Aerospace Part Materials - Solid Rocket
Booster Case - Case Study
Date of study
16 January 2023
Author
Nik Adam Muqridz Bin Abdul Hakham 2125501
Advisor
Prof. Dr. Meftah Hrairi
Abstract
This case study is exploring about the materials of the solid rocket boosters cases, maraging
steel (current) and superalloy composites (future), which are the best materials for the case.
This case study also covers the normal use and properties relations of them, the chemical
compositions, atomic crystalline structure, unusual extremes, heat treatment, failure prevention,
pros and cons of each material. The materials are examined by their mechanical and chemical
properties by their excellence in the tests of creep, fracture and fatigue tests. Then, they are
compared in each aspect: high creep resistance, high strength and stiffness, high strength to
weight ratio, inert, and anti corrosive to get the best result. For now, the best material is the
maraging steel 18Ni(250), while the best future is the Ni-based superalloy with gamma prime
(γ’)-[Ni3(Al,Ti)] + refractory wire W-Re-Hf-C fiber that is still in its costly and time consuming
research and development.
Keywords
Solid rocket boosters, Maraging steel, Superalloy composites, Materials, Development
Introduction
Solid rocket boosters are simple mechanism
solid propellant thrusters that have been
essential for space launching for years. They
work by Newton's third law, using the equal
and opposite of the propulsion force to thrust
upward .They are mainly used for the early
stage of the launch for 2 minutes high thrust,
later on being detached to reduce weight to
thrust even more upward. This is called
booster staging, most of the space launchers
use parallel staging as it can carry more solid
rocket boosters to have even more thrust.
(NASA, 2018)
After being detached, solid rocket boosters
parachute then land on the ocean, then
can be recovered by ships to the land and
then refurbished to be used again.
Due to uncontrollable thrust of the solid rocket boosters, they cannot be turned on and off,
because the solid propellant itself burns until it runs out, precise materials and manufacturing
selection must be conducted on this simple mechanism but catastrophic when in accidental
ignition or failure in action. Even one booster can be ignited accidentally when stored and then
igniting others thus will cause a big explosion. Another precaution is to avoid one of the strap on
boosters to stop working that will cause an imbalance of the rocket as the other cannot be
turned off in flight rather than controlling the rotatable nozzle but it is not enough to counteract
the force.
Also, note that the solid propellant is mixture of 450,000 kilogram 16% atomized aluminum
powder (fuel), 69.8% ammonium perchlorate (oxidizer), 0.2% Iron oxide powder (catalyst), 12%
polybutadiene acrylic acid acrylonite (binder), and 2% epoxy curing agent that will be casted into
the case (NASA, 2006). The propellant is famously known as PBAN-APCP.
Thus, the perfect planning on materials and
manufacturing process on the solid rocket
boosters will be analyzed in this and the future
case study.
Analysis
Normal use and major properties relations
Solid rocket boosters are normally used in the early stage of the
rocket launching, this is because a short, very high thrust force
(14.7 MN) upward in 2 minutes is needed to overcome the weight
of approximately 2,000,000 kg of fully assembled space shuttles
(NASA, 2006).
This means that the rockets need to be able to withstand that high
force in short period of time, and also high temperature and high
pressure as well, usually at 6,000 °F (3,300 °C, 3,600 K) and
10–200 bar (1–20 MPa, 150–3,000 psi) (NASA, 2016).
The boosters must be lightweight as well to maintain the center of
gravity higher in relation to center of pressure, to maintain the rocket
stability (NASA, 2021).
Last, the boosters must be storable and refurbishable from landing in the ocean so that they can
be reusable. This means that the boosters must be inert, anti-corrosive and have a long life
cycle.
In short, the materials must met the following properties requirement, to meet the normal use :
Major properties
Normal usage
High creep resistance
High temperature and high pressure
High strength and stiffness
Short and high trust
High strength to weight ratio
Lightweight
Inert
Storable
Anti corrosive
Refurbishable and reusable
Also, note these unusual extremes :
1. Storage ignition
2. Combustion instability
3. Explosion when hard falling or when being shooted by a bullet
The materials selected will be chosen according to their excellence in the tests of creep, fracture
and fatigue test.
Current materials
The current materials in use of the solid rocket booster is maraging
steel 18Ni(250) (Scott Manley, 2020). The martensite and age
hardening; maraging steel is a type of high steel strength with very
low carbon percentage (0.03% maximum) with alloying elements as
substitutions that produces age hardening of iron-nickel martensites
(Campbell, 2006, 200).
The maraging steel simply has the
body centered tetragonal crystal
structure (BCT). The crystal structure
is developed through these order :
Heat treatment of the maraging
steel is solution hardening, then air
cooling and then aging. The heat
treatment can to improve these
properties :
In short, the maraging steel 18Ni(250) is currently being used for solid rocket boosters case due
to its properties, appropriate creep strength,yield strength, ultimate tensile strength, fracture
toughness, inert and anti-corrosive.
Future materials
The
future
materials
in
development of the solid rocket
booster is Nickel based superalloy
composite. Superalloy is a heat
resistant alloy (Campbell, 2006,
221), and composite is the
combination of two or more
combinations of various chemical
and physical properties (Hashemi et al., 2018, 703). This specific composite is the Ni-based
superalloy with gamma prime (γ’)-[Ni3(Al,Ti)] + refractory wire W-Re-Hf-C fiber.
The Nickel based superalloy focused in this part
is Inconel X-750. The crystalline structure of it is
a face centered cube (FCC).
Some of the complex elements usage are : Aluminium and
Titanium,(γ’)-[Ni3(Al,Ti)] to increase creep strength, Ferum to reduce alloy
cost, Cobalt and Chromium to increase yield and ultimate tensile strength
slightly, Niobium to have low solubility, Cr-Al-Ni to be anti corrosive in
different situations,M23C6 to immobilize grain boundaries (Lemos, 2020,
11-12).
The Ni-based superalloy then heat treated by precipitation hardening at
1600F, it increases creep strength as gamma prime (γ’)-[Ni3(Al,Ti)] content
increases. Also increasing gamma double prime (γ’’)-[Ni3Nb], thus increasing
its yield and ultimate tensile strength.
The superalloy then will be improved by refractory wire
W-Re-Hf-C fiber. As they are more than 7 times as strong as
the strongest superalloys at 1093C (2000F) when taken in ratio
to density. Thus, making the superalloy composite with very
high creep strength (Petrasek, 1972).
In short, the Ni-based superalloy with gamma prime (γ’)-[Ni3(Al,Ti)] + refractory wire W-Re-Hf-C
fiber is being predicted to used for solid rocket boosters case due to its properties, very high
creep strength, yield strength, ultimate tensile strength,and fracture toughness to its density
ratio, inert and anti-corrosive.
Conclusion and Recommendation
The two materials can be differentiate from these aspects :
Major properties
Current - Maraging steel
Future - Superalloy composite
High creep
resistance
Enough
Better
High strength
and stiffness
Enough
Better
High strength to
weight ratio
Low
High
Inert
Yes
Yes
Anti corrosive
Yes
Yes
Cons
Lower fatigue resistance
Lower fracture toughness
Susceptible to stress corrosion
cracking
Complex development, and
manufacturing
Costly
As both of it is reusable and inert, the sustainability is high, and it is very environmentally
friendly. Also, the failure prevention has been considered in relation to reusability, as the
refurbishing manufacturing must be done after every launch. The fatigue resistance of
superalloy composite is higher making them more liable. Furthermore, very high creep
resistance, high strength and stiffness superalloy composite will be more indestructible to
unusual extremes of hard fall, making them bulletproof. Higher strength to weight ratio will
contribute to more boosters on space launchers with the same stability performance. Also,
thermal barrier coating of MCrAlY-type alloy is needed to have better creep resistance, and to
increase the efficiency of the heat energy to convert mostly to kinetic energy due to lower heat
and energy loss.
In conclusion, the superalloy composite has very high potential in replacing the maraging steel
case of current solid rocket boosters. However, the superalloy composite is very complex in
research and development making it costly and time consuming. But I believe that in the future
these developments will have better space launchers and will be more common in the future
around the world, specifically I hope the research and development is in Malaysia. The cost will
be lower as well in the future.
References
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Hashemi, J., Smith, W. F., & Presuel-Moreno, F. (2018). Foundations of Materials Science and
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Lemos, G. (2020, August 4). Development of Ni-based Superalloy Metal Matrix Composites,
Featuring High Creep Resistance.
MachineDesign. (2002, November 15). Metal-Matrix Composites. Machine Design. Retrieved
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from https://www.grc.nasa.gov/www/k-12/rocket/rktstab.html
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[Video].
YouTube. https://www.youtube.com/watch?v=Eis3A2Ll9_E