Scientists demonstrate a novel rocket for deep-space exploration

Date:
December 22, 2021
Source:
DOE/Princeton Plasma Physics Laboratory
Summary:
The growing interest in deep-space exploration has sparked the
need for powerful long-lived rocket systems to drive spacecraft
through the cosmos. Scientists have developed a tiny version of
a Hall thruster propulsion system that increases the lifetime of
the rocket and produces high power.



FULL STORY ==========================================================================
The growing interest in deep-space exploration has sparked the need for powerful long-lived rocket systems to drive spacecraft through the cosmos.

Scientists at the U.S. Department of Energy's (DOE) Princeton Plasma
Physics Laboratory (PPPL) have now developed a tiny modified version
of a plasma-based propulsion system called a Hall thruster that both
increases the lifetime of the rocket and produces high power.


==========================================================================
The miniaturized system powered by plasma -- the state of matter composed
of free-floating electrons and atomic nuclei, or ions -- measures
little more than an inch in diameter and eliminates the walls around the
plasma propellent to create innovative thruster configurations. Among
these innovations are the cylindrical Hall thruster, first proposed and
studied at PPPL, and a fully wall-less Hall thruster. Both configurations reduce channel erosion caused by plasma-wall interactions that limit
the thruster lifetime -- a key problem for conventional annular, or ring-shaped, Hall thrusters and especially for miniaturized low-power
thrusters for applications on small satellites.

Widely studied Cylindrical Hall thrusters were invented by PPPL physicists Yevgeny Raitses and Nat Fisch in 1999 and have been studied with students
on the Laboratory's Hall Thruster Experiment (HTX) since then. The PPPL
devices have also been studied in countries including Korea, Japan, China, Singapore, and the European Union, with Korea and Singapore considering
plans to fly them.

While wall-less Hall thrusters can minimize channel erosion, they face
the problem of extensive widening, or divergence, of the plasma thrust
plume, which degrades the system's performance. To reduce this problem,
PPPL has installed a key innovation on its new wall-less system in
the form of a segmented electrode, a concentrically joined carrier of
current. This innovation not only reduces the divergence and helps to
intensify the rocket thrust, Raitses said, but also, suppresses the
hiccups of small-size Hall thruster plasmas that interrupt the smooth
delivery of power.

The new findings cap a series of papers that Jacob Simmonds, a graduate
student in the Princeton University Department of Mechanical and Aerospace Engineering, has published with Raitses, his doctoral co-adviser;
PPPL physicist Masaaki Yamada serves as the other co-advisor. "In the
last two years we have published three papers on new physics of plasma thrusters that led to the dynamic thruster described in this one," said Raitses, who leads PPPL research on low- temperature plasma physics and
the HTX. "It describes a novel effect that promises new developments
in this field." Application of segmented electrodes to Hall thrusters
is not new. Raitses and Fisch had previously used such electrodes to
control the plasma flow in conventional annular Hall thrusters. But
the effect that Simmonds measured and described in the recent paper in
Applied Physics Letters is much stronger and has greater impact on the
overall thruster operation and performance.



========================================================================== Focusing the plume The new device helps overcome the problem for wall-less
Hall thrusters that allows the plasma propellant to shoot from the rocket
at wide angles, contributing little to the rocket's thrust. "In short, wall-less Hall thrusters while promising have an unfocused plume because
of the lack of channel walls," Simmonds said. "So we needed to figure out
a way to focus the plume to increase the thrust and efficiency and make
it a better overall thruster for spacecraft." The segmented electrode
diverts some electric current away from the thruster's high-voltage
standard electrode to shape the plasma and narrow and improve the focus of
the plume. The electrode creates this effect by changing the directions
of the forces within the plasma, particularly those on the ionized xenon
plasma that the system accelerates to propel the rocket. Ionization
turned the xenon gas the process used into free-standing electrons and
atomic nuclei, or ions.

These developments increased the density of the thrust by shaping more of
it in a reduced volume, a key goal for Hall thrusters. An added benefit
of the segmented electrode has been the reduction of plasma instabilities called breathing mode oscillations, "where the amount of plasma increases
and decreases periodically as the ionization rate changes with time"
Simmonds said.

Surprisingly, he added, the segmented electrode caused these oscillations
to go away. "Segmented electrodes are very useful for Hall thrusters
for these reasons," he said.

The new high-thrust-density rocket can be especially beneficial for tiny
cubic satellites, or CubeSats. Masaaki Yamada, Simmonds' co-doctoral
adviser who heads the Magnetic Reconnection Experiment (MRX) that
studies the process behind solar flares, Northern lights and other space phenomena, proposed the use of a wall-less segmented electrode system
to power a CubeSat. Simmonds and his team of undergraduate students
working under the guidance of Prof. Daniel Marlow, the Evans Crawford
1911 Professor of Physics at Princeton, took up that proposal to develop
a CubeSat and such a rocket -- a project that was halted near completion
by the COVID-19 pandemic and that could be resumed in the future.

Support for this work comes from the DOE Office of Science.

========================================================================== Story Source: Materials provided by
DOE/Princeton_Plasma_Physics_Laboratory. Original written by John
Greenwald. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. J. Simmonds, Y. Raitses. Mitigation of breathing oscillations and
focusing of the plume in a segmented electrode wall-less Hall
thruster.

Applied Physics Letters, 2021; 119 (21): 213501 DOI:
10.1063/5.0070307 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2021/12/211222153015.htm

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