Learning more about how spacecraft land

The focus this week has been on the launch of the spacecraft carrying the Perseverance rover to Mars (see mission status here), but scientists are rightly just as interested in how it – and future spacecraft – will land.

Among them are researchers at the University of Michigan who are using computer simulations to model the particulate mayhem set in motion by thruster-powered landings.

Mechanical engineer Jesse Capecelatro says exhaust plumes “fluidise” surface soil and dust during descent, forming craters and buffeting the lander with coarse, abrasive particles.

This presents a host of variables that can jeopardise the landing, but our understanding of millions of possible interactions is largely based on Apollo-era data.  It’s old, and doesn’t necessarily translate to locations other than the Moon.

“Landing-relevant data is very difficult to generate because you can’t just run an experiment on Earth,” he says. “Existing mathematical models break down in these more extreme conditions when particles approach supersonic speeds.”

Capecelatro’s team is developing physics-based models they say can be incorporated into codes used by NASA to help predict what will happen when a spacecraft attempts to land. This involves “messy turbulent flows” and simulating the behaviour of fluids made of two phases of matter – solid particles suspended in a gas.

Much of the work is done on a high-performance computing cluster that allows the team to partition the problem over hundreds or even thousands of processors simultaneously. But they can’t do it all.

To go deeper, Capecelatro says, he uses models – best guesses based on all available data – to push the simulations further. Data from the Perseverance landing on 18 February next year will be included.

“The largest supercomputers today can maybe handle a thousand particles where we directly capture all of the flow physics, so doing a full, square-kilometre landing site is out of the question.

“Our simulations provide the fundamental insight on the flow physics needed to develop improved mathematical models that their codes need to simulate a full-scale landing event.”

The goal is to provide a framework NASA can use to better predict how different designs will impact the ground and the landing, and adjust as necessary.

This will become even more important as NASA moves toward new crewed missions, Capecelatro says – and not just because there will be people on board.  Larger payloads mean stronger exhaust plumes interacting with the surface on landing.