Sur le toit d'un bâtiment du MIT Lincoln Laboratory se trouve un boîtier d'antenne radio en forme de dôme de 38 pieds de large, ou radôme. À l'intérieur de l'environnement climatisé, à l'abri des intempéries de la Nouvelle-Angleterre, une structure en acier supporte une antenne de communication par satellite (SATCOM) de 20 000 livres et 20 pieds de diamètre. L'antenne, appelée Multi-Band Test Terminal (MBTT), peut pivoter de 15 degrés par seconde, effectuant une seule révolution en 24 secondes. À cette vitesse, le MBTT peut détecter et suivre des satellites en orbite terrestre moyenne et basse (moyenne et basse font référence à l'altitude à laquelle les satellites orbitent autour de la Terre).

Avant l'installation du MBTT en 2017, le laboratoire s'appuyait sur une variété d'antennes plus petites pour les tests SATCOM, y compris le terminal de test en bande Ka en direct, ou OTAKaTT. Comparé à l'antenne OTAKaTT de près de huit pieds de diamètre, le MBTT est sept fois plus sensible. Et contrairement à son prédécesseur, le MBTT, comme son nom l'indique, est conçu pour être facilement reconfiguré pour prendre en charge plusieurs bandes de radiofréquences (RF) utilisées pour les systèmes SATCOM militaires et commerciaux par satellite.

"En tant qu'outil de test beaucoup plus grand, plus puissant et plus flexible que l'OTAKaTT, le MBTT change la donne en permettant le développement de la technologie SATCOM avancée", déclare Brian Wolf, membre du personnel technique des systèmes et opérations Satcom avancés du Lincoln Laboratory. Groupe.

Wolf a participé à l'installation et à la mise en service initiale du MBTT en 2017. Il a ensuite dirigé le MBTT à travers un processus de certification rigoureux avec le U.S. Army Space and Missile Defense Command, achevé en 2019, démontrant que les performances de transmission et de réception de l'antenne étaient suffisant pour qu'il fonctionne sur le système Wideband Global SATCOM (WGS). Constellation de 10 satellites détenus et exploités par le département américain de la Défense, WGS fournit une connectivité à haut débit entre différents points sur Terre. Depuis 2019, Wolf est chercheur principal sur un projet qui possède le MBTT, soutenant le développement des capacités SATCOM tactique anti-brouillage (PATS) de l'US Space Force.

"PATS développe la capacité de fournir des services de forme d'onde tactique protégée, ou PTW, sur WGS, ainsi que sur des satellites transpondeurs commerciaux et de nouveaux satellites DoD avec un traitement PTW embarqué dédié", déclare Wolf.

Comme l'explique Wolf, une forme d'onde est le signal transmis entre deux modems lorsqu'ils communiquent, et PTW est un type spécial de forme d'onde conçu pour fournir des communications hautement sécurisées et résistantes au brouillage. Le brouillage fait référence au moment où les signaux de communication sont perturbés, soit accidentellement par des forces amies (qui, par exemple, peuvent avoir mal configuré leur équipement SATCOM et transmettent à la mauvaise fréquence), soit intentionnellement par des adversaires cherchant à empêcher les communications. Lincoln Laboratory a commencé à développer PTW en 2011, contribuant à la conception initiale et à l'architecture du système. Au cours des années qui ont suivi, le laboratoire a participé à des efforts de prototypage et de test pour aider l'industrie à faire mûrir les modems pour le traitement de la forme d'onde.

"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. + Explorer plus loin

Flight testing validates waveform capability

Cette histoire est republiée avec l'aimable autorisation de MIT News (web.mit.edu/newsoffice/), un site populaire qui couvre l'actualité de la recherche, de l'innovation et de l'enseignement du MIT.