Spacecraft Structures and Materials

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Spacecraft Structures and Materials

• Lecture 23
• Space concepts

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Agenda

• Spacecraft structure
• Spacecraft stresses
• Stress and Strain relationships
• Common materials for spacecraft

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Spacecraft Structure
Spacecraft, unlike aircraft must be light and
also withstand high stress without flexing- they
are more heavily constructed than aircraft and
more rigid, rugged
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Spacecraft Stresses

• In ascending order
• Launch
• Stage Separations
• atmospheric entry
• Large ?V space maneuvers
• Spins for attitude control

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Spacecraft Stresses
Final separation (pyrotechnic)
Spin Stabilization
Nose faring separation
Stage separation (pyrotechnic)
Aerodynamic Forces-Pogomotion due to
thrust-body dynamics
Liftoff-Ignition transients
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Launch Stresses
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Spacecraft Load Emulation for Testing Individual
Components
Launch loads (gs)
Emulator-System of damped oscillators
Fourier spectrum
Shaker table for testing flight components
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Spacecraft Emulation
Mechanical analogs of spacecraft are formed from
large numbers of damped harmonic oscillators
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Stress-Strain Relationships
Stress ( Force per unit area) and Strain (
elongation per unit unit length) are related
linearly for most materials below yield
stress Stresses and strains can be in multiple
configurations Torsion, bending, shear, ect and
yield corresponding strains
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Stress-Strain
When materials reach yield stress they go beyond
their proportional limit , this varies widely
for materials
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Yield Stress
Yield stress for metals is defined as the stress
level that leads to more than 0.2 strain
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Yield Stress Units
Stress is often measured in ksi 1000lbs/sqr.
Inch 1ksi6.9Bars ( 1 Bar.99 atmosphere) 1bar
106 dynes / cm2105 N/m2 ( Pascals)
(100kPascals) Examples Stainless Steel has
yield strengths 700Bars or 100ksi Aluminum
(varies widely) has yield strengths 300Bars or
40ksi
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Relationship between Youngs Modulus and Yield
stress
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Yield Stress
Spacecraft are designed so that Yield and
Ultimate Strengths are greater than stresses
expected in flight by factors of 1.1 to 2.0
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Yield Stress Units
Stress is often measured in ksi 1000lbs/sqr.
Inch 1ksi6.9Bars ( 1 Bar.99 atmosphere) 1bar
106 dynes / cm2105 N/m2 ( Pascals) Examples
Stainless Steel has yield strengths 700Bars or
100ksi Aluminum (varies widely) has yield
strengths 300Bars or 40ksi
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Common Materials for Spacecraft

• Aluminum- light and inexpensive-similar to
  aircraft aluminums
• Steel- high strength components (stainless)
• Titanium High strength-low weight components (
  expensive)
• Graphite composite-high strength , rigidity
• Ceramics and ablative plastic-thermal protection
• Carbon carbon composites- high temperature
  resistance

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Cost Comparisons For Materials
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Relationship between Youngs Modulus and Yield
stress
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Strength Of Materials
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Aluminum Honeycomb
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Magnesium
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Tank materials
Space shuttle external tank in orbit
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Titanium
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Graphite Composite
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Graphite Composite Honeycomb
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Carbon Carbon Composite
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Heat shield Materials (Apollo)
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Heat Shield Materials (shuttle)
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Heat Shield Materials (new)
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Engine materials
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Engine Materials

• Cryogenic materials
• - must keep strength at low temperatures- used in
  high speed turbo-pumps for LOX, liquid hydrogen
• - stainless steels, titanium alloys
• High temperature materials must keep strength at
  high temeperatures
• -nozzles
• -Turbopump hot sections ( drivers)
• -Titanium and nickel alloys

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Nickel Alloys
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Sudbury Mine in Canada Produces Much of the
Worlds Nickel
The Nickle is extraterrestrial, due to a large
asteroid impact 2 Billion years ago.
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Homework Problems Set 5    

• ( 20 pts)The innermost moon of Mars, Phobos, is
  potato shaped , and like Mars , made of earthlike
  rock, and is 13 x 11x 9 km and is very dark. It
  orbits in a circular orbit around Mars every
  7and ½ hours keeping the same face to Mars
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• Find the mean surface temperature of Phobos
  surface facing the Sun after it has been in the
  sunlight for a while.

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• ( 20pts) A spacecraft is designed for a deep
  space mission and thus requires minimum weight.
  It also carries a small chemical rocket engine.
  It will require aerobraking at the Planet is will
  go to and this will be done using the backs of
  the solar panels , which will carry roughly the
  weight of the spacecraft as it slows.
• A. What would you build the major parts of the
  spacecraft out of and why?
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• B. Assume the same spacecraft will be put into a
  permanent earth orbit. What changes in materials
  should occur?
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• ( 30 pts) A space plane is to be built that will
  take off into orbit on a Atlas V and return like
  the space shuttle, only it will be much smaller,

• what materials would you use the thermal
  protection system of this craft and why?
• What power systems would you use to power the
  spaceplane in orbit?
• What power systems would you use to power the
  landing gear deployment and flight systems on
  reentry?
• D.( Extra credit) ( 10 pts) What will be the
  impact of including an internal cargo bay that
  can carry either additional orbital fuel or
  return payloads.
•