Engineers have developed an innovative guidance system that helps reusable rockets make more precise landings on Earth, even in challenging atmospheric conditions like strong winds and engine fluctuations. The advancement could make rocket landings more reliable while using less fuel.
Published in Chinese Journal of Aeronautics | Estimated reading time: 4 minutes
Landing a rocket vertically is an intricate ballet of physics and engineering. Unlike spacecraft landing on the Moon or Mars, rockets returning to Earth must contend with complex atmospheric conditions that can push them off course. Wind gusts create persistent aerodynamic forces, while variations in engine thrust and atmospheric dynamics add further complications.
A research team led by Professors Huifeng Li and Ran Zhang from Beihang University has developed a new approach to this challenge. Their method, called Endoatmospheric Powered Descent Guidance with Disturbance Rejection (Endo-PDG-DR), helps rockets adapt to both predictable and unpredictable disturbances during descent.
“In this work, we formulated a novel problem by dividing and conquering disturbances,” said Huifeng Li, professor at School of Astronautics at Beihang University. “The disturbances are divided into two parts, modeled and unmodeled disturbances; as a result, two different disturbance rejection strategies are accordingly adopted to deal with the two kinds of disturbances.”
The system works by continuously calculating optimal trajectories while actively compensating for atmospheric disturbances. When the rocket encounters known types of interference, like typical wind patterns, it proactively adjusts its path. For unexpected disturbances, the system reactively attenuates their effects through real-time course corrections.
The researchers validated their approach through extensive computer simulations. The results showed that rockets using this guidance system could land with errors of less than 0.1 meters in position and 0.1 meters per second in velocity – even under challenging conditions with wind speeds up to several meters per second and significant engine thrust variations.
This research represents an important step toward making reusable rockets more practical and reliable. While current rockets can already land successfully in good conditions, this new system could help them maintain precision even in difficult weather, potentially reducing launch delays and operating costs.
The team suggests several directions for future improvements, including online model identification, highly constrained optimal trajectory generation, and guidance parameter learning.
Glossary:
- Powered Descent Guidance (PDG): The technology that controls a rocket’s engines during landing to guide it safely to the ground
- Endoatmospheric: Occurring within Earth’s atmosphere, where aerodynamic forces significantly affect flight
- Disturbance Rejection: The ability of a control system to maintain stable performance despite external interference
Test Your Knowledge
What is the main challenge rockets face when landing on Earth compared to the Moon?
Earth’s atmosphere creates complex aerodynamic forces and disturbances that aren’t present during lunar landings.
How does the new guidance system handle different types of disturbances?
It divides disturbances into two categories: modeled (predictable) disturbances that it proactively adjusts for, and unmodeled (unexpected) disturbances that it reactively compensates for.
What level of landing precision did the system achieve in simulations?
The system achieved position errors of less than 0.1 meters and velocity errors of less than 0.1 meters per second.
How does the Pseudospectral Differential Dynamic Programming method improve upon traditional approaches?
It provides better computational efficiency and convergence characteristics by using global polynomial approximations and Gaussian quadrature collocation points, leading to more reliable numerical solutions.
Enjoy this story? Subscribe to our newsletter at scienceblog.substack.com.