Research Sheds Light on Using Multiple CubeSats for In-Space Servicing and Repair Missions

In a significant advancement in aerospace engineering, researchers from the Department of Aerospace Engineering at the University of Illinois Urbana-Champaign have developed a groundbreaking methodology that enables multiple CubeSats to function effectively as servicing agents in assembling or repairing space telescopes. Given the increasing trend of building satellites and telescopes for the purpose of repairability, it becomes imperative to establish reliable trajectories that allow servicing spacecraft to navigate safely to their targets. This research, recently published in The Journal of the Astronautical Sciences, offers new insights into trajectory optimization that could transform in-space servicing operations.

As the complexity of space missions evolves, ensuring the successful servicing of orbiting satellites and telescopes will play a crucial role in extending their operational lifespans. The methodologies outlined by Bommena and Woollands address critical parameters such as fuel consumption, distance management, and trajectory planning, while simultaneously ensuring that servicing agents maintain safe separation distances.

Key Features of the Research

The methodology developed by the Illinois research team introduces several innovative features aimed at enhancing the operational efficiency of CubeSats within space environments. Key aspects include:

• Fuel-optimal Trajectories: The method minimizes fuel consumption, which is vital for extending the operational range of CubeSats in the challenging environment of space.
• Anti-collision Constraints: It guarantees that servicing agents maintain a minimum distance of 5 meters from each other during operations, thus preventing collisions that could compromise missions.
• Precomputation of Trajectories: Given the limited computation capabilities of CubeSats, trajectories are precomputed by mission design engineers. This ensures that CubeSats can execute their tasks without running into computational bottlenecks during operations.
• Simultaneous Operation Capability: The algorithm allows the execution of multiple vehicles simultaneously, which can transport modular components between service vehicles and target spacecraft.

Understanding the Challenges

Operating in space presents unique challenges, especially regarding the calculation of optimal trajectories across vast distances. The James Webb Space Telescope (JWST), for instance, orbits approximately 1.5 million kilometers from Earth, at the sun-Earth Lagrange Point 2 (L2). At this location, the gravitational forces of the sun and Earth create a stable orbital environment ideal for deep-space observations.

Bommena explains that the primary difficulty lies not only in the complex calculations required to determine optimal paths but also in overcoming the numerical challenges associated with vast distances in space. Traditional trajectory optimization methods often lead to complex trajectories requiring multiple arcs, which can increase computational demand significantly.

Innovative Methodology

Instead of relying on traditional methods, the research team employed indirect optimization techniques to ensure that their solutions were as fuel-efficient as possible. Bommena emphasizes, “Indirect optimization methods guarantee optimal solutions, while direct methods do not necessarily provide that assurance.”

Additionally, anti-collision constraints were incorporated as hard constraints within the optimal control framework. This approach allows trajectories to be solved as single arcs from start to destination, further improving fuel efficiency and computational effectiveness.

Dynamic Modeling Techniques

Another impressive outcome from this research is the creation of a novel target-relative circular restricted three-body problem dynamical model. This model effectively mitigates numerical complexities originating from the significant distances involved in the Earth-sun system. By shifting the center of the frame along the x-axis from the sun-Earth barycenter to the L2 location, the researchers developed equations of motion relative to the target spacecraft.

Bommena states, “We also introduced a new distance unit by applying a scaling factor that proportionally adjusts in relation to the original distance measurement.” This innovative modeling technique has the potential to serve beyond space missions, providing insights into other trajectory optimization scenarios that involve varied constraints.

The Research Journey

The development of this methodology took approximately a year and a half, culminating in a breakthrough that occurred during one of Bommena’s long-distance flights. “I was wrestling with numerics while coding on a flight. After trying several approaches, I stumbled upon the solution that converged. I initially couldn’t believe it; the moment was thrilling,” recalls Bommena.

Implications and Future Directions

While the application primarily focuses on enhancing the efficiency and safety of in-space servicing for telescopes, the versatility of the developed methodology opens doors for its implementation in various trajectory optimization scenarios. Researchers are optimistic that future studies will apply these principles across a broader range of spacecraft missions.

Conclusion

The work completed by the team at the University of Illinois signifies a pivotal step toward realizing sophisticated in-space servicing capabilities that can enhance the longevity and functionality of vital space observatories. The combined efforts to refine trajectory optimization and address collision avoidance will undeniably contribute to the future success of exploration missions in the increasingly populated zones of outer space.

References

Ruthvik Bommena et al., Indirect Trajectory Optimization with Path Constraints for Multi-Agent Proximity Operations, The Journal of the Astronautical Sciences (2024). DOI: 10.1007/s40295-024-00470-7.

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