Venus Express Options

[tedstryk]

If all goes well, Venus Express will be a major topic for discussion in this forum a year from now. Does anyone know how good the surface coverage will be from VIRTIS and VMC? My understanding is that VIRTIS will obtain low resolution multispectral maps, and that VMC will, in addition to cloud monitoring, have one channel that can see the surface, but I don't know at what resolution or at what quality. It will be nice to have some non-radar images of Venus' surface besides the Venera snapshots and the shadowy images from Earth and Galileo's NIMS.

Ted

[cndwrld]

Venus Express Status on 30 October 2007

For those interested, here's an update on Venus Express. The Flight
Control Team publishes regular updates on the web at:
http://sci.esa.int/science-e/www/object/in...fobjectid=41488

The Main bus activity last week, on mission day 710, 19/10/2007, DOY 292
was the switch to quadrature offset (tilted) operations by the loading of
fake ephemereids. The process was fully automated following the
experience of the quadrature entry. For a two week period when
the Sun-Venus-Earth angle is 90 degrees, the Sun can fall directly
into the VMC field of view, which has no shutter, when we are Earth
poinging. The spacecraft needs to be rolled 10 degrees and maintained
there when in Earth pointing, which was not a planned state when the
spacecraft was developed. To do this, fake information (ephemerides)
are loaded; the spacecraft uses the same positioning system, but the
references are shifted by 10 degrees. The fake ephemeris was applied
after the science observations, and just before the acquisition of signal
(AOS) at the Cebreros ground station near Madrid. This 10 degree roll
also means that the Sun is kept for very long exposures on surfaces
that we normally keep cool. This means that for two weeks, our Earth
pointings (which should be cool and allow us to cool down) are hot
(so that cooling takes place during the normal science observation
periods). It is all quite messy, but doing it the second time was
much easier. We are in the transition to exit the quadrature period,
and only have to do this for a couple weeks.

We also switched from the small high gain antenna (HGA-2) to the bigger
one (HGA-1). The smaller one has to be used during quadrature because
of the Sun exposure angles on the spacecraft, to keep the Sun off of
the cooling arrays. Now we're back on the big dish, so our data rate
goes up. That's always a good thing. The TM bit rate starting on Orbit
549 (22-Oct-2007, DOY 295) was 38 Kpbs. After the antenna swap,
the bit rate went to 228 Kbps. But as Venus will be moving away
from Earth now, our data rate soon begins dropping a lot. The low point
comes in about May 2008, when we hit Superior Conjunction.

At the end of the Cebreros pass on Orbit 548 (21-Oct-2007, DOY 294),
at 18:00z, Venus Express was orbiting Venus at 94.6 million km from
the Earth. The one-way signal travel time was 315 sec.

The operations of the VIRTIS imaging spectrometer were disabled for the
past month. Really unusual currents in the cooling motors was detected
last month by the Flight Control Team in Darmstadt, Germany. To be safe,
the instrument was shut down except for unusually interesting
observations. The Virtis team in Frascati (Rome) has worked with the
motor manufacturer, and new procedures to use the motors were developed.
After which, the manufacturer changed their minds and decided that the
old procedures were better and safer. Operations are expected to
resume next week or the week after.

The rest of the instrument observations have been taking place routinely,
with the occasionaly glitch here and there.

Current NTO (Oxidizer) Mass (Kg): 46.761
Current MMH (Fuel) Mass (Kg): 29.514

During the NASA Phoenix mission's final approach to Mars, ESA will
support NASA by performing Delta-DOR measurements in order to get the
best positioning data possible. Venus Express was used as a test of the
Delta DOR procedures at the end of September and early October,
performing three Delta-DOR tests. The results show that we are still
at Venus.

The special issue of Nature magazine on Venus Express results is
expected to be published on 29 November, and should be accompanied by
a press conference the day before. The last paper was accepted
yesterday, so it should be all finalized. However, it has taken so
long to get these papers submitted that I'll believe it when I get
a hard copy in my hands.

The VEX teams are starting to get pretty good images of the surface
of Venus, through the frequency 'windows'. Hopefully a few web images
will come out before too long.

There are four science operations engineers working on Venus Express.
As of last week, three of the four have been re-located to work at
The European Space Astronomy Centre (ESAC) near Madrid. The fourth
engineer (me) will be moving at the end of January. All the ESA planetary
science operations will soon be based there. As a consequence, the
facility's name is expected to change, to The European Planetary and
Space Astronomy Centre (EPSAC).