EARTH FACTS

SATELLITES ORBITS

SATELLITES ORBITS

REASON FOR THE SEASONS

REASON FOR THE SEASONS Rotation vs. Revolution
Viewed from above, the Earth makes a complete counterclockwise rotation (spins on its axis) once in each 24-hour period. This is why the Sun appears to rise in the east and set in the west. But this daily rotation has nothing to do with seasons. The Earth also revolves counterclockwise around the Sun once every 365 1/4 days. This yearly revolution, combined with the Earth’s tilt (see below) gives us seasons.	Earth's yearly revolution, month-by-month.
Tilt and Revolution
The Earth's axis is not oriented vertically, but is tilted by 23.5 degrees. The north end of the axis is always pointed toward the North Star as the Earth revolves around the sun. This tilt, combined with its revolution around the Sun, causes seasonal changes. (When it’s summer in the northern hemisphere, it’s winter in the southern, and vice versa.) If the axis was not tilted, our year-round climate would be rather boring and many places on Earth wouldn’t receive much light!
Season Simulator
During our summer, the Northern Hemisphere leans toward the Sun in its revolution, there are more daylight hours, and the Sun’s angle is more perpendicular to us than at other times of year. The longer days and more concentrated sunlight result in more heating. (Shadows are shorter in the summer because the sun strikes Earth more directly.) During winter, the Northern Hemisphere leans away from the Sun, there are fewer daylight hours, and the Sun hits us at an angle; this makes it appear lower in the sky. There is less heating because the angled Sun’s rays are “spread out” rather than direct. (Shadows are longer because of the lower angle of the Sun.) In equatorial regions, the length of days and the directness of sunlight don't change as much. The further you get from the equator, the more dramatic the seasonal changes. During the spring and fall, the Earth leans neither toward nor away from the Sun; daylight and nighttime hours are more equal and temperatures are moderate. (The shadow of an object is similar during these seasons.)	Season Simulator Click and drag the Earth around the Sun, or play the animation, to see what's at the base of all seasonal change. Credit: Nebraska Astronomy Applet Project
Common Misconceptions about the Seasons  Many students (and adults) believe that the Earth is closer to the Sun in the summer and further away in the winter. (It’s actually somewhat closer to the Sun in the winter, but the angled rays and short days don’t give us much heat.) Another misconception is that the Earth orbits the Sun in an elongated ellipse, which makes the Earth’s distance from the Sun dramatically different at different locations. The reality is that the Earth’s orbit is nearly circular.
Solstice and Equinox
Solstice refers to the two times each year when the Sun's strongest rays are furthest from the equator (north of it during our summer solstice and south during the winter). For the northern hemisphere, summer solstice occurs around June 21st; we have the maximum number of daylight hours at that time. Winter solstice is around December 21st when we have the fewest daylight hours. Equinox refers to the two times each year when the Sun's strongest rays are directly hitting the equator. Everywhere on Earth has 12 hours of daylight on the spring and fall equinoxes. In the northern hemisphere, spring equinox occurs around March 21st and autumnal equinox around September 21st. Equinox Spring or fall equinox	Winter Solstice  in the Northern Hemisphere Summer Solstice  in the Northern Hemisphere

SEASONAL CHANGES

EARTH'S ROTATION

SOLAR SYSTEM UNIT SLIDES #49 -110

TIDAL EFFECT ????

please read this article carefully & complete the worksheet.

Does the Moon & Sun have a tidal effect on the atmosphere as well as the oceans? 

 It is the gravitational attraction of the sun and moon that cause waters of the ocean to raise and lower at different parts of the earth. Tides occur in oceans, and to a much smaller extent, tides also occur in large lakes, in the atmosphere, and within the solid crust of the earth. There are also non-astronomical factors, such as the configuration of the coastline, the local depth of the water, the ocean-floor topography, and other hydrographic and meteorological influences that play an important role in altering the range and interval between high and low water.  

The moon is a major influence on the Earth’s tides, but the sun also generates considerable tidal forces. Solar tides are about half as large as lunar tides and are expressed as a variation of lunar tidal patterns, not as a separate set of tides. When the sun, moon, and Earth are in alignment (at the time of the new or full moon), the solar tide has an additive effect on the lunar tide, creating extra-high high tides, and very low, low tides—both commonly called spring tides. One week later, when the sun and moon are at right angles to each other, the solar tide partially cancels out the lunar tide and produces moderate tides known as neap tides. During each lunar month, two sets of spring tides and two sets of neap tides occur (Sumich, J.L., 1996).

The elliptial orbits of the moon around the Earth and the Earth around the sun have substantial effects on the earth’s tides.

Just as the angles of the sun, moon and Earth affect tidal heights over the course of a lunar month, so do their distances to one another. Because the moon follows an elliptical path around the Earth, the distance between them varies by about 31,000 miles over the course of a month. Once a month, when the moon is closest to the Earth (at perigee), tide-generating forces are higher than usual, producing above-average ranges in the tides. About two weeks later, when the moon is farthest from the Earth (at apogee), the lunar tide-raising force is smaller, and the tidal ranges are less than average. A similar situation occurs between the Earth and the sun. When the Earth is closest to the sun (perihelion), which occurs about January 2 of each calendar year, the tidal ranges are enhanced. When the Earth is furthest from the sun (aphelion), around July 2, the tidal ranges are reduced (Sumich, J.L., 1996; Thurman, H.V., 1994).

So What is a Planet & the Categories???

So What Defines A Planet?
The International Astronomical Union defines a planet as a celestial body that orbits around a star (like our sun) and is big enough that it forms into a shape of a sphere by its own gravity. But a planet cannot be big enough that it can cause thermonuclear fusion. It also has to have a clear orbit with no other bodies of comparable size influencing its gravitational force.

Known dwarf planets are smaller than Earth's moon.

Pluto is a dwarf planet.  So are Cere, Eris, Makemake, & Haumea.  A dwarf planet is nearly round & orbits the Sun, but its orbit is not clear of other bodies.

 


Did You Know There Are Two Categories of Planets?
A Planet falls into two categories. It is either a Terrestrial Planet or a Gas Giant. Planets that have a body composed mainly of rock (like the Earth) is called a terrestrial planet. 

Terrestrial Planets:
This would include Mercury, Venus, Mars and Earth. 

Gas Giants:  
planets that are made of gas. They do not have a solid surface crust. Jupiter and Saturn falls into this category. Uranus and Neptune are also Gas Giants, but they also fall into sub category called Ice Giants because they contain a huge proportion of rock and ice as well.

What Is Earthshine?

Earthshine is a soft, faint glow on the shadowed part of the moon caused by the reflection of sunlight from the Earth. Specifically, Earthshine happens when the light from the sun is reflected from the Earth's surface, to the moon, and then back to our eyes. Because of this double reflection of light, Earthshine is many, many times dimmer than the direct light of the sun on the moon. Earthshine is even more faint because the moon's "albedo" (a specific kind of reflectivity) is less than Earth's. Even though this dim light is only a reflection it can still illuminate some features of the moon.

Earthshine can be best seen during the crescent phases (the 1-5 day period before or after a New Moon). During this time the sun is mostly behind the moon from our perspective and bathing the Earth in a lot of direct light that is reflected onto the shadowed parts of the moon.
Moons orbiting other planets can also experience this phenomenon, generally called "planetshine".

Leonardo Da Vinci explained the phenomenon nearly 500 years ago. He realized that both Earth and the Moon reflect sunlight. But when the Sun sets anywhere on the Earth-facing side of the Moon (this happens every 29.5 Earth-days) the landscape remains lit -- illuminated by sunlight reflected from our own planet. Astronomers call it Earthshine. It's also known as the Moon's "ashen glow" or "the old Moon in the New Moon's arms."

 

SOLAR SYSTEM VIDEOS

SOLAR SYSTEM
watch the videos & take the quiz.  Record your score on notebook paper & put in the box.  Due:  12/17

UNIVERSE

INNER PLANETS

DAY ON EARTH

OUTER PLANETS

MOON

SOLAR ECLIPSES

Solar Eclipses

A solar eclipse happens when the moon blocks our view of the sun. This happens when the Moon is exactly between the Sun and the Earth. 

How can something four hundred times smaller than the Sun block out its rays?

•  By a coincidence, the Moon is four hundred times closer to Earth than the Sun.  so it appears to fit right over the Sun, like a glove.

The longest solar eclipses occur when the Earth is at aphelion (farthest from the Sun, making the solar disc smaller) and the Moon is at perigee (closest to the Earth, making the Moons apparent diameter larger). 

• The Moon's shadow actually has two parts:

1. Penumbra

• The Moon's faint outer shadow.
• Partial solar eclipses are visible from within the penumbral shadow.

2. Umbra

• The Moon's dark inner shadow.
• Total solar eclipses are visible from within the umbral shadow.

STAGES IN A TOTAL SOLAR ECLIPSE

BAILY'S BEADS:
Baily's beads (often spelled Bailey's beads) are bead-like bursts of light that appear about 15 seconds before and after totality during a solar eclipse. Baily's beads are caused by light shining through valleys on the edge of the moon. They were named for the British astronomer Francis Baily (1774-1844), one of the founders of the Royal Astronomical Society. 

DIAMOND RING:
The "Diamond Ring" is a large burst of light that appears a few seconds before and after totality.

TOTALITY:
Totality is the short part of an eclipse when the moon entirely blocks the Sun. Totality usually lasts for just a few minutes (no more than 8 minutes in any one location on Earth).  Only 8 solar total eclipses will be visible from the continental U.S. during the 21st century.

What We Can See During Totality

During a total solar eclipse some parts of the Sun that we normally can't see become visible, including the corona (the outermost layer of the sun's atmosphere). The corona is mostly X-ray emissions (which we can't see), but light from the photosphere is scattered by the loose electrons in the corona's plasma and we can see this. Normally, the intensely bright light of the photosphere (the visible disk of the Sun) dominates the corona and we don't see the corona. During an eclipse, the moon blocks the photosphere, and we can see the faint, scattered light of the corona (this part of the corona is called the K-Corona). 

• The Moon blocks out the entire sun, except for a faint halo of light called a corona
  

Remember:  during a solar eclipse, the shaow the Moon casts on Earth is very narrow, covering an area up to only 168 miles wide.  So even though about 3 total solar eclipses occur every four years, few people in any one place see them. (Discovery Magazine)
In the few minutes of totality, we can see the coronal streamers, polar plumes, and prominences. 

Types of Solar Eclipses

• Partial Solar Eclipse - A partial solar eclipse is when the Moon only covers part of the solar disc. 
  

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• Total Solar Eclipse - A total solar eclipse is when the Moon appears to cover the entire solar disc. Total solar eclipses are only visible from a very small area on Earth, a narrow track that moves across the Earth's surface (as the Earth rotates). The partial phase of a total eclipse lasts about an hour. In any one place, totality (when the solar disc is entirely covered) lasts no more than 8 minutes. During totality, the sky is dark enough to see stars in the sky. 
  

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• Annular Eclipse - During an annular eclipse, the sun looks like an "annulus" or ring. The ring is visible when the Moon does not entirely cover the disk of the Sun during a solar eclipse. This type of eclipse happens when the Sun is at perihelion (closest to the Earth, making the solar disc appear larger) and the Moon is at apogee (farthest from the Earth, making it look smaller). 
• The Moon cannot block out the Sun totally because it is at a far point in its orbit.  The result is an annulus, or ring, that's brighter than a corona.
  

ASTRONOMY - SUN PARTS, FUNCTIONS & VOCABULARY

SUN

The sun is a star, just like the other stars we see at night. The difference is distance -- the other stars we see are light-years away, while our sun is only about 8 light minutes away -- many thousands of times closer.
­Officially, the sun is classified as a G2 type star, based on its temperature and the wavelengths or spectrum of light that it emits. There are lots of G2s out there, and Earth's sun is merely one of billions of st­ars that orbit the center of our galaxy, made up of the same substance and components.
T­he sun is composed of gas. It has no solid surface. However, it still has a defined structure. The three major structural areas of the sun:

• Core -- The center of the sun, comprising 25 percent of its radius.
• Radiative zone --The section immediately surrounding the core, comprising 45 percent of its radius.
• Convective zone -- The outermost ring of the sun, comprising the 30 percent of its radius.

Above the surface of the sun is its atmosphere, which consists of three parts:

• Photosphere -- The innermost part of the sun's atmosphere and the only part we can see.
• Chromosphere -- The area between the photosphere and the corona; hotter than the photosphere.
• Corona -- The extremely hot outermost layer, extending outward several million miles from the chromosphere.

­All of the major features of the sun can be explained by the nuclear reactions that produce its energy, by the magnetic fields resulting from the movements of the gas and by its immense gravity.
It begins at the core.

The Fate of the Sun

­T­he sun has been shining for about 4.5 billion years [source: Berkeley]. The size of the sun is a balance between the outward pressure made by the release of energy from nuclear fusion and the inward pull of gravity. Over its 4.5 billion years of life, the sun's radius has gotten about 6 percent bigger [source: Berkeley]. It has enough hydrogen fuel to "burn" for about 10 billion years, meaning it has a bit over 5 billion years left, and during this time it will continue to expand at the same rate [source: Berkeley].

When the core runs out of hydrogen fuel, it will contract under the weight of gravity; however, some hydrogen fusion will occur in the upper layers. As the core contracts, it heats up and this heats the upper layers causing them to expand. As the outer layers expand, the radius of the sun will increase and it will become a red giant, an elderly star.
The radius of the red giant sun will be 100 times what it is now, lying just beyond the Earth's orbit, so the Earth will plunge into the core of the red giant sun and be vaporized [source: NASA]. At some point after this, the core will become hot enough to cause the helium to fuse into carbon.
When the helium fuel has exhausted, the core will expand and cool. The upper layers will expand and eject material.
Finally, the core will cool into a white dwarf.
Eventually, it will further cool into a nearly invisible black dwarf. This entire process will take a few billion years.
So for the next several billion years, humanity is safe -- in terms of the sun's existence, at least. Other debacles are anybody's guess.

TERMS TO KNOW:

Corona
(halo or crown) Thin gases make up the outer layer of the sun's atmosphere, which is about 1,000,000 miles high.  The corona can be seen only during a solar eclipse

Photosphere
(sphere of light) this 340- mile- deep "surface" layer is the part of the Sun we see

SunSpots
as heat rises to the surface, magnetic fields get stirred up, creating dark patches that are about 2,200 degrees cooler than the surface

Convection Zone
currents of searing hot gas rise & fall here.  The sun is so dense that it takes energy at least 1,000,000 years to go from the core to the surface

Radiative Zone
energy here radiates out from the core


Solar Flares
are sudden, bright outbursts of energy that occur around sunsposts as magnetic fields tear & reconnect.  One solar flare can release the same energy as 40 billion atomic bombs. 

•   A solar flare is a magnetic storm on the Sun which appears to be a very bright spot and a gaseous surface eruption. Solar flares release huge amounts of high-energy particles and gases and are tremendously hot (from 3.6 million to 24 million °F). They are ejected thousands of miles from the surface of the Sun.

It has been recently discovered that solar flares can cause sunquakes. Sunquakes are violent seismic events on the Sun. When a sunquake occurs, energy is released in seismic waves on the relatively fluid surface of the Sun. These waves radiate in concentric circles from the epicenter of the sunquake.

Core
the sun's nuclear core is about the size of Jupiter (but much denser)
 
Chromosphere
(sphere of colors) this part of the sun's atmosphere gets its name from the faint reddish light it gives off.  Its average thickness is about 6,000 miles

Solar Wind
this stream of particles- IONS (electrically charged particles) that are given off by magnetic anomalies on the Sun which flow out from the Sun in all directions at up to 1,000,000 miles per hour!  The solar wind is in essence the solar corona expanding into space. 

•  The solar wind is emitted where the Sun's magnetic field loops out into space instead of looping back into the Sun. These magnetic anomalies in the Sun's corona are called coronal holes. In X-ray photographs of the Sun, coronal holes are black areas. Coronal holes can last for months or years.

• It takes the solar wind about 4.5 days to reach Earth; it has a velocity of about 250 miles/sec (400 km/sec). Since the particles are emitted from the Sun as the Sun rotates, the solar wind blows in a pinwheel pattern through the solar system. The solar wind affects the entire Solar System, including buffeting comets' tails away from the Sun, causing auroras on Earth (and some other planets), the disruption of electronic communications on Earth, pushing spacecraft around, etc.

Solar Granules
each line, or squiggle is about 600 miles across.  Granules occur because of the rising & falling of gases.  Each one lasts about 8 minutes

Coronal Loops
magnetic loops with very strong magnetic fields.  They often contain the dense, hot gas that emits intense X-ray radiation

Solar Prominences
giant arches of gas that erupt between sunspots.   

• A solar prominence (also known as a filament) is an arc of gas that erupts from the surface of the Sun. Prominences can loop hundreds of thousands of miles into space. 
• Prominences are held above the Sun's surface by strong magnetic fields and can last for many months. At some time in their existence, most prominences will erupt, spewing enormous amounts of solar material into space.

Coronal Mass Ejections
the most energetic solar eruptions CME's can grow larger than the Sun in a few hours.  When directed toward Earth, they can disrupt communications & damage satellites. 

• They are huge, balloon-shaped plasma bursts that come from the Sun. As these bursts of solar wind rise above the Sun's corona, they move along the Sun's magnetic field lines and increase in temperature up to tens of millions of degrees. These bursts release up to 220 billion pounds (100 billion kg) of plasma.  CME's usually happen independently, but are sometimes associated with solar flares.

SUN - QUIZ

• Answer the following questions on notebook paper. 
• Write the question & the answer on the next line.  
• Skip a line between the next question.  
• Turn into 6th grade drawer. 
• You may use your notes, NOT YOUR PARTNER!!!
• DUE:  Friday, 12/ 13

1. Is the Sun a star, a planet, or a nebula?_______________________


2. Is the Sun solid, liquid, or gaseous ?_______________________


3. During what month is the Sun closest to the Earth?_____________________


4. Where is the Sun hottest?_______________________


5. Where is the Sun coolest?_______________________


6. What element is most plentiful on the Sun?_______________________


7. What element was named after the Sun?_______________________


8. What is the primary atomic reaction that occurs within the Sun that converts hydrogen atoms into helium atoms? _______________________


9. How old is the Sun? ______________________


10. Are sunspots hotter or colder than the surrounding areas?_______________________ 

HERTZSPRUNG - RUSSELL DIAGRAM, TYPES OF STARS, & STAR LIFE - Activity

The following 3 sections - READ carefully & add the facts into your notes!  There is a Star activity for review.


I.  Click on the link & complete the activity.  Draw the diagram in color in your notebook.

Hertzsprung - Russell Diagram

****************************************************


II.  Click on the link below & read carefully for facts on the following types of stars.  Add the facts in your notes

• Red dwarf star
• yellow star
• blue giant star
• giant star
• super giant star

TYPES OF STARS

Scroll down on the webpage & use the Hertzsprung-Russell Interactive diagram to learn more about the stars.


**************************************************III.  LIFE CYCLE OF STAR
copy down this diagram in your notes

STARS PRACTICE QUIZ

SPACE JUNK - WHAT IS IT???

SATELITE ORBITS

WHAT IS SPACE JUNK?
Read the following article by NASA.  

Space debris is tracked as it orbits Earth.

Image Credit: NASA

More than 500,000 pieces of debris, or “space junk,” are tracked as they orbit the Earth. They all travel at speeds up to 17,500 mph, fast enough for a relatively small piece of orbital debris to damage a satellite or a spacecraft.
The rising population of space debris increases the potential danger to all space vehicles, but especially to the International Space Station, space shuttles and other spacecraft with humans aboard.
NASA takes the threat of collisions with space debris seriously and has a long-standing set of guidelines on how to deal with each potential collision threat. These guidelines, part of a larger body of decision-making aids known as flight rules, specify when the expected proximity of a piece of debris increases the probability of a collision enough that evasive action or other precautions to ensure the safety of the crew are needed.

Orbital Debris
Space debris encompasses both natural (meteoroid) and artificial (man-made) particles. Meteoroids are in orbit about the sun, while most artificial debris is in orbit about the Earth. Hence, the latter is more commonly referred to as orbital debris.
Orbital debris is any man-made object in orbit about the Earth which no longer serves a useful function. Such debris includes nonfunctional spacecraft, abandoned launch vehicle stages, mission-related debris and fragmentation debris.
There are more than 20,000 pieces of debris larger than a softball orbiting the Earth. They travel at speeds up to 17,500 mph, fast enough for a relatively small piece of orbital debris to damage a satellite or a spacecraft. There are 500,000 pieces of debris the size of a marble or larger. There are many millions of pieces of debris that are so small they can’t be tracked.
Even tiny paint flecks can damage a spacecraft when traveling at these velocities. In fact a number of space shuttle windows have been replaced because of damage caused by material that was analyzed and shown to be paint flecks.
“The greatest risk to space missions comes from non-trackable debris,” said Nicholas Johnson, NASA chief scientist for orbital debris.
With so much orbital debris, there have been surprisingly few disastrous collisions.
In 1996, a French satellite was hit and damaged by debris from a French rocket that had exploded a decade earlier.
On Feb. 10, 2009, a defunct Russian satellite collided with and destroyed a functioning U.S. Iridium commercial satellite. The collision added more than 2,000 pieces of trackable debris to the inventory of space junk.
China's 2007 anti-satellite test, which used a missile to destroy an old weather satellite, added more than 3,000 pieces to the debris problem.

Tracking Debris
The Department of Defense maintains a highly accurate satellite catalog on objects in Earth orbit that are larger than a softball.
NASA and the DoD cooperate and share responsibilities for characterizing the satellite (including orbital debris) environment. DoD’s Space Surveillance Network tracks discrete objects as small as 2 inches (5 centimeters) in diameter in low Earth orbit and about 1 yard (1 meter) in geosynchronous orbit. Currently, about 15,000 officially cataloged objects are still in orbit. The total number of tracked objects exceeds 21,000. Using special ground-based sensors and inspections of returned satellite surfaces, NASA statistically determines the extent of the population for objects less than 4 inches (10 centimeters) in diameter.
Collision risks are divided into three categories depending upon size of threat. For objects 4 inches (10 centimeters) and larger, conjunction assessments and collision avoidance maneuvers are effective in countering objects which can be tracked by the Space Surveillance Network. Objects smaller than this usually are too small to track and too large to shield against. Debris shields can be effective in withstanding impacts of particles smaller than half an inch (1 centimeter).

Planning for and Reacting to Debris
NASA has a set of long-standing guidelines that are used to assess whether the threat of such a close pass is sufficient to warrant evasive action or other precautions to ensure the safety of the crew.
These guidelines essentially draw an imaginary box, known as the “pizza box" because of its flat, rectangular shape, around the space vehicle. This box is about a mile deep by 30 miles across by 30 miles long (1.5 x 50 x 50 kilometers), with the vehicle in the center. When predictions indicate that the debris will pass close enough for concern and the quality of the tracking data is deemed sufficiently accurate, Mission Control centers in Houston and Moscow work together to develop a prudent course of action.
Sometimes these encounters are known well in advance and there is time to move the station slightly, known as a “debris avoidance maneuver” to keep the debris outside of the box. Other times, the tracking data isn’t precise enough to warrant such a maneuver or the close pass isn’t identified in time to make the maneuver. In those cases, the control centers may agree that the best course of action is to move the crew into the Soyuz spacecraft that are used to transport humans to and from the station. This allows enough time to isolate those spaceships from the station by closing hatches in the event of a damaging collision. The crew would be able to leave the station if the collision caused a loss of pressure in the life-supporting module or damaged critical components. The Soyuz act as lifeboats for crew members in the event of an emergency.
Mission Control also has the option of taking additional precautions, such as closing hatches between some of the station’s modules, if the likelihood of a collision is great enough.

Maneuvering Spacecraft to Avoid Orbital Debris
NASA has a set of long-standing guidelines that are used to assess whether the threat of a close approach of orbital debris to a spacecraft is sufficient to warrant evasive action or precautions to ensure the safety of the crew.
Debris avoidance maneuvers are planned when the probability of collision from a conjunction reaches limits set in the space shuttle and space station flight rules. If the probability of collision is greater than 1 in 100,000, a maneuver will be conducted if it will not result in significant impact to mission objectives. If it is greater than 1 in 10,000, a maneuver will be conducted unless it will result in additional risk to the crew.
Debris avoidance maneuvers are usually small and occur from one to several hours before the time of the conjunction. Debris avoidance maneuvers with the shuttle can be planned and executed in a matter of hours. Such maneuvers with the space station require about 30 hours to plan and execute mainly due to the need to use the station’s Russian thrusters, or the propulsion systems on one of the docked Russian or European spacecraft.
Several collision avoidance maneuvers with the shuttle and the station have been conducted during the past 10 years.
NASA implemented the conjunction assessment and collision avoidance process for human spaceflight beginning with shuttle mission STS-26 in 1988. Before launch of the first element of the International Space Station in 1998, NASA and DoD jointly developed and implemented a more sophisticated and higher fidelity conjunction assessment process for human spaceflight missions.
In 2005, NASA implemented a similar process for selected robotic assets such as the Earth Observation System satellites in low Earth orbit and Tracking and Data Relay Satellite System in geosynchronous orbit.
In 2007, NASA extended the conjunction assessment process to all NASA maneuverable satellites within low Earth orbit and within 124 miles (200 kilometers) of geosynchronous orbit.
DoD’s Joint Space Operations Center (JSpOC) is responsible for performing conjunction assessments for all designated NASA space assets in accordance with an established schedule (every eight hours for human spaceflight vehicles and daily Monday through Friday for robotic vehicles). JSpOC notifies NASA (Johnson Space Center for human spaceflight and Goddard Space Flight Center for robotic missions) of conjunctions which meet established criteria.
JSpOC tasks the Space Surveillance Network to collect additional tracking data on a threat object to improve conjunction assessment accuracy. NASA computes the probability of collision, based upon miss distance and uncertainty provided by JSpOC.
Based upon specific flight rules and detailed risk analysis, NASA decides if a collision avoidance maneuver is necessary.
If a maneuver is required, NASA provides planned post-maneuver orbital data to JSpOC for screening of near-term conjunctions. This process can be repeated if the planned new orbit puts the NASA vehicle at risk of future collision with the same or another space object.

SATELITE ORBITS