Days to Decades: Forecasting Space Weather and Climate in the Thermosphere
The largest uncertainty in orbital propagation for satellites and space debris in Low Earth Orbit (LEO) is atmospheric drag, due to thermospheric density. Space weather and space climate affect thermospheric densities on timescales ranging from hours to decades.
On the short time scale, forecasting thermospheric densities is critical to provide timely and actionable conjunction warnings to avoid satellite collisions. To address this, the UK is operationalizing the University of Birmingham’s model AENeAS, an assimilative model of the thermosphere and ionosphere to aid satellite operators.
On the longer time scale, carbon dioxide cools the upper atmosphere, as the less dense thermosphere can’t trap emitted infra-red radiation. This gradually reduces thermospheric densities at a rate of 2 to 5% per decade. As neutral densities decrease, orbital lifetimes will increase, raising the probability of a collision occurring during a satellite’s lifetime. This increases the speed of feedback loop of more collisions, more space debris, more collisions, and raises the prospect of a Kessler Syndrome at lower altitudes.
Matthew Brown completed a PhD entitled ‘Climate Change in Space: The Impact on Space Debris’ at the University of Southampton in 2023. He is now a research fellow in the SERENE group at the University of Birmingham, and as part of the SWIMMR programme improving and operationalizing the AENeAS model at the UK’s Met Office Space Weather Operations Centre (MOSWOC). His research interests cover the thermosphere, low Earth orbit, space debris, space weather and space climate.