Tech Briefs Magazine - July 2021 - 56

SPINOFF
Taking Out the Trash, NASA-Style
Plasma arc technology for testing heat shields transforms garbage into reusable chemicals.
A
stronauts pack several
thousand pounds of
trash into expendable cargo
resupply spacecraft. When
it is time to " take out " the
trash, the filled cargo spacecraft
undocks from the In -
ternational Space Station
and falls into Earth's atmosphere
at about 17,500 mph;
the spacecraft and its contents
are vaporized.
Objects entering the at -
mosphere experience significant
friction created by
the drag of compressing
atmospheric gases. As the
spacecraft plunges deeper
into the atmosphere where
the air is denser, a tremendous
amount of energy is
released as heat, forcing
the gas molecules to dissociate. A spacecraft
without a heat shield, like these
expendable cargo vehicles, experiences
the same heating, vaporizing the solid
material. Replicating this high-temperature
trash processing on Earth is precisely
what InEnTec is doing, with some
help from NASA arc jet research and
technology.
Replicating the conditions
of reentry on Earth
wasn't possible with 1950s
technology when NASA be -
gan testing heat
shields.
An oxy-acetylene torch was
used early on but the torch
could only reach a maximum
of around 6,290 F.
Arc heaters used in the
chemical industry were an
ideal alternative.
This cabin view of the space shuttle during reentry shows the color of atmospheric
plasma. Due to the compression and friction of the air, the molecules generate
a very hot plasma that glows in the red-orange spectrum. (Credit: NASA)
NASA learned how to recreate the
extreme temperatures and speeds of
atmospheric entry decades ago as a way
to test heat shields. InEnTec (Richland,
WA) looked to the power source modifications
NASA used to generate hightemperature
plasma and incorporated
them into its technology design to create
its Plasma Enhanced Melter (PEM) that
transforms waste material into synthetic
gas and other products.
Incinerators that rely on combustion
produce toxic pollutants but plasmaenabled
gasification does not. It heats
the waste, called feedstock, to extremely
high temperatures. At 1,800 to 27,000
F, carbonaceous material breaks down
into basic molecules - carbon, hydrogen,
and oxygen. By controlling the
combination of heat and pressure, it's
56
Cov
The Arc Jet Complex at Ames Research Center
tests thermal protection material with plasma
like that generated during atmospheric reentry to
make sure it will work effectively. (Credit: NASA)
www.techbriefs.com
ToC
possible to regulate the chemical activity
that leads up to gasification.
The molecules are separated and then
converted into products that can be
used to create anything from jet fuel to
clothing. Any inorganic material that's
left over, called slag, is added to superheated
glass. The resulting nontoxic
substance is safe for a number of industrial
uses including building materials.
The entire system generates no air pollution
or toxic waste.
The key to this efficiency is the heat.
The temperature is boosted with the same
kind of plasma that NASA created to test
the first heat shields used on spacecraft.
The plasma arc heaters
NASA uses now consist of a
tube about 3' in diameter
and up to 16' long that contains
hundreds of 3/8 " thick
copper discs, each
cooled with water. Two electrodes
at either end of the
tube provide the points for
each end of the electrical
arc to attach. At the end of the tube is a
supersonic nozzle designed to generate
supersonic speeds from Mach 3 to Mach
5, creating the environment in the test
chamber where the samples of heat
shield material are placed to simulate
entry conditions.
The design breakthrough was the use
of the individual copper discs to control
the arc inside the tube, dramatically
increasing the temperature. Cooling the
heater while in use prevents the components
from melting. In 1965, NASA
patented the segment-constricted arc
heater. InEnTec used the NASA information
while developing its power supply,
designing its own patented plasma arc
gasification technology.
InEnTec's gasification facility in Ore -
gon converts medical and other waste
into hydrogen for vehicles powered by
hydrogen fuel cells. In addition to dramatically
reducing vehicle pollution -
hydrogen cars emit only water vapor -
these systems could replace high-cost
toxic waste disposal by incineration and
specialized landfill.
Visit https://spinoff.nasa.gov/plasmaheating-recycles-waste.
Tech
Briefs, July 2021
Spinoff is NASA's annual publication featuring
successfully commercialized NASA technology. This
commercialization has contributed to the development
of products and services in the fields of health and
medicine, consumer goods, transportation, public safety,
computer technology, and environmental resources.

https://spinoff.nasa.gov/plasma-heating-recycles-waste http://www.techbriefs.com http://www.abpi.net/ntbpdfclicks/l.php?202107TBNAV

Tech Briefs Magazine - July 2021

Table of Contents for the Digital Edition of Tech Briefs Magazine - July 2021