AE Ph.D. student named one of NASA's FINESST

When a spacecraft lands on the Moon or a planet, the plume from the landing thrusters interacts with the surface, kicking up more than just a bit of dust. Aerospace engineering Ph.D. student Nicolas Rasmont was named as one of NASA’s Future Investigators in NASA Earth and Space Science and Technology Program to develop a method to accurately measure plume-surface interaction properties. FINESST is a highly competitive program, selecting only about 15 percent of the 800 to 900 proposals, and provides $150,000 of funding for up to three years of graduate studies.

“A human-class vehicle landing on the Moon generates several tons of highly abrasive, micron-sized supersonic ejecta that can cause significant damage to any infrastructure located near the landing site, as well as to the lander itself, and even possibly to spacecraft in lunar orbit,” Rasmont said.  “The risks of plume-surface interaction are not merely theoretical. The cloud of dust raised during the landing of Apollo 15 hid a large crater from astronauts Irwin and Scott’s view, for example, which caused a hard landing nearly aborting the mission. On Mars, one of the wind sensors of the Curiosity rover was destroyed by a debris kicked by its rocket exhaust during landing. And as spacecraft become heavier, the interaction will be greater, leading to increased risks for the astronauts. We can expect that plume-surface interactions will be a significant design challenge for the Starship Human Landing System, which is currently planned by NASA for its return to the Moon and is nearly 100 times heavier than the earlier Apollo Lunar Module.”

In preparation for its future missions to the Moon and Mars, NASA has undertaken a large project to study plume-surface interactions, and the development of innovative experimental diagnostics is an important part of this effort.  Rasmont said that state-of-the-art optical methods to measure ejecta properties are limited by the opacity of particles in the visible spectrum, and by the requirement to know their size to get correct measurements. This requirement is difficult to meet if the landing takes place on poorly characterized ground, like a lunar surface, and if a spatial segregation of particles takes place in the cloud.

The method Rasmont invented, called Radar Interferometry For Landing Ejecta, is based on a measurement concept commonly used in a wide range of fields, from plasma physics to medical and industrial applications.

“RIFLE consists in measuring the phase shift of an electromagnetic wave with a frequency of 10 to a 100 GHz traveling between a receiver and a transmitter,” Rasmont said. “When ejecta particles are present along this travel path, the waves are delayed slightly, which can be measured as a phase shift on the receiver signal and correlated with the concentration of the particles.

“This approach has two benefits,” Rasmont said. “RIFLE makes it possible to measure particle concentrations ten to a hundred times higher than optical methods, which makes this instrument particularly suitable for the study of dense ejecta clouds, for example near the jet impingement point on the surface.  Additionally, its measurements are independent from particle size, which makes it more robust and flexible than optical methods.”

In his Ph.D. program, Rasmont works with Professors Laura Villafañe Roca, Greg Elliott, and Joshua Rovey.

“The FINESST award provides us with a unique opportunity to develop RIFLE from the proof-of-concept stage to a practical laboratory instrument capable of providing high-quality data in large scale plume-surface interaction experiments, such as those conducted at NASA,” Rasmont said. “My ultimate goal would be to develop RIFLE into a flight instrument that would be sent on a lunar mission. Performing measurements in-situ on the moon would be invaluable for advancing PSI studies, and FINESST is a first step in this direction.”