The Glowbug mission was a gamma-ray telescope berthed on the International Space Station (ISS). It was launched on March 14, 2023, and installed on the Japanese Experiment Module Exposed Facility (JEM-EF). It began operations on March 20 2023, and operated through April 2024. The mission was led by the Naval Research Laboratory through the Department of Defense Space Test Program and funded through the NASA Astrophysics Research and Analysis program. Its primary mission was to detect short gamma-ray burst (sGRBs) from binary neutron star and neutron star-black hole binary mergers. It was also a proving ground for a proposed future SmallSat mission called GAMERA, the StarBurst Multimessenger Pioneers mission, and Glowbug-2 instrument.

The instrument had a wide field of view and was sensitive to gamma-rays in the 30 keV–2 MeV range. The detector consisted of 12 CsI(Tl) detector panels arranged to allow reconstruction of burst location with modest accuracy. There were also a set of six Cs₂LiLaBr₆(Ce) (CLLB) cylindrical detectors to extend sensitive above ∼1 MeV. Both detectors used silicon photomultipliers (SiPMs) to detect light from gamma-rays absorbed by the scintillation material. The SiPMs and mission and data acquisition systems were based on earlier technology from the Strontium Iodide Radiation Instrumentation missions (SIRI-1 & SIRI-2).

The instrument was mounted on a pedestal to protude above the zenithal (sky-facing) side of the ISS, ideal for observing astronomical gamma-ray sources. Glowbug was also able to detect some terrestrial gamma-ray flashes.

Mission Characteristics

Lifetime

Energy Range : 30 keV–2 MeV

Special Features :

• Mounted on the zenithal (sky-facing) side of the ISS with wide field of view. ISS mounting and integration allowed use of power systems and high bandwidth communications with limited onboard systems requirements.
• Leveraged flight-proven design and software for reduced cost and faster development.
• Improved gamma-ray detector design permitted greater sensitivity than older designs.

Payload :

• CsI(Tl) Gamma-ray Detector. A suite of 12 CsI(Tl) detectors provided an ultra-wide field of view of the unocculted sky (8 steridan). Each large-area detector panel was a 150 mm x 150 mm, 10 mm thick crystal, with a 1 x 21 array of 6 mm x 6 mm SiPMS used to read out the thin edge of the crystal. The SensL J-series SiPMs were flight-proven on the SIRI-1 mission. The individual detectors were arranged in bi-packs, in pairs along the +/- x and y axis, and with four on the +z (zenith-facing) side. The outward facing side of each panel had a thin aluminum window while the crystal was backed with a steel and tantalum shield which attenuated gamma rays below ∼300 keV to stop photons entering the rear-facing side. Localization of bursts by maximum likiehood algorithms provided typical localization of <5° (compared to 10° for comparable sGRBs with the Fermi GBM) and roughly twice Fermi GBM's effective area with a typical sGRB spectrum. This expanded the horizon for faint objects in the local Universe by a factor of ∼1.4 (and thus encompassed roughly 3 times Fermi GBM's detectable volume of space).

• CLLB Gamma-ray Detector. There were 6 Cs₂LiLaBr₆(Ce) cylindrical scintillation detectors in the interior of the detector (surrounded by the CsI(Tl) panels). These were a new type of detector: a secondary goal of the Glowbug mission was to flight-test the new technology. Each cylinder was 5 cm in diameter and 10 cm long with an array of 44 SensL J-series SiPM at one end. They had <4% FWHM spectral resolution at 662 keV and were sensitive to thermal neutrons. They provided additional effective area above 1 MeV to the total instrument.

• SAA Detector. The South Atlantic Anomaly detector consisted of a single 25 mm x 25 mm x 12 mm plastic scintillator cube with a 4 x 4 array of SiPM readouts. This detector remained on during transits of the SAA in order to detect entry to and exit from the high radiation region.

Science Highlights:

• Observed 65 GRBs (54 long and 11 short) during eight months of science operations (The full year included initial boot-up, commissioning phases, and Safe Holds).
• Co-observed with other multi-messenger astronomy observatories.
• Provided additional data on terrestrial gamma-ray flash sources and solar flares.
• Flight proving of new CLLB scintillation detectors.
• Characterized the response of silicone photomultipliers on orbit, and determined minimum power requirements for future missions to maintain operations through end-of-mission timeframes for future Glowbug-2 and StarBurst missions.

Archive: HEASARC will host Glowbug data, products, and catalogs