August 24, 2021

While there are numerous ways to land a spacecraft on Mars, there’s no single perfect method. One strategy might get a rover there faster, but demand a lot of computational power on board. Another might land with more precision but take longer to reach its destination, requiring more fuel. Complicating the issue is that technology is advancing rapidly, meaning scientists and engineers have to keep up if they want to optimize planetary landings.

“We still need to develop more advanced guidance strategies for future planetary exploration missions,” said Ming Xin, a professor of mechanical and aerospace engineering. “The technology in sensing and computation is progressing very fast, so we will have new challenges and capabilities. We need to take advantage of these technological advancements and design new strategies to achieve better performance to make future exploration safer, more accurate and more efficient.”

To help guide that process, Xin and his collaborators recently conducted a comprehensive study of five popular guidance laws and strategies for power descent planetary landings. They published their findings in Acta Astronautica, a journal sponsored by the International Academy of Astronautics.

Guidance laws help engineers plan the trajectory of a vehicle’s path from Earth to either Mars or the moon.

When determining the best way to land a spacecraft on another planet, there are a lot of considerations. The unmanned vehicle has to be autonomous since there’s no way to remotely control it in real time once it reaches a certain distance from Earth. There are also considerations such as fuel consumption, how long the trip will take and computational resources inside the spacecraft.

Terrain also plays a major role — the surface of Mars and the moon have hills and craters that can damage a spacecraft, making it necessary to equip the lander and rover with the ability to avoid hazards.

To compare the guidance strategies and various considerations, Xin and his collaborators developed simulated models using data from the Mars Science Laboratory, a robotic space probe mission NASA launched in 2011. The laboratory successfully landed the Curiosity rover on Mars in 2012.

“In the past, these guidance strategies have been intensively researched, but nobody has done a very comprehensive comparison among the guidance strategies,” Xin said. “In this paper, we found some strategies are better in one aspect but not other aspects. Every guidance strategy has its own pros and cons.”

While the paper compared current landing methods, Xin is also working on new ways to guide future landings.

“Many researchers, including my group, are designing new guidance strategies for the power descent landing of space vehicles,” he said. “We need to plan the trajectory of vehicles in the most optimal way.”