Venus Express Options

[cndwrld]

Venus Express Status

At the end of the last Cebreros pass in the reporting period (DOY 251, 15:00z) Venus Express was orbiting Venus at 52.0 million km from the Earth. The one-way signal travel time was 172 seconds.

Overall, the spacecraft is performing well, and most of the instruments are working great. During MTP 018, which is finishing this week, we completed 500 orbits and have sent to Earth around 1 Terabit of data so far.

Of the four science operations engineers, two are now moved to the European Space and Astronomy Centre near Madrid, Spain. Another will join them in October. And I expect to move down from The Netherlands sometime in January. Within the next half year, all of ESA's planetary science operations, as well as their astronomy science operations, will be based at ESAC, Spain.

on 23/08/07, DOY 235, we performed an S-Band test. As you may recall, our S-Band downlink on the main antenna HGA-1 is very much reduced in output. Tests had earlier shown that the problem was definitely in the HGA-1; these tests confirmed that it was in the antenna itself, but there's no telemetry on the antenna. It is possible that some physical deformation took place, but anything is just speculation. 14. VMOC has scheduled a mapping and calibration of the S-Band downlink, which will occur in MTP021. The calibration put out a carrier over the S-band HGA-1 output, and slew the spacecraft back and forth past the Earth. Since the downlink is so reduced, we will need a 70 meter antenna to pick up the carrier very well, so we will do the test using the Canberra DSN to capture the downlink signal strength. We can then look for distortions in the signal pattern.

The S-band calibration slot is currently scheduled for Orbit 584, DOY 330, on 26-Nov-07 between 00:30 and 04:00Z.
It will take place over the Canberra DSN antenna, towards the end of the visibility period and coming up directly before the Cebreros AOS. It will occupy the pericenter arc, with some margin due to its relatively long duration (3hr 30min).

The calibration is HOT (sun exposure on sensitive faces), and so there can be no hot observations prior to it in orbit 584 and we must be thermally recovered from any previous observations. The recovery time from the calibration is covered within the following Cebreros pass, which will allow hot observations to resume as normal in Orbit 585. The VMC camera was approved for observations during the antenna calibration, as the +Z axis will be pointing at the planet.

We need the S-band for bi-static radar observations. That's where they point the big antenna at the surface of Venus, blast out the carrier signal (but in a very stable oscillator mode) and catch the reflections on Earth using a DSN antenna. Without the S-Band, they can't correct out for the Earth's atmospheric distortion. They thought they could use models to do it, but I guess it didn't work out as well as hoped. In the mean time, we aren't doing any BSR observations. Since we seldom get the right geometry to do them, we are not missing many. But then again, there aren't many to miss.

On August 23rd, the spacecraft came into view at the Cebreros station bearing bad news. There had been some type of problem wtih a solar array drive motor, during the observations, and the system had switched to the B side units. The spacecraft controllers and engineers cleaned it up and reset everything. Now they needed to figure out why it happened, since the A side stuff seemed to be just fine.

They didn't have long to wait to get more data. The next day, on 24/08/07, DOY 236, VEX came back into Earth view with the same problem, only worse. The solar array drive electronics (SADE) showed a motor with a failed status and a mispointing between the two solar panels. The control team manually switched off all the payload and as much power-sucking stuff as possible, and cleaned it back up again. Given that it happened twice in two days, the spacecraft left Earth pointing and with payload off until it was figured out.

This is believed to be related to a known MEX anomaly, which uses the same motors and electronics. The anomaly testing was completed, after a couple days of the spacecraft being left Earth pointing with the payload off. The solar panel pointing has been successfully corrected. I haven't seen a full report on the problem yet, but it hasn't come back.

In other Payload Activities, the ASPERA nuetral and charged particle detector, MAG magnetometer, SPICAV stellar/solar spectrometer and VMC camera seem to be working well.

And the VIRTIS imaging spectrometer? Well, not so much. Virtis is in two wholly separate parts: the M and H instruments. The M instrument has a large field of view (FOV), the H a very small one. They both need to be cooled prior to use of the IR detectors, and use motors to move the cooling fluid around. It was noted by the Flight Control team that one of the motor telemetry channels went out of limits. And that is when they noticed that the cooler motor currents had been fluctuating wildly for some time, just not out of limits. A test that included the VIRTIS H cooler was performed on DOY 251. Otherwise only Virtis M part has been operated during this period as the failure on H cooler is still under investigation. And since the cooler motors are the same, M is operated in a somewhat limited mode. So far, it seems that the M motor is not effected. Testing on the H motor continues, to try and characterize it. The Virtis instrument team is really good, so we trust them to do a good characterization, and we'll see if we can do anything or not. We can run the motor the way it is, of course. But once it fails, no coolant motor means no coolant, which means no crycooler cooling, which means Virtis-H IR detector data.

To summarize, things go well but not perfectly. Keeps it interesting.

[cndwrld]

Nature Papers

On 29 November 2007, a special issue of Nature magazine will highlight the first major papers from each of the instruments on the Venus Express mission. A press conference is planned for 28 November to highlight the release.

Should be a great issue.

[elakdawalla]

Hooray hooray hooray! According to what Hakan Svedhem told me, waiting for this publication has been a logjam that prevented more science from coming out (not necessarily by press releases, I mean as presentations by scientists at meetings). It will be a great relief to see some Venus Express results in publication.

cndwrld, does your posting of this date mean that all of the teams have gotten their papers submitted?

--Emily

[cndwrld]

Yes, my understanding is that everything is in, accepted and ready to go. Given the history of this issue, I wouldn't say that nothing can go wrong now. But we hope that it is finally going to happen. Three months into the Extended Mission, it would be nice to see something published....

[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).

[nprev]

Thanks for the update, CND. Sounds like good things are coming in about a month...looking forward to the surface imagery! Will be interesting to compare it to Magellan radar data.

[helvick]

The results show that we are still
at Venus.

That must be a relief.

Excellent update again don. Thanks.

[The Messenger]

There are a few things still orbiting Mars that we do not hear from either;)

[ustrax]

There are a few things still orbiting Mars that we do not hear from either;)

You are probably slightly deaf...

[rlorenz]

Venus Express Status on 30 October 2007
......
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.

Are you gonna miss Noordwijk ?
I was a YGT at ESTEC 1990-1991 on Huygens, still fond memories of
the beach, Koop Avond, Annies Verjahrdag etc..... At least Madrid
should be sunny...

[rlorenz]

Are you gonna miss Noordwijk ?

Duh sorry - you're at ESOC, right? Of course you won't miss Darmstadt,
very few redeeming features, except maybe the Ratskeller.

[cndwrld]

I'm at ESTEC now, in Holland. And I am definitely going to miss this place, both ESTEC and Holland. The Netherlands is a wonderful place, Leiden a beautiful, fun town.
I can't afford to live in Madrid, so it will be nearby. If Spain and the new town aren't wonderful, too, 'll be very upset.

[cndwrld]

Stellar Occultation Studies at three planets

The Principal Investigator for on of the Venus Express instruments has written a short brief about the use of stellar occulation measurements being performed by European spacecraft now at three planets: Venus, Earth and Mars. You can read the release at:

http://www.esa.int/SPECIALS/Venus_Express/SEMEH3FWB8F_0.html

[cndwrld]

Eleven VEX Papers On-Line

On the ESA Science and Technology page for Venus Express, eleven papers have been put on line. They cover the seven science instruments, the spacecraft, the ground segment and mission planning, science data handling and science planning.

They can be accessed by going to the VEX Science web page at

http://sci.esa.int/science-e/www/area/index.cfm?fareaid=64

and then clicking on 'Publications' under the 'Services' header at the lower left.

[ustrax]

VMC surface images released.