spacecraft structure requirements –mass, strength, stiffness, cleanliness (particulate/magnetic)...
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Spacecraft Structure• 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• None • Gravity Gradient• Spinner• Despun (Momentum Biased)• 3-Axis Stabilized
– Mission they are performing• Flyby• Orbiter• Probe• Lander• Penetrator
None
Sputnik1957
Gravity GradientLDEF
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
CassiniOrbiter
Probe
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
Radiation Belts
Trapped Protons and Electrons
Changing Magnetic Field
Atmosphere
South Atlantic Anomaly
Solar WindMagnetopause
Magnetosphere
Environment and Effects - Sun
UV Wavelength
Solar Wind
CMEs - Protons, Neutrons and X rays
Coronal Mass Ejection
Space Environmentfrom the Spacecraft
Perspective
• 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 Contaminationhttp://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
• Single Events Upsets
• Latchup
• Long term exposure (Total Dose)
• Electronics Degredation– Threshold Levels and Timing– Semiconductors – Holes
Magnetic
11
Dipole (bar magnet)
•Rotating magnetic field
•Magnetometer
•Fixed and Changing Fields on Instruments
•Non-magnetic materials
EarthAxis
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.
• 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.
GlowAurora 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
Radiation Environment
• Radiation Belts around the Earth
• Electrons
• Protons
• Cosmic Rays
Debris and Micrometeorites
• Humans
• Damage to Spacecraft and Systems