SpaceX and NASA are set for the launch of the agency’s newest space telescope and solar research mission. A Falcon 9 will liftoff from California with the Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer (SPHEREx) near-infrared observatory, with the Polarimeter to Unify the Corona and Heliosphere (PUNCH) heliophysics mission flying as a rideshare.
During its mission, SPHEREx will complete surveys of the entire sky in optical and near-infrared light, observing over 450 million galaxies and more than 100 million stars in the Milky Way. From these surveys, scientists will identify the source of the early universe’s inflation and search for organic molecules throughout the universe. Meanwhile, PUNCH will utilize four small satellites to investigate the Sun’s inner heliosphere and how the corona becomes solar wind.
Falcon 9 is scheduled to liftoff from Space Launch Complex 4E (SLC-4E) at Vandenberg Space Force Base in California on Saturday, March 8, at 7:10 PM PST (03:10 UTC on March 9).
Falcon booster B1088 will support this mission. Following liftoff and stage separation, the booster will return to the launch site and perform a landing at Landing Zone 4 (LZ-4), located just a couple hundred meters west of SLC-4E. This launch will serve as B1088’s third flight, having previously flown the Transporter 12 and NROL-126 missions from Vandenberg.
Falcon 9 will launch on a southwestern trajectory out of Vandenberg, flying SPHEREx and PUNCH to a Sun-synchronous orbit. In total, SPHEREx and PUNCH mass 256 kg. Assuming an on-time launch, this mission will mark the 445th Falcon 9 mission, the 27th SpaceX mission of 2025, and the 45th orbital launch attempt of 2025 worldwide.
SPHEREx
Designed as a medium-class mission within NASA’s Explorers program, SPHEREx was selected by NASA for funding and development in February 2019. The mission is managed by NASA’s Jet Propulsion Laboratory (JPL) in California, with James Bock of the California Institute of Technology (Caltech) serving as principal investigator.
SPHEREx’s first proposal was submitted to NASA in December 2014 and was subsequently selected for continued development as part of the Small Explorer Program (SMEX) in July 2015. However, SPHEREx’s proposal was ultimately not selected for funding as part of SMEX, and the SPHEREx team resubmitted an upgraded proposal for SPHEREx as a Medium-Class Explorer (MIDEX) mission in December 2016. The SPHEREx MIDEX proposal was selected as a finalist in August 2017 and was later announced as the winner in February 2019.
SPHEREx entered Phase C of NASA’s Project Life Cycle in January 2021, allowing mission teams to finalize the mission’s design and begin constructing and assembling spacecraft components. NASA selected SpaceX’s Falcon 9 to launch the mission in February 2021 and announced the addition of PUNCH as a rideshare payload in August 2022.
SPHEREx fully assembled, with the three photon shields visible. (Credit: BAE Systems/NASA/JPL-Caltech)
The observatory was fully assembled by April 22, 2024, and entered final testing soon after. These tests were conducted in late 2024 and, following completion, SPHEREx was shipped to Vandenberg for final integration with the Falcon 9 upper stage and payload fairing encapsulation.
Rather than relying on a suite of highly technical instruments, SPHEREx will utilize a single, wide-field aluminum telescope instrument designed for a single observing mode in either visible or near-infrared light. This telescope features three mirrors, an aperture diameter of 20 cm, and six mercury cadmium telluride photodetector arrays. These characteristics give the telescope an 11 degree by 3.5 degree field of view, with the telescope obtaining spectra through multiple exposures and placing an object at different positions within its field of view. Observing an object at different locations within the telescope will allow SPHEREx to measure the light from the object across multiple wavelengths.
SPHEREx also features six linear variable filters (LVF). These LVFs produce spectra, and do so by the telescope moving in the wavelength-varying directions of the LVFs — a method that was proven on NASA’s New Horizons mission to Pluto with the LEISA instrument.
Sectional view of SPHEREx, with the three photon shields, telescope, and solar panel visible. (Credit: NASA/JPL-Caltech/SPHEREx)
Extending away from the telescope is SPHEREx’s three-stage V-groove system, which gives the observatory its recognizable conical shape and allows for the cooling of its optics and internal systems. This three-stage V-groove design consists of three nested photon shields that protect the spacecraft’s cooler and telescope optics from radiation emitted by the Sun, Earth, and the spacecraft. Like the James Webb Space Telescope, SPHEREx must be cooled to extremely low temperatures of less than 55 degrees Kelvin to ensure that any heat from the observatory doesn’t interfere with infrared observations, as a significant portion of infrared light is emitted as heat.
Diagram showing the design of SPHEREx’s mirror. (Credit: SPHEREx)
The design of SPHEREx is simple, robust, and efficient, requiring no moving parts except for the jettison of the telescope’s aperture cover early in the mission. SPHEREx’s telescope will collect surveys of the entire sky approximately once every six months. During these observations, the observatory will collect 0.75 to 5.0 micrometer near-infrared spectral data on galaxies and stars, creating the most colorful sky map ever.
SPHEREx’s primary mission is set to last approximately 25 months and achieve three main scientific objectives: constrain the physics of cosmic inflation, trace the history of galactic light production, and investigate the presence and characteristics of water and biogenic ices in young star systems.
Cosmic inflation was a phenomenon that occurred in the very early universe, wherein the universe began to expand at an extremely rapid, exponential rate in the moments immediately following the Big Bang. This cosmic inflation is at the backbone of much of modern cosmology and is generally responsible for the shape of our universe and its smoothness. Using measurements from telescopes, cosmologists have been able to discern the rates of cosmic inflation well, however, the exact processes that drove cosmic inflation are still very unknown. Understanding cosmic inflation is among the most sought-after goals in all of cosmology.
SPHEREx will enable scientists to learn more about the universe’s inflationary processes by investigating the three-dimensional distribution of galaxies via the measurement of galaxy redshifts. Redshifting is a phenomenon in physics in which light is stretched due to increasing distance from an observer. As light is stretched, its wavelength increases further into the “red” regions of the electromagnetic spectrum, hence the name “redshifting.” Through these measurements, scientists expect to see “inflationary ripples” in galaxies.
As mentioned, SPHEREx will also investigate the origins of galactic light production in the universe. SPHEREx’s observational techniques will provide scientists with a wide and deep-field map of the sky at each ecliptic pole. These maps are expected to highlight spatial fluctuations in extragalactic background light (EBL). Understanding EBL and its origins will allow scientists to further investigate the history of galaxy formation in our universe. Within the EBL, SPHEREx will specifically search for intra-halo light (IHL) and epoch of reionization (EOR) signals, down to the smallest levels of detectable EBL.
Lastly, SPHEREx will investigate the abundance of water, ice, and other biogenic and organic compounds throughout our universe, and attempt to understand how these ingredients are stored in interstellar space and delivered to protoplanetary disks. SPHEREx will employ infrared absorption spectroscopy to search for ices in galaxies, stars, star systems, and protoplanetary disks. More specifically, SPHEREx will collect absorption spectrum observations of the Milky Way, Large Magellanic Cloud, and Small Magellanic Cloud, generating spectra for approximately eight to nine million objects within them. Furthermore, SPHEREx’s observations will increase the number of ice spectra available for observation, with telescopes like JWST also contributing to increasing the number of these spectra.
SPHEREx will observe these cosmic objects from a 700 km Sun-synchronous orbit inclined 97 degrees, with an orbital period of 90 minutes. As mentioned, SPHEREx’s mission is expected to last 25 months into 2027. However, the observatory’s operational lifetime could be extended through mission extensions awarded by NASA.
PUNCH
Hitching a ride to Sun-synchronous orbit alongside SPHEREx is NASA’s PUNCH mission. Comprised of four, suitcase-sized small satellites, PUNCH will perform heliophysics research and investigate the atmospheric characteristics of the Sun, particularly solar wind.
In June 2019, after completing the initial phases of development and design, PUNCH and the Tandem Reconnection and Cusp Electrodynamics Reconnaissance Satellites (TRACERS) mission were selected by NASA to become the agency’s next pair of SMEX missions. TRACERS is scheduled to launch in April atop a Falcon 9. PUNCH was announced as a rideshare with SPHEREx in August 2022, and the spacecraft were shipped to Vandenberg at the start of the year for final integration and testing.
Together, the four small satellites will create global three-dimensional observations of solar wind, particularly young solar wind, throughout the Sun’s inner heliosphere and the outer corona. Each satellite masses around 40 kg and is just over a meter in length, and each satellite carries at least one of three primary instruments.
One of the spacecraft is equipped with the Narrow Field Imager (NFI) coronagraph, which will block out the light from the Sun to allow for more detailed observations of the heliosphere. Three of the four spacecraft are outfitted with a Wide Field Imager (WFI), a side-looking wide-field heliosphere imager similar to that of a coronagraph that utilizes linear geometry rather than circular. The WFI will attenuate sunlight by more than 16 orders of magnitude. All four spacecraft are equipped with a polarimeter that uses three polarizing filters.
The final instrument is the student-built Student Thermal Energetic Activity Monitor (STEAM) instrument, a solid-state X-ray spectrometer that will measure the Sun’s X-ray spectrum to better understand why the solar corona is significantly hotter than the surface. STEAM is mounted on the satellite with the NFI.
The orbital formation of each of the satellites will be established over the first 90 days of their mission. Once commissioned and flying in formation, the four spacecraft will capture seven images — one unpolarized and six polarized images — every eight minutes. From there, the spacecraft, which are synchronized in flight, will relay the images and data back to ground stations, where programs will then be used to produce the three-dimensional imagery. The field of view of all four satellites overlaps, allowing the imager instruments to create images that cover approximately six orders of dynamic range.
A PUNCH satellite and its components. (Credit: PUNCH)
The mission aims to “determine the cross-scale physical processes that unify the solar corona with the rest of the solar system environment (the heliosphere).” PUNCH’s two primary science objectives are to understand how coronal structures evolve into ambient solar wind, and to understand the dynamic properties of transient structures, like coronal mass ejections (CME), within young solar wind.
Earth is constantly subjected to varying amounts of solar wind, with its magnetosphere safely deflecting much of it away from Earth’s surface. However, enough solar wind can occasionally pile up, usually through coronal mass ejections, to surpass the magnetosphere and fall down Earth’s magnetic field lines and into the planet’s atmosphere, creating aurora.
The four PUNCH satellites undergoing final checkouts before integration. (Credit: PUNCH)
However, while these CMEs and other solar wind events can create gorgeous displays of light within our atmosphere, they can also severely damage and interfere with spacecraft in orbit around Earth. For example, several SpaceX Starlink satellites have failed to reach their intended orbits due to CMEs “fluffing” out Earth’s atmosphere, increasing atmospheric drag on the satellites. Furthermore, the charged particles within CMEs can interfere with spacecraft communications and disrupt electrical grids and power systems on Earth.
Scientists currently use a variety of solar-focused satellites to forecast solar weather and predict solar activity and potential impacts on Earth. However, no spacecraft continuously monitors solar wind; thus, it can often be difficult to predict when CMEs will occur and where they will be aimed. PUNCH will fill this void, as its continuous observations of the Sun’s heliosphere will enable scientists to accurately predict solar wind and understand its formation and evolution characteristics more completely.
(Lead image: SPHEREx and PUNCH integrated during payload fairing encapsulation. Credit: BAE Systems/Benjamin Fry)
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