Tracking Satellites with the Murchison Widefield Array

The increase in satellites orbiting Earth has led to a greater need for understanding what is happening in space. This understanding is known as Space Domain Awareness (SDA). To help with SDA, scientists are using tools like wide field-of-view sensor systems that can detect many objects in the sky at once. This article discusses how one such tool, the Murchison Widefield Array (MWA), is being used to track satellites in Low Earth Orbit (LEO).

#What is the Murchison Widefield Array?

The MWA is a radio telescope located in Western Australia. It was originally built for astronomy but has shown it can be useful for tracking satellites. The MWA has many antennas that work together to observe radio waves from space. By listening for these signals, scientists can gather information about various celestial objects, including satellites.

#How Does the MWA Work for Tracking Satellites?

The primary method the MWA uses is called non-coherent passive radar. Instead of emitting radar signals, it listens for signals reflected off satellites. These signals are often terrestrial FM radio signals that bounce off satellites and return to Earth. The MWA can detect these reflected signals even though they may appear smeared across the sky due to the movement of the satellites.

#Challenges of Tracking Satellites

When the MWA detects signals from satellites, it faces challenges. The signals are distorted, making it difficult to pinpoint the exact location of a satellite. To address this issue, scientists have developed techniques to extract meaningful data from these distorted signals. By analyzing the patterns of the reflected signals, they can estimate the satellite's position at various times.

#Collecting Data from LEO Satellites

Researchers performed tests using the MWA to track multiple LEO satellites. They aimed to gather data on the satellites' locations and movements. By monitoring 32 different satellite passes, they were able to collect enough information to estimate satellite orbits. This information is crucial in maintaining an accurate record of where satellites are located in their paths around Earth.

#Improving Accuracy in Predictions

To enhance prediction accuracy, scientists use a method called least-squares fitting. This statistical technique helps them compare their satellite position estimates with known data. They can adjust their models based on discrepancies between the observed and estimated positions. This way, they can refine their understanding of how satellites move.

#Comparing to Existing Data

One way researchers validate their findings is by comparing their estimated positions with publicly available data from the Space Surveillance Network (SSN). The SSN regularly updates two-line element (TLE) data, which provides information about the orbits of satellites. By matching their predictions against the TLE data, researchers can confirm whether their methods are accurate.

#The Need for Regular Updates

Satellites do not follow fixed paths; their orbits can change due to factors like atmospheric drag and gravitational influences. To ensure the data remains accurate, the orbital elements of the satellites must be updated regularly. This involves using techniques that allow for timely adjustments to the satellite catalog.

#The Role of Multiple Sensors

To maintain an updated catalog of satellites, multiple sensors are essential. The MWA works with other sensors that may have different capabilities. For instance, some sensors can provide more precise measurements from a smaller field of view. By combining data from various sources, scientists can create a comprehensive understanding of the satellite environment.

#Using Archived Data

Interestingly, many of the techniques and analyses developed for current observations can also be applied to archived data. This means that scientists can revisit earlier observations made by the MWA and extract useful information that could help improve satellite tracking.

#How Observations are Made

The MWA gathers data over short time frames, typically around seconds. During these brief periods, it captures the signals from satellites as they move across the sky. This high-speed monitoring allows researchers to detect and track the motion of satellites more effectively.

#Signal Processing Techniques

To get the most accurate readings from the detected signals, various signal processing techniques are employed. These include stacking signals from different frequency channels to enhance the overall quality of the data. By improving the signal-to-noise ratio, scientists can better isolate the satellite signals from other background noise.

#Understanding the Effects on Observations

The MWA's ability to detect satellites relies on understanding how the signals behave. For instance, the layout of the antennas and the design of the telescope can affect the clarity of the signals received. Researchers need to consider these factors to improve detection and tracking of satellites.

#Validation of Tracking Methods

To prove that their methods are reliable, scientists conducted tests for re-acquisition of tracked satellites. They used the data collected during previous passes to predict where a satellite would appear next. When the predicted position closely matched the actual observation, it confirmed the effectiveness of their tracking methods.

#Accuracy of Position Measurements

Measuring the position of satellites involves careful calculations and the use of statistical models. Scientists have found that the angular position measurements they obtain through the MWA are accurate enough to support collaboration with other sensors. While precision is crucial, the overall approach must also focus on gathering data in real-time.

#The Importance of a Reference Catalog

For the MWA to function effectively within the global SDA framework, it must maintain a reliable reference catalog. This catalog contains information about satellites that reflect FM signals, enabling researchers to predict and filter out potential sources of interference in their observations.

#The Impact of LEO Satellites on Astronomy

The presence of LEO satellites can interfere with astronomical observations. Understanding the orbit and behavior of these satellites allows researchers to adjust their methods and mitigate any disruption. By maintaining an accurate catalog of reflective satellites, scientists can implement strategies to minimize any adverse effects.

#The Future of SDA Observations

As the number of satellites in low Earth orbit continues to grow, the importance of SDA will only increase. The MWA can play a critical role in this landscape by providing valuable data that can help scientists and engineers understand the risks posed by satellite congestion.

#Conclusion

The ongoing development of Space Domain Awareness capabilities using tools like the Murchison Widefield Array represents an exciting advancement in our ability to monitor and understand the environment around Earth. By constantly refining methods and collaborating with other systems, scientists can help ensure safe and efficient operation in increasingly crowded orbital pathways. The work done with the MWA is just one part of a larger effort to maintain awareness and understanding of the ever-evolving space environment, benefiting both satellite operators and the broader astronomical community.