μDose @ FemtoSat

Motivation

In space, we are constantly exposed to cosmic radiation. Cosmic radiation consists of high-energy particles that hit a satellite or the Earth's atmosphere from space. These particles originate from the sun, from other stars and even from distant galaxies. They consist mainly of protons (approx. 90 %) and other ionizing radiation, with the contribution of free electrons in the Earth's near field making an important contribution. The largest proportion comes from the solar wind (protons, helium nuclei and electrons) and is strongly dependent on solar activity. Cosmic radiation leads to various effects such as charging, material changes, changes in the electrical properties of electronics and the generation of secondary radiation. Cosmic radiation and the associated space weather are therefore important for satellites and spacecraft, as they can affect electronic systems. The high-energy particles of cosmic radiation can damage individual electronic components on satellites or lead to malfunctions. During solar storms, charged particles can influence the Earth's magnetic field, which in turn can disrupt satellite electronics. Space weather and solar activity are therefore continuously monitored using various measurements and concepts.
For this purpose, an own compact dosimeter concept is developed, which measures the count rate of ionizing radiation and the dose rate (deposited energy of radiation per time interval) and uses these as parameters for simple functional analyses or failure rates of electronic components, e.g. microcontrollers. In addition, the developed concept can be used as a self-sufficient battery-operated dosimeter.

Operating Principle and Design

Semiconductor dosimeters: Semiconductor dosimeters are important instruments for monitoring and measuring exposure to ionizing radiation. Their ability to detect different types of radiation, distinguish between energy levels, provide accurate dose measurements and offer real-time monitoring makes them valuable instruments for monitoring the radiation environment. The key functionalities of solid-state dosimeters include:

1. Detection of ionizing radiation: Semiconductor dosimeters are sensitive to various types of ionizing radiation such as alpha, beta and gamma radiation. They can efficiently detect and quantify radiation exposure.
2. Detection of ionizing radiation: Semiconductor dosimeters are sensitive to various types of ionizing radiation such as alpha, beta and gamma radiation. They can efficiently detect and quantify radiation exposure.
3. Dose measurement: Semiconductor dosimeters provide precise measurements of the absorbed radiation dose. They convert the charge in the semiconductor material caused by the radiation into an electrical signal, which is then correlated with the absorbed dose.
4. Real-time monitoring: Semiconductor dosimeters provide real-time monitoring that allows radiation levels to be continuously monitored. This is particularly valuable in environments where radiation exposure can fluctuate over time.
5. Compact and portable design: Semiconductor dosimeters are often compact and portable, making them easy to integrate into different systems.
6. Long-term stability: Semiconductor dosimeters usually exhibit long-term stability to ensure reliable and constant performance over a long period of time. This feature is important for keeping accurate records of radiation exposure over time.
7. Storage of dose data: Many solid-state dosimeters are equipped with data storage capabilities to record cumulative radiation exposure over specified time periods.

The detection of small but fast charge pulses caused by radiation in a semiconductor (e.g. a silicon diode) is generally based on a circuit with amplifier stages and the detection of the maximum pulse amplitude by a sample-and-hold stage, which holds the maximum amplitude until it is determined by an analog-to-digital converter and then further processed by a microprocessor, for example. To determine the dose rate, an energy calibration is usually carried out beforehand and a histogram of the measured amplitudes or energy input is recorded over a time interval. The calibration can be used to determine the total energy per measured time interval and thus the dose rate.

Femtosattelite: A femtosatellite usually weighs no more than 100 grams, and therefore often contains only the most necessary functions or subsystems of a satellite. The concept used for the present microdosimeter concept is based on the femtosatellite design of the company AmbaSat Ltd, which is essentially based on a microcontroller (Atmega328p) and a board design (3.5 x 3.5 x 0.37 cm3), on which the power supply is regulated via solar cells, communication takes place via a Long Range (LoRa) module (RFM95) with the Long Range Wide Area Network (LoRaWAN) and offers space for a payload in the form of various environmental sensors, which we used for the dosimeter.
In addition, the company wants to disseminate the concept in education and launch up to 200 femtosatellites into space with a 3U Cubesat as a carrier satellite, so that everyone can operate their own mini-satellite.

Goals of the Projects

The overriding aim is to develop an independent compact dosimeter concept that can be used in different environments and projects by communicating with LoRAWAN. This step is largely complete and still needs to be refined. The specific goal of μDose @ FemtoSat is to measure the radiation dose in space and to prove its feasibility. A further goal is to develop an independent concept for determining radiation damage to electronics under real space conditions (in orbit) on the basis of commercially available components in the sense of the NewSpace approach, where the dosimeter concept is to be used in a CubeSat concept for monitoring.

3D view of the board construction

First prototype of a femtosatellite and dosimeter using a large-area silicon diode.