Venus Express: One Year In Orbit

On 11 April 2006, VEX went into orbit around Venus. The ESA Science web page contains an article about it, which focuses on the oxygen airglow which is being investigated. The page is at:

http://www.esa.int/esaSC/SEM26GLJC0F_index_0.html

Nice, finally some new images and a cool movie!

It seems like this glow would be invisible to the eye. My mind leaps for an explanation for the ashen light, but it will probably end up being an optical illusion, not a real phenomenon.

I'm not so sure. It's not clear from the press release whether this glow is monchromatic at 1.27 microns. It could just mean that it is being detected with that particular filter. Anyhow there could be more than one fluorescence-producing process, involving different molecules, operating either together or at different times and places in the atmosphere. The eye has the advantage over the camera when it comes to seeing over a very wide dynamic range of brightness, so I wouldn't discount the ashen light yet. What a wonderful atmosphere this is!

VEX Mission Status

As of 14 April, Venus Express was orbiting Venus at 169 million km from the Earth. The one-way signal travel time was 564 sec.

From 08 April through 12 April, a series of special mosaic images of the south pole were taken with higher than normal resolution. The amount of data would exceed the capability of the nominal ESA ground station at Cebreros, Spain. The data was instead downlinked via the DSN 70-meter Madrid station, under a cross-support agreement between ESA and NASA. This South Pole 'movie' should show excellent coverage and detail of the south polar vortex.

was interesting to note that the brand-new Cebreros 35-meter antenna was 'shadowing' the DSN 70-meter, with no margin built in, and had as good a data rate capture as the much bigger DSN antenna. Which seems to indicate that the DSN 70-meter dish needs a little maintenance.

Some data was lost on DOY 101 due to bad weather in Spain. The data was recovered due to the shadowing with the Cebreros antenna. And all of us in Holland were glad to hear about bad weather in Spain.

Quadrature period begins in May. During this period, the spacecraft will switch to our smaller high-gain antenna, sharply reducing our data rate. The VEX bus is designed so that only two of the eight faces can be exposed indefinitely to the Sun. In the quadrature phase, we would get Sun exposure on the prohibited faces during Earth communications, which lasts at least eight hours per day. The spacecraft is then flipped, and Earth communications is done via the smaller high-gain antenna to keep the Sun exposure only on the allowed faces. The spacecraft is designed for this situation, but this is the first time in the mission we have been in this quadrature situation, so a lot of details on the ground have needed to be worked out and verified. The Flight Control Team at ESOC, in Darmstadt Germany, have been working on it for a while now, and final testing of the changes are underway now. The science planning for this period was wrapped up some time ago.

All spacecraft systems continue to operate nominally, with the occasionaly hiccup just to make sure that people are paying attention.

Much appreciated update Don.

New VEX Science Information Released

On the ESA Science page at: http://www.esa.int/SPECIALS/Venus_Express/
there are two new releases that you might find interesting.

The first shows some great 'movie' images taken by the VIRTIS imaging spectrometer of Venus' south pole. Combining the IR images with a UV image of the dayside, you can see the full rotation of the south polar vortex. Over a period of five orbits, VIRTIS took images centered around apocenter. The page strings them all together, so that you see the five or so shots from one orbit, and the sudden jump is when the data jumps to the images from the next orbit. You can really see the change in the cloud structure over time in the vortex.

Just released is an article about ground-based observations that will be taking place in coordination with VEX. This will extend up to the Messenger Fly-By in early June, when we will be (sort of) simultaneously taking data from Messenger, VEX and the ground.

Over the next few months, Venus will be around its closest distance to Earth (inferior conjunction). Planning began this week for late August through late September, slightly past conjunction, and during that period we'll also be coordinating VEX observations with some ground observations:
- Infrared observations will be made by the Infrared Telescope Facility (IRTF) facility in Hawaii, USA.
- Sub-millimetre observations will be made for two days with the James Clerk Maxwell Telescope (JCMT), located in Hawaii, USA.

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.

Ground - based observatories join forces with Venus Express
European Space Agency
23 May 2007

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

You're right. The PFS instrument
(http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=33964&fbodylongid=1444)
never worked. The mechanical scanner is stuck.

I guess I don't count that because technically, they are still trying to free it. The flight control team is working with PFS to do a test shortly where they try to move it while we are doing a burn. Which is trying to kick it and turn it at the same time.

We don't hold out much hope. But one never knows.

There was some discussion about getting data down from spacecraft, and frustration with the amount of time it takes. I think I finally figured out how to post images, so I'll put up a couple examples from VEX to show how this stuff gets downloaded.

When we do our planning, our ESA proprietary simulation tool will create a prediction of how much data the instruments accumulate each orbit, as well as how much we are able to downlink during each comm pass with the Cebreros Station in Spain.

The resulting up-and-down graph looks like this, for our 18th monthly plan which I just finished:

Click to view attachment

This is a bad, bad MTP, because the data does not go to zero at the end of it. We have some restrictions on our downlink towards the end, and one can see that at the end of the 28 day simulation period, we have accumulated data which has not been downlinked. This causes problems with the planning, not on the spacecraft.

This image is the same simulation output, but for MTP015. The Messenger fly-by was in orbit 411, as I recall. We had a few passes where we could not downlink data, while we were accumulating data in support of the fly-by. Once the Messenger pass was over, we started our downlinks, but it took a while to get the data down.
Click to view attachment

Some instruments, who don't take large data volumes, had their data down within a couple passes. The instrument with the highest data volume, the VIRTIS imaging spectrometer, took days to get it all down.

I don't know how the Messenger data came down. But I'd assume that they got a certain amount of time on one antenna each day, so the data would get downlinked in pieces over a period of days. Their downlink would look different, but probably similar: A big increase in on-board data, followed by one or more dumps of a few hours each to get the data down.

hi cndwrld

thanks for providing a window into the dataflow workings

"There was some discussion about getting data down from spacecraft, and frustration with the amount of time it takes. I think I finally figured out how to post images, so I'll put up a couple examples from VEX to show how this stuff gets downloaded.

When we do our planning, our ESA proprietary simulation tool will create a prediction of how much data the instruments accumulate each orbit, as well as how much we are able to downlink during each comm pass with the Cebreros Station in Spain."

Is the storage capacity on V.E. heavily-burdened?

As to transmission back to earth, I wonder if there could be a software on the spacecraft similar to the program that updates a web page, looking for numbers that change. For example, once a normal temperature range in a given area over a given time period has been established, the craft prioritizes data that appears outside the norm for sending back to earth.

Similarly, I've wondered how "smart" the Mars orbiters can get as they "pushbroom" their way around the planet. Perhaps they can automatically notice small changes like new gullies.

>>Is the storage capacity on V.E. heavily-burdened?
Well, yes and no. The instruments (particularly the imaging spectrometer VIRTIS and the VMC camera) could take much more data than they do. We are usually limited by our data rate, and our ground contact periods, not the SSMM volume.

>>I wonder if there could be a software on the spacecraft similar to the program that updates a web page, looking for numbers that change.

I'd see two problems with this. First, it only would work with housekeeping telemetry, not with science data. And the housekeeping is much less in volume than the science data. We dump a fixed 216 Mbits per orbit for housekeeping data; we dump about 4200 Mbits per orbit of science data. It might be a useful idea in some circumstances, though. Say, on spacecraft on long duration missions in cruise phase, where all you have housekeeping telemetry and no science, or commercial spacecraft.

Two, you'd only get data when it changed. But in that case, if you are looking at telemetry to find a problem, you would have to trust the numbers you don't have. You'd have to believe that if no data came down, that everything was working and the number you got last week is still the number you have now. I would have real trouble doing that. In my experience, data that doesn't exist has an unknown value, and the item generating the data doesn't work unless it proves it works by putting out data. Things 'fail silent' all the time.
Again, though, in certain circumstances, it might be useful.

VEX Status, 22 June 2007

At the end of the last Cebreros ground station pass on DOY 167, 18:00z,
Venus Express was orbiting Venus at 97 million km from the Earth. The
one-way signal travel time was 323 sec. We are executing our 15th monthly
plan, MTP015, and beginning the first week of MTP016 next week. We are still
operating on the small high-gain antenna, HGA2, due to Sun angle on the
spacecraft during Earth Pointing.

We are currently in the Quadrature Period, meaning that the angle
Sun-Venus-Earth is less than 90 degrees. Only two faces of the spacecraft
can take long-term solar exposure, +X and +Z. During parts of this
Quadrature Phase, these two faces can only face the Sun if we point with
the smaller antenna. So our data rate, when we are closest to Earth, is
pretty low. Kind of counter-intuitive, one could say.

During short periods of Quadrature, near the beginning and end, when in
normal Earth pointing the +Z face of the spacecraft (the one with all the
instrument fields-of-view) was too close to the Sun. We want to prevent light
falling in the VMC camera field-of-view, as they don't have a shutter and found
out after launch that direct sunlight on their camera CCD causes degradation
to the plastic lenses. So for the past few weeks, we were operating with a
10 degree roll whenever we were in Earth pointing, to keep the Sun out of
the VMC field-of-view. For a spacecraft with tight pointing requirements and
precise pointing systems, it was not easy to find a way to make it continually
position itself 10 degrees off what it knew to be correct. But the team in ESOC
in Darmstadt figured out how to do it. Last week, we finished our need for this
offpointing, so we are back to normal pointing modes now. Still on the darn
small antenna, though.

No new problems have developed lately. Flight control systems and power are
fine; still have plenty of gas. Some instrument glitches occur now and then,
but nothing too worrisome. VIRTIS did a big upload to their instrument to
update their operating system and take care of some small errors they were
getting. The PFS instrument, stuck since launch, is going to be operated
during some momentum wheel off-loadings, when the thrusters are fired, in
the hope that moving it and kicking it at the same time might jar it loose.
The other earlier problems have not gone away: S-band downlink is way too
weak due to expected thermal damage on large antenna or cabling; thruster
abnormal firing which occurred but has not re-appeared; SPICAV shutter
gives odd readings now and then. But nothing new lately.

The radio science experiment team was able to do a Bi-Static Radar test last
week. This is where we turn on a special, ultra-stable transmitter, point the
big antenna at a feature on the surface, and blast away at full power at such
an angle that the reflected signal goes towards Earth, where it is usually
captured at Europe's antenna at New Norcia, Australia. The geometry between
Venus Express, a surface feature of interest and the ground station have to
be just right in order to do it, so we've only done five or six of these so
far in the mission. With low staffing, data analysis has not been what you
would call timely. Upcoming BSR observations have been cancelled because
they have discovered that the latest BSR data are significantly different
from what was expected and won't give them the information they need. It
will take a bit of time for them to figure out what to do next.

All the data from the Messenger fly-by support is on the ground, and being
looked at. We hope to see some press releases soon. The ground-based
observing campaign will be ending soon, as Venus moves further away from
Earth. We had a bit of a panic last week with the Moon's occultation of
Venus. One of our team realized that our downlink files didn't take the
occultation into account, and there was much rushing about. Turns out that
the occulation occurred in The Netherlands and Germany, but the Cebreros
station in Madrid was just outside of the occulation area. Which is why the
files didn't take it into account.

Planning began this week for two monthly plans in parallel, meaning double
the work for us and the instrument teams for the next four weeks. But we
are doing this because most of the teams take a month off for the summer
holidays. We'll work harder for a month so they can take a month off. I
think most of our team will not take a lot of time off during the summer.
Since none of us have kids, we can take our holidays outside of the rush
period in the summer.

In this planning period, we are introducing a new type of pointing that our
software will now support, called 'track pointing'. We should be able to
give a start time, and end time, and the lat/lon/elevation of a point, and
the spacecraft will track the point. Or we can give it
the name of a astronomical object in our database, and it will track the
object. I say that we should be able to do these things. The software has
a few 'issues' that were discovered recently, so we are going to just
allow a couple of them in each of the MTPs we are starting to plan now.
We'll see how it goes. If it works, though, it will probably get heavily
used.

In summary, things have not gotten calm and boring yet, we're doing a lot
of science that people can whine about not seeing but which should be more
published soon, and the spacecraft is doing well. Our next Science Working
Team meeting is near Rome in July, and I'm going to stay over an extra
day to finally go see the Pantheon, and the remains of the Venus temple
in the Forum. I'll pay my respects to Venus while I'm there.

So, here's a question -- is the download rate limited more by intrinsic limits on data transfer rates (i.e., the spacecraft's transmitter power and the size of its dish), or by the relatively short periods of time you have the Cerberus facility available to receive downlink? (I know you have some attitude issues which result from VEX being designed to orbit Mars and not Venus, but I'm looking for average data transfer rates, here, not those that are constrained by other parameters.)

What I'm getting at, here, is whether or not a vastly expanded Deep Space Network would aid appreciably in getting more data off of the vehicle, thereby letting you take as much data as the instruments can actually collect.

I hate to see a valuable resource being under-utilized because of bottlenecks in our ability to get data back from it. And I'm wondering if it just isn't time for an expanded DSN to be started. If it could be funded by an international consortium that gets its seed money from something other than charging rapacious hourly rates, that would be even better... but I keep hearing more and more issues with the ability to get data back from our spacecraft that are out there exploring the unknown, and it just seems bass-ackwards to spend billions of dollars on a well-designed probe and then hamstring its science return because we have an antiquated DSN that can't keep up with demand and yet still charges thousands of dollars (or Euros, or what-have-you) an hour for the privilege of using it.

Maybe we ought to have everyone convert their unused Dish Network dishes into a vast distributed amateur Deep Space Network and offer its services to all comers, first-come-first-serve...?

-the other Doug

Well, I should hope so. Imagine the whining if you weren't doing a lot of science!

Well, let me mumble a bit while I try to think of something to say. Hmmph, hmm.

The limits on the downlink data volume are basically data rate and time of contact.

How to increase time of contact for an orbiting planetary spacecraft? We could have a steerable antenna, so that the only time we didn't have the ability to point at Earth was when we were occulted. We could transmit data and point the instrument platform to take new data at the same time.

We'd have more contact time, and more flexibility, if we could get as much time on the Earth networks as we wanted. VEX is limited to using the Cebreros station. But if Europe had its full network up (i.e. the third antenna, in addition to New Norcia, Australia and Cebreros, Spain), and each station had multiple antennas large enough for planetary probe reception (> 30 meter, say), and we could jump from station to station as the stations rotated out of view, then we could continue our downlinks as long as we wanted. It is worth keeping in mind that most stations are quite heavily booked these days. So it isn't just about upgrading networks, but expanding support would mean building additional dishes.

To increase the data rate, the spacecraft (steerable) antenna should be larger (while also pointing very accurately). And the ground station antennas should be larger, while also pointing very accurately. We use Cebreros, which is 35 m. DSN can give us 70 meters, which we used once and it let us pump a lot more data through. Transmitter power isn't really a problem for VEX, because power is not a problem. On some probes, it might be an issue. But its a design issue; it is easily scaled up for most missions, probably with minimal weight increases. The data rate also changes with distance from Earth, but there's not much we can do about that. I'm gonna assume for the foreseeable future that antennas will be fixed in size.

The problem with all of this, of course, is cost. No surprise there. A 35 meter antenna, with sufficient accuracy and senstivity, is incredibly expensive. A 70 meter is, well, more. Mulitple sets of antennas in the same location multiplies the price. Bigger antennas on spacecraft are expensive, but more (I am guessing) for launch cost than construction cost. You've got to get it in the launch fairing. The extra weight is expensive. And if you are too heavy and get pushed from one class of vehicle to another (say, Delta to Titan, or whatever), the difference in cost can be enormous. The ability to steer larger antennas accurately gets more expensive: motors, sensors, etc. Also more expensive in operations, although it can be largely autonomous now, I think (i.e., if you're on star trackers, you should be able to just say, 'point to Earth'.)

Can we simulate a bigger antenna on a spacecraft if we use two or three small antennas, separated from each other? Someone will have to tell me the highs and lows of that idea. But one promising thing is somehow getting a bigger antenna for smaller launch cost. Some commercial telecom spacecraft (like the Thuraya cell phone system) and military death stars use collapsible (or expandable) antennas, but I don't know much about them and I'm not a comm guy. Since they don't seem to have taken off, I'm assuming there are reasons for that. Cost again, probably.

I would spend all the money that people are willing to pony up, of course. I'm an engineer, and more expensive toys are always more fun. I happen to feel that we are already spending an awful lot of money, and we are getting the science down. So if we hit some constraints along the way, it doesn't bother me too much. When I worked on Magellan mapping Venus (or in my case, looking at radar telemetry while smart people mapped Venus), it was great fun. I hear that Magellan mapped about 73% of the surface. If we had spent an extra $20 million and gotten 80%, would it have changed very much? I guess the answer to that is up to the individual, but I'm pretty happy with 73%. With VEX, we should outlive our design life, and meet all our science goals, for an amount of money that Europe was willing to pay. And they are paying for Rosetta, and Bepi-Columbo, and ExoMars, one of which I hope to have an opportunity to work on. I guess I'd rather have mulitple missions with reasonable contraints than one or two more perfect missions. I'm biased, of course; I need a job.

I hope that answered some of your questions, Doug.

Yes, that answers a lot of my questions -- thanks! I guess one thing I was wondering was whether a dozen, or a hundred, little (like half- to one-meter) dishes on the ground could be used in a sort of an "antenna farm" mode to simulate a 70m or larger receiving antenna.

You see, there are literally hundreds of thousands of people here in the U.S. who have at one time or another used a satellite cable system (like Dish Network) but who no longer use that service. That's a lot of parabolic dish receiving antennas that are just going to waste.

If all of those unused dishes were mounted with decent views of the ecliptic (where most of the unmanned probes spend their lives) and tracking mounts, and set to communicate to a central data collection center, we could have a "distributed" DSN network made up of thousands of dishes. And heck -- some of them could be tracking Venus, some Mars, some Mercury, and some Saturn. And some tracking points in between.

I know it's probably a foolish pipe dream, but it would seem that you could vastly expand the DSN (within North America, at least) at relatively little overall cost (certainly at relatively little cost per dish) by making use of these unused dishes.

Your response tells me that such a network of dishes could be useful for getting additional science out of the assets we have in place around the Solar System. That's the information I was looking for. Now all we have to do is find the seed money for outfitting these unused little dishes, and we can get started...

-the other Doug

An upgrade for the DSN based on arrays of modest ( <30m but >1m ) sized dishes is under serious study - with a test dish being used at JPL - (I think it's 12m).

Doug

From the Magellan page on Wikipedia: <<By the end of its first such eight-month orbital cycle between September 1990 and May 1991, Magellan had sent to Earth detailed images of 84 percent of Venus' surface. The spacecraft then conducted radar mapping on two more eight-month cycles from May 1991 to September 1992. This allowed it to capture detailed maps of 98 percent of the planet's surface.>>

I think your recollection of the low-ish figure around 73% may be based on one of the three distinct imaging campaigns covering (only) that much of the planet. Magellan had unexpected operational issues that cost some of the expected coverage. Eventually those issues were worked out and the orbiter could have been kept running to finish the job had funding been available. As it happens, there was decent "fill" data for the 2% Magellan didn't cover, so no one's lost much sleep over it. The next radar mission to Venus will be about higher resolution coverage of what Magellan did map.

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.

Click to view attachment

Thanks for the update! I always enjoy reading them even if I don't always comment.

When will we know about the PFS?

PFS has delivered their inputs for the Scanner test during a wheel off-loading. The tests are to be run over 6 days, during the last three weeks of July.

They'll want to look pretty closely at the data for any signs of movement, and no one is in a hurry to announce bad news. So I wouldn't expect us to get any official word on the result until about mid-August. But that's just my guess.

Of course, if the thing actually moves, we'll hear about it in no time. This test is a Hail Mary pass, so I'm not holding my breath. Still, would be nice if it worked.

...so no news is bad news...



The ESA gets kudos for a brave, daring, and resourceful use of a 'hammer'

We have a bigger hammer in reserve. This test is during a wheel offloading, where we hold the spacecraft steady with thrusters while dumping the momentum from the reaction wheels. The thruster burns are quite small.

If this hammer doesn't work, they might do the same thing but during an orbit correction maneuver. An OCM is usually a bigger burn, proportional to the amount of delta-V(elocity) that flight dynamics decides we need to get back into our correct orbit.

It still seems unlikely to help. But what the heck. The PFS team is operating their instrument on Mars Express, but it isn't like their too busy to do this test. And the flight control team is probably starting to get bored. Can't hurt to try it.

So we'll kick it. And in the noble and honorable tradition of engineering, if it doesn't do what we want then we'll kick it harder. While calling it a naughty name.

PFS Still Non-Operational

The PFS scanner was commanded during recent momentum dumps (wheel off-loadings). Reaction wheels speed up in order to capture unwanted spacecraft momentum and maintain pointing; when the wheels are slowed back down to their zero level (generally once a day), thrusters are fired to hold the spacecraft steady. It was hoped that the physical shock of the thruster firings, performed at the same time the scanner was commanded to move, might jog the scanner lose.

However, kicking the scanner in this way didn't work. No more tests are planned, that I'm aware of. The orbit correction maneuvers, which I thought might be tried, turn out to be smaller than the wheel off-loadings. So trying them is not thought likely to help.

So, we'll have to see if the PFS team can come up with another Hail Mary pass, or if this is the end.

Thanks for the update, though I wish the news was better. I guess the problem with moving parts is that they sometimes aren't moving parts.....

Are ESA missions allowed to use American football sports idioms? But if they come up with a long shot that works, I would gladly allow them to use whatever idioms they deem necessary....

I work on an ESA project, but I'm an American. I'm afraid I don't know any European sports idioms.

I was trying to think of what the football (soccer) equivalent of a "Hail Mary" would be myself but couldn't. I think this reflects the poor state of my sports knowledge and of European slang.

Thanks again for all your inside reporting, cndwrld.

I'm afraid I don't know any European sports idioms.


Try Sven Goran Erikson. Oh, sorry, idioms... I thought you said something else...

Based on a casual Google, perhaps ESA might consider launching the aforementioned individual on a purely ballistic intercept trajectory with VEX in order to jar PFS loose...didn't see a whole lotta love there, Stu!

Coordinated observations of Venus between VEX and Messenger

The ESA web page for the Messenger fly-by is now up, on the ESA Space Science page, at
http://www.esa.int/esaSC/index.html

If you click on the third story, labeled, "Venusian rendezvous results: chapter one", you go to the dedicated fly-by page at:
http://www.esa.int/esaSC/SEMVN4HYX3F_index_0.html

The fly-by page can also be reached from the dedicated Venus Express page at:
http://www.esa.int/SPECIALS/Venus_Express/index.html

500 days at Venus, and the surprises keep coming
http://www.esa.int/esaCP/SEMNOCMPQ5F_index_0.html

...Some of the first detailed analyses are now being completed and will soon be published in acclaimed scientific journals...

About this anniversary I'm starting today a special issue at spacEurope, today's guest is Pierre Drossart, VIRTIS Co-PI, no shocking announcements but the fact of having people from the team sharing some thoughts is quite revolutionary...and appreciated...

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.

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.

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

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....

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).

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.

That must be a relief.

Excellent update again don. Thanks.

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

You are probably slightly deaf...

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...

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

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.

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

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.

VMC surface images released.