Speaker
Description
In recent years Low Earth Orbit (LEO) satellites are becoming rapidly the main source of space-based public services: LEO satellites can provide extremely low latencies and can deliver gigabit speeds, similar to wired infrastructure, providing high-quality services even to rural areas. However, LEO space weather prediction remains largely inadequate, as monitoring space weather in real time and acquiring data for operational space weather applications is significantly lagging in comparison to geostationary orbit (GEO) and with respect to the rapidly increasing user needs. Exacerbating the situation, unlike GEO spacecraft, most LEO spacecraft have minimal shielding/radiation hardness requirements so as to minimize size and cost, making them vulnerable to space weather effects, which are underestimated but ever-present at LEO. At the same time, modern semiconductor-based devices keep shrinking in size, with increasingly small junction areas and correspondingly smaller amounts of charge to control the state of critical circuit nodes (e.g., memory nodes): this makes them vulnerable to ionizing particles of even lower energies than in the past.
In addition, the business model and economics of the LEO-constellations have a strong emphasis on capital cost reduction, leading to dramatically reduced testing activities in comparison to traditional, heritage spacecraft programmes.
One of the most sensitive components aboard the spacecraft is the memory. Memory components are used in every system and in increasing numbers and densities. Most memories used on modern day LEO missions are in the best case up-screened commercial components. Their Single Event Upset Sensitivity (SEU) range is in the order of a few MeV/cm2/mg. Thus, SEUs can become the cause of many problems in the functionality of the satellite. It would be useful to have onboard an SEU detection device with known, stable and programmable levels of SEU sensitivity. This would give the satellite operator useful and timely knowledge regarding the environment and action could be taken accordingly.
In this paper an integrated circuit (IC) has been developed to measure the SEU environment and provide information to the satellite operators is presented. The IC contains a bank of memory elements that have a programmable SEU sensitivity ranging from a less than 1 up to a few tens of MeV.cm2/mg and a program and readout circuits that are very immune to SEUs. The SEU sensitivity can be programmed for each bank separately. The SEU sensitive memory banks are constantly being programmed and readout by an SEU immune readout circuit. The numbers of SEUs on the sensitive memory elements are constantly being recorded and analyzed. From the analysis (number of SEUs and SEU Linear Energy Transfer (LET) onset of the memory bank analyzed) information about the environment is extracted. This information can fed to the On Board Computer (OBC) of the spacecraft through a single digital communication interface.
The design and initial measurements of the SEU detection scheme is presented. The design of the programmable SEU sensitivity memory bank and threshold variation with process, power supply and temperature is discussed as well as the method of keeping the program and readout and analysis circuits immune to SEUs.
The developed device consumes very little power (less than 2 mA).The SEU LET onset on the SEU sensitive memory can be programmed according to the mission needs. Thus, the proposed device and can find use in many LEO constellation satellites.
