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European Space Agency

Press Release

Eyeing orbits from a new perspective - your PC
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24 February 2003

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 60x60x80 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. 

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