ESA mission control team readies for Venus arrival (Forwarded)

ESA News
http://www.esa.int

27 March 2006

Mission control team readies for Venus arrival

Venus Express mission controllers at ESA's Space Operations Centre (ESOC)
are in intensive preparation for an 11 April arrival at the spacecraft's
namesake destination.

The critical manoeuvre will involve a deft combination of basic physics,
expert spacecraft engineering and precise timing.

Next month's Venus Orbit Insertion (VOI) will mark the arrival of the
first ESA mission at Venus, one of the Solar System's most enigmatic
planets.

Orbit insertion comprises a series of telecommands, engine burns and
manoeuvres designed to slow the spacecraft from a velocity of 29 000 km
per hour relative to Venus just before the first burn to an entry velocity
some 15 percent slower, allowing it to be captured into orbit around the
planet.

Pointing engine for braking

Controllers will command the spacecraft to 'slew' (rotate) so as to point
the engine nozzle in the direction of motion starting at 08:03 (all times
CEST on Earth [0603 UTC]) 11 April. Venus Express will perform an
approximately 51-minute main engine burn starting at 09:19 [0719 UTC].

The spacecraft's solar arrays will also be positioned so as to reduce the
possibility of excessive mechanical load during engine ignition.

Over the subsequent days, a series of additional burns will be done to
lower the orbit apocentre (point furthest from the planet) and to control
the pericentre (point closest to the planet). The aim is to end up in a
24-hour orbit around the 'hothouse' planet early in May.

Critical manoeuvres require precise timing

All steps must take place in the correct sequence and the spacecraft must
be brought into the correct configuration in time for the main engine
burn, which itself can only happen at a specific moment. The risk is that,
if any problems occur, the spacecraft could miss its 'window' for capture,
making any recovery extremely challenging.

During the engine burn, the spacecraft will also enter an occultation,
which occurs when Venus Express travels behind the planet so that the line
of site to Earth is blocked; it will lose radio contact for almost 10
minutes. Controllers will closely watch for reacquisition of radio contact
once the occultation ends at 09:56 [0756 UTC].

"Venus orbit insertion is a complex step. The main challenge is that the
manoeuvre must happen at the right time," says Jean-Baptiste Gratadour,
Attitude and Orbital Control Systems Engineer for Venus Express at ESOC
and one of the dozens of engineers and scientists now readying for arrival
at Venus.

Venus Express in great shape

To prepare for orbit insertion, the spacecraft has had to pass a series of
important tests and milestones.

"In the night between 16 and 17 February, Venus Express passed its VOI
readiness review after a successful burn of its main engine, providing a
thrust of 400 Newtons," said Don McCoy, Venus Express Project Manager.
"This was followed by a minor mid-course correction provided by the
spacecraft's four 10-Newton thrusters on 24 February."

A 400-Newton engine generates 625 kilowatts of power, making a typical
automotive engine seem feeble in comparison.

NASA to provide direct support

Recent rehearsals have included establishing the communication link
between the Venus Express control room at ESOC and the 70-metre deep-space
antenna at Madrid, part of NASA's Deep Space Network (DSN).

This ground station will support VOI due to its geographic location. For
routine operations, Venus Express communicates using X-band via ESA's new
35-metre deep-space antenna at Cebreros, near Madrid (Spain).

The link was tested by broadcasting a live signal from the Venus Express
low-gain antenna to Madrid and then into ESOC.

This test was fundamental because, during orbit insertion, the low-gain
antenna will be used to track the spacecraft's velocity. The Venus Express
high-gain antenna, normally used to communicate with Earth, will in fact
be rotated away and out of line of sight of ground stations during the
operation.

"We are also conducting continuous tracking of the spacecraft position
through different techniques and using several ground stations, including
ESA's Cebreros station and NASA Deep Space Network stations at Goldstone
(USA) and Canberra (Australia) and Madrid," says Andrea Accomazzo, Venus
Express Spacecraft Operations Manager. "All our efforts are in fact now
concentrated on the spacecraft navigation to prepare for the big day of
arrival at Venus," he added.

During orbit insertion, the spacecraft will be 125 000 000 kilometres from
Earth and the round-trip signal time will be 13 minutes and 32 seconds.

More about...

* Looking at Venus
http://www.esa.int/SPECIALS/Venus_Express/index.html
* Status reports
http://sci.esa.int/science-e/www/obj...objectid=31575
&farchive_objecttypeid=30 &farchive_objectid=30930
* Venus Express factsheet
http://www.esa.int/esaSC/SEM2EE1A6BD_index_0.html

Related articles

* And now straight to Venus!
http://www.esa.int/esaSC/SEMIMWMVGJE_index_0.html
* Successful Venus Express main engine test
http://www.esa.int/esaCP/SEMVX5MVGJE_index_0.html
* First light for the Venus Monitoring Camera
http://www.esa.int/esaCP/SEMLWVULWFE_index_0.html
* Venus Express performs flawlessly, LEOP complete
http://www.esa.int/esaCP/SEMK9UJBWFE_index_0.html
* Venus Express mission operations update
http://www.esa.int/SPECIALS/ESOC/SEM780738FE_0.html
* Venus Express en route to probe the planet's hidden mysteries
http://www.esa.int/esaCP/SEM56Q638FE_index_0.html

Related links

* ESA Mission Operations

http://www.esa.int/spacecraftops/ESO...551445449.html
* Cebreros webcam

http://www.esa.int/spacecraftops/ESO...749851476.html

IMAGE CAPTIONS:

[Image 1:
http://www.esa.int/esaCP/SEMJITM65LE_index_1.html]
Artist's impression of the ESA spacecraft Venus Express in orbit around
Venus, launch date 26 October 2005.

Credits: ESA

[Image 2:
http://www.esa.int/esaCP/SEMJITM65LE...html#subhead1]
VEX mission control team in MCR during training for launch, October 2005

Credits: ESA

[Image 3:
http://www.esa.int/esaCP/SEMJITM65LE...html#subhead3]
An artist's impression of the first firing test of the Venus Express
spacecraft main engine, being performed in space during the night of 16/17
February 2006. The burn started at 01:27 CET and lasted about three
seconds.

Credits: ESA

[Image 4:
http://www.esa.int/esaCP/SEMJITM65LE...html#subhead5]
Andrea Accomazzo, SOM, in MCR during VEX launch, 9 November 2005

Credits: ESA