Venus Express Has Reached Final Orbit

http://www.esa.int/esaCP/SEM33O8ATME_index_0.html

Venus Express has reached final orbit
European Space Agency
9 May 2006

Less than one month after insertion into orbit, and after sixteen loops
around the planet Venus, ESA's Venus Express spacecraft has reached its
final operational orbit on 7 May 2006.

Already at 21:49 CEST on 6th May, when the spacecraft communicated to
Earth through ESA's ground station at New Norcia (Australia), the Venus
Express ground control team at ESA's European Spacecraft Operations
Centre (ESOC) in Darmstadt (Germany) received advanced confirmation
that
final orbit was to be successfully achieved about 18 hours later.

Launched on 9 November 2005, Venus Express arrived to destination on 11
April 2006, after a five-month interplanetary journey to the inner
solar
system. The initial orbit - or "capture orbit" - was an ellipse ranging
from 330 000 kilometres at its furthest point from Venus surface
(apocentre) to less than 400 kilometres at its closest (pericentre).

As of the 9-day capture orbit, Venus Express had to perform a series of
further manoeuvres to gradually reduce the apocentre and the pericentre
altitudes over the planet. This was achieved by means of the spacecraft
main engine - which had to be fired twice during this period (on 20 and
23 April 2006) - and through the banks of Venus Express' thrusters -
ignited five times (on 15, 26 and 30 April, 3 and 6 May 2006).

"Firing at apocentre allows the spacecraft to control the altitude of
the next pericentre, while firing at the pericentre controls the
altitude of the following apocentre," says Andrea Accomazzo, Spacecraft
Operations Manager at ESOC. "It is through this series of operations
that we reached the final orbit last Sunday, about one orbital
revolution after the last "pericentre change manoeuvre" on Saturday 6
May".

Venus Express entered its target orbit at apocentre on 7 May 2006 at
15:31 (CEST), when the spacecraft was at 151 million kilometres from
Earth. Now the spacecraft is running on an ellipse substantially closer
to the planet than during the initial orbit. The orbit now ranges
between 66 000 and 250 kilometres over the Venus and it is polar. The
pericentre is located almost above the North pole (80? North
latitude),
and it takes 24 hours for the spacecraft to travel around the planet.

"This is the orbit designed to perform the best possible observations
of
Venus, given the scientific objectives of the mission. These include
global observations of the Venusian atmosphere, of the surface
characteristics and of the interaction of the planetary environment
with
the solar wind," says H?kan Svedhem, Venus Express Project Scientist.
"It allows detailed high resolution observations near pericentre and
the
North Pole, and it lets us study the very little explored region around
the South Pole for long durations at a medium scale," he concluded.

Until beginning of June, Venus Express will continue its "orbit
commissioning phase", started on 22 April this year. "The spacecraft
instruments are now being switched on one by one for detailed checking,
which we will continue until mid May. Then we will operate them all
together or in groups" said Don McCoy, Venus Express Project Manager.
"This allows simultaneous observations of phenomena to be tested, to be
ready when Venus Express' nominal science phase begins on 4 June 2006,"
he concluded.


For more information:

Don McCoy, ESA Venus Express Project Manager
Email: Don.McCoy @ esa.int

Andrea Accomazzo, ESA Venus Express Spacecraft Operations Manager
Email: andrea.accomazzo @ esa.int

H?kan Svedhem, ESA Venus Express Project Scientist
Email: Hakan.Svedhem @ esa.int