TRAJECTORIES

Robot maker

96

AEROPUZZLER

What does this plane need?

8LOOKING BACK94

Goddard’s moon treatise and more2019
YEAR IN REVIEWArtemis
INCLUDING PAGES
16, 42, 45,61-64, 67, 72, 75

DECEMBER 2019 | A publication of the American Institute of Aeronautics and Astronautics | aerospaceamerica.aiaa.org

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Advanced manufacturing extends
operational boundaries of hybrids
BY TIMOTHY MARQUARDT AND JOSEPH MA JDAL ANIThe Hybrid Rockets Technical Committee studies techniques applied tothe design and testing of rocket motors using hybrid rocket systems.
Virgin Space Ship
Unity in space with threecrew members aboard.
Virgin Galactic50|V

irgin Galactic in February launched VirginSpace Ship Unity into space with a crewof three aboard, 10 weeks after its first trip
beyond the 80-kilometer space boundary.
Powered by a hybrid motor that provided 320
kilonewtons of thrust for nearly 60 seconds, thisspaceship reached Mach 3.04 and an apogeeof nearly 90 km before returning to the Mojave
Spaceport in California.
Researchers at Stanford University demonstrated laser ignition of a hybrid fuel grain in alab-scale slab burner. They presented high-speed
imaging results in July that identified the underlying ignition mechanism as the entrainment andlaser heating of small soot particles formed during
fuel pyrolysis or chemical decomposition. A small
and lightweight laser diode, combined with a few
simple optical elements, provided energy to a
specific point on the fuel surface and heated sootparticles well beyond the temperature required
for fuel pyrolysis. These particles then transferredenergy to the vaporized propellant mixture, igniting the motor. Experiments have confirmed that
only those fuels that produced soot were compatible with this technique, but the method holds
promise for broader applicability. Tests in a single-port motor that aimed the laser at a small target area of a compatible fuel embedded in a larger,
non-soot-producing fuel grain demonstrated ignition of the motor at both atmospheric and vacuum exit conditions.
NASA’s Jet Propulsion Laboratory in California
and Marshall Space Flight Center in Alabama con-DECEM B ER 2019|aerospaceamerica . aiaa .org

tinued to lead technology development
for a Mars Ascent Vehicle intended todeliver samples from the surface ofMars into orbit. To this end, Whittinghill Aerospace of California carried out
full-scale motor testing of a wax-based
fuel with MON-25, a mixed oxide of nitrogen, in April and July at the Mojave
Spaceport. Test motors and oxidizer
were conditioned to an assumed Mars
operational temperature of minus 20
degrees Celsius. In this study, researchers achieved high-performance, stableburns with durations of 60 seconds. TheSpace Propulsion Group of California
and Montana performed similar but smaller, separate tests in Butte, Montana, in January and April
and had the same results. In addition, researchers
at Purdue University in August presented findingsthat they demonstrated the hypergolic ignition
and multiple relights of a paraffin-based hybrid
motor with various hypergolic solids added tothe headend of the fuel grain containing MON25. Tests showed good agreement with previously
completed MON-3 testing, with some tests experiencing ignition delays.
The additive manufacture of advanced hybrid rocket motors to enhance burn rates andefficiencies continued to grow. This year, the Aerospace Corp. of California produced hollow liquid
fuel grains that used 3D-printed features to meter the delivery of liquid fuels such as kerosene.
This arrangement combined the capabilities ofliquid-engine performance with the safety andsimplicity of hybrids. In the first half of the year,
Aerospace Corp. flight-tested an advanced hybrid
rocket with these new liquid grains and a 54-millimeter rocket motor.
In a separate program, Aerospace Corp. andPenn State continued development of a hybrid
propulsion unit for cubesats. Collaborators atPenn State demonstrated start, stop and restartcapabilities of the unit early in the year before
returning it to the Aerospace Corp. for furtherdevelopment. The propulsion unit consists of a
3D-printed solid fuel grain in a combustion chamber integrated into and surrounded by a toroidal
oxidizer tank. The chamber/tank component wascreated with direct metal laser sintering, a form of
3D printing that melts metal powder together withlasers. This technique eases the production of intricate parts that possess the necessary thermaland mechanical properties for use in propulsionsystems.★
Contributors: David Dyrda, Andrew Cortopassi andGeorge Story

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2 supersonic aircraft programs reachtesting milestones
BY JONATHAN S. LITT, TIM CONNERS AND JEFFREY D. FL AMM

The Inlets, Nozzles and Propulsion Systems Integration Technical Committee
focuses on the application of mechanical design, fluid mechanics andthermodynamics to the science and technology of air vehicle propulsion
and power systems integration.

B

oom Supersonic made substantial progress in the design, assembly and testing ofits XB-1 supersonic demonstrator aircraft.
This work culminated in engine groundtesting, which concluded in February at the U.S.
Air Force Academy in Colorado. The test demonstrated that measured inlet distortion levels were
acceptable for XB-1’s three GE J85-CAN-15 engines. This achievement followed wind tunnel
testing of the inlet at the Boeing Polysonic Wind
Tunnel in St. Louis in late 2018.
The XB-1’s 2D hybrid compression inlet model was designed for sustained Mach 2.2 operationand uses modular fore and aft ramps, spill door
geometry and a wide-throat bleed slot that wasbased on Concorde’s. An aft-mounted auxiliary
intake effectively reduces low-speed distortion,although it is not required to meet flow demand.
Analysis of test data proved that high throat bleed
gives the inlet a modest amount of efficient internal compression and produced test-based pressure recoveries across the operating range that met
or exceeded Concorde’s published performance.

The X-59 Quiet Supersonic Technology 9.5%
scale model was tested
at Mach numbers from
0.3 to 1.55 in the 8-by6-foot Supersonic Wind
Tunnel at NASA’s Glenn
Research Center.
NASAThe functional design and analysis of the inlet wascompleted in nine months, with the model fabrication taking an additional three months. A shortened development phase was made possible bybaselining the design from a known successful example, Concorde’s wide-throat slot inlet; by judicious use of well-understood computational tools
and methods along with the ability to upsurge
CPU demand as needed using cloud computing;and by restrained parametric surveys that allowed
rapid convergence toward a high-performance,
though not necessarily optimized, design.
Another noteworthy XB-1 development at
Boom this year is the design of the vehicle’s
aerodynamically complex secondary flow paththrough the extensive use of computational tools.
This involved modeling the throat bleed management, engine bay cooling flow, pressure relief systems, integrated ejector nozzle and J85 variable
nozzle geometry. Ejector nozzle performancewas characterized using high-fidelity computational fluid dynamic models of the fully coupledsecondary flow path. This effort improved aero-model fidelity and reduced uncertainty of theoverall vehicle mission performance. Along withaxisymmetric inlet concepts, the test-verified 2D
inlet geometry and architecture are supporting
conceptual design studies for Overture, Boom’scommercial supersonic airliner.
In preparation for the X-59 Quiet SupersonicTechnology critical design review, which occurredin September, engineers from Lockheed Martin,
General Electric and NASA completed NASA’s
low-boom flight demonstrator inlet dynamic
distortion test entry at
the 8-by-6-foot Supersonic Wind Tunnel atNASA’s Glenn ResearchCenter in Cleveland inMay. The test verified
the acceptability of theunsteady inlet distortion characteristics. The
9.5% scale model wastested at Mach numbers
from 0.3 to 1.55. A mass
flow plug was used tovary inlet mass flow. Instrumentation included
an 80-probe rake at the
aerodynamic interface
plane: 40 pitot pressureprobes and 40 high-response Kulite probes inside-by-sidearrangement. ★

aerospaceamerica . aiaa .org|

DECEM B ER 2019|51

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Advances in science and technology ofpressure gain combustion
BY AJAY AGR AWAL AND DON FERGUSONThe Pressure Gain Combustion Technical Committee advances theinvestigation, development and application of pressure-gain technologies
for improving propulsion and power-generation systems and achieving
new mission capabilities.

A rotating
detonation engine
was tested at Nagoya
University in Japan in
preparation for asounding rocket
experiment planned for2020.
Nagoya University

54|For propulsion and power-generation systems,
detonation-based pressure-gain combustion has the potential to deliver higher fuelefficiency at reduced weight and footprint.
This makes PGC attractive for terrestrialsystems, as well as aerospace applications such as
rockets and hypersonics. Recent investments haveenabled quantitative flow and combustion diagnostics and improved the technology readiness level bytransitioning laboratory concepts toward practice.
Government, industry and academic institutions
around the globe this year continued to advance
PGC to a new and higher technical level.
The U.S. Air Force, Navy, Department of Energy
and NASA continued to support several PGC research
efforts. In June, the Air Force Research Laboratory andInnovative Scientific Solutions Inc. conducted a grounddemonstration of a rotating detonation engine,or RDE,
capable of propelling a Long-EZ aircraft. This effort
demonstrated adequate thrust for takeoff and cruiseoperation, and acoustic measurements confirmed asafe noise level for ground operations.
The Department of Energy’s National Energy
Technology Laboratory funded RDE development
efforts by Aerojet Rocketdyne with teammates fromPurdue University, University of Michigan, University of Alabama, University of Central Florida andSouthwest Research Institute. In May, the campaign
conducted hot-fire testing of a 30-centimeter diameter natural gas and air RDE at Purdue’s Zucrow
Labs. Using multiple hardware configurations, theteam demonstrated detonation combustion with alow loss injector and an exhaust diffuser designed

DECEM B ER 2019|aerospaceamerica . aiaa .org

to condition the exit flow for a downstream turbine.
NASA researchers continued in-house numericalinvestigation and optimization efforts in resonant
pulse combustion and RDE systems for application to gas turbine engines. Additionally, under
an internal Center Innovation Fund, a rotating
detonation rocket engine nozzle optimization
study and high-level rocket system benefits model
development were initiated. In May, NASA solicited
development proposals under Phase I Rocket Engineand Research, Development, Demonstration, andInfusion Early-Stage Innovations grants programs.
In August, researchers at Purdue University reported development of an axial and outflow radial
turbines suitable for small core RDEs. In an effort
to assess the performance of the turbine-combustor
interactions, an optically accessible test rig wasdeveloped in cooperation with Spectral Energies.
In February, University of Michigan researchers
identified and quantified regions of parasitic andcommensal secondary combustion that affect thedetonation wave in an RDE and identified the presence of secondary waves. Secondary combustionand secondary waves couple together, ultimatelychanging the stability and structure of the primarydetonation wave.
In March, a team of researchers at the University of Alabama used time-resolved particle image
velocimetry to measure the exhaust flow of an RDE
operated on methane and oxygen-enriched air
mixtures and demonstrated that the circumferential
flow oscillations decreased by operating the RDE athigh pressures, and a downstream diffuser further
homogenized the flow for turbine applications.
Activities at the Naval Postgraduate School from
April through June focused on RDE parametricstudies of combustor inlet area ratios, channel widthand back-pressurization conditions to determinepressure-gain performance. This was done throughthe application of equivalent available pressure
which is an important parameter in evaluating theperformance of a PGC device.
In Japan, Nagoya University, Keio University,
Institute of Space and Astronautical Science of Japan
Aerospace Exploration Agency, and Muroran Instituteof Technology fabricated the preflight model of adetonation engine system toward a sounding-rocket
spaceflight test scheduled for August 2020.
At Tsinghua University in Beijing, the effects
of a perforated wall on the hydrogen/air rotating
detonation were studied emphasizing analysis ofacoustics and propagation stabilities. Experiments
were also performed on kerosene/oxygen-enriched
air rotating detonation. Using an Eulerian-Lagrangian two-way coupling model, a 2D simulation of
two-phase kerosene-air rotating detonation wasconducted using high-order numerical methods. ★