Tech Briefs Magazine - June 2022 - 48

APPLICATION
BRIEFS
To the Moon and Beyond with
Additive Manufacturing
Aerojet Rocketdyne
Sacramento, CA
www.rocket.com
Velo3D
Campbell, CA
www.velo3d.com
B
eginning in 2022, NASA will place unmanned Orion spacecraft
into lunar orbit, followed by crewed landings, construction
of lunar habitats and supporting infrastructure, and
ultimately, preparation for a visit to Mars.
Additive manufacturing (AM), or 3D printing, is one of the
technologies that enables such ambitious plans. " As with any
complex endeavour, the more affordable you can make it, the
greater the chance that you will ensure its completion, and the
Moon is no different, " said James Horton, Aerospace Engineer
and Mission Architect at Aerojet Rocketdyne. " Metal AM plays
a key role in achieving these goals. "
Building on a Legacy
Aerojet Rocketdyne has a long history in metal AM. The
aerospace manufacturer has been able to successfully design
and integrate 3D-printed end-use components for a variety of
projects, among them the massive RS-25 engines that will carry
the Artemis mission into space.
Horton has been there for much of it. Since 2008, he has
held lead roles in rocket engine design, development, and test
flight operations for NASA and the DOD. His advanced propulsion
team at Aerojet Rocketdyne is currently working on chemical,
electric, and nuclear propulsion to support NASA's deep
space exploration efforts, the Artemis project included.
According to him, metal AM, when used in conjunction with
advanced design and simulation software, gives today's aerospace
engineers " an entire buffet of solutions that were comApollo
SM / LM
RCS R-4D Bi-prop
pletely unavailable to their predecessors, providing the unparalleled
ability to innovate without compromise. "
One recent example of this is a critical subsystem that Apollo
engineers knew as a " quad " reaction control system (RCS).
The Apollo RCS included four individual R-4D bipropellant
thrusters, originally designed by Marquardt Corp., that used
hypergolic (spontaneously igniting) nitrogen tetroxide and
hydrazine as propellants. Every lunar lander and service module
had four quads, each of which generated more than 100
pounds of thrust to control the spacecraft's roll, pitch, and yaw
during flight. Following a series of acquisitions, Aerojet Rocketdyne
eventually took ownership of the R4-D, intending to
use what is now called the " reaction control system " (RCS) on
the future spacecraft.
Given that the original RCS design is more than 60 years old,
Horton and his team recognized an improvement opportunity
and began what would become one of the many internal research
and development (IRAD) projects intended to optimize
the systems required for the Artemis program and other commercial
lunar projects. In the case of the RCS, they looked for
ways to reduce the number of engine parts, increase its reliability,
and make assembly and serviceability easier, all of which
would decrease project costs while enhancing spacecraft performance.
Metal AM checked all these boxes.
They also wanted to take advantage of rocket fuel advancements.
As Horton explained, propulsion engineers had learned
over the years that adding 25 percent nitric oxide to the fuel
oxidizer mentioned previously - nitrogen tetroxide - would
reduce its freezing point from −9 °C (16 °F) to −55 °C (−67 °F).
Since this reduces the mass and power consumption of the
heating systems needed to prevent frozen fuel lines in space, it
presented Aerojet Rocketdyne with a significant opportunity.
There was just one problem: the MON-25 fuel just described is
unstable, a condition that Horton suggested is a " bad thing to
have in rocketry. "
Proving the Concept
Here again, metal AM was the answer, as it allowed the team
to print special injector geometries that could burn the fuel in
ISE-100 Bi-prop
MMH/MON-25
(Left and right) Even the first 3D-printed version of the revamped R-4D reaction control system was a huge improvement over its predecessor. (Image:
Velo3D)
48
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