Abandoned cosmic-ray experiment awaits potential incineration

Nearly three years ago, a cosmic-ray experiment was abruptly canceled in a squabble between NASA and a University of Maryland (UMD)–led collaboration that operated the instrument. Now the device, which is mounted on the International Space Station (ISS), has moved one step closer to its destruction.

The Cosmic Ray Energetics and Mass for the ISS (ISS-CREAM) apparatus to detect and measure high-energy cosmic rays was moved from its original attachment point on the ISS’s Japanese Experiment Module last month. In its place is a three-instrument package of weather and gamma-ray instruments known as Space Test Program–Houston, which was launched on 21 December. Paul Hertz, director of NASA’s astrophysics program, says there are no plans to reactivate ISS-CREAM, and if its new ISS mooring spot is needed for another experiment, the instrument will be disposed of by reentry burnup.

NASA switched off ISS-CREAM in February 2019 after the collaboration, which included researchers from the Pennsylvania State University, Northern Kentucky University, and South Korea’s Sungkyunkwan University and Kyungpook National University, rejected the agency’s demands to install a new principal investigator (see Physics Today, June 2019, page 30 ). NASA was following the recommendation of its external review committee, which concluded that without new management, it was unlikely that the collaboration would produce substantial scientific results. NASA paid $22.4 million, and the Korean universities $10 million, to build ISS-CREAM, and the agency provided another $1.2 million a year to operate it. The instrument was attached to the ISS in August 2017.

Hertz says NASA had asked UMD to identify another principal investigator “to attempt to recover science return from the mission.” He says the university declined to offer an alternative. But ISS-CREAM team members said NASA had demanded that principal investigator Eun-Suk Seo of UMD be replaced by Scott Nutter, a Northern Kentucky University physicist who was the collaboration’s data manager. After most of the team members refused to accept Nutter’s appointment, NASA terminated the mission.

Seo says the collaboration had no recourse to the termination, which UMD, one of NASA’s largest grant recipients, didn’t contest. “There really was nothing we could do. If the project were bigger, maybe at the $100 million scale, we could have probably brought the issue up to Congress,” she says. “It’s sad because we tried to develop a space mission in a cost-effective way, and yet that very fact caught us.” Although NASA said that it would consider proposals to restart the instrument, Seo asserts that no one outside the ISS-CREAM collaboration could have legitimately taken over its operation.

The impact of ISS-CREAM’s loss on cosmic-ray physics is unclear. Seo says ISS-CREAM was the only space-based experiment that was optimized to measure hadrons, ranging from protons to iron nuclei, at energies of 10¹² eV to 10¹⁵ eV and higher. The origins of those particles, the most energetic subatomic particles known to science, remain a mystery. But two other instruments, the Japanese-led Calorimetric Electron Telescope (CALET) on the ISS and the Chinese-led Dark Matter Particle Explorer (DAMPE) satellite, were also designed to measure hadrons, plus electrons and gamma rays, in a similar energy range, says John Wefel, the Louisiana State University emeritus physics professor who is US spokesperson for CALET.

Yet ISS-CREAM’s loss has reduced the amount of hadron data collected, Wefel says. “In this ultrahigh-energy region, exposure is everything. Having multiple instruments operating increased the overall data set, allowing a greater chance for new discoveries.” CALET and DAMPE members have published results on the energy spectrum of hydrogen, carbon, oxygen, iron, and nickel nuclei, in addition to papers on electrons and gamma rays, he says.

Seo says that NASA terminated her grant with just two weeks’ notice and provided no funding for analyzing the data from ISS-CREAM. Most of her team had to find employment elsewhere. “Members presented five papers at last summer’s cosmic-ray conference, and others will be submitted for publication,” she says. “With the limited manpower, it takes some time. My students are working hard to complete the analysis.”