“`html
Chi Nguyen recalls the instance when she connected her laptop to a sizable monitor in a conference hall, prompting the audience to applaud. She was showcasing a group of scientists, engineers, and administrators at NASA’s Jet Propulsion Laboratory (JPL), which is overseen by Caltech, with the initial “aliveness test” image captured by the agency’s space telescope SPHEREx (Spectro-Photometer for the History of the Universe, Epoch of Reionization and Ices Explorer). The telescope successfully launched into the cosmos from Vandenberg Space Force Base in central California on March 11, 2025. On March 18, mission specialists directed the telescope’s lens cover to release; roughly a week later, SPHEREx took a picture, not of focused stars yet—that would occur later in a historic event termed “first light”—but an image to evaluate the health of the detectors.
“The image was stunning,” states Nguyen, a postdoctoral researcher at Caltech, whose responsibility was to meticulously characterize the detectors. “It appeared indistinct, similar to a photograph taken from a moving vehicle. This was anticipated because we had yet to instruct the spacecraft to maintain steady alignment, but this snapshot was sufficient to indicate that our detectors were functioning correctly. We exhaled deeply, knowing our years of effort were rewarded.”
Nguyen is a member of a small group of Caltech scientists, including post-baccalaureate and undergraduate students, who contributed to the construction and testing of the SPHEREx instrument, which encompasses the telescope, two focal-plane cameras, and readout electronics. The mission is currently active in space capturing 3,600 distinct images daily that encompass over 100 wavelengths of infrared light. Over the next two years, SPHEREx will survey the entire sky four times, creating 3D maps of hundreds of millions of galaxies in our universe. The mission’s scientific objectives include examining the formation of our universe, the development of galaxies, and interstellar ices in areas of our Milky Way galaxy where stars and planets come into existence.
The Caltech scientists collaborated closely with various partners to construct and test SPHEREx. BAE Systems developed the telescope and spacecraft, while the Korea Astronomy and Space Science Institute (KASI) created a customized testing chamber in a basement laboratory at Caltech. Caltech spearheaded the design and construction of the instrument electronics, while Caltech’s IPAC astronomy center devised the mission’s data pipeline—software that converts raw data into calibrated images and spectra (detailed analyses of the distinct wavelengths of light emanating from an object).
However, the most crucial partnership in creating the instrument was located just a brief 15-minute drive away. Teams from Caltech’s facility and JPL cooperated effectively to test SPHEREx and prepare it for launch into space.
“The success of SPHEREx underscores the close collaboration with JPL personnel, which thrived largely due to personal relationships built over decades,” notes Jamie Bock, the mission’s principal investigator, the Marvin L. Goldberger Professor of Physics at Caltech, and a senior research scientist at JPL.
Every group contributed their expertise. JPL excels in launching missions into space, while Bock’s team specializes in constructing instruments meticulously designed for cosmological measurements. For instance, some members of the SPHEREx team, including Bock, also developed instruments for the ongoing BICEP (Background Imaging of Cosmic Extragalactic Polarization) cosmology experiments at the South Pole.
“When you are involved in space missions, you can’t just grab a screwdriver and dive in,” explains Stephen Padin, a research professor of physics at Caltech and the SPHEREx optics team leader. “This is where the balance between the Lab and campus proves beneficial. JPL comprehends how meticulous one must be for a space mission, as repairs cannot be conducted once in orbit. Conversely, academic groups like ours are adept at designing, constructing, and testing astrophysical instruments. Merging that academic expertise with JPL’s knowledge leads to exceptional achievements.”
Bock concurs, emphasizing that campus and the Lab persist in exploring innovative methods to create lower-cost space missions. SPHEREx, he states, exemplifies an “instance of how the distinctive environment that harnesses expertise from Caltech and JPL operates effectively in practical terms.”
Not All Pixels Are Created Equally
Howard Hui, the mission’s calibration scientist, remarks that his experience with BICEP—a ground-based endeavor he began collaborating on with Bock as a graduate student in 2010—has been crucial for designing and testing SPHEREx. Similar to SPHEREx, the BICEP project aims to detect signatures from the dramatic emergence of our universe, an event known as cosmic inflation, during which our universe expanded by a trillion-trillion-fold within a fleeting moment. The microwave detectors at BICEP’s core continue to yield the most sensitive measurements to date for the type of cosmology it explores.
SPHEREx is on the hunt for a different array of signatures from the inflationary epoch. Although it employs a different sort of detector than BICEP, Hui asserts that his work on the ground-based telescope equipped him for the meticulous tasks required for a space mission like SPHEREx.
“We have dedicated the past three years to comprehending how our instrument operates,” he states. “There’s no such thing as a flawless experiment. There are artifacts emanating from Earth’s upper atmosphere, satellites, and our instrument. To examine inflation, we must understand all that noise thoroughly, enabling us to isolate it and accurately observe galaxies and other cosmic entities.”
One of Hui’s responsibilities involved characterizing the 24 million pixels constituting the SPHEREx detectors. “Each pixel exhibits a unique wavelength response which we must meticulously quantify,” Hui clarifies. “What distinguishes the SPHEREx team is our academic background in astrophysics coupled with extensive hands-on experience.”
Sapphire Window
To replicate the frigid conditions of outer space in their laboratory, the Caltech team collaborated with colleagues at KASI, who constructed a customized chamber the size of an SUV. This chamber cooled the instrument to frigid temperatures of minus 350 degrees Fahrenheit (approximately minus 200 degrees Celsius). Numerous tests were conducted within the chamber, including adjustments of the telescope’s focus and various measurements to calibrate and characterize the instrument’s detectors as well as its specialized spectrometers—devices that divide light into distinct colors.
A specialized gold-coated sapphire window facilitated the team in projecting an artificial star inside the chamber while deflecting ambient light away.
“The lab is illuminated at infrared wavelengths,” explained Phil Korngut, instrument scientist for SPHEREx, in a Caltech news article concerning the chamber testing. “We must prevent that troublesome thermal background light from entering the telescope as it would completely overwhelm the detectors.”
“`
Hui mentions that he, Korngut, and Brad Moore, the mission’s payload thermal engineer at JPL, journeyed to Korea to create the chamber alongside their KASI partners. “Our objective was to replicate the identical conditions that SPHEREx will experience in space,” Hui explains. “We were scheduled to return to Korea every few months, but then COVID struck, making the development process across continents more intricate.”
In the meantime, JPL associates, who had also contributed to various facets of the instrument’s design, came to campus to assist with testing. During this period, the telescope was transported to JPL for a shake test, which confirmed that SPHEREx’s delicate equipment could endure the tumultuous journey to space aboard a rocket.
Ultimately, after the instrument had been meticulously characterized, calibrated, and examined, it was dispatched to BAE Systems in Colorado for integration with the spacecraft ahead of the launch.
“Calibrating the instrument in space isn’t straightforward, so we aimed to comprehend as much about it as we could in our Caltech lab. I am passionate about the lab work and thrilled that we were deeply involved in characterizing the instrument,” Nguyen states. “We made it feasible for SPHEREx to gaze into the universe and precisely identify galaxies surrounding us.”
Besides SPHEREx, three additional NASA space missions of a comparable size class, referred to as Explorer missions, have been spearheaded by Caltech, including GALEX, NuSTAR, and the forthcoming UVEX. Notably, the NuSTAR team contributed their electronics specialists, led by Rick Cook of Caltech, to assist the SPHEREx team in constructing the instrument.
An academic environment also provided students working on the missions with exceptional, hands-on training. One SPHEREx team member, Sam Condon, who dedicated three years to the mission after completing college, was inspired to enroll in physics courses while working, so he could pursue graduate studies. He is currently pursuing his PhD in physics at Stanford University.
“There’s no other institution like Caltech, where, as a student, you can construct a space telescope in the basement of a laboratory,” Bock remarks. “It’s a unique place where NASA and academia intersect.”