New research computes first step toward predicting lifespan of electric space propulsion systems

Electrical space propulsion programs use energized atoms to generate thrust. The high-speed beams of ions bump towards the graphite surfaces of the thruster, eroding them a bit extra with every hit, and are the programs’ major lifetime-limiting issue. When ion thrusters are floor examined in an enclosed chamber, the ricocheting particles of carbon from the graphite chamber partitions can even redeposit again onto the thruster surfaces. This adjustments the measured efficiency traits of the thruster.

Researchers on the College of Illinois Urbana-Champaign used information from low-pressure chamber experiments and large-scale computations to develop a mannequin to raised perceive the results of ion erosion on carbon surfaces —step one in predicting its failure.

“We want an correct evaluation of the ion erosion price on graphite to foretell thruster life, however testing services have reported various sputtering charges, resulting in massive uncertainties in predictions,” mentioned Huy Tran, a Ph.D. pupil within the Division of Aerospace Engineering at UIUC.

Tran mentioned it’s troublesome to copy the setting of space in a laboratory chamber as a result of it’s troublesome to assemble a sufficiently massive chamber to keep away from ion-surface interactions on the chamber partitions. And though graphite is usually used for the accelerator grid and pole covers within the thruster, there is not settlement on which sort of graphite is most proof against erosion, often called sputtering.

“The fundamental problem with testing an ion thruster in a chamber is that the thruster is constantly spitting out xenon ions that additionally affect with the chamber partitions made out of graphite panels, however there are not any chamber partitions in space,” Tran mentioned.

“When these xenon ions hit the graphite panels, in addition they sputter out carbon atoms that redeposit on the accelerator grids. So as an alternative of the grid changing into thinner and thinner due to thruster erosion, some folks have seen in experiments that the grids get thicker with time as a result of the carbon is getting back from the chamber partitions.”

The simulation resolved the constraints and uncertainties within the experimental data and the researchers gained perception right into a vital phenomenon.

“Whether or not it’s pyrolytic graphite on the grided ion optics, isotropic graphite on the pole covers, or poco graphite or anisotropic graphite on the chamber partitions, our molecular dynamics simulations present that the sputtering charges and mechanisms are similar throughout all these totally different referenced constructions,” mentioned Huck Beng Chew, Tran’s adviser.

He mentioned the sputtering course of creates a novel carbon construction in the course of the bombardment course of.

“When the ions come and injury the floor, they rework the floor into an amorphous-like construction whatever the preliminary carbon construction,” Chew mentioned. “You find yourself with a sputtered floor with the identical distinctive structural traits. This is among the primary findings that we’ve noticed from our simulations.”

Chew mentioned they even tried it with diamond. Whatever the a lot decrease preliminary porosity and the extra inflexible bond configuration, they bought the identical sputtered construction.

“The mannequin we developed bridges the molecular dynamics simulation outcomes to the experimental information,” Chew mentioned. “The following factor we need to take a look at is the evolving floor morphology over time as you place an increasing number of xenon ions into the system. That is related to ion thrusters for deep space exploration.”

The paper is printed within the journal Carbon.