El martes, un avión L-1011 Stargazer despegará de las Islas Marshall, a 2.300 millas al suroeste de Hawaii. Un cohete caerá del avión y luego ascenderá para llevar una nave espacial llamada LINK a la órbita terrestre baja. LINK’s mission is to rescue one of the most scientifically productive astronomical facilities in operation: NASA’s Neil Gehrels Swift Observatory, which astronomers call “Swift.”
Swift se está hundiendo. El satélite ha orbitado la Tierra aproximadamente una vez cada hora y media durante más de dos décadas y, con el tiempo, la fricción con las partículas de la atmósfera superior ha provocado que su órbita decaiga. La actividad solar inusualmente intensa de los últimos años aceleró el declive. Si no se hace nada, la nave espacial y los tres telescopios a bordo se quemarán en la atmósfera en unos meses.
Para salvar a Swift, la NASA contrató a la empresa Katalyst Space Technologies, con sede en Arizona, para construir LINK. Katalyst had just nine months to design, construct, test and launch a satellite to do something that has never been done: grab a spacecraft that was not designed to be serviced (the “capture” stage of the mission), then carry it back to its original orbit (the “boost”). If it’s successful, the mission will demonstrate an important capability for the commercial space industry and give Swift decades more life at a much lower cost, in much less time, than it would have taken to build a new space observatory.
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Lo que estaba en juego en mi propia investigación quedó muy claro un día de febrero. As an astronomer, I did what I have done almost 100 times before: I filled out a short web form, called a “target of opportunity” (ToO) request, to ask Swift to swivel and point at a particular part of the sky. My colleagues and I had discovered a supernova in a distant galaxy there, and we urgently needed x-ray and ultraviolet data—the star had exploded only a few days before, and the glow from the debris would potentially soon be too faint to study. As usual, we turned to Swift, which is named for an agile, insect-chasing bird: despite being as long as a pickup truck, Swift can point toward anywhere in space within minutes. I expected a response within 24 hours, so when I didn’t hear anything for a day, I contacted a member of the operations team, who told me that Swift had stopped taking ToO requests in order to point in whatever direction minimized orbital drag. Sabía que Swift estaba en peligro, pero fue entonces cuando me di cuenta de que sin él no podría obtener los datos que necesitaba.
La captura es la etapa más arriesgada de la misión de LINK. El plan provisional es que los brazos robóticos de la nave espacial agarren paneles de metal sólido en las esquinas de Swift. But the observatory is covered in something like aluminum foil for thermal insulation, and no one knows what state this layer is in because no one has seen Swift up close for 20 years.
Ingenieros de Katalyst Space Technologies en Flagstaff, Arizona, estabilizan su nave espacial de servicio robótico LINK mientras se mueve hacia una cámara de vibración en el Centro de Vuelo Espacial Goddard de la NASA en Greenbelt, Maryland, el 15 de abril de 2026. La cámara de vibración simuló la intensa sacudida que LINK experimentará durante el lanzamiento.
When LINK arrives in orbit, it will first do a photoshoot, imaging Swift in different orientations and lighting conditions to figure out which part it should try to grasp. La fase de impulso de la misión es menos arriesgada que la captura, pero también complicada. Después de que LINK se apodere de Swift, LINK utilizará sus propulsores de propulsión iónica para empujar a la pareja a órbitas cada vez más altas durante varios meses. During that time, LINK must follow numerous rules about which direction the spacecraft can face in order to charge their solar panels and protect Swift’s mirrors and instruments. Cuando alcancen una altitud cercana a la órbita original de Swift, LINK los soltará. En este punto, los astrónomos tomarán el relevo para devolver al observatorio su papel como una de las herramientas más importantes para la astronomía transitoria.
La astronomía transitoria es el estudio de los fenómenos cósmicos que van y vienen en escalas de tiempo humanas, siendo las más famosas las explosiones de estrellas en forma de supernovas. Swift was originally designed to study a rare type of transient called gamma-ray bursts—seconds-long flashes of gamma-ray light that arise from the most energetic explosions in the universe. Swift has discovered almost 2,000 gamma-ray bursts and revolutionized our understanding of their origins, helping establish that they can come from merging neutron stars in addition to the explosions of single stars, and it has even found bursts from the earliest generations of stars in the universe.
Swift has also helped discover new and unexpected phenomena, driven by its users: any astronomer anywhere in the world can submit a ToO request on short notice. For example, in 2018 a ground-based optical facility called ATLAS (Asteroid Terrestrial-Impact Last Alert System) discovered a transient that was evolving so quickly and was so bright that astronomers all thought it must be some kind of foreground source in the Milky Way. Liliana Rivera Sandoval, now an assistant professor at the University of Texas Rio Grande Valley, submitted a ToO request to Swift, which to everyone’s surprise revealed bright x-rays—a sure sign it was much farther away and therefore much, much more energetic than something in our own galaxy. That event, AT2018cow (“the Cow”), turned out to be one of the most exciting objects I studied when I was a doctoral student and became the prototype of a fascinating new class of transients: today the menagerie includes events we nicknamed the Camel, the Tasmanian Devil and the Whippet. Sin Swift, probablemente nos habría llevado semanas en lugar de días convencernos de que la fuente era interesante.
Ningún otro telescopio existente o planificado puede observar múltiples rangos del espectro electromagnético simultáneamente y en tan poco tiempo. Además, Swift tiene la capacidad de asumir riesgos. In 2023, 87 percent of Swift’s time was spent on ToO observations: an average of five requests are received each day, and a small operations team evaluates the requests scientifically (“Is this interesting?”) and practically (“Is this doable?”). Swift receives more annual observing requests than any NASA facility except the James Webb Space Telescope, and its scientific portfolio is broad, extending to comets and planets in other solar systems.
Las capacidades de Swift son cada vez más importantes. So far transient astronomers have catalogued about 200,000 cosmic explosions, most discovered by optical telescopes when they are days or weeks old. Ahora el panorama de los descubrimientos se está transformando. Because of new facilities coming online soon, we’re about to discover huge numbers of transients in unexplored parts of the electromagnetic spectrum. For example, Israel’s ULTRASAT (Ultraviolet Transient Astronomy Satellite), launching in 2027, and NASA’s UVEX (Ultraviolet Explorer), set to go up in 2030, will be the first transient space telescopes dedicated to the high-energy ultraviolet part of the spectrum. Y se prevé que el Observatorio Rubin en Chile, inaugurado el año pasado, descubra 10 veces más transitorios que los telescopios ópticos anteriores. Los detectores de ondas gravitacionales deberían encontrar agujeros negros fusionados y estrellas de neutrones incluso en las partes más distantes del universo. And it will become much more common to discover explosions when they are just a few minutes old, thanks to facilities such as the Argus Array, under development in Texas.
Sin embargo, descubrir decenas de millones de posibles transitorios por noche no es suficiente. Necesitamos Swift para medir sus propiedades básicas, como la temperatura y el tamaño de la explosión. Swift will also help us figure out where exactly these explosions are taking place, enabling other telescopes to point there, too, and make decisions about which ones are unusual and therefore worth pursuing in more detail. If the LINK mission succeeds, it will give Swift a new lease on life at just the right time for us to answer longstanding questions about the most powerful explosions known in nature.