Tech Briefs Magazine - May 2021 - 38

Propulsion

Rocket Thruster Exploits the Mechanism Behind Solar Flares
Thrusters based on magnetic reconnection could complete long-distance missions in a
shorter period of time.
Princeton Plasma Physics Laboratory, Princeton, New Jersey

new type of rocket thruster could
take humankind to Mars and beyond. The device would apply magnetic
fields to cause particles of plasma -
electrically charged gas also known as
the fourth state of matter - to shoot out
the back of a rocket and because of the
conservation of momentum, propel the
craft forward. Current space-proven
plasma thrusters use electric fields to
propel the particles.
The new concept would accelerate
the particles using magnetic reconnection, a process found throughout the universe - including the surface of the
Sun - in which magnetic field lines
converge, suddenly separate, and then
join together again, producing lots of
energy. Reconnection also occurs inside doughnut-shaped fusion devices
known as tokamaks.
Fusion, the power that drives the Sun
and stars, combines light elements in
the form of plasma - the hot, charged
state of matter composed of free electrons and atomic nuclei that represents
99% of the visible universe - to generate massive amounts of energy. Scientists
are seeking to replicate fusion on Earth
for a virtually inexhaustible supply of
power to generate electricity.
Current plasma thrusters that use
electric fields to propel the particles can
only produce low specific impulse, or
speed. Computer simulations showed
that the new plasma thruster concept
can generate exhaust with velocities of

PPPL physicist Fatima Ebrahimi in front of an artist's conception of a fusion rocket. (Photo by Elle
Starkman, PPPL Office of Communications, and ITER)

hundreds of kilometers per second -
ten times faster than those of other
thrusters. That faster velocity at the
beginning of a spacecraft's journey
could bring the outer planets within
reach of astronauts. Long-distance travel
takes months or years because the specific impulse of chemical rocket engines is
very low, so the craft takes a while to get
up to speed.
There are three main differences
between the new thruster concept and
other devices. The first is that changing
the strength of the magnetic fields can
increase or decrease the amount of
thrust. Second, the new thruster pro-

duces movement by ejecting both plasma particles and magnetic bubbles
known as plasmoids. The plasmoids add
power to the propulsion and no other
thruster concept incorporates them.
Third, unlike current thruster concepts
that rely on electric fields, the magnetic
fields in the new concept allow the plasma inside the thruster to consist of
either heavy or light atoms. This flexibility enables scientists to tailor the amount
of thrust for a particular mission and use
any type of gas.
For more information, contact Office of
Communications at pppl_communications@
pppl.gov; 609-243-2755.

Rotating Detonation Engines for Rocket Propulsion
These engines will allow upper stage rockets for space missions to become lighter, travel
farther, and burn more cleanly.
University of Central Florida, Orlando

esearchers have developed a rocket
propulsion system, known as a rotating detonation rocket engine, that will
allow upper stage rockets for space missions to become lighter, travel farther,
and burn more cleanly.
Rotating detonations are continuous,
Mach 5 explosions that rotate around
the inside of a rocket engine. The

explosions are sustained by feeding
hydrogen and oxygen propellant into
the system at just the right amounts.
This system improves rocket engine
efficiency so that more power is generated while using less fuel than traditional rocket energies, thus lightening the
rocket's load and reducing its costs and
emissions.

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Mach 5 explosions create bursts of
energy that travel 4,500 to 5,600 miles
per hour, which is more than five times
the speed of sound. They are contained
within a durable engine body constructed of copper and brass. The technology,
studied since the 1960s, had not been
successful due to the chemical propellants used or how they were mixed.
Tech Briefs, May 2021

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Tech Briefs Magazine - May 2021

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