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Spacecraft Structure

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

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Spacecraft Structure

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  1. 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

  2. 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

  3. Launch Vehicle

  4. Payload Planners Guide http://www.boeing.com/defense-space/space/delta/docs/DELTA_II_PPG_2000.PDF

  5. 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

  6. None Sputnik1957

  7. 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.

  8. Spinner SNOE Circular orbit 580 km altitude 97.75 degrees inclination sun synchronous precession, 26 Feb. 1998.

  9. 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

  10. 3-Axis Stabilized TERRA (EOS AM) 12/18/1999

  11. 3-Axis Stabilized TERRA (EOS AM) Solar Array

  12. Flyby Voyager 1977 Jupiter Saturn Uranus Neptune

  13. CassiniOrbiter

  14. Probe

  15. Viking Lander

  16. Earth Planet Mass Iron Core Atmosphere Sun Mass Solar Activity Planets Planet environment Proximity to sun Space Environment and Effects

  17. Spacecraft Systems Computers Batteries Propellant Electronics Instruments Windows Mirrors Mechanisms Detectors

  18. Environment and Effects - Earth Magnetosphere Radiation Belts Trapped Protons and Electrons Changing Magnetic Field Atmosphere South Atlantic Anomaly Solar Wind Magnetopause

  19. Environment and Effects - Sun UV Wavelength Solar Wind CMEs - Protons, Neutrons and X rays

  20. Coronal Mass Ejection

  21. Thermal: Solar, IR, S/C Dissipatoin Solar UV Charged Particles – Solar Wind, Sun Materials Outgassing and Contamination Magnetics Spacecraft Charging Atomic Oxygen Space Environmentfrom the Spacecraft Perspective

  22. 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

  23. Solar UV Flux Short wavelength energy Reactions Changes material properties Optical Properties of Surfaces Glass darkens Polymerize hydrocarbons

  24. 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%

  25. Single Events Upsets Latchup Long term exposure (Total Dose) Electronics Degredation Threshold Levels and Timing Semiconductors – Holes Effects of Radiation

  26. Magnetic Earth Axis 11 Dipole (bar magnet) • Rotating magnetic field • Magnetometer • Fixed and Changing Fields on Instruments • Non-magnetic materials

  27. 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

  28. 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.

  29. Glow 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

  30. Radiation Belts around the Earth Electrons Protons Cosmic Rays Radiation Environment

  31. Humans Damage to Spacecraft and Systems Debris and Micrometeorites

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