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]

VEX Mission Status

Quadrature is the period when the Earth-Venus-Sun angle is less than 90 degrees, which includes inferior conjunction. At the start and end of quadrature, we have to undertake special operations in order to avoid Sun exposure into the VMC instrument which has no shutter. On 16 June, the spacecraft's 10° +Y tilt was removed at the end of the first quadrature transition period.

Removal of the 10° +Y tilt was removed by execution of previously
uploaded commands, just prior to start of the Earth communications pass.
It was done this way so that the spacecraft orientation could be checked
immediately upon the start of communications with Earth, and time for the
science downlink would not be used to observe the orientation change.


Routine observations took place during this reporting period, and
occurred as planned. A full VIRTIS software upload was carried out
including the related testing on DOY 165 and 166.

On DOY 167, the telemetry bitrate changed to 45 kbps.

At the end of DOY 167, Venus Express was orbiting Venus at 97 million km
from the Earth. The one-way signal travel time was 323 seconds.

Payload Activities have been routine. Two VeRA radio science occultation
observations were performed using the ESA New Norcia antenna in Australia
on DOY 164, 166, 168, 170 and 173. For these observations, a highly stable
local oscillator is used to generate the downlink signal to Earth, a ground
antenna locks on the signal, and the signal is measured as the spacecraft
is occulted behind the planet. This is repeated when the spacecraft leaves
occultation and emerges from behind the planet. The spacecraft is re-oriented
during the occulation to account for the diffraction of the atmosphere, to
maintain the link withe the ground station. The changes in the signal are
used to determine properties of a deep slice of the atmosphere. Since this
was in the quadrature period, the smaller high gain antenna was used, greatly
limiting the signal strength.

A VeRA Bistatic Radar observation was also performed, using the 70m Canberra
DSN station on DOY 163. In these experiments, the stable oscillator is used
for the downlink to the big high gain antenna, and the antenna is pointed at
a ground feature and tracks it. The reflected signal is detected by the Earth-
based antenna, which is why the large 70 meter DSN antennas must be used.

For the VIRTIS imaging spectrometer, a full instrument operating software
upload and related testing were carried out on DOY 165 and 166.

On DOY 170, a new on-board control procedure (OBCP) was uploaded for
SPICAV shutter operation. The OBCP is expected to automate the operations of
the SPICAV shutter. The shutter is closed when the instrument is not in use,
because exposure to direct sunlight would damage the instrument optics.
The commands have been inserted into the normal command uploads to the
spacecraft for shutter operations, but in the case of a spacecraft safe
mode the shutters would not have gotten closed and might have exposed the
instrument to hours of exposure in the worst case.

PFS spectrometer tests are being prepared to try to move the instrument's scanner during
a wheel off-loading (WOL). The instrument is non-functional due to a stuck
scanner. It is hoped that operating the scanner motor while the thrusters
kick the spacecraft might free the scanner. Hoped, but not expected.

Today I plotted out the fuel, oxidizer and helium pressurant since the start of the mission.
The state of the consumables is just fine, and VEX life will be limited by money much more than
by fuel. The plot below shows how much was used to get into orbit; since then, we've been using
very little. We've got room for some big orbit changes if it is decided to try something new.