KENNEDY SPACE CENTER, Fla. — The next step in understanding some of the most energetic parts of the galaxy lifted off from the Space Coast at 1 a.m. Thursday. 

NASA launched the X-Ray Polarimetry Explorer (IXPE) mission on a SpaceX Falcon 9 rocket at 1 a.m. EST from the Kennedy Space Center.

The first-stage booster landed successfully on the droneship Just Read the Instructions in the Atlantic Ocean several minutes later.

While NASA has used other, larger observatories for X-ray astronomy, such as the Chandra X-Ray Observatory launched in 1999, the IXPE will be the first dedicated mission to observing what are known as polarized X-rays.

What is polarization?

Polarization, whether light or X-rays, is essentially the way electromagnetic waves are oriented as they travel through space. For instance, polarized sunglasses reduce reflective glare from something like a car or a body of water because that reflected light mostly vibrates in one direction and the lens is designed to filter that out.

Observing the polarization of objects that emit X-rays can tell astronomers more about them in ways not previously observable. 

“(An X-ray) comes from gases that are over a million degrees hot. And so, that X-ray comes from objects we’ve read about, like black holes, like pulsars, these amazing almost lighthouse structures, very compact stars or exploding stars,” said Dr. Thomas Zurbuchen, NASA’s associate administrator for science, in a NASA video explaining the IXPE mission. “That what X-rays are coming from.”

Martin Weisskopf, the IXPE principal investigator at NASA’s Marshall Space Flight Center (MSFC) in Huntsville, Ala., noted during the prelaunch press conference that X-ray astronomy has been around since about 1962, which is important because the kinds of objects that emit X-rays are some of the most fascinating.

“By doing this mission, we’re adding two variables to the astrophysics toolkit to understanding these sources: that’s the degree of polarization and the direction associated with the polarization,” Weisskopf said.

Having this information can tell us a great deal about some of these energetic objects, he said, but it depends on which object is being observed. One example he pointed two is that of a binary black hole system.

“Theoretical calculations show us that the degree of polarization as a function of energy, so look and see how polarization varies with energy for those systems,” Weisskopf said. “And if you do, you can measure the spin of the black hole. Black holes don’t have many properties, but one of them is spin. So this is a fascinating way of using the polarimetry to determine something about the source.”

The spacecraft

IXPE was developed as a primary collaboration between MSFC in Huntsville, Ala., and the Italian Space Agency and Ball Aerospace.

Florida-based Redwire Space also contributed two pieces of important hardware to the spacecraft — the company’s Rigid Solar Panel arrays that provide power and the 12 Coarse Sun Sensor (CSS) detectors that “provide payload protection and navigation capabilities for the spacecraft,” according to the company.

During a prelaunch press conference, Sandra Connelly, NASA deputy associate administrator for science, noted that IXPE is part of the Small Explorers (SMEX) missions that are part of the Explorers Program at NASA that focus on a single topic.

“We’re in a really interesting time. It’s the golden age of X-rays and gamma-rayed observations,” Connelly said. “We have multiple missions in that classification.”

She noted that so far, the only X-ray polarization of an object that’s been documented has been from the Crab Nebula.

“IXPE is sensitive enough, based on its detectors, to measure dozens and dozens of these types of objects,” Connelly said. “Understanding our galaxy and our place in the universe is awe-inspiring, and we want to make sure that we’re inspiring the future generation of our scientists and engineers. And this type of mission — our Small Explorers class as well as our CubeSats, smallsats, our sounding rockets and balloon programs — are all great platforms for new scientists and engineers to develop their skills.”

Makenzie Lystrup, the vice president and general manager of civil space at Ball Aerospace, noted that the design of the IXPE spacecraft is integral to its function, with a long, origami-like boom that folds out to separate the trio of identical telescopes from the detectors.

“This is critical because, due to the nature of X-rays and how we need to focus the light, the mirrors and the instruments have to be about 13 feet apart. That’s just the design of this telescope,” Lystrup said. “But you can’t fit that inside of a spacecraft fairing. So, what we do is we build it to fit inside of the rocket, and that boom compresses down to about 12 inches.”

The launch

The IXPE mission is the final mission of the year for the NASA Launch Services Program (LSP) managed at Kennedy Space Center. It is also the fifth mission that SpaceX has launched as a part of LSP.

The mission took off from Launch Complex 39A, the first time that a launch from LSP would have taken off from that pad. Tim Dunn, the IXPE launch director from LSP, said the reason SpaceX bid for that launch pad was because of a technical need from the spacecraft.

“The IXPE spacecraft is very sensitive to acoustic effects. So, those soundwaves that are generated at liftoff that can come back up and rattle the rocket before it leaves the pad vicinity,” Dunn said. “So as it turns out, Launch Complex 39A has a better water acoustic system than the other East Coast capability that SpaceX has over at Space Launch Complex 40.”

The previous launch for LSP was the planetary defense DART mission, which launched from Vandenberg Space Force Base in California about two weeks ago.

This was the second time SpaceX has used a flight-proven first-stage booster for an LSP mission.

The booster being flown on the IXPE mission was previously used to launch the following missions:

• Crew-1 – Nov. 15, 2020
• Crew-2 – April 23, 2021
• SXM-8 – June 6, 2021
• CRS-23 – Aug. 29, 2021

SpaceX conducted a unique type of launch maneuver to allow IXPE to reach an equatorial orbit or zero-degree inclination orbit. 

“What that means is, after two burns of our second stage, we’ll be deploying the spacecraft at an orbit that’s essentially parallel with the equator, which is quite performance intensive,” said Julianna Scheiman, the director for civil satellite mission for SpaceX. “So, despite IXPE actually being the lightest payload we’ve ever launched, it’s so performance-intensive that we’ll be landing the booster on the droneship Just Read the Instructions."