A white box the size of a refrigerator, called Cosmic Ray Energetics and Mass (CREAM), will head to the International Space Station (ISS) this month, thanks to the work of UMBC astrophysicist Jason Link and colleagues. Inside, four scientific detectors will work together to detect cosmic rays coming from far flung regions of the universe. The instruments will transmit the data from the ISS to Earth, to scientists reckoning with the tantalizing question, “What is the universe made of?”
Link, an astrophysicist with UMBC’s Center for Space Science and Technology, part of the recently-renewed CRESST consortium, is a co-investigator on the project and the technical lead for one of the detectors. Cosmic rays, particles from beyond the solar system, arrive with hundreds of times more energy than the Large Hadron Collider particle accelerator can produce, Link explains. Some of these particles will pass through the detector and interact inside, where they break up into a “shower of subatomic particles.” CREAM’s goal is to measure the composition and energy of individual particles, which will help scientists deduce where the rays came from and what phenomena caused them to accelerate so much.
Are the particles produced by supernovae or perhaps merging binary stars? “If we get into what accelerates the cosmic rays, we’re getting into one of the murky mysteries of science,” Link says.
Link has been working for more than 15 years on hardware to detect cosmic rays, including a version of CREAM that has taken seven balloon flights above Antarctica. Sending instruments to space poses new challenges, and also creates new opportunities.
“Balloons have a relatively short mission life,” Link shares, usually only a few dozen days. “But going up on the space station, you’re now talking about years.” Also, “When particles enter Earth’s atmosphere, they start to interact,” Link says. That means data analyses must incorporate a correction factor to account for these interactions, which introduces error. That’s much less of a problem in space.
Research instruments traveling to the ISS must reckon with constraints on size and mass, and be able to withstand extreme vibration. Link’s balloon-based instruments didn’t fit these constraints, so he and colleagues from NASA Goddard Space Flight Center, Penn State, and Northern Kentucky University undertook the challenge of building a new detector, based on the balloon detectors, that could safely survive the rigors of a rocket launch and deploy on the International Space Station.
The new detector can also collect additional scientific measurements. It can distinguish between negatively charged electrons and positively charged protons, based on the way they interact inside the detector.
“Designing a new detector from scratch on the limited budget for building balloon hardware required creativity, innovation and a bit of luck,” Link notes. “We did it and it successfully passed all of the environmental and safety requirements for deployment on the ISS.”
Colleagues from Kyungpook National University in South Korea built a detector that serves the same purpose, but with a different approach. Together, Link says, the two detectors provide a powerful way to distinguish between electrons and protons, and quickly verify findings, specifically because they use different techniques.
Link looks forward to diving into the data the instruments send from outer space. “If we see an excess of electrons,” he says, “that suggests that there is a local source of cosmic rays. That’s not something we expect.” That discovery would spur further research into what and where the source might be.
Instruments on CREAM will also help physicists better understand the “cosmic energy spectrum,” Link says. The energy of detected rays falls along a spectrum, with many more rays coming in with lower energies, and very few at the highest energies. The number of rays at each energy level falls off in a smooth curve, but, Link says, “There’s a kink in the cosmic energy spectrum,” where there’s an unexpected bump up in the number of rays with a specific energy. Scientists are very interested in what might be causing that kink, and CREAM is intended to help explain it.
Beyond the potential for groundbreaking scientific discovery about the fundamental makeup of the universe, the CREAM launch is special for Link. “This is the first time that I’ve actually built something that’s going to go into space,” he says.
Scientists are often heavily involved in designing instruments and analyzing the resulting data, but most of the time the actual construction of space instrumentation is handed over to engineers and technicians with specialized expertise. Not this time. “Yes, I actually tightened bolts and wired sensors on the detector,” Link is proud to report, “and it’s going to fly in space.”
Image: Sunrise from the International Space Station. Photo provided by NASA, captured by a member of the Expedition 52 crew.
The CREAM mission is headed by Dr. Eun-Suk Seo at the University of Maryland, College Park. NASA’s Wallops Flight Facility in Virginia provided overall management of CREAM and integration for space station deployment, led by Linda Thompson. The full project team includes scientists from the United States, France, Mexico, and South Korea.