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

At the end of the last Cebreros pass in DOY 132, 18:00z, Venus Express
was orbiting Venus at 139 million km from the Earth. The one-way
signal travel time was 463 seconds. We are approaching inferior
conjunction, when Venus will be between Earth and the Sun.

The Venus Express spacecraft has been operating nominally, with only
relatively minor exceptions. One of these was a problem related to an
anomaly where a thruster failed to close. The thinking on that is
its "probably due to a missed pulse in the commanding
circuitry". I'd feel better if I knew what that meant, but even then
it would still mean that we don't know. We haven't seen a repeat, and
the best spacecraft problems are the ones that fix themselves.

With the installation of a flight software patch and the update of the
on-board ephemeris, Venus Express was configured for the quadrature
phase. This phase is defined as the period during which the
Sun-Spacecraft-Earth angle is between 75° and 95°.

During the quadrature phase, revised operating constraints on the
VMC camera lead to the necessity for changing the spacecraft attitude to
prevent unacceptable illumination of the VMC camera. To this end, fake
ephemerides on the positions of the spacecraft and the Earth were
uploaded to Venus Express.

On 11 May 2007, for the first time, Earth pointing was achieved
using fake ephemerides with a Sun illumination of ~10 degrees on
the +Y spacecraft face. The first pass with a tilted attitude was
closely monitored by the Flight Control Team (FCT). No anomalies
related to quadrature operations were detected and the performances
of the system was nominal. The flight control team and flight
dynamics teams at ESOC, in Darmstadt Germany, spent a large amount
of time and effort in planning this 'quadrature' exclusion period,
but it all looks good now. We're in Quadrature, in the
exclusion period, and it is all working perfectly. The ESOC flight
control and flight dynamics teams are very good.

Later in the quadrature phase, a swap to the smaller High Gain Antenna 2
is required for Earth communications, as the spacecraft attitude for
continued use of HGA 1 would result in illumination of spacecraft
faces not designed to cope with such exposure. This is scheduled for
01 June, and will immediately drop our downlink data rate from 228 Kbps
to 28 Kbps. Its unfortunate that during inferiour conjunction, our data
rate has to drop so much. Re-using the Mars Express design allowed
the VEX mission to get funded, but one consequence is that the thermal
constraints force things like this.

It looks like we've had our first non-recoverable failure. It appears that
the S-Band downlink path has a problem which significantly reduces our
downlink power on S-Band. That's the bad news. The current indications
suggest that the problem lies in the path between the entry to the RF
switch immediately prior to the HGA 1 antenna, and the antenna itself.
The good news is that radio science, which used to rely on having both
the X-band and S-band downlink, can now use only the X-band downlink
along with models of the Earth ionosphere (which replaces the need for
the S-band signal). There is still a lot of work being done, to try and
figure out exactly what happened, and more importantly, why.

Some delays have been encountered in the data deliveries for ingestion
to the archive, but a first release of (a subset of) Venus Express
data in the Planetary Science Archive (PSA) is still expected for
this summer.

The preparations for a special section on Venus Express results
(some 9 papers), to be published in Nature, are ongoing.

Planning for our sixteenth monthly medium-term plan of operations (MTP016)
are completed. We are just now finishing MTP017, and MTP018 planning started
this week.

[The Messenger]

It looks like we've had our first non-recoverable failure. It appears that the S-Band downlink path has a problem which significantly reduces our downlink power on S-Band. That's the bad news.

???
Wasn't one of the instruments non-functional from the get-go? PFS? Fourier IR or something?