ss 3011 Space Technology and Applications

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ss 3011Space Technology and Applications

• The Space Environment

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References

• Introduction to the Space Environment, 2nd
  Edition
• Thomas F. Tascione
• http//www.sel.noaa.gov/
• http//see.msfc.nasa.gov/
• http//powerweb.lerc.nasa.gov/
• pvsee/publications/TheBasics.html
• http//www.spaceweather.com/

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What/Where is Space?
Orbiting Object with altitude less than 600 km
experiences effects of Earths' outer atmosphere
Resulting Drag is a non-conservative force, and
removes energy from the orbit Energy Loss
causes orbit decay
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Where is Space (concluded) ?
Various Definitions 1) Top of the atmosphere -
99.9 of air is below 50 km 2) Navigable air
space - limit of dynamic lift - 40 km 3)
Shuttle reentry over-flight (Canada) at 80 km
without permission 4) USAF Astronaut Wings
awarded above 90 km 5) Soviet Delegates to UN
called for 110 km 6) The lowest short term
stable satellite orbit (130 - 160 km) WHY DO WE
CARE? Is the definition arbitrary?
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Aspects of the Space Environment
Gravity Atmosphere Vacuum Space Debris and
Micro-meteoroids Radiation Charged Particles
Fusion by-products
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Gravitational Physics
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Free-Fall
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Zero-Gravity vs Micro-gravity

• Newton Inverse-square law
• Objects in Orbit are not at zero gravity
• They are in freefall, moving just fast enough to
  miss the earth as they fall towards it
• Since the whole satellite is falling at the
  same rate, objects on board do not exert force
  on each other
• Hence the term Micro-gravity

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Atmosphere

• Drag forces on satellites up to at least 600 km
• Height of atmosphere dependent on solar cycle
• Non-linear decrease in density
• Narrow beam tracking/pointing can lose
  satellite
• Re-boost low orbits circularize elliptical orbit
• High in atmosphere, Oxygen does not
  re-associate into molecules. The individual
  atoms are much more corrosive than molecular
  oxygen, and can damage structures, coatings and
  sensors

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Distribution of the Atmosphere?
Atmospheric Density
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Vacuum
Out-gassing - under a vacuum, any gasses
trapped in a material will be expelled, and can
contaminate adjacent components with either
corrosive effects or conductive paths. Cold
Welding - perfectly smooth surfaces usually are
lubricated by a layer of air that keeps them
separated. In a vacuum, there is no separation,
and the surfaces stick together. Heat Transfer
- In a vacuum the only heat transfer mechanisms
are conduction and radiation - no convection.
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Space Debris and Micro-meteoroids

• Even small particles have large energies
• 7 km/sec or 16,000 mph
• 400 times greater kinetic energy than an
  equivalent sized bullet
• Over 7000 baseball or larger size objects
• 100,000 estimated smaller objects
• Space debris
• Growing problem but not yet serious enough for
  
• expensive mitigation costs
• Prevention and satellite disposal efforts

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Radiation

• The sun produces radiation in the visible, IR,
  X-ray, and gamma ray spectrums
• 99 in Visible/IR/Near UV
• Thermal and Power Implications
• UV can degrade solar cells and coatings
• ª Solar pressure - small (1 lb/sq km) but impacts
  satellite design

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Charged Particles

• Come from three general sources
• The Sun
• Steady state - solar wind (1 Billion Kg/sec)
• Bursts - solar flares/CME (intensity fluctuations
  due to Mag Field distortion from differential
  rotation
• electrons, protons, and some heavier ions
• Galactic Cosmic Rays - Similar to solar sourced
  particles, but with more heavy ions.
• The Van Allen radiation belts - a collection of
  particles trapped in the earths magnetic field

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The Van Allen Belts

• Van Allen radiation belts
• Two belts (sometimes considered as a single belt
  of varying intensity) of radiation outside the
  earth's atmosphere
• Discovered by first U.S. earth satellite,
  Explorer 1
• Named for James A. Van Allen, American
  astrophysicist who first predicted the belts and
  then interpreted the findings of Explorer 1
  satellite
• Phenomenon of the magnetosphere as opposed to
  the atmosphere

Responsible for Aurora in Polar Regions
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The Van Allen Belts (contd)

• Particles trapped in the Earths Magnetic
  Fields
• Particles originate in periodic solar flares and
  are Carried to earth by the solar wind
• Electrons and Protons, in two regions
• Inner Belt 2000 - 10,000 km
• High energy protons
• Outer Belt 10,000 - 30,000 km
• Lower energy protons and electrons
• Present Significant hazard for orbiting
  spacecraft
• Implications Higher LEO pushing into Inner Belt
  
• Growing interest in MEO constellations (Iridium,
  GPS)

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Van Allen Belts (contd)
Proton belt
Electron belt
Must mean something "H" in front of the "Allen"
and to remove one "l" to make "Van Halen,"
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High Energy Protons in the Inner Belt
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Electron Belts
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6.0
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South Atlantic Anomaly(Off-set of Dipole Field)
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Space Environment Induced Anomalies

• Spacecraft Charging
• Potential arcing/discharge - both on surface and
  deep within electronics
• Sputtering
• Sandblasted coatings and sensors
• Single Event Phenomenon
• Upset, Latch-up, Burnout

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Space Environment Induced Anomalies(contd)

• Upset
• Single high energy particle causes bit-flip
• in computer memory altering logic or data

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Space Environment Induced Anomalies(concluded)

• Upset
• Hazardous situation

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Solar Cycle (sunspots and flares)
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Solar Cycle (sunspots)

• 11 Year repeating cycle
• 4 year rise, 7 year fall
• Solar Minimum - Sunspots form _at_ 40 deg latitude
• Solar Maximum - Sunspots form _at_ Equator
• Solar Magnetic Poles reverse each cycle (no
  dominant polarity at Solar Max

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Solar Cycle (11 year repeating cycle)
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Homework
Pages 70-90 in Sellers Section 3.2 Homework
Questions, Page 99