Trajectory calculations problematics with the Earth atmosphere entering bodies and FSSAC probabilistic solution approach

Study Problematics

Space situational awareness (SSA) main object is to produce as real-time an overall picture of the space situation as possible. By developing abilities, methods and models to observe objects and bodies located in near Earth space and by predicting space weather phenomena, the risks of damage to both people and property caused using space can be reduced.

In this study discussion we focus into problematics that we have especially with the final phase trajectory calculations for space debris, deorbiting satellites and other bodies. Despite we can know the orbits of the satellites or debris very well, the final atmospheric entry determination is challenging. This challenge will be discussed and the main elements of future improvements that should be developed to reach more precise determination capabilities will be introduced. The main problematics to predict the atmospheric entering bodies (manmade and natural) can summarized to following focus areas:

• Earth atmosphere is not perfect circle in real life. Space weather events cause significant changes in the upper atmosphere composition and altitude [1] [2]. 
• Satellites aren’t optimal nor unified in shape and satellite mass is not really known. Satellite models for de-orbiting calculations simplifies [3] the shape and surface area of the satellite.
• The velocity of the satellite is high and hard to follow in the end and angle of attack of the atmospheric re-entry is unclear. 

FSSAC Probabilistic Solution Approach

The Finnish Space Situational Awareness Center (FSSAC) is developing systems to estimate the impact areas and effects of space objects entering Earth’s atmosphere. Accurate orbital parameters are critical for determining impact points [4], but publicly available data, such as TLEs processed with the SGP4/SDP4 model, lack precision. These datasets are updated infrequently and exclude certain objects, such as military satellites.

To address this, FSSAC integrates additional data like covariance matrices, SGP4-XP, CPF, and Sp3c products, alongside Satellite Laser Ranging (SLR) data. The Metsähovi SLR telescope is being upgraded with a new laser emitter to expand coverage of RSOs, enhancing orbit modeling accuracy. Reliable atmospheric models are also essential, but existing options, such as NRLMSISE‐00 [5], are outdated and can produce errors of 20–30% during high solar activity.

FSSAC is advancing atmospheric models and orbit propagation tools to support accurate re-entry predictions. These efforts aim to provide timely warnings for high-risk RSOs, prioritizing public safety.

References
[1] https://www.ilmatieteenlaitos.fi/ajankohtaista/1244013

[2] Baruah, Y., et.al. (2024). “The loss of Starlink satellites in February 2022: How moderate geomagnetic storms can adversely affect assets in low-earth orbit”. Space Weather, 22, e2023SW003716. https://doi.org/10.1029/2023SW003716

[3] https://sdup.esoc.esa.int/

[4] Pardini, Carmen, and Luciano Anselmo. "Overview of some basic requirements for a reentry prediction service for civil protection applications." Proc. 1st NEO and Debris Detection Conference, Darmstadt, Germany. 2019.

[5] Picone, J. M., et al. ”NRLMSISE-00 empirical model of the atmosphere: Statistical comparisons and scientific issues”, JGR Volume107, IssueA12, 2002, https://doi.org/10.1029/2002JA009430