Photo of the FOXSI team at WSMR


The first three iterations of the FOXSI sounding rocket launched from White Sands Missile Range (WSMR) in New Mexico. Through these successful campaigns, FOXSI became the first solar-dedicated instrument to observe hard X-rays with focusing optics. The direct imaging techniques employed enabled FOXSI to achieve improved sensitivity and dynamic range compared to previous, indirect imaging methods. FOXSI’s novel technologies and approach to imaging have paved the way for clearer solar flare observations in the future.

Solar Flare Campaign

FOXSI-4 will build on its legacy of innovation with an unprecedented solar flare campaign. Launching in April 2024 from Poker Flat, Alaska, FOXSI-4 will continue to improve upon direct solar imaging with its new launch site and coordinated observations. Sister payload Hi-C FLARE will wait with FOXSI-4 for an opportunistic signal to launch for a simultaneous observation of a solar flare. Joining this effort will be several spacecraft observatories, which will provide coordinated data.

The launch is to take place during solar maximum—the phase of the roughly 11-year solar cycle during which major flare activity occurs. Though sounding rockets historically launch from White Sands, the solar flare campaign requires a more flexible launch schedule than the busy New Mexico missile range can allow. At Poker Flat, FOXSI-4 will be able to stand ready on the launch pad for two weeks, waiting for the perfect opportunity to capture a flare.

Read the full solar flare campaign concept

Instrumentation Upgrades


FOXSI-4 features significant upgrades to instrumentation. New high-resolution optics developed at both the NASA/Marshall Space Flight Center and at Nagoya University have highly polished Wolter-I mirrors that offer two times better resolution than the optics flown in previous FOXSI campaigns. These improvements will allow for more detailed study of particle acceleration and plasma heating in the solar corona.

Detectors & Attenuators

Upgrades to the focal plane include improved detectors and novel attenuators. The National Astronomical Observatory of Japan and the Kavli IPMU institute, along with the Japanese Aerospace Exploration Agency (JAXA), provide FOXSI-4 with finely pixelated silicon CMOS sensors and fine-pitch cadmium telluride strip detectors. The Timepix collaboration, led by UC Berkeley, provides a new high spatial resolution cadmium telluride detector as well. A set of perforated attenuators developed at the NASA/Goddard Space Flight Center enables the simultaneous measurement of low and high energy spectra for medium or large flares. 

FOXSI-4 Flare Campaign Logo

FOXSI-4 Schedule

Milestone Timeline
Event Date
Kickoff November 2020
Design Review March 2023
Experiment Components Delivered to UCB Summer 2023
Experiment Integration at UCB Fall 2023
Flight System Integration at WSMR February 2023
Flare Campaign April 2024