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VEX Science Planning
cndwrld
post Mar 9 2007, 02:16 PM
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Hello-

I wasn't sure how most people would like to see stuff posted. Or if this would interest many people. But in the interests of putting out more information, I created this topic as a place to put information on Venus Express science planning.

If you have any ideas about this, let me know.

Cheers-

Don Merritt


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cndwrld
post Mar 9 2007, 02:53 PM
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Science Planning Overview

The VEX science planning is done in three phases: Long term (covering nominal mission, extended mission, etc.); medium term (months in advance, one month at a time, submitted early to allow for review/analysis by the flight control team at ESOC/Darmstadt); short term (final operational files, provided one week prior to execution on the spacecraft, ideally the same as the medium term files). Each Medium Term Plan (MTP) covers 28 days, broken into four seven day periods. When the operational files are provided in the short term cycle a week before execution, the flight control team then typically breaks the files into smaller pieces for upload; the on-board command buffer being sized to hold about two days of commands, each day will have today's and tomorrow's commands uploaded.

The science observations are broken down into "cases", which are rough templates based upon either the instrument doing the observation, the location in the orbit (distance from cloud tops effecting data resolution) or other spacecraft pointing.

Note that the orbit has an inclination of 90 degrees (polar), and pericenter is at about 80 degrees north:
Pericentre altitude (km) 250
Apocentre altitude (km) 66 000
Period (h) 24
Inclination (°) ~90
Pericentre latitude (°) 80


The basic science observation cases are:
Case 1: observations near pericenter, typically from Venus Pericenter (VPER) - 00:47 (47 minutes), until VPER + 00:47. High spatial resolution spectroscopic and imaging of northern hemisphere, plasma and magnetic field studies (although these are also done at all points in the orbit when spacecraft operations and data volumes allow).

Case 2: Off-pericenter, ascending branch, typically between VPER-10:00 and VPER-01:00. Mainly used by VMC camera and VIRTIS imaging spectrometer, for studying upper atmospheric dynamics.

Case 3: Apocenter observations, typically between VPER-14:00 and VPER-10:00. Global spectrographic imaging of south pole using the VIRTIS imaging spectrometer.

Case 4: Radio Science Bistatic Radar observations, where the spacecraft transmitter is directed at surface features and the reflection is detected on Earth. VeRA experiment only. Used to study surface properties. Can only be done when spacecraft/Venus object of interest/Earth line up.

Case 5: Stellar occultations by SPICAV instrument, following a star as the spacecraft goes behind the planet and re-emerges from behind the planet (relative to the star used), useful for upper atmosphere studies.

Case 6: Solar Occultation using the SPICAV/SOIR experiment, tracking the Sun as it is occulted by the planet, to study the upper atmosphere.

Case 7: Limb observations, mainly for SPICAV but also by VMC camera and VIRTIS, to study atmospheric composition and structure.

Case 8: Earth radio occultaions by VeRA radio science experiment to study fine structure of the atmosphere. Or at least to capture the data, to be studied some day.

Case 9: VeRA sounding of solar corona, when near Superior Conjunction with the Sun directly (or nearly directly) between spacecraft/Venus and the Earth. Limited use due to geometry required.

Case 10: Venus Gravity anomaly studies using VeRA radio Science. Not yet done due to geometry, thermal constraints.

If I knew how to get drawings in here, it would be more clear with pictures.

Cheers-

Don Merritt

Some references:
http://en.wikipedia.org/wiki/Venus_Express
http://www.esa.int/SPECIALS/Venus_Express/


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ngunn
post Mar 9 2007, 02:54 PM
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Excellent. I'll be following with great interest.
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cndwrld
post Mar 9 2007, 03:08 PM
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MTP012 Science Plan

The time span of the MTP012 operations is the following:
START: Orbit 324 (pericenter on 11 March 2007, DOY070)
END: Orbit 351 (pericenter on 07 April 2007, DOY097)

The MSP contains one MTP. One MTP contains 4 Command Periods (CPs) of one week (7 days). In total the MTP covers 28 days of operations.


Science Plan Overview

MTP012 includes the end of mission phase #5, phase # 6 and the beginning of Phase 7. In the first orbits, conditions for the off-pericenter night side observations will be fulfilled. This period provides 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 repeated in several consecutive orbits will be used to study composition and dynamics of deep atmosphere on the night side. Conditions will be 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 would 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 in this phase. Two bi-static sounding experiments are scheduled.

VSOC has been alerted (Peter Jenninskens, personnel communication) that meteor showers are likely to occur on orbits 326, 329, 331 and 338. The meteors are expected to have their peak brightness at about 100-115 km altitude. The most promising wavelength range would be a narrow band at 777 nm, where meteors may generate atomic oxygen emission from the dissociation of CO2. The forbidden line at 577 nm may also be observed in the meteor’s wake. Magnesium emissions at 280 and 285 nm may be also detected on the dayside. One atmosphere-grazing fireball track may have been observed by the Pioneer Venus Orbiter Ultraviolet Spectrometer instrument orbiting Venus in 1979. The satellite measured three correlated spectra during orbit 75 containing a strong NO (C-X) emission at 155-257 nm, which was confined in the Venus atmosphere in a narrow band at least 900 km in length and less than 5 km wide.

The following observations are proposed in this MTP:
• 15 solar occultation measurements (case #6) will be given relatively 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.

• Four 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.

• Two bi-static sounding experiments are planned, covering the theme: Surface properties and geology.

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

• 27 cases 2 at apocenter and 21 cases 1 at pericenter are considered, covering basically all themes.

MTP012 Medium Term Planning was completed 22 December 2006. Short term planning has begun, with delivery of files for the upcoming command period from the VEX Science Operations Center at ESTEC (European Science and Technology Center, Noordwijk, The Netherlands) to the flight control team at ESOC (European Space Operations Center, Darmstadt, Germany). All communications with the spacecraft are performed via the facility in Cebreros, Spain (50 Km west of Madrid).

Worth noting is that the flight control team and flight dynamics team at ESOC have performed extremely well in every phase of the mission; if there has been a human-induced error from them, it doesn't come to mind. And the three engineers at the science operations center with whom I work have done an amazing job for being such a small team with such a never ending amount of work. And our TEC department at ESTEC has been unsung heros for getting us better and better tools so we can keep on doing it.

Hope this is useful-

Don Merritt


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cndwrld
post Mar 15 2007, 09:29 AM
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Venus Express Support Of NASA's Messenger Spacecraft Fly-By of Venus

In about 82 days, NASA's Messenger spacecraft will fly by Venus on its way to its final destination of Mercury.

The Venus Express team is planning special observations ov Venus during the fly-by, to coordinate their observations with the data taken by the Messenger instruments.

The first complication was the location, and its effect on planning. The VEX orbit is rigidly controlled to maximize savings on the ground. The orbit period is maintained so that the downlink to Earth can be done during normal working hours at the Cebreros station near Madrid, minimizing mission cost. Unfortunately, the location of the Messenger closest approach to Venus is during our nominal downlink period.

Since VEX is re-using as much as possible of the Mars Express design, a bus designed for a cold planet is operating at a hot one, which causes us to have a lot of restrictive thermal constraints. If certain panels of the spacecraft are exposed to the Sun, a cooling period in an approved cooling attitude is required.

The solution we're using is to skip three downlink opportunities. In orbit 409, the downlink is skipped so that we can stay within our rigid thermal constraints for instrument operation in orbit 410. In orbit 410, on 05 June 2007, orbservations will be done to capture the cloud data "before" images for the pass prior to Messenger closest approach. The time of the observations, in our descending branch, is during the time we would normally be communicating with Earth, so that Earth communication window is skipped.

At the point of Messenger closest approach, at about 00:05 UTC on 06 June, VEX is in our orbit 411 but not within sight of the area. We will be on the other side of the planet, in our ascending branch. In the descending branch, we will observe the area that Messenger saw previously, making our observations between about 09:30 and 11:30 UTC. This requires skipping this Earth comm pass, too.

For orbits 409 - 411, all the data taken by the instruments must be stored on board within the spacecraft memory. It is not usual for an instrument to take more in one orbit that can be downlinked in the next pass, we just need to keep track of what is expected to be used, so that the circular buffer does not get overwritten by new data. The amount of data that is taken in support of the Messenger fly-by, over three orbits, must fit within the on-board memory allocated to each instrument, so what they take must be limited. Since our first post-Messenger downlink is in orbit 412, and the instruments also want to take their normal observations in orbit 412 ascending branch and pericenter, there are actually four observation possibilities which must be made to fit into their memory allocations. Each instrument team has to make the trade-offs of what they want to take, how much they want to take, and how long they expect it to take to download it.

The Magnetometer will not be making any attempts to change their normal observations. And radio science will not be done in this period. The ASPERA, SPICAV, VMC and VIRTIS instruments are all making special observations to support the fly-by. The data for all but VIRTIS will be on the ground no later than 16 June, and all of the VIRTIS data should be down no later than 18 June.

There's information on Messenger at: http://messenger.jhuapl.edu/. VEX information is at:
http://sci.esa.int/science-e/www/area/index.cfm?fareaid=64.

Cheers-

Don Merritt


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Stu
post Mar 15 2007, 10:03 AM
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Thanks for sharing all this info with us Don, it's very much appreciated, believe me.


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cndwrld
post Mar 15 2007, 11:25 AM
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No problem, Stu. I'll toss out there whatever I have available. I think it is all pretty cool stuff, and I'm happy to share it with the other five people in the world who think so, too.


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Stu
post Mar 15 2007, 11:35 AM
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QUOTE (cndwrld @ Mar 15 2007, 11:25 AM) *
I think it is all pretty cool stuff, and I'm happy to share it with the other five people in the world who think so, too.


I think you can tell from comments in, um, another thread that there are MANY more than 5 people who think this stuff is cool Don! smile.gif


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centsworth_II
post Mar 15 2007, 02:47 PM
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Even though the details are mostly over my head, I like seeing these kind of
updates just to get a general feel for what's going on around the solar
system and the types of complexities involved in doing planetary studies.
I also vicariously enjoy seeing those who can understand the details
get into them.
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dvandorn
post Mar 15 2007, 03:13 PM
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Don, does the science team there *really* believe that only five other people in the *world* are interested in VEX science operations? Or how VEX will supoprt Messenger's Venus flyby?

If you're being accurate and not just trying to be clever and funny, that would go a long way towards explaining the knd of extremely faulty assumption that's driving ESA's poor excuse for public outreach... mad.gif

-the other Doug


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cndwrld
post Mar 15 2007, 04:22 PM
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I think an awful lot of people are interested in the results we get from Venus Express. Most people are impressed by pictures, but there are ( I think ) a surprising number of people who are also interested in results that aren't really visual, like plasma and magnetometer results.

I just don't know how many people are interested in what I do. You see calendars with cool space pictures, but you don't see any calendars showing me hunched over my keyboard, trying to figure out why my pointing commands aren't working as I expected, or why the actual data downlinked from an instrument was 20% less than predicted.

If people are interested in this side of it, though, I'm happy to put it out there. Since I don't know what might be interesting to people, I'm just making it up as I go along. And if the responses are positive, I can keep doing it.

Cheers-

Don


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centsworth_II
post Mar 15 2007, 05:23 PM
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QUOTE (cndwrld @ Mar 15 2007, 12:22 PM) *
...trying to figure out why my pointing commands aren't working as I expected, or why the actual data downlinked from an instrument was 20% less than predicted.

These sorts of challages and (hopefully) how they were overcome can be fascinating.
Even if it's a forgotten comma in a command.

In Steve Squyres' book "Roving Mars", some of the most gripping stories involved
writing and presenting proposals. Who'd 'a' thunk?
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4th rock from th...
post Mar 15 2007, 05:30 PM
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QUOTE (cndwrld @ Mar 15 2007, 04:22 PM) *
If people are interested in this side of it, though, I'm happy to put it out there. Since I don't know what might be interesting to people, I'm just making it up as I go along. And if the responses are positive, I can keep doing it.

Cheers-

Don


It is interesting! Of course, It's not a visual thing, so I wouldn't say that it is exciting, but it is interesting and informative. Please keep posting updates!


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dvandorn
post Mar 15 2007, 05:31 PM
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It's quite interesting to me, Don. I know I can't actually speak for anyone else here, but I think it's probably interesting to a lot more of us who read and post to this forum.

These kinds of details, which let all of us share the daily challenges and rewards of those of you who are our proxies in this grand exploration, are tremendously worthwhile.

I welcome them!

-the other Doug


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helvick
post Mar 15 2007, 06:36 PM
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QUOTE
I just don't know how many people are interested in what I do. You see calendars with cool space pictures, but you don't see any calendars showing me hunched over my keyboard, trying to figure out why my pointing commands aren't working as I expected, or why the actual data downlinked from an instrument was 20% less than predicted.

You can add me to the list of folks who are very intereted in this stuff - the cool pictures are fantastic and all that but me, I like to understand what it takes to keep these things running and bringing home the bacon, so to speak. And the more boring detail about why the downlink data volume was 20% below expected the better. smile.gif
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