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

http://stardust.jpl.nasa.gov/photo/aerogelhand.jpg

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