Ever wonder where your favourite ESA Earth observation
satellites are, right now?

Now that curiosity can be satisfied from your PC, thanks
to ESA’s Satellites in Orbits website and the new
addition of its Earth observation missions. The Earth
Observation Orbits site displays real-time information
and animations about the orbital tracks and current
locations of ESA’s four Earth imaging satellites that
were launched to help us better understand our own planet.

The interactive display includes a 3D model of the Earth
and the ESA Earth observation satellites orbiting it,
including:

* ERS–1 and –2 satellites, ESA’s first spacecraft
providing global measurements of earth’s atmospheric
and surface properties using advanced microwave
techniques. ERS-1, although still orbiting, was
retired from service in 2000;

* Envisat, Europe’s largest and most capable Earth
observation satellite, launched last year with a
suite of ten sensors to measure various aspects of
the Earth’s atmosphere, ocean, land, and ice;

* Proba, short for Project for On-Board Autonomy, a
mini-satellite measuring only 60 x 60 x 80 cm to
demonstrate advanced spacecraft and imagery
technologies.

Perspectives on the sky and Earth

On the Orbits website the display, you control several
interactive perspectives on the satellites with the
capability of toggling between them. You can alter the
time, rotate the view, zoom in and out, and learn more
about the various satellites and their missions.

The “Earth View” offers a unique perspective on the
Earth and the orbital tracks of the EO satellites,
presented as if you were “standing” thousands of
kilometres high in space and looking “down” on the
Earth and the satellites below.

The perspective can be zoomed and rotated to create
dazzling views of the Earth and outline clearly the
areas of the globe visited by the Earth observation
satellites. By “grabbing” the display with your mouse
or using the controls on the display, you can rotate
the view of the sky and zoom in on particular spots
in the sky. By animating the display with the video
controls you can watch the stately procession of the
ESA spacecraft as they travel in a never-ending circle
between the North and South Poles with the Earth
rotating underneath them.

A “Sky View” shows the satellites that along with the
Moon, planets and stars, are visible from any location
on Earth. It also displays the Moon, planets and major
stars that are visible or just below the horizon for
a particular location, date and time.

By choosing the Location radio button, you can enter
longitude and latitude settings, or pick from a
drop-down list of selected world cities, for a glimpse
of the visible sky from that location, including the
orbital tracks and current location of the spacecraft.

Like the Earth View, you can move and rotate the
display, as well as zoom in on particular spots in
the sky. By entering date and time parameters,
different sky views are presented and then animated
by using VCR-type controls to see how the sky and
satellite positions change over time.

The positions of the satellites are defined by two-line
orbital element (TLE) data. The TLEs are provided by the
North American Aerospace Defense Command, better known
as NORAD, which tracks all manmade objects in space.
The information is updated weekly, on average, to
ensure that the satellite positions are as accurate as
possible within a 40-day window, forward and back, from
the time set on your computer.

For the best view of the site, you’ll need to have Java
Virtual machine and the Flash Plug-in installed on your
computer. If you don’t have these, you’ll see links for
these add-ons.

Come and take a look if your favourite ESA Earth
observation satellite is over your neighbourhood right
now by visiting Earth Observation Orbits. Depending on
your Internet connection, the applet could take a few
moments to load.

Related links

* Earth Observation Orbits
http://orbits.esa.int/eo
* About Observing the Earth
http://www.esa.int/export/esaSA/GGGIMV7RVDC_earth_0.html
* Envisat
http://envisat.esa.int/
* Envisat Results
http://www.esa.int/envisat/
* Envisat Images
http://asimov.esrin.esa.it:8766/queryIG.html?searchType=general&col=mmg&rf=3&ql=a&showcase=Envisat results&tipo=All&lk=8&nh=12&op2=%2B&tx2=ESAJCTG18ZC&fl2=showcase%3A&ty2=w&op0=&tx0=&fl0=&ty0=&op1=&tx1=&fl1=&ty1=

* ERS
http://earth.esa.int/ers/
* Proba
http://www.esa.int/export/esaMI/Proba_web_site/index.html

[NOTE: Images supporting this article are available at
http://www.esa.int/export/esaCP/SEM9B72A6BD_Protecting_1.html ]