Communication is key to just about any endeavor. NASA’s ability to update and modify communication capabilities to reflect the latest upgrades without impacts to mission time or a trip back to Earth ensures optimal communication continues. In-orbit reconfiguration for spacecraft radios and systems, including those on the International Space Station, is the goal behind NASA’s Space Communications and Navigation (SCaN) Testbed.

From its invention until now, the radio has undergone some mighty technological advances. Conventional or legacy radios are not programmable; they are designed for one fixed configuration. They are built to produce a single waveform at a specified frequency. Conventional radios often also have limited tuning options and fixed data rates. While some conventional radios carry multiple types of data, they are incapable of adapting to new waveforms. To make changes on these legacy radios, the radio would physically need to be changed. Once a radio is out in space, that task becomes nearly impossible to accomplish. These limitations created a need for improved communication in space.

Ground testing and processing of SCAN Testbed hardware. (JPL)

NASA engineers needed radios to be more flexible, adaptable, and evolvable. In the late 20th century, a new type of radio was developed that would be able to meet those needs. Software defined radios (SDR) are a type of reconfigurable radio in which some or all of the physical layers of functionality are implemented in software and/or firmware.

SDR is a relatively new wireless technology based on the familiar radio technology that has been used for many years. Traditional Earth-based radio technology involves the transmission of a signal — typically “analog” speech or music — as electromagnetic waves using a single-purpose radio transmitter. The electromagnetic waves travel through the air until they encounter a radio receiver that has been tuned to receive the right frequency. This receiver processes the signal and sends the result to a speaker. You then hear whatever was broadcast from the radio station. In SDR, the transmitter mod u lation is produced by a digital signal processor to produce digital signals; the signals are then converted to “analog” and sent to the transmitter’s antenna. The receiver uses a computer to recover the signal intelligence.

"For NASA, SDR applies to the transmission of data, rather than sound," said Jason Soloff, an SDR technologist at NASA’s Goddard Space Flight Center in Greenbelt, MD. However, Soloff adds that you may be most familiar with the sound-related commercial applications of SDR. "When you are in your car, and you use your MP3 player to receive an FM signal digitally, you are using SDR-like technology. Or, when you travel from an area with an analog cellphone signal to a digital signal, and your phone switches automatically, your phone is acting as a software defined or reconfigurable radio."

Glenn Research Center engineers prepare the SCaN Testbed flight system hardware for thermal-vacuum testing. (NASA)
With SDR, manufacturers could install a generic radio chip into electronic devices and later “educate” them to perform functions quite different than their original job through a simple software download. Similarly, engineers could reconfigure future SDR-enabled NASA missions at will, allowing formerly independent satellites to be linked and give a more complete picture of a unique scientific event. In other applications, two satellites could interact and share information, or an older satellite could be updated with a new function and mission, extending its life and usefulness.

"Many of our current satellites were developed with a fixed set of data rates and modulations, so they can only talk to the ground or the space network," said Soloff. "SDR would allow us to switch between a ground network and a space network with simple uploads, making the satellite or instrument much more flexible."

The growth of SDRs offers NASA the opportunity to improve the way space missions develop and operate space transceivers for communications, networking, and navigation. Reconfigurable SDRs with communications and navigation functions implemented in software 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.

An On-Orbit Testbed

External image of ISS showing SCAN Testbed installed on ELC 4 nadir side. (NASA)
The NASA Space Communications and Navigation (SCaN) Program is responsible for providing communications and navigation services to spaceflight missions throughout the solar system. Astronauts, mission controllers, and scientists depend upon the reliable transmission of information between Earth and spacecraft, from low-Earth orbit to deep space. The SCaN Testbed, designed and built at NASA’s John Glenn Research Center in Cleveland, OH, is an advanced integrated communications system and laboratory facility that was installed on the International Space Station (ISS) in July 2012. Using a new generation of SDR technologies, this ISS facility allows researchers to develop, test, and demonstrate new communications, networking, and navigation capabilities in the actual environment of space.

NASA’s SCaN office 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, as well as methods of instantiation, operation, and testing among different compliant hardware and software products. These common interfaces within the architecture remove the application software from the underlying hardware to enable technology insertion independently at either the software or hardware layer.

The SCaN Testbed began conducting experiments last April after completing its checkout and commissioning operations aboard the ISS. The testbed is installed on the EXPRESS Logistics Carrier-3 on the ISS truss. The installation, activation, checkout, and commissioning activities resulted in a healthy report card for the launch software, the three software defined radios (SDRs), and the antennas, avionics, and other subsystems.

The testbed's purpose is to allow for the development, testing, and demonstration of cutting-edge communications, networking, and navigation technologies in the challenging environment of space. These advances will enable technology developers and mission planners to understand how NASA can use SDRs in future missions, as well as develop new concepts such as new algorithms for determining orbits using GPS. The technology also can help advance similar communications tools here on Earth. SDRs are a viable technology for ground-based platforms, and are already being used in smartphones and other terrestrial applications. NASA's support for a common, open architecture aids in the development of open standards for other domains beyond space.

The testbed is the first space hardware to provide an experimental laboratory to demonstrate many new capabilities, including new communications, networking, and navigation techniques that utilize SDR technology. Research and technology areas the SCAN Testbed was designed to support include SDRs operating at S, L, and Ka-band; onboard data management function and payload networking; radio science experiments using the unique capabilities of the SDRs; and precise navigation and timing.

“A software defined radio is purposely reconfigured during its lifetime, which makes it unique,” said Diane Cifani Malarik, a project manager for the SCaN Testbed. This is made possible by software changes that are sent to the device, allowing scientists to use it for a multitude of functions, some of which might not be known before launch. Traditional radio devices cannot be upgraded after launch.

By developing these devices, future space missions will be able to return more scientific information, because new software loads can add new functions or accommodate changing mission needs. New software loads can change the radio's behavior to allow communication with later missions that may use different signals or data formats.

The SCaN Testbed is comprised of three SDRs, each with unique capabilities aimed at advancing different aspects of the technology. These devices will be used by researchers to advance this technology over the testbed's five-year planned life in orbit. Two SDRs were developed under cooperative agreements with General Dynamics and Harris Corp., and the third was developed by NASA's Jet Propulsion Laboratory (JPL) in Pasadena, CA. JPL also provided the five-antenna system on the exterior of the testbed that’s used to communicate with NASA's orbiting communications relay satellites and NASA ground stations across the United States.

NASA Glenn led the design, development, integration, test, and evaluation effort, and provided all the facilities needed to fabricate, assemble, and test the SCaN Testbed, including a flight machine shop, large thermal/vacuum chamber, electromagnetic interference testing with reverberant capabilities, a large cleanroom, and multiple antenna ranges, including one inside the cleanroom.

"The SCaN Testbed represents a significant advancement in SDRs and its applications for NASA," said David Irimies, a project manager for the testbed at NASA Glenn. "Investigating these SDR technologies in the dynamic space environment increases their technology readiness level and maturity, which in turn can be used for future missions as risk reduction."

The future of communications aboard the space station will improve with the SCaN Testbed's ability to update and modify capabilities with minimal impacts to crew and mission. This technology also stands to provide time and cost savings for future hardware platforms. With the ability for industry and government agencies to partner with NASA to use the SCaN Testbed, this development can advance space communications of today and tomorrow.


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Aerospace & Defense Technology Magazine

This article first appeared in the February, 2014 issue of Aerospace & Defense Technology Magazine.

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