Camella Nasr, Research Scientist Scientists are always looking for better ways to model the ionosphere, the upper layer of Earth’s atmosphere that affects radio signals. One promising but underutilized tool is the Oblique Ionogram (OI) , which measures how long high-frequency (HF) radio waves take to travel between a transmitter and a receiver that are far apart. Unlike Vertical Ionograms (VIs) —which measure signals traveling straight up and down—OIs are more complex because HF waves take different paths depending on frequency. Until now, their potential for improving ionospheric models had not been fully explored.  Converting Oblique Ionograms into Vertical Ionograms   To make OI data easier to use, Orion developed a method to convert OIs into equivalent VIs , placing them at the midpoint between the transmitter and receiver. This transformation allowed researchers to test whether incorporating OI data into ionospheric models would improve their accuracy.  The approach was tested using a simulation experiment over the continental U.S. (CONUS), which involved:  Simulating OIs  – Tracing HF signals at different frequencies and recording the time delays.  Transforming the Data  – Converting these delays into vertical equivalents using a midpoint formula.  Generating Electron Density Profiles (EDPs)  – Using the POLAN program to calculate electron density in the lower ionosphere.  Assimilating Data  – Feeding the EDPs into Orion’s Modern Modular Model for Space Data Assimilation (M3SDA) using an Extended Kalman Filter (EKF).  Comparing Model Performance   The study compared how well ionospheric models performed with and without OI data:   Baseline 1 (I)  – Models using only ionosonde (ground-based radar) data.  Baseline 2 (IRG)  – Models using ionosonde data plus Total Electron Content (TEC) and Radio Occultation (RO) data.  Key Findings:   In the ionosonde-only baseline , adding OI data improved accuracy by reducing foF2 errors (a key ionospheric measurement) by about 0.5 MHz on average . However, results varied by location and time. In the Midwest, accuracy actually decreased, likely due to strong horizontal ionospheric gradients (sudden changes in electron density) affecting OI data.  In the IRG baseline , adding OI data improved accuracy by about 0.25 MHz across CONUS , but certain areas—like the West Coast and Florida—saw performance drop by 0.15 MHz .  Lessons Learned and Next Steps   This research shows that while OI data can significantly improve ionospheric models, it doesn’t always help. In some regions, the transformation method struggled with complex ionospheric conditions, particularly where horizontal gradients were strong.  Moving forward, Orion will refine the transformation process to better handle these challenges. Future research will focus on identifying when and where OI data is most beneficial, ensuring it is used in ways that maximize its value for space weather forecasting.  This study marks an important step in harnessing Oblique Ionograms to enhance our understanding of the ionosphere . Stay tuned as we continue to unlock their full potential in space science!  Click the link below to view the poster presentation of this work.

Joseph Hughes, Research Scientist Space debris presents a growing challenge for satellite missions, and even small pieces of debris pose significant risks to operational spacecraft. However, tracking these small objects, particularly those smaller than 10 cm, has proven difficult. At Orion, we are exploring innovative methods to tackle this issue, focusing on disturbances in the very low frequency (VLF) electric field as a potential solution through our Space Debris Identification and Tracking (SINTRA) program. The problem of space debris detection   While larger pieces of space debris (greater than 10 cm) can be tracked, smaller objects are harder to detect with traditional radar or optical systems. However, these tiny objects still have the potential to cause mission-ending damage, so finding a way to detect them has become a critical focus in the field of space safety. As we become more of spacefaring society, tracking and mitigating this debris will be essential to ensuring the safety and sustainability of future space travel and exploration. A novel approach: Disturbances in the electric field To address this, we investigated the potential of using plasma waves excited by "generator" objects in low Earth orbit (LEO) to detect disturbances in the VLF electric field. The idea is that certain objects, particularly those with unique electromagnetic signatures, could cause measurable perturbations in the electric field that could be detected by nearby spacecraft with appropriate instruments. In our study, we leveraged data from the Plasma Wave Experiment (PWE) onboard the Japanese Aerospace Exploration Agency (JAXA)’s Arase spacecraft. The PWE instrument, which includes an Onboard Frequency Analyzer (OFA), measures VLF electric field power in space, providing valuable insights into plasma waves and disturbances caused by nearby objects. Analyzing the data To comprehensively analyze the conditions that lead to these electric field perturbations, we examined five months of data from the Arase spacecraft. During this period, we identified conjunctions—instances when Arase came within 300 km of objects in the Space-Track database1. These conjunctions were particularly valuable as they occurred during Arase’s highly elliptical orbit, where it spends approximately 15 minutes per orbit at altitudes below 1,000 km (the “perigee passes”). For each perigee pass, we collected detailed information on the geometry of the conjunctions, the Earth’s magnetic field (using IGRF data), electron density (using IRI data), and the corresponding VLF E field measurements from Arase’s instruments. Results: Disturbances and plasma waves Through the analysis of hundreds of perigee passes, we observed frequent plasma wave occurrences that exhibited characteristics consistent with different wave types. We focused on testing three hypotheses related to the electric field power and its correlation with nearby space debris: Arase measures higher E field power when near a generator object Arase measures higher E field power when in the wake of a generator object Arase measures higher E field power when along the same magnetic field line as a generator object Our results strongly supported the first and third hypotheses, with a significant correlation (p ~ 0.0001) observed for both. This means that when Arase passed near a generator object or along the same magnetic field line, we saw a measurable increase in E field power, indicating the presence of disturbances that may be linked to nearby space debris. Implications for space debris detection   These findings provide promising evidence that disturbances in the VLF electric field could serve as an effective method for detecting small space debris. By monitoring plasma wave activity during spacecraft orbits, we could potentially track objects that are too small to be detected by traditional means. This approach opens up new possibilities for space safety, allowing for earlier detection of debris and better protection for active spacecraft. Space debris poses significant challenges for the future of space exploration and satellite operations. Innovative approaches, such as detecting VLF electric field disturbances, offer promising pathways for improving debris detection and mitigation strategies. This research contributes to a deeper understanding of the space environment and helps advance efforts to ensure the long-term sustainability of space activities. This work was previously presented at the American Geophysical Union’s Fall Meeting for 2024. Click the link below to view the poster. 1 Space-Track.org promotes spaceflight safety, protection of the space environment and the peaceful use of space worldwide by sharing space situational awareness services and information.