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Spacecraft Structure
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Requirements
– Mass, Strength, Stiffness, Cleanliness (Particulate/Magnetic)
Constraints
– Fields of view (instruments, thrusters, motors)
– Thermal control
– Center of mass
– Ratio of moments of inertia
– Propulsion lever arm
– Constraints of launch vehicle shroud
– Constraints of sun and earth vector
– Component Collocation
– Launch Vehicle Environment (loads, shock, acoustics)
• Steady state
• Transient
– Random Vibration
– Acoustic vibration
– Testing
Design Approach
• Accessibility
– Test, Repair
• Harness and Cables
– Routing
• Standard Approaches?
– Attempts at “generic” spacecraft have failed
• Building blocks
– Boxes, Truss (tube), Cylinders, X-agons
– Materials: Metals, Honeycomb, Composites
Launch Vehicle
Payload Planners Guide
http://www.boeing.com/defense-space/space/delta/docs/DELTA_II_PPG_2000.PDF
Spacecraft
• Spacecraft are generally classified by:
– Attitude Control System
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None
Gravity Gradient
Spinner
Despun (Momentum Biased)
3-Axis Stabilized
– Mission they are performing
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Flyby
Orbiter
Probe
Lander
Penetrator
None
Sputnik
1957
Gravity
Gradient
LDEF
Deployed on orbit on
April 7, 1984 by the
Shuttle Challenger.
Circular orbit
Altitude of 275
nautical miles
Inclination of 28.4
degrees.
Attitude control of the
LDEF spacecraft was
achieved with gravity
gradient and inertial
distribution to
maintain three-axis
stability in orbit.
Spinner
SNOE
Circular orbit
580 km altitude
97.75 degrees
inclination
sun synchronous
precession,
26 Feb. 1998.
Despun (Momentum
Biased)
OSO-8
Launched on 21 June
1975.
550 km circular orbit
33 degree inclination
scanning and pointing
mode.
spin period was 10.7
seconds.
rotating cylindrical base
section
non-spinning upper
section
3-Axis Stabilized
TERRA (EOS AM)
12/18/1999
3-Axis Stabilized
TERRA (EOS AM)
Solar Array
Flyby
Voyager
1977
Jupiter
Saturn
Uranus
Neptune
Cassini
Orbiter
Prob
e
Viking Lander
Space Environment and
Effects
– Earth
• Planet Mass
• Iron Core
• Atmosphere
– Sun
• Mass
• Solar Activity
– Planets
• Planet environment
• Proximity to sun
Spacecraft Systems
Computers
Batteries
Propellant
Electronics
Instruments
Windows
Mirrors
Mechanisms
Detectors
Environment and Effects Earth
Magnetosphere
Radiation Belts
Trapped Protons
and Electrons
Changing
Magnetic Field
Atmosphere
South Atlantic
Anomaly
Solar Wind
Magnetopause
Environment and Effects - Sun
UV Wavelength
Solar Wind
CMEs - Protons, Neutrons and X rays
Coronal Mass Ejection
Space Environment
from the Spacecraft
Perspective
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Thermal: Solar, IR, S/C Dissipatoin
Solar UV
Charged Particles – Solar Wind, Sun
Materials Outgassing and
Contamination
• Magnetics
• Spacecraft Charging
• Atomic Oxygen
Thermal
• Total radiant-heat energy emitted from
a surface is proportional to the fourth
power of its absolute temperature.
E
= T4
• Direct Solar Exposure
• Eclipse
• Orbit transition
• Changing response of spacecraft
• Temperature of planet body
Solar UV Flux
Short wavelength
energy
Reactions
Changes material
properties
Optical Properties
of Surfaces
Glass darkens
Polymerize
hydrocarbons
Outgassing and
Contamination
http://epims.gsfc.nasa.gov/og/
Earth vs Space: Pressure, water, oil, unpolymerized materials
Fingerprint
Total Mass Loss (TML) <1%
Collected Volatile Condensible Materials (CVCM) < 0.1%
Effects of Radiation
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Single Events Upsets
Latchup
Long term exposure (Total Dose)
Electronics Degredation
– Threshold Levels and Timing
– Semiconductors – Holes
Magnetic
Earth
Axis
11
Dipole (bar magnet)
•Rotating magnetic field
•Magnetometer
•Fixed and Changing Fields on
Instruments
•Non-magnetic materials
Spacecraft Charging
• Spacecraft moving through a
plasma
• Plasma density
• Debye length
• Field around spacecraft
• Photo-electric emission
– Photons hit surface, release
electrons
• Insulators on spacecraft
surfaces
– Near earth ~1-2 volts
– 10 Earth Radii (10RE) ~10,000
Volts
Atomic Oxygen
• In low Earth orbits, satellites encounter the very low
density residual atmosphere. At orbital altitudes, this
is composed primarily of oxygen in an atomic state.
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A satellite moves through the atomic oxygen (AO) at
a velocity of about 7.5 km/sec. Although the density
of AO is relatively low, the flux is high (speed x
density x surface area).
• Highly reactive atomic oxygen can produce serious
erosion of surfaces through oxidation. Thermal
cycling of surfaces, which go in and out of the
earth's shadow frequently in this orbit, can remove
the oxidized layer from the surface.
Aurora Australis or
Southern Lights, in
the 80 - 120 km
altitude region
Charged plasma
glow around shuttle
Excitation of atomic
oxygen in the upper
atmosphere by the
van Allen Radiation
Belts
Glow
Radiation Environment
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Radiation Belts around the Earth
Electrons
Protons
Cosmic Rays
Debris and Micrometeorites
• Humans
• Damage to Spacecraft and Systems