An experiment led by researchers at Washington University in St. Louis is one step closer to space.
The Trans-Iron Galactic Element Recorder for the International Space Station (TIGERISS) was officially assigned an attachment location on the Columbus laboratory module of the International Space Station (ISS). This location assignment is a milestone on the path to a targeted 2027 launch date, researchers said.
“TIGERISS is finally real to the ISS,” said Brian Rauch, research associate professor of physics in Arts & Sciences and principal investigator for the project. Rauch has led the TIGERISS mission since it was selected for development under the NASA Astrophysics Pioneers program in 2022.
The experiment will measure the abundances of ultra-heavy galactic cosmic rays, increasing scientists’ understanding of how the galaxy produces and distributes the elements.
TIGERISS is the first instrument capable of measuring cosmic ray abundances with single-element resolution spanning the periodic table from boron to lead. It is an evolution of the TIGER and SuperTIGER instruments — also built by teams led by physicists W. Robert Binns and Martin Israel, now both professors emeriti in Arts & Sciences, and flown on stratospheric balloons from Antarctica.
“The exciting part about this effort is going from balloons to space,” said Rauch, who is a faculty fellow of the university’s McDonnell Center for the Space Sciences. “Much of what is known about heavier elements in galactic cosmic rays comes from the predecessor TIGER and SuperTIGER balloon-borne instruments.”
The term “cosmic rays” is actually misleading as they are not rays at all. In the early 1900s, when cosmic rays were first discovered, they were thought to be made of electromagnetic radiation. However, within a few decades, experimental data showed that cosmic rays were actually made from pieces of atoms: protons, electrons and atomic nuclei.
These high-energy particles were set in motion by supernova shock waves and constantly bombard the Earth. For scientists, cosmic rays represent one of the few direct samples of matter from outside the solar system. “The entire periodic table is out there, but the stuff above iron is very rare,” Rauch said. “What we are hoping to do, for the first time, is to measure the abundances of elements up to lead in the cosmic rays, and then to compare that with the solar system.
“The fundamental question that we’re trying to answer is where the matter that makes up our world comes from,” he said.
The TIGERISS mission was designed to address important questions from the National Academies of Sciences, Engineering and Medicine’s Decadal Survey on Astronomy and Astrophysics 2020 — specifically, are neutron star mergers the main site of r-process nucleosynthesis, or are there supernovae and other core collapse events that contribute significantly to the r-process budget of the universe?
Mounted on the space station, TIGERISS will orbit the Earth about 250 miles above sea level, completing one circuit every 90 minutes. From this vantage point, the experiment will use a unique combination of silicon and Cherenkov light detectors to measure ultra-heavy galactic cosmic rays.
TIGERISS will occupy one of four exterior mounting platforms on the Columbus laboratory module. “There’s a rectangle-shaped frame that acts as a support structure,” Rauch said. “We will be mounted on one of the side platforms, where we can intercept particles heading toward the Earth.”
“We’re happy to finally have our spot on the station,” said Wolfgang Zober, a postdoctoral research associate in physics in Arts & Sciences and project scientist for TIGERISS. “That placement allowed us to go from having two significantly different designs to just being able to focus on the one that we’re actually building.”
The mechanical structure design is now very mature, Zober said. Most of the TIGERISS payload electronics have advanced from prototyping to nearly completed flight designs.
“We are preparing to fabricate engineering demonstration units for the aerogel and silicon detector mounting schemes and to test them under launch vibration conditions,” he said. “Our thermal control system design is advanced enough to have preliminary sizing of the thermal radiator panels, as shown as the flat panels on the left and top sides in the payload model. The right side is the top of the instrument that faces to zenith (away from the Earth).”
WashU is leading the overall TIGERISS project implementation, as well as the science, integration, testing and outreach. Certain parts of the mechanical structure, as well as the detector electronic boards and cable harnessing, will be built at the physics shop on the Danforth Campus.
Richard Bose, a senior research engineer in physics, is developing the readout electronics for the new silicon strip detector, while Izabella Pastrana, a research engineer in physics, is working on test electronics and a digital control board. Lindsey Lisalda, a postdoctoral research associate in physics, will be involved with TIGERISS integration and testing activities.
Other contributing institutions include NASA’s Goddard Space Flight Center; NASA’s Wallops Flight Facility; Howard University; Pennsylvania State University; University of Maryland, Baltimore County; and Northern Kentucky University.
NASA has announced plans to decommission the ISS in the early 2030s. “Our initial target for our experiment is one year, but we hope to stay on until the end of the space station,” Rauch said.
