By Alan Toth
June, 10, 2026
The Space Weather Follow On – Lagrange 1 mission, operated by the National Oceanic and Atmospheric Administration (NOAA), launched in September of last year, and in January it performed its final burn to enter orbit around the Sun at some 1 million miles from the Earth. The mission was renamed Space Weather Observations at L1 to Advance Readiness – 1 (SOLAR-1), and it has begun monitoring the energetic particles that stream from the Sun, which are known as the solar wind.
SOLAR-1 reinforces the small fleet of aging spacecraft that monitor space weather, and it allows for more refined measurements of the solar wind thanks to a suite of state-of-the-art instruments like the SupraThermal Ion Sensor (STIS), built and led by the UC Berkeley Space Sciences Laboratory (SSL). Based on a similar instrument used on previous missions, key refinements developed at SSL allow STIS to gather much more accurate measurements than previous iterations.
“The modifications have really made the instrument much better,” says STIS principal investigator and SSL project scientist Davin Larson. “I’m really pleased that we made the changes.”
Larson first came to SSL as a graduate student in 1987. At the time, he was primarily focused on research in his role as a teaching assistant for Kinsey A. Anderson, a professor of physics and a former director of SSL. Anderson offered Larson a position as a research assistant at the lab studying data from the European Space Agency’s Giotto mission, which had observed Halley’s Comet from a distance of 596 km the previous year. Larson found that Halley’s passage excited and compressed electrons well ahead of the comet’s path. He wrote his PhD thesis on those findings and has been at SSL ever since.
Larson’s affinity for instrument development began with NASA’s WIND satellite, which launched in 1994 and measured radio waves and plasma in the solar wind. SSL built the Wind/3DP instrument suite, which included five instruments designed to measure electrons and ions in 3-dimensions. The experiment led to the discovery in 1997 that some electrons are cooled substantially by the solar wind. It also revealed that ions can be reflected by the Earth’s bow shock—the sunward edge of the magnetosphere that’s compressed by the solar wind. Larson calibrated several of the instruments for the suite.
“So many good things came from that instrument, and it’s still working well more than 30 years later,” says Larson.
Larson went on to serve as instrument lead for the solid-state telescope on NASA’s Time History of Events and Macroscale Interactions during Substorms (THEMIS) mission, which launched in 2007. He also led the Solar Energetic Particle (SEP) instrument on the Mars Atmosphere and Volatile Evolution (MAVEN) mission and participated in the development of the In-situ Measurements of Particles and CME Transients (IMPACT) instrument for the Solar TErrestrial RElations Observatory (STEREO) mission.
In 2009, NASA posted an announcement of opportunity seeking experiment proposals for the Parker Solar Probe (then called Solar Probe Plus). The mission would combine Larson’s two passions: instrument development and investigating mechanisms that accelerate the solar wind. He was part of the team that was awarded a contract to develop the Solar Wind Electrons Alphas & Protons (SWEAP) experiment, which measures solar plasmas.
From left to right: the Parker Solar Probe, the SPAN-i instrument and the SPAN-e instrument
Most of SWEAP’s instruments were designed and built at SSL, and Larson serves as institutional lead for two of those instruments (SPAN-Ai and SPAN-B), which measure ions and electrons. Another instrument suite for the Parker Solar Probe called FIELDS, which measures magnetic and electric fields, was designed and built at SSL at the same time as SWEAP. This allowed both suites to be run on the same internal sampling clock, which allows synchronized measurements across instrument suites and very precise modeling of plasma effects that result from high-frequency waves at the ion scale.
In 2024, NASA, on behalf of NOAA, awarded SSL a contract to build the STIS instrument with Larson as the instrument principal investigator. STIS contains a stack of solid-state detectors that measure energetic particles above 20 kilo-electron volts with two apertures, one that allows ions through and another that allows electrons through. Having built similar detectors for five previous missions, Larson worked with STIS deputy principal investigator and SSL research scientist Ali Rahmati and many others at SSL to perfect the design. He removed a mechanical attenuator and incorporated detectors in two different sizes, and he believes that this is proving a better way to build the solid-state telescope.
STIS will contribute to critical monitoring of solar activity, specifically coronal mass ejections (CMEs), which can disrupt satellites and ground-based infrastructure. Another instrument on SOLAR-1, the Compact Coronagraph, will detect CMEs that resemble a halo expanding from the Sun. Such halos indicate that energetic particles could be traveling either directly toward or away from the Earth. STIS measures suprathermal particles—ions and electrons that move faster than the thermal solar energetic particles (SEPs) that form the densest part of a CME. When CMEs travel toward the Earth, STIS will detect the leading edge of suprathermal particles, providing one to two days advanced warning to satellite and electrical infrastructure operators of inbound SEPs.
STIS proved its value late last year, when it detected suprathermal particles following a CME that was travelled toward Venus, which was then on the opposite side of the Sun in relation to the Earth. The CME was so powerful that it spread suprathermal particles throughout the solar system, which STIS detected. Measurements like these are already informing Larson’s research.
Throughout his 39 years at SSL, Larson has been trying to understand the microphysics of how electromagnetic energy flux is transferred to solar wind plasma, and he’s progressively improved his instrument designs in pursuit of that goal. He believes that understanding instrumentation has made him a better scientist.
“It shouldn’t be so unusual for researchers to build the instruments they use,” said Larson. “That should just be the way it’s done.”