En la azotea de un edificio del Laboratorio Lincoln del MIT se encuentra un recinto de antena de radio en forma de cúpula de 38 pies de ancho, o radomo. Dentro del entorno de clima controlado, protegido del clima de Nueva Inglaterra, una estructura de acero sostiene una antena de comunicaciones satelitales (SATCOM) de 20,000 libras y 20 pies de diámetro. La antena, llamada Terminal de prueba multibanda (MBTT), puede girar 15 grados por segundo, completando una sola revolución en 24 segundos. A esta velocidad, el MBTT puede detectar y rastrear satélites en órbita terrestre media y baja (media y baja se refieren a la altitud a la que los satélites orbitan la Tierra).

Antes de la instalación del MBTT en 2017, el laboratorio dependía de una variedad de antenas más pequeñas para las pruebas de SATCOM, incluida la terminal de prueba de banda Ka por aire, o OTAKaTT. En comparación con la antena OTAKaTT de casi dos metros y medio de diámetro, la MBTT es siete veces más sensible. Y a diferencia de su predecesor, el MBTT, como sugiere su nombre, está diseñado para reconfigurarse fácilmente para admitir múltiples bandas de radiofrecuencia (RF) utilizadas para sistemas satelitales militares y comerciales SATCOM.

"Como un activo de prueba mucho más grande, más poderoso y más flexible que OTAKaTT, el MBTT es un cambio de juego para permitir el desarrollo de tecnología SATCOM avanzada", dice Brian Wolf, miembro del personal técnico en Advanced Satcom Systems and Operations de Lincoln Laboratory. Grupo.

Wolf participó en la instalación y puesta en marcha inicial del MBTT en 2017. Luego dirigió el MBTT a través de un riguroso proceso de certificación con el Comando de Defensa de Misiles y Espacio del Ejército de los EE. UU., completado en 2019, demostrando que el rendimiento de transmisión y recepción de la antena era suficiente para operar en el sistema Wideband Global SATCOM (WGS). Una constelación de 10 satélites propiedad y operados por el Departamento de Defensa de los EE. UU., WGS proporciona conectividad de alta velocidad de datos entre varios puntos de la Tierra. Desde 2019, Wolf se ha desempeñado como investigador principal en un proyecto que posee el MBTT, apoyando el desarrollo de las capacidades SATCOM Tácticas Antiinterferencias Protegidas (PATS) de la Fuerza Espacial de EE. UU.

"PATS está desarrollando la capacidad de brindar servicios de forma de onda táctica protegida, o PTW, sobre WGS, así como sobre satélites de transpondedores comerciales y nuevos satélites del Departamento de Defensa con procesamiento de PTW integrado dedicado", dice Wolf.

Como explica Wolf, una forma de onda es la señal que se transmite entre dos módems cuando se comunican, y PTW es un tipo especial de forma de onda diseñado para proporcionar comunicaciones altamente seguras y resistentes a interferencias. La interferencia se refiere a cuando las señales de comunicación son interferidas, ya sea accidentalmente por fuerzas amigas (quienes, por ejemplo, pueden haber configurado mal su equipo SATCOM y están transmitiendo en la frecuencia incorrecta) o intencionalmente por adversarios que buscan evitar las comunicaciones. Lincoln Laboratory comenzó a desarrollar PTW en 2011, contribuyendo al diseño inicial y la arquitectura del sistema. En los años transcurridos desde entonces, el laboratorio ha participado en los esfuerzos de creación de prototipos y pruebas para ayudar a la industria a madurar los módems para procesar la forma de onda.

"Our prototype PTW modems have been fielded to industry sites all over the country so vendors can test against them as they develop PTW systems that will be deployed in the real world," says Wolf. The initial operating capability for PTW services over WGS is anticipated for 2024.

Staff originally conceived the MBTT as a test asset for PTW. Directly underneath the MBTT is a PTW development lab, where researchers can run connections directly to the antenna to perform PTW testing.

One of the design goals for PTW is the flexibility to operate on a wide range of RF bands relevant to satellite communications. That means researchers need a way to test PTW on these bands. The MBTT was designed to support four commonly used bands for SATCOM that span frequencies from 7 GHz to 46 GHz:X, Ku, Ka, and Q. However, the MBTT can be adapted in the future to support other bands through the design of additional antenna feeds, the equipment connecting the antenna to the RF transmitter and receiver.

To switch between the different supported RF bands, the MBTT must be reconfigured with a new antenna feed, which emits signals onto and collects signals from the antenna dish, and RF processing components. When not in use, antenna feeds and other RF components are stored in the MBTT command center, located underneath the main platform of the antenna. The feeds come in a range of sizes, with the largest registering six feet in length and weighing nearly 200 pounds.

To swap out one feed for another, a crane inside the radome is used to lift up, unbolt, and remove the old feed; a second crane then lifts the new feed up into place. Not only does the feed on the front of the antenna need to be replaced, but all of the RF processing components on the back of the antenna—such as the high-power amplifier for boosting satellite signals and the downconverter for converting RF signals to a lower frequency more suitable for digital processing—also need to be replaced. A team of skilled technicians can complete this process in four to six hours. Before scientists can run any tests, the technicians must calibrate the new feed to ensure it is operating properly. Typically, they point the antenna onto a satellite known to broadcast at a specific frequency and collect receive measurements, and point the antenna straight up into free space to collect transmission measurements.

Since its installation, the MBTT has supported a wide range of tests and experiments involving PTW. During the Protected Tactical Service Field Demonstration, a PTW modem prototyping effort from 2015 to 2020, the laboratory conducted tests over several satellites, including the EchoStar 9 commercial satellite (which offers broadband SATCOM services, including satellite TV, across the country) and DoD-operated WGS satellites. In 2021, the laboratory used its PTW modem prototype as the terminal modem to conduct an over-the-air test of the Protected Tactical Enterprise Service—a ground-based PTW processing platform Boeing is developing under the PATS program—with the Inmarsat-5 satellite. The laboratory again used Inmarsat-5 to test a prototype enterprise management and control system for enabling resilient, uninterrupted SATCOM. In these tests, the PTW modem prototype, flying onboard a 737 aircraft, communicated through Inmarsat-5 back to the MBTT.

"Inmarsat-5 provides a military Ka-band transponded service suitable for PTW, as well as a commercial Ka-band service called Global Xpress," explains Wolf. "Through the flight tests, we were able to demonstrate resilient end-to-end network connections across multiple SATCOM paths, including PTW on military Ka-band and a commercial SATCOM service. This way, if one satellite communications link is not working well—maybe it's congested with too many users and bandwidth isn't sufficient, or someone is trying to interfere with it—you can switch to the backup secondary link."

In another 2021 demonstration, the laboratory employed the MBTT as a source of modeled interference to test PTW over O3b, a medium-Earth-orbit satellite constellation owned by the company SES. As Wolf explains, SES provided much of their own terminal antenna equipment, so, in this case, the MBTT was helpful as a test instrument to simulate various types of interference. These interferences ranged from misconfigured users transmitting at the wrong frequencies to simulation of advanced jamming strategies that may be deployed by other nation states.

The MBTT is also supporting international outreach efforts led by Space Systems Command, part of the U.S. Space Force, to extend the PATS capability to international partners. In 2020, the laboratory used the MBTT to demonstrate PTW at X-band over SkyNet 5C, a military communications satellite providing services to the British Armed Forces and coalition North Atlantic Treaty Organization forces.

"Our role comes in when an international partner says, "PTW is great, but will it work on my satellite or on my terminal antenna?'" explains Wolf. "The SkyNet test was our first using PTW over X-band."

Connected via fiber-optic links to research facilities across Lincoln Laboratory, the MBTT has also supported non-PTW testing. Staff have tested new signal processing technology to suppress or remove interference from jammers, new techniques for signal detection and geolocation, and new ways of connecting PTW users to other Department of Defense systems.

In the years ahead, the laboratory looks forward to performing more testing with more user communities in the Department of Defense. As PTW reaches operational maturity, the MBTT, as a reference terminal, could support testing of vendors' systems. And as PTS satellites with onboard PTW processing reach orbit, the MBTT could contribute to early on-orbit checkout, measurement, and characterization.

"It's an exciting time to be involved in this effort, as vendors are developing real SATCOM systems based on the concepts, prototypes, and architectures we've developed," says Wolf. + Explora más

Flight testing validates waveform capability

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