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

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 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 degrees inclination sun synchronous precession, 26 Feb

Despun (Momentum Biased) OSO-8 Launched on 21 June 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 Radiation Belts Trapped Protons and Electrons Changing Magnetic Field Atmosphere South Atlantic Anomaly Solar Wind Magnetopause Magnetosphere

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

Coronal Mass Ejection

Space Environment from 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 =  T 4 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 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 Earth Axis

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 (10R E ) ~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.

Glow Aurora Australis or Southern Lights, in the 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