SAHAB: A Compact Balloon-Borne Radiation Detection Platform for Solar X-Ray and Gamma-Ray Physics Development

The Sun is a restless star, constantly churning with magnetic energy that occasionally snaps and releases in violent explosions called flares. When these flares erupt, they accelerate particles to incredible speeds, creating a flood of high-energy light known as hard X-rays and gamma rays. Because Earth's atmosphere acts like a thick blanket, it absorbs most of this energetic radiation before it reaches the ground, making it impossible to study these events with telescopes sitting on the surface. To see the Sun's most violent moments, scientists must send instruments high into the sky, above the thickest part of the air, where the view is clear. For decades, the most powerful tools for this work have been satellites, but they are incredibly expensive and take years to build. A more agile alternative exists: high-altitude balloons that float in the stratosphere, offering a cheaper, faster way to test new detectors and gather data before committing to a full space mission.

A new project called SAHAB, which stands for Saudi Arabia High-Altitude Balloon, represents a significant step forward in this approach. Developed through a partnership between King Fahd University of Petroleum and Minerals in Saudi Arabia, the University of California, Merced, and the Space Sciences Laboratory at the University of California, Berkeley, this initiative aims to build a compact, affordable platform for studying solar physics. The first version of this instrument was designed not just to collect data, but to prove that a low-cost, student-led team could build a reliable system capable of surviving a balloon flight and measuring the radiation environment around our planet. The researchers successfully designed, built, and tested a payload that fits inside a small chassis, carrying a set of sensors to measure radiation, temperature, and pressure while floating at the edge of space.

The heart of the SAHAB payload is a simple but effective arrangement of four different sensors housed within a sturdy, layered frame made of aluminum plates. The primary instrument is a crystal detector that glows when struck by high-energy particles, allowing scientists to measure the energy of incoming radiation. Alongside it sits a Geiger counter to track the total number of particles hitting the balloon, a sensor to monitor the local temperature and air pressure, and a camera to capture images of the surroundings. All of these components are managed by a small, widely available computer board that records the data onto a memory card. The entire assembly is designed to be modular, meaning the different layers can be taken apart and reassembled easily for testing or upgrades, a feature that simplifies the complex process of preparing for a flight.

To ensure the delicate electronics could survive the rigors of a balloon launch, the team subjected the design to rigorous computer simulations. They modeled the forces the payload would experience during takeoff, the climb to high altitude, and the eventual landing, checking to see if the structure would bend or break under pressure. The simulations showed that the aluminum frame held together perfectly, keeping the internal components aligned and secure even when subjected to forces equivalent to eight times the pull of gravity. This structural integrity is crucial because any shift in the position of the detectors could ruin the accuracy of the measurements. The design also includes specific features to hold the main crystal detector in place, using metal collars that clamp it firmly so it does not wobble during the flight.

The first flight of this system was not a solo mission but a hosted ride aboard a larger platform operated by NASA called BOOP. This arrangement allowed the SAHAB team to focus entirely on their instruments while relying on the host platform for power and communication. The balloon is designed to carry the payload up to an altitude where the air is thin enough to let high-energy X-rays pass through, a region roughly 30 to 40 kilometers above the Earth. During the flight, the SAHAB sensors will continuously record the radiation levels, mapping how the intensity of cosmic rays changes as the balloon rises from the ground, through a peak in radiation activity, and up to the floating altitude. The data is streamed to the ground live via a satellite link, while a full copy is simultaneously saved on the onboard computer for later retrieval and analysis.

Before the flight, the researchers carefully calibrated their main crystal detector in a laboratory using a known radioactive source. They confirmed that the device could accurately distinguish between different energy levels of radiation in a controlled setting, a capability essential for identifying the specific signatures of solar flares. The tests showed that the detector could measure energies ranging from about 30,000 electron volts up to several million electron volts, covering the spectrum where solar flares are most active. While the current version of the detector is sufficient for measuring background radiation and proving the concept works, the team has already outlined a clear path for future improvements. The next stages of the project will involve adding more sensitive detectors, building a system that can point directly at the Sun, and creating a standalone balloon that does not rely on a host platform.

The success of this first iteration is about more than just the data collected; it is about building a new capability within Saudi Arabia. By involving students and early-career researchers in every step, from the initial design and mechanical assembly to the flight operations and data analysis, the project is cultivating a local expertise in space instrumentation. The paper details how the team managed the power supply, ensuring that the various sensors received the correct voltage from the host balloon's battery, and how they organized the data flow to prevent the different instruments from interfering with one another. The result is a fully functional, compact system that has been proven to work in the harsh environment of the upper atmosphere.

Looking ahead, the SAHAB program plans to evolve rapidly. The next phase will introduce detectors made of different materials that can see finer details in the energy of the radiation, allowing scientists to separate specific types of nuclear lines that are currently blurred together. Future versions will also include advanced shielding to block out unwanted background noise and a pointing system to keep the instruments locked on the Sun during a flare. The ultimate goal is to create a national capability for solar physics research, where Saudi scientists can design, build, and launch their own instruments to study the dynamic behavior of the Sun. This first flight serves as the foundation, demonstrating that a cost-effective, modular approach can successfully open a window onto the high-energy universe.