Swift Re-entry and Thermosphere Neutral Density Modeling Challenge

Background

NASA’s Neil Gehrels Swift Observatory was launched in 2004 to detect and monitor gamma-ray bursts. After 21 years of science operations, Swift’s low Earth orbit began to rapidly decay because of increased solar activity. Swift is expected to reenter later this year, around November. More information and news about Swift can be found at https://science.nasa.gov/mission/swift/

Thermospheric density is the dominant source of uncertainty in the atmospheric drag and associated satellite orbit determination and reentry. Thermosphere models estimate neutral density, composition, and temperature based on the solar and geomagnetic drivers. To make advances in orbit computation and determination, accurate specification and forecasting of the thermosphere are required. The uncontrolled Swift reentry event provides a natural experiment opportunity to test community capabilities for thermosphere mass density forecasting, in particular, at VLEO below ~300 km untill it reaches ~100 km. The goal of this research modeling challenge is to evaluate the sources of error in orbit predictions, ranging from model inputs, solar and geomagnetic driver prediction, model accuracy, the debiasing/drag coefficient tuning process, and orbit propagation.

The NASA Heliophysics Space Weather Program is supporting the Swift Re-entry and Thermosphere Neutral Density Modeling Challenge, led by the Community Coordinated Modeling Center (CCMC) and the Collaboration for Observational and Numerical Thermosphere with Integrated Geospace Orbits (CONTIGO). Thermosphere modeling groups are invited to participate in the challenge: we are accepting submissions in any combination of the following:

F10.7 and Kp forecasts,
Thermosphere density forecasts,
Reentry times and trajectories.

To facilitate the challenge, CCMC will provide a standard set of drivers, run community models (in coordination with model developers) driven by standard and submitted driver forecasts, gather model forecast submissions, and CONTIGO will propagate the Swift spacecraft through your thermosphere 4D cube (for CCMC Kamodo-supported model output formats) using the General Mission Analysis Tool (GMAT), and conduct the comparison with the actual Swift trajectory and reentry time. A preliminary report and community discussion will be held at the CEDAR Workshop 2027 followed by a final community publication.

Note: No funding is available for contributions to this effort. Due to sensitivities, CCMC will not publicly post any orbit predictions until the challenge period has ended and Swift deorbits.

Guidance for Challenge Participants

Basic Swift Info

Low-drag mode was 24-Jan-2026 to 27-Aug-2026
Starting state vector and ballistic coefficient will be provided to those who want to run their own orbit propagation with standard initial conditions.

Thermosphere Submissions

Predictive F10.7 and Kp/Ap will be provided for those who want to run their own thermosphere models with standard inputs.
All thermosphere data will be accepted, but Kamodo-compatible formats are preferred for inclusion in the CONTIGO-run reentry predictions.
- Kamodo can read the following file formats:  https://ccmc.gsfc.nasa.gov/publicData/KAMODO_TestData/ or the HASDM file format provided by Space Environment Technologies (SET-HASDM).
- DTM or NRLMSIS format is suggested if you are reformatting your model output for this challenge.
We realize not all thermosphere models extend below 200 km. In order to accommodate a wider variety of models, comparisons will be done at both 200 and 120 km altitude.

General Submission Guidelines

Teams should upload all inputs and parameters used, whether those are the provided inputs and parameters or are different than those provided.
Teams should specify any information that they do NOT wish to become public. Unless otherwise specified to the CCMC team, all submitted solar/geomagnetic inputs and thermosphere densities will be made public soon after submission. All submitted reentry predictions will be made public after reentry.
Secure FTP links will be provided via email to upload contributed files.