The Effect of the Solar Cycle on Satellite Orbital Lifetime

Abstract

The lifetime of a satellite in Low Earth Orbit (LEO) is affected by the 11-year solar cycle. At a fixed altitude, increasing solar activity increases atmospheric density which leads to an increase in drag, and a decrease in mission lifetime without using propulsion to recover altitude. Satellites may have longer orbital lifetimes if more of their mission is operational during a solar minimum due to lower solar activity and lower atmospheric drag. Satellites with larger area-to-mass ratios generally have shorter orbital lifetimes than satellites with small area-to-mass ratios. Missions that get delayed and have more of their operations during solar maximum than planned originally may have too short of a mission lifetime or, conversely, may be at risk of increasing their orbital lifetime past regulatory limits (five years for satellites in LEO according to the FCC) if they launch closer to solar minimum. For example, a satellite with an area-to-mass ratio of 0.014 m2/kg – such as a 1U CubeSat – and a one-year mission that is launched in 2021 without onboard propulsion, would have an orbital lifetime of 1.051 years. However, if that mission were delayed a year, a common occurrence in the industry, it would no longer be able to achieve its mission as its orbital lifetime with a deployment in 2022 is 0.44 years. Conversely, if the same 1U CubeSat is launched during solar max in January 2025, it would have an orbital lifetime of 2.2 years, and would re-enter in February of 2027. However, if that mission were delayed a year, the satellite would launch in January 2026 and instead be in orbit for 6.4 years before re-entering. They could be fined for violating the FCC deorbit limit of five years. This thesis quantifies the effect of launch or processing delays on satellite orbital lifetime based on their orbit altitude and vehicle parameters such as mass, cross sectional area, altitude, and bus size. In general, it is found that four-year and six-year delays have the greatest effect on a satellite’s orbital lifetime because the satellite will be deorbiting almost half a solar cycle (5.5 years) from its intended deployment year. However, two-year delays can still affect satellite operators, as they can increase the orbital lifetime, even by up to 1.5 years for low area-to-mass ratio satellites in 400 km orbits and almost five years for satellites in orbits higher than 500 km. Two-year delays can also decrease the orbital lifetime of a satellite by up to 1.7 years for low area-to-mass ratio satellites in 400 km orbits and almost two years at altitudes higher than 500 km.