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Introduction:
Very Low Earth Orbit (VLEO), defined as altitudes below 450 km, offers several advantages for satellite operations. However, the significant atmospheric drag at these altitudes poses a challenge for maintaining satellite stability and lifespan. The Defense Advanced Research Projects Agency (DARPA) recognizes the potential of energy harvesting technologies to overcome this hurdle and is seeking innovative solutions for the VLEO environment. This article explores the challenges and opportunities in energy harvesting for VLEO, and outlines the key areas of interest for DARPA’s energy harvesting demonstration program.
Benefits and Challenges of VLEO:
Satellites have traditionally been launched to orbits above the Earth’s residual atmosphere to avoid atmospheric drag limiting their orbital lifetime. In VLEO, generally considered to be orbital altitudes between 90km-450km, atmospheric drag has a significant impact on the design of satellites that operate there, with drag increasing significantly at the lower altitudes.
VLEO offers numerous benefits for satellite operations. Firstly, operating within the residual atmosphere provides a more benign radiation environment, which can enhance the reliability and longevity of satellites. Additionally, launching payloads to lower altitude orbits reduces launch costs, as less energy is required to reach these orbits.
However, the atmospheric drag at VLEO altitudes poses a significant challenge. Satellites and debris objects in VLEO are naturally pulled from orbit within a short period unless drag is compensated. This necessitates the development of energy harvesting technologies to sustain power and counteract the effects of atmospheric drag.
For in-depth understanding on VLEO Satellites technology and applications please visit: VLEO Satellites: Unlocking the Potential of Very Low Earth Orbit
Technical Challenges in VLEO Energy Harvesting:
- Energy Harvesting Approach: Determining the most suitable approach for energy harvesting in the VLEO environment is crucial. Researchers need to identify physics phenomena with the highest potential for maximum energy harvesting. This may involve exploring concepts such as solar power, electromagnetic induction, thermoelectric conversion, or other innovative methods.
- Energy Harvesting Technology Integration: The energy harvesting technology should be optimized to operate in the harsh VLEO environment. Designers must consider the survivability of materials and approaches over several years, accounting for extreme temperature fluctuations, radiation exposure, and other environmental factors.
- Energy and Thermal Management: It is essential to control the energy harvesting process to avoid overwhelming the electrical supply and storage system. Excessive heating resulting from energy harvesting approaches must also be addressed to prevent damage to the spacecraft.
- Modeling and Simulation (M&S): Developing and validating new design tools, experimental approaches, and computational codes are critical for better understanding and characterization of VLEO energy harvesting technologies. These tools can aid in the optimization of energy harvesting systems and their integration into spacecraft design.
- Technology Maturation and Application: Energy harvesting technology must be sufficiently matured to be incorporated into the design process of new spacecraft. This requires addressing reliability, scalability, manufacturability, and cost-effectiveness to enable widespread adoption in the industry.
DARPA’s Focus and Requested Information:
DARPA is seeking responses from various sources, including private and public companies, research institutions, universities, and government-sponsored labs. The following areas of interest should be addressed in the responses:
- Technical Description: Provide a detailed description of energy harvesting component-level technologies and their scalability to different altitudes within the VLEO regime, with a focus on solutions relevant to lower altitudes.
- Confidence in Designing Spacecraft: Assess the current state of the art modeling and simulation tools and design tools, and evaluate the industry’s confidence in designing spacecraft with energy harvesting capabilities.
- Testing and Feasibility: Describe completed testing and compare the results to modeling and simulation predictions to demonstrate the feasibility and performance of energy harvesting technologies.
- Modeling and Simulation Tools: Describe existing modeling and simulation tools that are relevant to integration with spacecraft design and optimization techniques, with a specific interest in rarefied, multi-species flow field results.
- Flight Demonstration Concepts: Present initial concepts for the flight demonstration of a space platform at a relevant scale and operating conditions to showcase the capabilities of energy harvesting in VLEO.
Harnessing the Atmosphere for Space Travel
Traditional satellites are constrained by their reliance on finite propellant supplies, which limits their operational lifespan and mission scope. Air-breathing propulsion offers a revolutionary shift from this paradigm by capturing atmospheric gases and using them as fuel. This could enable satellites to operate indefinitely, significantly extending their mission capabilities in data collection, communication, and scientific research.
Air-breathing plasma propulsion for satellites is an innovative concept that could significantly extend the operational lifespan of satellites in very low Earth orbit (VLEO). Unlike traditional satellites that rely on finite onboard propellants, this technology proposes using atmospheric gases available at VLEO altitudes as a continuous source of propellant. By ionizing these gases into plasma and expelling them through thrusters, satellites could maintain their orbits for longer periods without the need for refueling, potentially reducing launch costs and increasing mission flexibility.
A key technical challenge in developing air-breathing plasma thrusters is ensuring the neutralization of the plasma as it exits the thruster. If the ions and electrons expelled are not balanced, it could lead to electrical imbalances on the satellite, causing operational issues. Researchers at the Princeton Plasma Physics Laboratory (PPPL) are working on sophisticated plasma diagnostics to measure and control the plasma’s properties, ensuring that the positive and negative charges are properly neutralized to avoid these problems.
The project, a collaboration between George Washington University (GWU) and PPPL, is funded by the Defense Advanced Research Projects Agency (DARPA), reflecting its strategic importance. Researchers are using advanced techniques like laser-induced fluorescence and specialized probes to study and refine the plasma thruster design. If successful, this technology could revolutionize satellite operations, making them more sustainable, cost-effective, and capable of longer and more ambitious missions in space.
The Potential Benefits
The successful implementation of air-breathing propulsion could have profound implications for space exploration:
- Extended Lifespan: Satellites equipped with air-breathing technology could operate for much longer periods, reducing the need for frequent and costly launch missions.
- Enhanced Capabilities: With a virtually limitless fuel supply, satellites could embark on more ambitious missions, including prolonged Earth observation and deep space exploration.
- Lower Costs: By reducing dependence on traditional propellants, operational costs could decrease, making space more accessible for a wider range of applications.
Despite the promise, the road to fully realizing air-breathing propulsion is fraught with technical challenges. One critical issue is ensuring the thruster operates efficiently while neutralizing charged particles to prevent damage to the satellite. Additionally, the complex interaction between the thruster and the Earth’s atmosphere requires sophisticated engineering and extensive testing.
Neutralization of Plasma: When ions are expelled from the thruster, they must be balanced by an equal number of electrons to avoid creating an electric charge on the satellite. If the charge isn’t neutralized, it can cause issues like attracting the expelled ions back to the satellite or creating electrical imbalances that can disrupt satellite electronics.
PPPL’s Role: The Princeton Plasma Physics Laboratory is focusing on ensuring that the plasma beam is neutralized as it leaves the thruster. This involves sophisticated plasma diagnostics to measure ion velocities, densities, and temperatures, ensuring that the positive and negative charges are balanced. Special probes developed at PPPL measure the density and temperature of the plasma’s negatively charged particles (electrons). This helps in fine-tuning the thruster design to ensure effective neutralization.
Companies like Kreios Space are also advancing in the development of air-breathing technology, reflecting the growing interest and competition in this cutting-edge field.
The pursuit of air-breathing propulsion technology represents a pivotal moment in satellite technology’s evolution. If successfully developed, it could usher in a new era of space exploration characterized by satellites that are longer-lasting, more capable, and cost-effective.
Conclusion:
Energy harvesting technologies hold immense potential to overcome the challenges of operating in Very Low Earth Orbit. By addressing the technical challenges, optimizing integration, ensuring energy and thermal management, developing modeling and simulation tools, and maturing the technology, we can unlock the benefits of VLEO while extending satellite lifespans and reducing launch costs. DARPA’s energy harvesting demonstration program seeks innovative ideas and concepts to shape the future of VLEO operations, ultimately leading to more sustainable and efficient satellite missions.
