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Hi, I'm Chris and this is NASA Now.
So how do satellites stay in orbit and what's the difference
between a geostationary orbit and a polar orbit?
We'll talk to an expert who'll explain the use of each kind
of orbit and how it works.
That's ahead.
But, first here's what's happening at NASA Now.
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Update: NASA's MESSENGER spacecraft, which has been
in orbit around Mercury for over six months,
is sending back information
that has revolutionized the way scientists think
about the closest planet to the sun.
For decades, scientists have wondered whether Mercury has
volcanic deposits on its surface.
The answer is yes and in a big way.
New data shows a huge area
of volcanic plains surrounding Mercury's North Pole,
covering as much as 6% of the planet's surface.
Scientists will use data gathered by MESSENGER
as they continue to piece together the origins
of our solar system.
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Now let's take a look at the past.
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December 18, 1999, Terra: the flagship
of the Earth Observing System, was launched
from Vandenberg Air Force Base in California.
Terra is the Latin word for Earth.
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It is estimated that there are
around a thousand satellites currently
in operation around Earth.
Each of these satellites has been put into a specific kind
of orbit depending upon its mission.
So how does a satellite stay in orbit and why are satellites put
in different kinds of orbits at different altitudes?
Joining us is NPP Satellite Project Scientist Dr. James
Gleason from the Goddard Space Flight Center.
Hello Dr. Gleason, tell us about the different kinds of orbits.
Geostationary or geosynchronous orbit is an orbit
around the equator where the satellite orbits
at the same speed as the Earth.
So, it has the effect of staying in the same place all the time.
If you're looking for short-term time varying things, hurricanes,
tornados, fires that might be changing quickly,
you want to be staring all the time at one spot.
If you are trying to understand the global picture, what's going
on in Asia, what's going on in Africa,
you need to make those observations,
and for that you need a polar orbiting spacecraft,
which is an orbit that goes over the poles.
What affects the orbit of satellites?
The sun-Earth distance changes
as the Earth goes around the sun.
So, small changes in the gravity field and small changes
as the gravity of the sun affects the spacecraft,
makes it push slightly out of its observing time orbit.
So, you're currently working
on the NPP project, tell us about it?
NPP is a mission that is designed to make sure
that certain advanced measurements are continuously
made to help us understand the Earth, weather and climate.
Starting in the 2000 time period,
NASA flew several research satellites,
which demonstrated the effectiveness
of making a large number of environmental observations.
These observations have proved their worth
over the intervening decade so much so that we feel the need
to continue those measurements.
What kind of orbit is NPP going to be in?
NPP is in a polar sun synchronous orbit.
And what that means it is, it's a polar orbit,
which means it goes around the poles.
Sun synchronous mean it flies overhead at the same spot
of the Earth at the same local time every day.
So how does NPP stay in orbit?
The orbit is maintained with fuel on board.
So, essentially as the orbit begins to drift,
which means that the time of observation changes slightly,
we use a little bit of fuel and push it back
to where it should be.
Why are satellites like NPP important?
One of the things we're trying
to understand is essentially the entire Earth system,
which is very complicated and has a number
of systems that all interact.
And then we try to take a step back
and say is the entire system changing and is that important?
And if it is important, what should we do about it?
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Did you know that the NPP satellite weighs 4,600 pounds?
That about the same as a small school bus.
Now you know.
Now it's time to check out what's up.
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There's no better way to get a bird's eye view of Earth
than from satellites in orbit.
Check out this NASA website called Earth Observatory.
You'll be amazed at what you can see.
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Now that you know how satellites stay in orbit, here's a chance
to conduct your own experiment.
It's called Around the World, and it's easy
to do right in your classroom.
You can find this activity
on the NASA Explorer Schools' Virtual Campus.
Well that's it for NASA Now, join us next time
when we examine high tech survival
on the International Space Station.
See you then on NASA Now.
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NASA Now comes to you from the Virtual Campus
at NASA Explorer Schools.