastructure will increase the efficiency, autonomy, and reliability of these systems.
The SCAN Testbed, formerly known as Communications, Navigation, and Networking reConfigurable Testbed (CoNNeCT), was launched in 2012 and installed in the ISS to provide an on-orbit, adaptable SDR facility with corresponding ground and operational systems. Mission operators can remotely change the functionality of radio communications through software once deployed to space, offering them flexibility to adapt to new science opportunities and recover from anomalies within the science payload or communication system.
The SCAN Testbed conducts a variety of experiments with the goal of further advancing other technologies, reducing risks on other space missions, and enabling future mission capabilities. It provides NASA, industry, other government agencies, and academic partners the opportunity to develop and field communications, navigation, and networking technologies in the laboratory and space environment based on reconfigurable SDR platforms.
The testbed exercises various components of the SDRs’ operating environments (OE), waveforms (WF), and performance characteristics. An OE is like the operating system on a computer and provides a common infrastructure for waveforms and applications. A waveform or application is like a program running on the computer. OEs and WFs have parameters that can be changed in the course of an experiment using a standardized method.
The testbed houses three SDRs in addition to a variety of antennas and apparatus that can be configured from the ground or other spacecraft.
The SCaN Testbed consists of three reconfigurable and reprogrammable SDR transceivers/transponders:
SDR from Jet Propulsion Laboratory (JPL) with both S-Band and L-Band (GPS) capabilities,
General Dynamics SDR that is S-Band only, and
Harris Corporation (HC) SDR that is Ka-Band.
The testbed points to a series of NASA Space Network (SN) Tracking and Data Relay Satellite System (TDRSS) satellites in geosynchronous orbits and NASA Near Earth Network (NEN) stations, as well as experimenter-provided facilities.
The three SDRs will provide S-band (duplex) microwave radio frequency links directly with the ground (NEN), S-band (duplex) microwave RF links with the TDRSS (SN), Ka-Band (duplex) with TDRSS, and L-Band (receive-only) with the Global Positioning Satellite System (GPSS). The operating systems and waveforms within these radios are reconfigurable and will be changed (modified or replaced) during on-orbit operations.
Each SDR has an OE that provides a software infrastructure (including an operating system), command processing, interaction with hardware, and configuration of the SDR. All three OEs comply with the STRS standard. SDRs must run waveforms that implement the capability of the radio and generate the RF signal that will be transmitted. The OE does not actually generate or receive signals or perform communication functions — that is done by loadable waveforms that use the resources provided by the hardware platform and OE to communicate, network, or keep time (or anything else the experimenter wishes to do).
The RF subsystem enables the SDRs to transmit/receive RF signals from the SN and NEN and receive GPS signals through one of five antennas (3 fixed, 2 movable). The RF Subsystem is comprised of:
Traveling Wave Tube Amplifier (TWTA)
Three coaxial transfer switches
Transmission lines to interconnect the RF subsystem components with the SDRs.
The RF subsystem radiates RF signals intended for the TDRS and the ground and receives RF signals from the TDRS, the ground, and the GPS system. The architecture of the SCAN Testbed enables the ability to send RF signals from two separate SDRs to two antennas simultaneously. The RF subsystem interfaces with the avionics subsystem, the flight enclosure, the antenna pointing subsystem, and the three SDRs.
Antenna Pointing System (APS)
The APS allows the Ka-Band High Gain Antenna (HGA) and S-Band Medium Gain Antenna (MGA) to be moved to track TDRSS (or other experimenter-selected targets). The antenna pointing may be done in either open loop or closed loop mode. In the former, the antennas are pointed according to a precomputed track profile. In closed loop mode, the tracking algorithm uses signal strength information from the Ka-band radio to point the Ka-band HGA more accurately to the Ka-band source. The ISS is sufficiently large and flexible that open loop pointing of the Ka-band antenna may have pointing errors, reducing the maximum data rate that can be carried. The gimbaled antennas are locked for launch and deployed on-orbit.
The Avionics Subsystem provides general control and data handling, as well as supporting network routing. Just like the radios, the software loaded in the Avionics Subsystem will be changed for experiments. The radios are mounted to the Flight Enclosure and functionally interface with the Avionics and RF Subsystems.
Technology Benefits to Society
The ability to track signals from multiple GNSS receivers enables NASA to improve both space operations and science missions that benefit society as a whole, ranging from better observation of Earth for more precise weather forecasting, sea-level height measurements, and climate change monitoring. It also assists in improving understanding of Earth’s crustal movements and allows advanced tsunami warnings.
Some of the technologies developed as part of the SCaN program include a Ground-Based Inflatable Antenna from GATR Technologies that was originally developed as a solar concentrator for power generation as a technical requirement for SCaN. This technology was licensed exclusively and transferred to GATR Technologies to develop the inflatable antenna that was used to support communication efforts in the Haitian earthquake, Hurricane Katrina, and Hurricane Ike.
XCOM Wireless designed lightweight RF microelectromechanical systems (MEMS) that are used to improve satellite communication systems. The RF MEMS have the potential to outperform semiconductor technologies at increased speeds and less power.
General Dynamics Decision Systems’ Multi-Mode Transceiver brings the advantages of SCaN’s Tracking and Data Relay Satellite System to a variety of applications, including university satellite programs, small commercial Earth imaging programs, and Arctic and Antarctic science programs.
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