SATPC0042727 TAB 07 SOW PRINTED.pdf

Statement of Work (SOW) Thermospheric Observing System Simulation Experiments (OSSEs) for Future NASA/Heliophysics Missions Period of Performance: August 1, 2026 (or upon award) September 30, 2027

1. Background

A central motivation for this investigation is to quantify how the unique measurement capabilities of the GDC Trailblazer and DYNAMIC missions contribute to thermospheric specification and prediction relative to existing or emerging observational systems. This eEort builds directly upon recent NASA-supported work that ported a thermosphere/ionosphere data assimilation (DA) and Observing System Simulation Experiment (OSSE) capability to NASA. Under that effort, the Iterative Driver Estimation and Assimilation (IDEA, Sutton, 2018) framework was ported to the NASA High-End Computing (HEC) environment, and in this environment, IDEA can use either of two physics-based thermosphere-ionosphere models: (1) the Thermosphere-Ionosphere-Electrodynamics General Circulation Model (TIE-GCM, Wu et al., 2025), and (2) the Whole Atmosphere Model-Ionosphere Plasmasphere Electrodynamics (WAM-IPE, Akmaev et al., 2008) model.

The capabilities include a complete OSSE infrastructure, including nature-run generation, synthetic observation creation, driver estimation, and tools to evaluate synthetic nowcasts. Although NASA's HEC architecture has since transitioned from the original Pleiades compute nodes to the Aitken and Athena systems in the last year, the underlying IDEA framework and models, workflows, and simulation environments continue to operate under the Aitken Cascade Lake architecture and can be extended to newer architectures as need be.

As part of the previous effort, OSSEs were performed using synthetic observations based on the DYNAMIC mission concept (National Research Council, 2013). These initial studies demonstrated that assimilation of lower-thermospheric observations could substantially improve specification of the middle and upper thermosphere, revealing a strong connection between the altitude region where energy is deposited and the higher-altitude environment occupied by many operational and commercial satellite constellations. This result is particularly relevant given the increasing availability of commercial tracking data and GNSS-derived orbit-effective density products (Sutton et al., 2021; Fitzpatrick et al., 2026), which provide information about the integrated thermospheric state but are further removed from the physical processes driving thermospheric variability.

The DYNAMIC OSSEs also produced an unexpected and important result regarding the relative information content of the observables under investigation. For instance, assimilation scenarios incorporating neutral wind measurements consistently outperformed temperature-only assimilation scenarios during a major geomagnetic disturbance. In addition to improving representation of the thermospheric state, wind assimilation produced substantially more realistic estimates of the external geomagnetic drivers used by the model. This distinction is important because the IDEA framework seeks to estimate the physical drivers responsible for the observed atmospheric response rather than simply correcting model state variables, and by improving the realism of the energy inputs to the system, the assimilation process preserves physical consistency and enables improvements that can persist beyond the assimilation window and into the forecast window. The ultimate source of this advantage remains unclear, however. The result may reflect fundamentally higher information content within the wind observations, stronger coupling between winds and external forcing, or simply the higher-altitude coverage of the simulated wind measurements relative to the temperature observations used in the initial investigation.

These findings underscore several important questions that are directly relevant to GDC Trailblazer, DYNAMIC (now selected by NASA and renamed the Dynamic Atmosphere- IonosPHere Neutral Explorers: DAPHNE), and the growing ecosystem of operational and commercial observations. While commercial constellations are increasingly capable of producing GNSS-derived orbit-effective density measurements, the extent to which such integrated density products alone can constrain thermospheric forcing and support accurate forecasts remains largely unknown. In contrast, science-grade instrumentation such as the MoSAIC instrument on GDC Trailblazer and the remote-sensing measurements planned for DAPHNE will provide direct observations of key thermospheric state variables, including composition, temperature, and winds. Of particular interest are global composition measurements, which have been largely unavailable for several decades despite their strong connection to thermospheric circulation, composition transport, and external forcing. Determining the relative and combined value of these diverse observing systems is therefore a critical step toward the development of future thermospheric DA systems and operational forecasting capabilities.

Previous OSSE studies have highlighted important open questions regarding the relative information content of thermospheric observables. For example, results suggest that wind measurements can, in some cases, provide stronger constraints on external drivers than temperature measurements, potentially due to differences in altitude sensitivity or dynamical coupling. Additionally, global composition measurements largely absent for several decades are expected to provide strong constraints on large-scale circulation and forcing processes. These considerations motivate a focused investigation into the specific contributions of the future GDC Trailblazer and DAHNE mission observables within a modern data assimilation context.

2. Scope of Work To address these questions, targeted OSSEs will employ a physics-based thermospheric model as

-based assimilation experiments. Synthetic observations and errors will be constructed for thermospheric parameters sensed by the GDC Trailblazer and DAPHNE missions, based on the most up- to-date mission CONOPS and instrument performance requirements that are available. The OSSEs will be designed to isolate the impact of specific GDC Trailblazer and DAPHNE measurement types and quantify their contribution to thermospheric specification and short-term prediction.

The OSSEs conducted during this 1-year eEort will consist of several potential scenarios:

1. In situ GDC Trailblazer/MoSAIC observations:

a. composition,

b. temperature, and/or

c. winds

2. Remotely sensed DAPHNE observations:

a. day-time relative composition profiles,

b. day-time temperature profiles, and/or

c. winds

3. GNSS-derived orbit-effective mass densities

4. Combinations of observables

The OSSEs will be conducted with a nature run driven by realistic storm-time forcing (that is unknown to the assimilative OSSE scenarios) and a control/analysis framework that estimates key drivers (i.e., solar irradiance and geomagnetic indices). Simulations will focus on representative geomagnetic storm periods to capture conditions where observational constraints are most critical. Results will be evaluated in terms of their ability to reconstruct thermospheric state variables and accurately recover estimates of the true forcing history.

3. Deliverables The Contractor shall determine answers to the following:

What is the relative impact of composition, temperature, and/or winds on the performance of an assimilative system?

What is the relative importance of altitudinal coverage on the performance of an assimilative system?

How can missions with science-grade instrumentation work alongside GNSS-based observables to enhance predictability?

4. Period of Performance The Period of Performance shall extend from the effective August 1, 2026 (or upon award) September 30, 2027.