Background

The risk indicators provide a high-level indication of the risk of damage to satellites due to space weather. They combine information on the space radiation environment with effects on materials which are commonly used on satellites. Thus they should provide a more direct indication of satellite health than the radiation environment can provide alone.

Two risk indicators are provided:

• Risk of internal satellite charging due to high energy electrons
• Risk of the degradation of electronic components due to dose rate and total ionising dose. The total ionising dose is due to electrons and ions computed since 1 June 2018.

The risk indicators are provided at the location of 2 specific satellites, GOES-16, in geosynchronous orbit, and GIOVE-A in an inclined circular orbit. Risk indicators are also provided for a circular satellite orbit at 8,000 km altitude in the equatorial plane where radiation levels are usually very low, but which can increase rapidly and decay slowly after a space weather event. For more information click on each orbit on the main page.

The risk indicators are Green - 1, Yellow - 2, Amber – 3, Red – 4, where red is the highest risk. The risk levels are based on numbers given in the European Cooperation for Space Standardisation (ECSS, 2008) and the NASA Handbook (2011).

The risk indicators use real-time satellite data where possible and augment the data with results from the BAS radiation belt model (BAS-RBM). This information is then used as input to radiation effects software and used to calculate the risk indicators.

The risk indicators are updated every hour and operate 24/7.

Representative orbits

Most satellites are located in one of three orbit types, Geosynchronous Orbit at 36,000 km altitude, Medium Earth Orbit, such as the GPS and Galileo constellations which are at 20,200 km and 23,222 km altitude, and Low Earth Orbit below about 1,500 km altitude. The radiation environment can vary by 5 orders of magnitude with location and time. To help assess the risk for each orbit we have provided the risk indicator along the track of a representative spacecraft for 4 orbits. These are:

• GOES-16 (at a longitude of 75.2° West) at geosynchronous orbit
• GIOVE-A which is in circular orbit at 23,222 km altitude with inclination 56°
• A satellite in a slot region orbit at 8,000 km altitude at the equator

GOES-16 provides a measure of how the risk varies with geographic longitude. GIOVE-A is representative of the Galileo radio-navigation fleet. The circular slot region orbit is included since new satellites are being launched into this orbit and while the radiation risk is usually very low research shows that the radiation levels can increase by 5 orders of magnitude in that region during a geomagnetic storm and take weeks or months to decay.

References

• ECSS-E-ST-20-06C (2008), European Cooperation for Space Standardization, Space Engineering: Spacecraft charging, ESA Requirements and Standards Division, ESTEC, P.O. Box 299, 2200 AG Noordwijk, The Netherlands.
• NASA Technical Handbook (2011), Mitigating in-space charging effects - A guideline, NASA Technical Handbook, NASA-HDBK-4002A, National Aeronautics and Space Administration, Washington, DC 20546-0001, USA.