X-Ray Vision: A KSJ Tour of Chandra

A composite image from several telescopes of a spiral galaxy, NGC 4258. X-rays photographed by Chandra are in blue.

 

Shortly after midnight on July 23, 1999, the space shuttle Columbia lifted off from Cape Canaveral, Florida, on a mission whose prosaic name — Shuttle Transportation System 93 — gave no hint of its soaring scientific promise. Soon the spacecraft and its five astronauts were hurtling through Earth’s atmosphere and into outer space, where they bade farewell to the rocket carrying the Chandra X-Ray Observatory satellite and released it to higher orbit.

On the afternoon of October 25, 2016, exactly 17 years, 94 days, and 16 hours into the mission, the Knight Science Journalism fellows arrived at the Chandra X-Ray Observatory Control Center. (The mission’s duration is displayed, to the second, on digital wall clocks.) The observatory monitors and maintains the satellite telescope, and also distributes the data to researchers by request. As Claude Canizares, the Chandra mission’s lead scientist and now the observatory’s associate director, noted, “The technology may be old, but it’s still the best in class and has yet to be superseded.”

The KSJ fellows received a private tour of the observatory, part of Harvard but located near MIT, on the seventh floor of a modern office building near Kendall Square in Cambridge. The X-ray satellite itself was built through a collaboration between the Smithsonian Institution and MIT on behalf of NASA. The observatory is overseen by the Smithsonian Astrophysical Observatory.

The satellite is the same size as the famous Hubble Space Telescope, launched in 1990, but there’s a big difference: Chandra looks at X-rays emanating from celestial objects rather than visible light. While visible light has been used for millennia to better understand the universe, X-rays permit astronomers to study more specific phenomena—like density, chemical composition, and temperature. For instance, green billows radiating from a star may signify the presence of iron, while blue in another image could indicate intense heat. X-rays allow scientists to view highly energetic and explosive entities, like neutron stars, black holes, and supernovas, which reach tens or hundreds of millions of degrees.

Claude Canizares with the KSJ fellows. Photo: Raleigh McElvery.

Canizares, a former vice president of MIT, explained that the field of X-ray astronomy began “not long ago and not far from here.” Just after World War II, scientists from the U.S. Naval Research Laboratory captured V-2 rockets from the Germans, and launched them into the atmosphere to measure X-rays from the Sun. But no one seriously considered examining higher-energy objects until after the war, when the MIT physics professor Bruno Rossi entered the scene.

Rossi teamed with MIT astronomers to submit a grant request to the Air Force. While the proposal involved examining solar X-rays reflected from the Moon, the Air Force was more interested in a second purpose — detecting possible Soviet nuclear blasts. Instead, the experiment wound up fulfilling a third, unforeseen aim when Rossi and his colleagues identified an entirely new source of X-rays: black holes.

While Rossi is heralded as the “grandfather” of X-ray astronomy, his successor Riccardo Giacconi (the “father” of the field) ultimately laid the groundwork for Chandra, earning the Nobel Prize in Physics in 2002. Since the satellite was slated to last only five years in outer space, Canizares likes to say, “It’s 17 years into its five-year lifetime.”

Chandra itself has three major components: First, the telescope, containing four pairs of mirrors that focus the incoming X-rays. Second, the array of scientific instruments that note the number, position, and energy of the rays. And finally, the spacecraft, which functions as the vessel for the entire operation. Since one side of the satellite is baked by the blistering Sun while the other faces cool, deep space, Chandra is wrapped in a protective covering similar to tinfoil.

Every 64 hours and 18 minutes, the spacecraft completes its large, elliptical orbit — about 6,200 miles by 87,000 miles, which takes Chandra more than a third of the way to the Moon before turning back. (The closest it comes to Earth is about 10,000 miles.)

Back at the observatory, controllers are busy at their computers processing the data and performing system checks. There’s a day shift and a “swing” shift, each of which lasts nine and a half hours.

The observatory receives requests from all over the world for this data, and the scientific proposals are reviewed once a year by a committee of researchers. In total, Chandra collects 70 million to 80 million seconds of observations each year.

The peek inside the control room left the KSJ fellows much to ponder, including the people behind the technology. “There’s an emotional component that fascinates me,” Maura O’Connor said. “One of the guys in the operations room said he was sitting in that very same seat when the satellite went into orbit, 17 years ago.”

Darell Wicker, operations controller at the observatory, talks about his work. Photo: Raleigh McElvery.