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VEX Science Planning
Rakhir
post Mar 15 2007, 09:21 PM
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I appreciate reading these kind of details from the daily life of the missions which cannot be found in any press release or broad public web sites.
Thanks for sharing, Don.
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ngunn
post Mar 16 2007, 10:11 AM
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It's probably true to say that for every post expressing appreciation there are 20 or 30 other forum users following with interest - probably just as well or Doug's hard drive would be overflowing with individual 'thank you's to those few professionals like yourself who are generous enough to share an insider's view of the discovery process on this (largely) amateur forum. Please don't stop posting if the tip of the appreciation iceberg looks a bit small at times. We're still listening . .
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cndwrld
post Mar 20 2007, 03:52 PM
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VEX Weekly Status

At the end of the last Cebreros ground station (CEB) pass in the reporting period (DOY 069, 18:00z) Venus Express was orbiting Venus at 202 million kilometers from the Earth. The one-way signal travel time was 672 sec.

On 2007-066, after intermittent losses of TM had been observed, the CEB team reported high winds and requested to move the 35 meter antenna to a safe position. Normal operations were resumed 43 minutes later. As a result of this and some minor hardware issues, science data was not correctly received and had to be copied on board to a dedicated packet store for a subsequent dump. No data will be lost.

VIRTIS movie passes are now scheduled for the second week of April (DOY 98-101). This will involve use of a NASA DSN station 70-meter antenna for a higher capacity downlink, and five days of intense VIRTIS imaging spectrometer data taken of the south pole. This should allow excellent imaging with high detail of the southern vortex and the rest of the polar cloud cover. Planning of science operations for this event is now finished.

The testing of operations for quadrature is on-going; the next quadrature phase will start in May 2007. In this phase, the face of the spacecraft with the instruments would normally be pointed directly at the Sun during Earth contact. The spacecraft will be offset 10 degrees in roll during the Earth contact periods, to provide enhanced protection to the instrument suite. Since this operation wasn't foreseen, the Darmstadt operations team has come up with a good solution. When the spacecraft is told to go to Earth pointing, it will automatically go into the correct orientation, even if it is in Safe Mode. However, nothing is ever simple. This Earth-Pointing-with-roll offset exposes other spacecraft faces to the Sun which have limited exposure times due to thermal constraints, so the Earth communications phase which are normally cool (and allow us to cool down from hot science operations) must now be followed by mandated cooling periods. During the cooling periods, observations can only be cool, with the science instruments and spacecraft pointed such that the direct solar exposure is to the two spacecraft faces which are designed to allow for this continuous exposure.

To complicate matters more, in the middle of the quadrature period the operations team will need to flip the spacecraft in order to use our second, smaller High Gain Antenna (HGA). As mentioned, only two spacecraft faces are designed for long durations of direct solar exposure. At about the midpoint of the quadrature season, the use of the large HGA1 for Earth communications would expose senstive faces to the Sun. The spacecraft is designed to be flipped and flown with the smaller HGA2 used for Earth communications, putting the Sun back onto the full exposure faces. The small HGA2 is located directly behind HGA1, and points directly opposite of it. For those interested, you can see the location of the components on the 3-D model which is at the ESA VEX home page:
http://sci.esa.int/science-e/www/area/index.cfm?fareaid=64


Venus is relatively close to the Earth right now, so our data rate is about as good as it gets. When we switch to HGA2, our data rate plummets from 228.531kilobits per second to 28.566 kilobits per second, which of course means we must reduce our science observations accordingly.

And it is in this quadrature period, with the extra operational thermal constraints limiting our science observations, with the switch to the smaller HGA2, and the loss of our data rate, that the NASA Messenger spacecraft does its fly-by of Venus, over a portion of the planet coverd by the portion of the orbit where VEX always dedicates that time to Earth communications instead of science observations. Of course. So the spacecraft team, flight dynamics team and the science operations team have now completed all their planning, and the testing of those plans are underway.

Best regards-

Don


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cndwrld
post Mar 30 2007, 01:05 PM
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VEX Science Operations and Planning, 17 - 24 March 2007

Venus Express was orbiting Venus at 189 million km from the Earth. The one-way signal travel time was 632 sec. All subsystems are operating nominally. We are currently executing the commands in MTP012, where our ascending branch is on the dark side of Venus, just about at local midnight. 30 March is our orbit 343. We are taking a lot of night-side observations in the ascending branch, as well as using the SPICAV/SOIR instrument to catch the sunrise as we come up into the Sun at the pole, which is useful for atmospheric composition studies.

Ground station support has been verified for the VIRTIS south pole movie sequence scheduled for the second week of April (DOY 98-101). Planning of science operations during this event is now finished. Initial problems communicating with DSS-63 (Madrid 70-m DSN antenna) have been overcome.

The science planning is done in two blocks: spacecraft pointing, and instrument commands. The pointing is first verified by Flight Dynamics at ESOC/Darmstadt. Output files generated by FD are used as input into the command verification done by the ESOC Venus Express Flight Control Team. MTP014, our fourteenth monthly plan, has had both pointing and commanding verified now. MTP015 has had pointing verified, and our commanding files will be verified (I hope) in the coming week.

MTP016 planning has officially begun. A new thermal envelope has been approved for use recently, and will be used for the first timein MTP016. This will allow the spacecraft to be repeatedly pointed at nadir for about 15 minutes, then pointed away to an off-track angle; repeatable over a few hours. On VEX, the instruments are body mounted, on the +Z axis, and the spacecraft must be pointed to make observations. The VEX thermal constraints do not allow lengthy pointing that exposes the -Z face to the Sun. So, if the spacecraft has the Sun behind it, and the planet in front of it, nadir observations put the Sun right up our butt. The newly approved thermal profile means that we can do such a nadir pointing, then offpoint to get the Sun off the -Z face and cool off; then repeat these observation/heating periods with cooling periods. This will allow us to make nadir observations on the ascending branch of our orbit, near local noon when the illumination is very unique, that were not possible before. The responsible engineer for MTP016, who is also our lead engineer, has put a lot of work into creating the detailed files that translate an approved concept into something that can actually be implemented. This is very detailed, time consuming work that will allow the instrument teams to get good science data, but which garners little recognition because it is buried in all the preparatory work. Given the illumination angles, this new 'pendulum' sequence will be heavily used in MTP016. We'll also have good angles to use the SPICAV/SOIR instrument to look at the Sun as it goes behind the planet as we whip over the North Pole, which provides excellent data on the atmospheric composition. These Sun occulations near pericenter, coupled with the new pendulum observations done in the ascending branch, will make up the bulk of these 28 days of observations. We'll also be doing a single orbit correction maneuver at one pericenter pass, and a unique SPICAV calibration near local noon whose thermal profile means we have to dedicate an entire orbit to just the calibration. All this planning will be proceeding over the next four weeks.

A VEX Science Working Team (SWT) meeting was held last week. A lot of good science results are getting ready to go to press in the near future, with papers in the pipelines. The meeting included an update on the VEX Education and Public Outreach, which is based at http://venus.wisc.edu/. Some coming events they are participating in:

- ALPO Conference presentation on Venus Express June 2007
- Native Sky Stories conference at Lac du Flambeau reservation April 2007
- Presentation at EGU 2007
- Planetarium program in Brussels April 2007

Past activities have included:
- Venus E/PO workshop at Europlanets
- Teacher workshop at Belgium Institute for Research in Aeronomy, Brussels, September 2006
- Visiting Scientist International School of Brussels - September 2006
- Planetary Science 101 Teacher Workshop at DPS 2006, Pasadena, California, October 2006

A curriculum module on Venus cloud tracking is under development

The SWT included a presentation on VEX communication activities that are planned, and the instrument teams agreed to support the plans by providing inputs. These include:

End of March Web publication of recent images
11 April Web story on the orbit insertion anniversary, accompanied by new VIRTIS and VMC images
End of April Web publication of new images from VIRTIS south pole movie, assuming
processing completed.
Mid-May Web story on the ground-based observation campaign
Early June The Messenger Fly-By of Venus is on 05 June 2007. A few days before the Messenger fly-by,
a Web story will be published on the coordinated VEX/Messenger observing campaign
Mid June After the Messenger fly-by, VEX early science results from the Messenger fly-by will
be published.

Cheers-

Don


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elakdawalla
post Mar 30 2007, 02:49 PM
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Huh. Thanks for the information and heads up on pending image releases, Don.

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cndwrld
post Apr 3 2007, 03:36 PM
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VEX Virtis Cloud Images

At the ESA web site, http://www.esa.int/SPECIALS/Venus_Express/SEM9N77DWZE_1.html,

photos have just been published in an article entitled, "Tracking alien turbulences with Venus Express". You can see some excellent details, showing the complexity of the cloud structures. Be sure to click on the images to get the more high-resolution versions.

Cheers-

Don Merritt


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cndwrld
post Apr 4 2007, 07:56 AM
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Venus Express Status, 25 March - 31 March

At the end of the last CEB pass in the reporting period (DOY 090, 18:00z) Venus Express was orbiting Venus at 183 million km from the Earth. The one-way signal travel time was 610 sec.

Mechanical and electrical systems continue to work without problems. We've got plenty of fuel, more than enough to take us through the recently approved Extended Mission until mid-2009. Batteries are fine.

The testing of operations during quadrature is on-going; the next quadrature phase will start in May 2007.

On 28/03/07, a proficiency test with the DSN Madrid 70-meter antenna (DSS-63) was held. This was in preparation for the five days of operations that will be used to take movies of the south pole region using the VIRTIS imaging spectrometer. VIRTIS movie passes are scheduled for the second week of April.

MTP014 (06 May - 03 June 2007) science pointing and command files have been accepted by the flight control team and flight dynamics team at ESOC, Darmstadt, Germany. MTP015 (04 June - 30 June) pointing files have been accepted; waiting to hear about the instrument command file processing.

MTP016 science planning has begun, with the spacecraft pointing files being worked on this week. This will include use of a recently approved pointing profile called 'pendulum pointing'. With our current thermal constraints, we have to follow pre-approved illumination profiles for each face of the spacecraft, each with a defined cooling period afterwards. If the spacecraft illumination from a desired pointing is not covered by a profile, the pointing is not allowed. If it is allowed, mandatory periods must be afterwards in a cooling attitude. These rules effectively forbid VEX from pointing to nadir when the Sun was directly behind the spacecraft; the +Z face has the instrument apertures, so pointing to nadir in such a situation exposed the -Z face for much longer periods than was allowed. The manufacturer, Astrium, has approved a profile that will allow us to look for about 24 minutes with reasonably high -Z exposure angles, then turn to a cooling attitude for similar periods. We will be able to get images now with the Sun at high angles while we are in the ascending arc of our orbit.

As with any device, whether spacecraft or new car, time is slowly taking its toll on VEX. The occasionaly spurious alarm or anomalous piece of telemetry; occasional minor malfunctions for no clear reason. Cosmic ray events that have to be separated from possible real problems. At this point, nothing unexpected, and enough so that checking it all out keeps the teams busy. In general, the thing is performing like a champ.

The last few months of science operations have included refinement of data modeling. In the fall of 2006, our technical support people put together a very nice system to allow the science operations engineers to see how much science data was returned by each instrument, and compare that with what was predicted. Given the margins that engineers put into everything when doing something for the first time, and the science teams not having lots of time to work on their models due to the rush to get ready for launch and operations, the predicted amounts were probably 25% higher than the actual received data. The good news is that it was too high, not too low, which would have caused us to lose data. But we were, in effect, "losing data" by not taking data for which we had capacity. The science engineers have worked with the instrument teams over the past six months, and the data predictions are becoming much better. This process will continue over the coming months. We are now beginning to review MTP011 results; MTP012 finished this week, and we have begun looking at the first week's results. We'll continue to refine the models to squeeze out every bit we can, to maximize the possible science return.

Cheers-

Don


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cndwrld
post Apr 26 2007, 08:42 AM
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VEX Planning and Status on 26 April 2007

I haven't been real consistent about what topic I use to put this information
out there. I'll just put it all in this one from now on.

A couple weeks ago, special operations were done with VIRTIS to make movies
of the South Pole of Venus. For this, the spacecraft telemetry downlink
rate was increased, and the DSN Madrid (DSS-43) station was used to
capture the high volume of data. The TM bit rate is now back to 154 kbps.
The preliminary version of the VIRTIS movies are very cool, but will
require a lot of cleaning up before release.

At DOY 104, Venus Express was orbiting Venus at 169 million km
from the Earth. The one-way signal travel time was 564 sec. Everything
continues to work just fine. However, the spacecraft seems to be getting
into its adult years. We seem to be getting more one-off, weird things
occurring. Things like an alarm going off for one frame of telemetry due
to some weird number, but it doesn't recur and everything is fine. Or
something sticks once, but never repeats itself. Or the data from an
instrument gets some strange hiccup, which self corrects. This sort of
thing is common on spacecraft, which get old in pretty much the same
way we do. It starts with little creaks and unexplained pains. But for
now, everything is fine, we just aren't as young as we used to be.

Below, I try to provide some detail about the observing plan we are about
to finish (MTP013), and the one that is about to start (MTP014). MTP015
has been scheduled and approved, and is waiting for its turn. MTP016
planning will be finished next week. MTP017 planning starts today. MTP018
is currently being looked at for long-term, early analysis.

If I haven't made anything clear that you're curious about, let me know.

MTP013
======
We are currently executing the last week of MTP013, our thirteenth monthly
observing plan. I don't believe I put anything down about what we've been
doing in this MTP.

The definition of science cases is shown down in MTP014 section, and in
earlier posts.

MTP013 is included in the mission phases 6 (until orbit 369) and 7. This
MTP provided good conditions for observations of the night side and
atmospheric sounding in solar occultation geometry (eclipse season 3). Solar
occultation observations will be used to study composition and structure of
the atmosphere above the cloud top. Campaigns of Cases #2 (no Cases 3 are
possible in this MTP) will be used to study composition and dynamics of deep
atmosphere on the night side. Conditions were also favourable for
observations of nightglows to study composition and dynamics of the
thermosphere and search for lightning. Limb observations in forward
scattering geometry (spacecraft in eclipse) will provide good opportunity
to study vertical structure of hazes above the main cloud. Relatively
high downlink rate allow the experiments to use high resolution
operation modes to study small scale features and dynamics. Thermal mapping
of the surface and search for active volcanism will be performed. This
MTP also included an Earth occultation season.

The following observations were done in this MTP:

solar occultation measurements (Case #6) were given high priority
in order to achieve good latitude coverage. This will cover the themes:
o Cloud layer and haze
o Atmospheric composition
o Atmospheric dynamics
o Atmospheric structure
o Escape processes.

limb observations (Case #7), to study vertical structure of haze
layers. This will cover the themes:
o Cloud layer and haze
o Atmospheric composition
o Atmospheric dynamics.
For a limb observation, we point the SPICAV instrument at a star, and it then
follows the star as it scans the entrance limb, traverses the planet and then
leaves the disc at the exit limb.

Plasma and magnetic field measurements on the nightside and on the
dayside, covering the theme Plasma environment/escape processes.

Cases 2 at apocenter and Cases 1 at pericenter covering basically all
themes.

MTP014
======
We start MTP014 next week. MTP014 is part of the mission phase 7, which
includes an Earth occultation season. Proximity to the Earth creates excellent
conditions for bi-static sounding and radio-occultation experiments that
can reach maximum sounding depth. A very good downlink data rate is
available, allowing the study of the atmosphere with high spatial resolution.
The terminator sector of the planet will be available for observations in
this phase. Thus cloud structure and atmospheric dynamics will be important
goals.

This will take place during the end of the so called COLD SEASON. The
terminator crossing is around the 31st of May.

The time span of the MTP014 operations is the follow:
START: 06 May 2007 (ORB 380)
END: 02 June 2007 (ORB 407)


During this MTP, the flip from HGA1 to HGA 2 will occur on June 1 (orbit 406).

The official ground-observation campaign starts on May 23 (orbit 397). To
our knowledge, the following observations will be performed:
- Wind measurements by IRTF: 18-21 May (orbits 392-394)
- Winds measurements by Kitt Peak: 23 May to 9 June (orbits 397-414)
- Atmospheric composition by AAT: 31 May to 6 June (orbits 405-411)
Due to the complexity of this MTP, no complicated pointings were
considered.

The following observations were planned in this MTP:

radio-occultations experiments (Case #8) will be conducted, covering
the following science themes: Atmospheric dynamics, atmospheric structure,
atmospheric composition and plasma environment/escape processes.

stellar occultations (Case #5) are planned. This will cover the
themes:
o Cloud layer and haze
o Atmospheric composition
o Atmospheric dynamics
o Atmospheric structure.
o Atmospheric structure.

Cases 7 or 1 could also be planned instead.

Plasma and magnetic field measurements covering the theme Plasma
environment/escape processes.

long Cases 2 at all apocenters, and Cases 1 at
pericenter are considered, covering basically all themes.

The final pointing plan was:

Orb # apocenter Pericenter
science Case science Case
====== ============ ============
380 2 8 Case 1: around pericenter, nadir looking
381 2 8 Case 2: Ascending branch, nadir looking
382 2 8
383 2 5+1 Case 3: from apocenter, nadir looking
384 2 8 Case 5: stellar occultation
385 OCM 2-7 Case 7: stellar occultation through limbs
386 2 8 Case 8: radio science occultation
387 2 5-7-2
388 2 8 OCM: orbit correction maneuver,
389 2 5-7-1 regularly scheduled
390 2 8
391 2 7-1
392 3 8
393 2 7-1
394 2 8
395 2 7-1
396 2 8
397 2 7-1
398 2 8
399 2 8
400 2 8-1
401 2 8-1
402 2 8-1
403 2 7
404 2 8-1
405 - 8-1
406 - 8-1
407 - 7-1

The last 3 weeks of MTP014 (from Orb 386) run in the Quadrature
Period. Technically, the quadrature phase is defined as the period during
which the Sun-Spacecraft-Earth angle is between 75 and 95 degrees, requiring
a swap to High Gain Antenna (HGA) 2 for Earth communications in order to
avoid illuminating faces of the spacecraft not designed for such exposure.
But in our loose usage of late, it has come to refer mainly to the period
when we require changes to the spacecraft operations to avoid excessive
VMC illumination.

Due to revising operating constraints on the VMC camera, in quadrature phases
the default Earth pointing orientation results in unacceptable illumination
of VMC. To avoid that, the nominal Earth attitude guidance was modified
by adding a rotation of the S/C around the HGA axis, such that a constant
+10deg illumination is achieved in the +Y panel (the least sensitive
to continuous heating, of the panels which are not supposed to be heated).
This is actually implemented onboard by commanding
fake ephemeredes (i.e. with non-real S/C and Earth positions). By proper
selection of the fake ephemeredes, the distortion of the Earth pointing
guidance computation on-board achieves Earth pointing with the HGA and
a tilt angle around the HGA axis. The Flight Dynamics team and the Flight
Control Team at ESOC in Darmstadt, Germany, are finalizing their planning
to initiate this. They have, as usual, done excellent work on this, and
no problems are anticipated.

As MTP014 is mainly in COLD season, long Cases 2 will be possible, with cold
Cases 1 until pericenter. The Earth communication phase stop times do
not allow Cases 3 to be done at apocenter. Inertial cold pointings
(Cases 5 and 7) can be done after pericenter. A pericenter change (number 3)
orbit change maneuver (OCM) is scheduled.


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helvick
post Apr 26 2007, 10:22 AM
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Excellent updates Don, much appreciated.
This detail caught my eye
QUOTE
This is actually implemented onboard by commanding
fake ephemeredes (i.e. with non-real S/C and Earth positions). By proper
selection of the fake ephemeredes, the distortion of the Earth pointing
guidance computation on-board achieves Earth pointing with the HGA and
a tilt angle around the HGA axis.

Is this an unusual approach to a problem like this?
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cndwrld
post Apr 26 2007, 03:54 PM
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>> Is this an unusual approach to a problem like this?

Well, yes and no. VEX has never had to do such a thing. It is not unusual to have to do some sort of pointing which is offset from normal, but in my experience this is different because you are changing the references used by the flight code, rather than changing your pointing in relation to the references.

But the required offset wasn't designed for, so something had to be done. This was a possible way, so it was done this way. In a sense, every mission always ends up having to find work-arounds for things that aren't planned. So in that sense, it isn't unusual.


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edstrick
post Apr 28 2007, 07:15 AM
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Back in the days of chipped flints and ...
Early Mariner's were designed to use Canopus, which is near the south ecliptic pole and 2'd brightest star in the sky, as roll-reference. Before Mariner 10, they didn't have articulated high-gain antennas, so during extended missions, they often used alternate guide stars for roll reference. Not really a "faking it" program, but something similar.
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