Download Space Environment

Space Environment
(4/8/11)
ARO 203L – Fundamental of Astronautics
Space Environment
•
•
•
•
•
•
•
Background
Gravity
Atmosphere
Vacuum
Micrometeoroids (and Space Junk)
Radiation Environment
Charged Particles
ARO 203L – Fundamental of Astronautics
Why Worry about the Space Environment
• Space is a harsh environment for satellites and humans
• About 25% of all spacecraft anomalies are related to the
space environment
• Some examples:
– Skylab, first US space station re-entered the atmosphere and
disintegrated due to unpredicted increase drag
– Contamination to solar arrays and solar collectors (GPS and Boeing
702 comm sats)
– Short circuits of solar cells due to plasma charging
– Galactic Cosmic Rays
ARO 203L – Fundamental of Astronautics
Introductions
•
•
•
Space is incorrectly thought of as a vast, empty vacuum that begins at
the outer reaches of the Earth's atmosphere and extends throughout the
universe.
Space is a dynamic place with energetic particles, radiation, and trillions
of objects ranging all sizes
Compared to what we experience on Earth, it is a place of extremes
– Distances and scale are vast
– Velocities can range from zero to the speed of light
– Temperatures on the sunny side of an object can be very high, yet extremely
low on the shady side
– Charged particles and debris continually bombard exposed surfaces.
– Some have so much energy that they pass completely through an object in
space.
– Magnetic fields can be intense.
•
The environment in space is constantly changing. All of these factors
influence the design and operation of space systems.
ARO 203L – Fundamental of Astronautics
Where is Space?
• Astronaut wings (100 km)
ARO 203L – Fundamental of Astronautics
Where is Space?
Temperature increases with height
due to low density of molecules.
Poorly mixed atmosphere. Molecule
travels almost 1 km before collisions.
The temperature in this layer can rise
to 1,500 deg C (2,730 deg F)
Atmosphere min. temperature marks
to the top of the Mesosphere.
Meteors burns up.
The thin ozone layer resides near the
top of the stratosphere. Temperature
increases due to UV absorption by
the ozone layer.
Almost all weather occurs. Contains
99% of the atmosphere’s water vapor
ARO 203L – Fundamental of Astronautics
and 90% of the air
Gravity
•
Gravity is what keeps us in orbit and determine the size and
shape of an orbit
– Objects in orbit are continuously falling around the Earth, it’s
velocity determine if the object impacts Earth, orbit Earth, or
escape.
•
Low Earth Orbit (LEO) are orbits below 1000 km where Earth’s
gravitational forces dominates
– For most cases we can ignore the gravity of the Moon and Sun
•
Gravity is not uniform around Earth and this cause orbit
perturbations and torques on the spacecraft
ARO 203L – Fundamental of Astronautics
Atmosphere
• Earth’s atmosphere is dynamics, even at 500 km
above the Earth’s surface
• Solar activity causes the Earth’s atmosphere to
expand and contracts as its temperature increases
and decreases
• Two main affects on a spacecraft
– Drag
– Interaction with atmospheric neutrals (mainly Atomic
oxygen)
ARO 203L – Fundamental of Astronautics
Drag
Velocity
FDrag
Drag Force
Surface Area
Normal to Direction
of Motion
1
2
 V C D An
2
Density
Coefficient of
Drag

= atm. density
-
dependant of solar activity and height from
surface
-
Very difficult to model and predict
ARO 203L – Fundamental of Astronautics
Drag: Solar Cycle
~11 Year Solar Cycle
ARO 203L – Fundamental of Astronautics
Atomic Oxygen and Ozone
• Atomic Oxygen (AO) is corrosive
– Radiation in the upper atmosphere causes O2 to
dissociate into free atomic oxygen
– AO is very reactive and potentially damage spacecraft
surface
• A benefit of AO is that is combines is O2 to form O3,
ozone
– Ozone help blocks harmful ultraviolet (UV) radiation from
the Sun
• Impacts with other atmospheric molecules at high
velocity can also cause “sputtering” on surfaces
ARO 203L – Fundamental of Astronautics
Vacuum Effects
• Space’s near vacuum environment cause problem with
–
–
–
–
Outgassing
Cold-welding
Heat Transfer
Solar UV degradation
• Outgassing
– The release of trapped gasses from material over time when
exposes to a vacuum or low pressure
– Similar to escaping gas bubbles in carbonated solda
– Escaping gases can cause re-condensation on sensitive surfaces:
Thermal control system, solar arrays, optics
ARO 203L – Fundamental of Astronautics
Vacuum Effects (continue)
• Cold welding
– Can be a problem with metal fusing together in a vacuum
– People are still debating if this is true or not
• Heat transfer
– Convection and conduction does not work well in getting rid of heat
from a spacecraft
• Conduction works fine internally in a spacecraft but no externally
– Electromagnetic radiation (infrared, IR) is the primary means of heat
transfer
• UV degradation
– Lining and film change color
– Emissivity and absorption properties change color
ARO 203L – Fundamental of Astronautics
Vacuum Test Chamber
ARO 203L – Fundamental of Astronautics
Micrometeorites and Space Debris
• Space is full of junk
• Earth is bombarded by about 20,000 tons of natural
material from space each year
• NORAD tracks over 9,000 man-made objects,
baseball sized and larger, in Earth orbit
• No international laws exist on space debris and
controlling it
ARO 203L – Fundamental of Astronautics
ARO 203L – Fundamental of Astronautics
ARO 203L – Fundamental of Astronautics
ARO 203L – Fundamental of Astronautics
ARO 203L – Fundamental of Astronautics
Radiation
•
The Sun constantly emits particles and electromagnetic radiation in the
form of light and radio frequency noise
– The constant stream of these forms of radiation is called the solar wind.
– At seemingly irregular intervals, there are solar flares, the explosive ejection
of particles (mostly protons and electrons) accompanied by sporadic
emissions of electromagnetic radiation.
•
Solar activity is also characterized by cycles of various lengths.
– The Sun has a rotation period of 28 days, which exposes Earth to the
surface features of the Sun, such as sunspots.
– The number of sunspots is characterized by an 11-year cycle.
– Sunspots are normally associated in a complex, but not completely
understood, way with solar flares, i.e., the more the sunspots, the more the
solar flares.
– A change in polarity of the overall solar magnetic field is characterized by a
22 year cycle. It seems to govern the frequency of flares.
ARO 203L – Fundamental of Astronautics
Radiation
•
•
The spectrum of solar electromagnetic radiation extends from the radio
frequency (RF) range to the x-ray frequencies, and slightly higher frequencies
during solar flares
The total energy incident on Earth's atmosphere is called the "solar constant".
– This radiation can be harmful to an unprotected human and can change the surface
properties of various materials.
– The radiation received from the Sun varies according to the Sun's rotation period.
– The sun emits three general classes of radiation in the RF range.
• First, there is a constant background noise over the whole radio spectrum from the "quiet
sun".
• Second, there is a slowly varying component related to sunspots.
• Third, there is sporadic emission related to centers of activity, such as solar flares. Solar
activity during solar maximum can be catastrophic, especially if solar flares are involved. The
greatest concerns are possible interference with communications and the threat to humans.
•
Radiation, mainly from the Sun, can cause
–
–
–
–
Heating on exposed surface (both IR and thermal)
Damage to surfaces and electronic components
Disruption in communication (especially in the radio region)
Solar pressure can cause changes to a spacecraft’s orientation (photons impart
momentum ~ 5 N/km2)
ARO 203L – Fundamental of Astronautics
Radiation
ARO 203L – Fundamental of Astronautics
Particle Sources
• Three primary source of these particles
– Solar wind and Solar Particle Events (SPE)
– Galactic Cosmic Rays (GCRs)
• Particles similar to those found in the solar wind or in solar flares,
but originate outside of the solar system.
– Van Allen Radiation belts
• Regions of Earth’s magnetic field that trap charged particles
• Spacecraft try to avoid these regions (or require more shielding)
ARO 203L – Fundamental of Astronautics
Earth’s Magnetosphere
• Earth’s liquid iron core
creates a strong magnetic
field
– Field lines extend from the
south magnetic to the north
magnetic
– The volume this field encloses
is called the magnetosphere
• The magnetosphere
protects the Earth from most
of the solar wind’s ionizing
radiation
ARO 203L – Fundamental of Astronautics
Plasma Environment
•
Magnetic storms that dissipate stored magnetic energy in the Earth’s
magnetotail are the primary source of energized plasma
– Low energy charged particles, electrons and ions with energies between 5 to
50 keV
•
Spacecraft moving though the plasma cause spacecraft charging on the
surface to high potentials
– In LEO, it is most severe in high latitudes (> 60 deg)
– In GEO, it is most severe magnetic storms between longitudes
corresponding to midnight and dawn
•
Problems on spacecraft
– Arcing – electrostatic discharge; large potential differences, through
materials, EMI
– Increased current
– Ion drag or sputtering
– Contamination
– Electric Problems – False command, bit flips, and memory change
ARO 203L – Fundamental of Astronautics
High Energy Particle Effects
• Single event phenomenon (SEP)
– A single charged particle can penetrate deep into the spacecraft and
disrupt electronics
– One type of SEP is a single event upset (SEU) or “bit flip”
– Spacecraft shielding offers some protection
– Radiation hardened components helps
– Coding can help negate the SEU effects by having redundancy and
cross checking
• Total dose effects
– Total dose damage is a long-term effect to the crystal structure of the
semiconductors with the computer
– Caused by electrons and protons in the solar wind and the Van Allen
belts
– Wears down the efficiency of the material and may cause computer
problem
ARO 203L – Fundamental of Astronautics
Space Environments Summary
• Space Environment is responsible for about 25% or
more of spacecraft anomalies
• The Sun dominates the space environment,
emitting electromagnetic radiation and charged
particles (solar wind)
• Spacecraft must address the space environment
and the effects of Gravity, Atmosphere, Radiation,
Charged Particles, Debris, the Vacuum
ARO 203L – Fundamental of Astronautics
MATLAB HOMEWORK
• Homework #1
Problem 1
Make a single plot in Matlab of
sin()
cos()
2*sin()
2*cos()
for  = 0 to 2*pi. Make sure the plot is smooth by having
enough data points. Plot each line in difference cover,
starting with “red”, “green”, “blue”, and then “black”.
ARO 203L – Fundamental of Astronautics
MATLAB HOMEWORK
• Homework #1
Problem 2
Same as problem #1, but make a single figure in Matlab
BUT with 4 subplots instead.
ARO 203L – Fundamental of Astronautics
Orbits
(4/15/11)
ARO 203L – Fundamental of Astronautics