Nilton Renno: Harnessing Hypervelocity Signals to Detect the Invisible Threat of Space Debris

EcoAero had the privilege of interviewing Professor Nilton Renno, an esteemed aerospace engineering professor at the University of Michigan. With over three decades of experience in planetary science, particularly in the field of Mars missions, Professor Renno’s expertise spans the entire spectrum of space exploration.

Around three years ago, Professor Renno embarked on a collaborative journey with private companies, aiming to develop cutting-edge technologies for future space missions. This endeavor led him to confront a critical challenge: the detection of space debris, particularly those too small to be tracked with current technologies. Professor Renno drew parallels between monitoring the Martian atmosphere and the detection of space debris. He observed the collisions of sands in Martian storms, which produced a charge and a range of signals that could be detected. This observation inspired him to develop technologies capable of detecting signals generated by space debris collisions, specifically involving small debris and meteorites. The signals generated during collisions at orbital velocity were found to be strong enough to be detected. This became Professor Renno’s primary focus, and after two years of dedicated work, his team was astounded by their remarkable discoveries. Professor Renno and his team had uncovered the astonishing strength of the signals generated during hypervelocity collisions. These collisions occur when the relative speeds of the colliding objects exceed the speed of sound in the materials involved. The resulting shockwave and substantial heat vaporize the materials, creating an expanding plasma cloud. At the heart of Professor Renno’s team’s research lies the concept of harnessing these powerful signals to detect collisions in space debris. Their ongoing efforts aim to unlock the potential of these signals, paving the way for more efficient and effective space exploration. 

Professor Renno’s research on detecting small debris led to the discovery of a technique to detect electromagnetic signals from space debris collisions. Unlike traditional radar or optical detection methods, this technique offers several advantages. Traditional radar involves a radar on Earth’s surface emitting a signal to space. As the signal travels further, it weakens. Additionally, the small collision cross-section (the area of material to be detected) limits the smallest size detectable to approximately 10 centimeters by 10 centimeters, known as CubeSats. Consequently, radar is primarily used in low Earth orbit (LEO) to detect objects like CubeSats. In higher orbits, optical signals are employed due to the availability of large optical telescopes on the ground and the sunlight as the source of optical signals. For geostationary orbits (GEO), objects are typically detected after sunset when the sun is still present but the sky is darkening. This allows telescopes to observe these objects as bright. However, the minimum size detectable in these orbits is a meter by a meter, making conventional radar and optical methods ineffective in detecting millimeter-sized debris. The proposed technique by Professor Renno has a significant advantage: it can detect peanut-sized debris. Moreover, it can detect objects at any distance from LEO to GEO and vice versa. This technique can also be utilized with instruments in space, enabling detection from both ground-based and space-based satellites. 

We then inquired about the scalability of this technology from Professor Renno. He advised us to focus on his current projects, which involve two main steps. The first step involves solving numerical equations for collisions and the signals they emit. It also involves conducting lab experiments where debris is shot at high velocities to measure the signals and compare them to simulations. These experiments serve as a verification of the simulation’s accuracy. The second step that Professor Renno and his team are currently working on is utilizing ground-based telescopes and observatories to make measurements. They have identified the signatures they seek, but they are facing challenges due to the presence of noise. For instance, lighting can produce significant noise during detection, and atmospheric changes can alter the frequency and signals that are typically present in space. The primary challenge for separating signals from noise in the case of small debris is the current focus of their research. Detection in space becomes easier due to the reduced noise levels. If these challenges are successfully overcome, we can proceed to the next phase, which involves scaling this technology. This would require the establishment of a ground network of optical telescopes to monitor traffic in LEO.

Given the industry’s and mainstream discussions about artificial intelligence and machine learning in the aerospace field, Professor Renno shared his insights. He’s currently collaborating with a company called Blue Halo, which focuses on AI and developing AI to distinguish signals from various objects. Similarly, with the advancement of space debris mitigation technologies, Professor Renno believes that achieving long-term sustainability in space orbit requires preventing catastrophic events in space. While robotic debris capturing systems can be costly and inefficient, the best strategy is to capture satellites before they disintegrate and become debris. Lastly, Professor Renno emphasizes the crucial role of space policy in achieving space sustainability. He believes that pre-launch approvals are essential and provides an example of SpaceX’s Starlink, where improper precautions led to collisions in orbit, creating a significant field of space debris.

In conclusion, EcoAero’s interview with Professor Renno provided valuable insights into the field of space sustainability. The exponential growth in the use of LEO is causing it to become increasingly congested, leading to more dangerous collisions within the orbital domain. Therefore, it’s crucial that academics like Professor Renno and companies like Northrop Grumman collaborate to find creative and innovative solutions that are financially feasible and realistic. At EcoAero, we continue to pursue research in this area to promote the best solutions for achieving space sustainability.