FOXSI-4

Foundation

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 built on its legacy of innovation with an unprecedented solar flare campaign. Launched in April 2024 from Poker Flat, Alaska, FOXSI-4 observed a large solar flare in progress, the first time that a flare has been the dedicated target of a rocket launch campaign.  Specifically the flare was a GOES class M1 flare observed in its decay phase.  Sister payload Hi-C FLARE launched one minute after FOXSI-4 for a simultaneous view of the same flare in ultra high resolution extreme ultraviolet light. Joining this effort were several spacecraft and ground based observatories, providing coordinated data.

The launch took 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 required a more flexible launch schedule than the busy New Mexico missile range could allow.  Instead, the flare campaign occurred at the Poker Flat Research Range - a launch facility near Fairbanks owned by the University of Alaska.  At this facility, the twin rockets were able to stand ready on neighboring launch pads for several days until the perfect flare occurred.

Read the full solar flare campaign concept

Instrumentation Upgrades

Optics

FOXSI-4 featured 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  allow for more detailed study of particle acceleration and plasma heating in the solar corona.

Detectors & Attenuators

Upgrades to the focal plane included 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.