This Echo is READ ONLY !   NO Un-Authorized Messages Please!
 ~~~~~~~~~~~~~~~~~~~~~~~~   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

European Space Agency

Press Release

OK, our next caller is... from Mars!
====================================
25 February 2003

It is midnight on 1 January 2004 and you want to send a greeting on
your mobile phone to a friend. Sorry, the line is too busy, try again
later. If you think you are alone with this problem, you are wrong.

Space agencies have had to work out ingenious solutions to prevent
similar 'engaged, call later' tones from happening on Mars. For the
first time, there will be seven spacecraft on the Red Planet at the
same time. Will they all be able to 'phone home'?

Mars is a popular place to go nowadays. ESA's Mars Express mission
will be entering orbit around Mars and releasing its lander Beagle 2
at the end of December 2003. The two NASA Mars Exploration Rovers will 
be landing about the same time. Japan's Nozomi, after five years in 
space, will be entering Mars's orbit not long after also. Finally,
there are two other probes already orbiting the Red Planet: NASA's
Mars Global Surveyor and Mars Odissey. What happens if they all try to 
communicate at the same time?

Scientists need to transmit messages continuously to their
interplanetary spacecraft. Receiving data concerning the status of the 
instruments and their results is essential. Since the late 1950s, they 
use antennas in three NASA stations, which form the Deep Space Network 
(DSN). The stations are located in Goldstone (California), Madrid 
(Spain), and Canberra (Australia).

The core of each DSN station is an enormous 70-metre-diameter antenna. 
It can capture the signal of a spacecraft more than 16 thousand 
million kilometres away from Earth. Several smaller antennas surround 
that dish. The goal of the network is to constantly talk to
spacecraft.

Soon, ESA's completely new ground station will help us listen to deep
space also. Located in Australia, just outside the town of New Norcia, 
near Perth, the station has a new 35-metre antenna. It will become the 
main communications link between all future ESA deep-space missions 
and ESA's operation centre, ESOC (European Space Operation Centre), in 
Darmstadt (Germany).

Thanks to this new ground station, there will not be any 'busy-line'
signals, explains Rudi Schmidt, Mars Express Project Manager. "We're
not expecting communications difficulties between the ground stations
and the orbiters. NASA, ESA, and the Japanese spacecraft use different 
frequencies to transmit their signals. In addition, each spacecraft 
has its own internationally recognised 'call sign', as an identifier."

Communications between landers and orbiters will be even more
complicated. ESA and NASA have worked very closely to ensure crossover 
support between American and European landers and orbiters.  ESA's 
Mars Express will therefore be able to talk to the NASA Rovers and 
ESA's lander Beagle 2 with NASA's Mars Odissey. "This guarantees that 
we receive the maximum amount of science data possible. In addition, 
this makes sure that we can help each other if there are problems," 
says Schmidt.

Don McCoy, Mars Express Project Engineer, adds: "Another good trick we 
will use is to store the lander's data on the orbiter, and then
transmit them to Earth later. The orbiter will be visible longer from
the Earth and it can use a bigger and more efficient antenna than the
lander, which has a smaller solar panel and uses less transmission
energy."

According to Agustin Chicarro, Mars Express Project Scientist, "We'll
need DSN as a back-up during critical mission phases, such as the
orbit intersection manoeuvres. The important thing is the
coordination: don't forget that DSN will also have to track other
important missions, such as Cassini and Deep Space 2."

Scientists want to be able to hear what exciting news their spacecraft 
have to tell once they reach their destinations. Now there is more 
certainty that they will. 

 - End of File -
================

---