Evaluating SiPM Performance in Space Over Three Years

Today, many small satellites, known as CubeSats, use special sensors called Silicon Photomultipliers (SiPMs) to detect light. These sensors are great at picking up tiny amounts of light because they can register individual photons. However, there’s a catch: SiPMs can be damaged by Radiation in space.

As more space missions use SiPMs, it’s super important to learn how they hold up under these harsh conditions. This article discusses a study showing how SiPMs behaved during over three years of flying through space.

#What Are SiPMs?

Silicon photomultipliers are tiny sensors that use avalanche photodiodes to convert light into electrical signals. They are small, require low power, and respond quickly, which makes them excellent for use in space missions. However, space isn’t an easy place for these sensors.

When they are exposed to radiation from outer space, they can get damaged. Because of this, scientists need to figure out how well these sensors work over time in a space environment.

#A Look at the Missions

This study focuses on two CubeSats: GRBAlpha and VZLUSAT-2. The GRBAlpha was launched in March 2021, and VZLUSAT-2 followed in January 2022. Both were sent to a sun-synchronous polar orbit, which means they pass over the same area of the Earth at the same time each day.

GRBAlpha carries a gamma-ray detector made up of a shiny material called CsI(Tl) and is equipped with eight SiPMs. This satellite regularly detects strong bursts of gamma rays, which happen during events like solar flares and gamma-ray bursts. Similarly, the VZLUSAT-2 has two gamma-ray detectors, closely resembling the one on GRBAlpha.

#The Challenge of Radiation

Space is filled with radiation from the sun and cosmic rays, and this can really take a toll on electronics. The sensors on GRBAlpha and VZLUSAT-2 are protected by a lead alloy shield that is about 2.5 mm thick. This shield helps to keep the SiPMs safe from the radiation damage that can happen over time.

Through this study, the research team was able to analyze how the sensors aged while flying in low Earth orbit. They gathered data over three years, making this study unique in its length and focus.

#What They Did

The researchers collected data by examining the performance of the SiPMs onboard both CubeSats for an extended period. They particularly looked for changes in two key areas: the low-energy Sensitivity Threshold and the Dark Count Rate. The sensitivity threshold is the minimum energy level needed for the sensor to detect light, while the dark count rate refers to the amount of noise that isn’t caused by actual light but rather by random fluctuations.

To measure these factors, they regularly collected background spectra, which help to highlight the noise levels and any changes in the sensors’ performance. By doing this, they could see how much radiation had affected the sensors over time.

#Findings on Sensor Performance

Over three years, the results showed that the sensitivity threshold of the GRBAlpha sensor decreased from its original level. This means that the sensor became less capable of detecting faint light signals. As for the dark count rate, this increased, meaning the sensor started to pick up more noise.

The study also found that the conditions in space affected the performance of the sensors. The increase in dark counts suggested that the sensors were aging due to radiation exposure. This is not surprising, as many electronic devices can struggle with longevity under harsh conditions.

#Temperature Matters

Interestingly, the researchers also noticed how temperature influenced the sensors. They could tell that at different times, when the temperature varied, the performance of the SiPMs changed too.

For example, when the temperature on the onboard sensors went up, the sensitivity threshold also went up. This means that the sensors might perform differently based on their temperature.

The researchers had three thermometers on the detector board of the GRBAlpha satellite, which allowed them to track this temperature variation during its mission.

#The Effects of Solar Activity

Another factor considered was solar activity, which tends to change throughout the year. When the sun is more active, it can send out bursts of radiation which could impact the performance of electronic devices on satellites.

However, the researchers didn’t find a direct link between the solar activity and the changes they observed in the performance of the sensors. This is a bit surprising, as one might think that the sensors would be more affected when the sun is blasting out more energy.

#What’s Next for SiPMs?

Given the findings of this study, researchers are optimistic about the use of SiPMs in future space missions. The study successfully showed that with proper shielding, these sensors can operate in space for over three years, which opens up opportunities for more complex missions. We can certainly expect to see more CubeSats using SiPMs to detect gamma rays in high-energy astrophysics missions.

#Conclusion

In summary, the research assessed the performance of silicon photomultipliers in space over an extended period.

• They found that radiation can indeed damage these sensors, leading them to be less sensitive to light over time.
• The increase in dark counts was also a clear indicator of aging.
• Temperature changes played a role in how well the sensors performed.
• Although there was no clear link found between solar activity and sensor performance, the study still demonstrated the potential for SiPMs in future space missions.

So, while space may be the final frontier, it's also a tricky playground for electronics. With ongoing research and development, we can look forward to exciting findings in the world of space exploration. Who knows? Maybe one day, we'll have CubeSats that can tell us when aliens send us a signal!