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Future Venus Missions
JRehling
post Nov 6 2005, 06:29 AM
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QUOTE (BruceMoomaw @ Nov 5 2005, 07:15 PM)
there's a very nicely detailed description of the precise measurments that MESSENGER will make during its second Venus flyby in June 2007.
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I haven't seen anyone note this yet, but this means that two spacecraft will be operational near Venus at the same time, as Venus Express will be near the very end of its primary mission. Very analogous to the simultaneous readings at Jupiter in December 2000 by Galileo (in orbit) and Cassini (just passing by). Venus isn't as lively in a particles-and-fields way as Jupiter is, but it sets up some nice opportunities for synergy. Interestingly, *three* US spacecraft were at Venus in 1990, when Pioneer Venus was late in its extended mission, Magellan was in checkout phase prior to the beginning of science operations, and Galileo flew by. In 1978, two Soviet landers arrived while a US orbiter and five entry probes, crowding the planet with *eight* pieces of hardware within a short time. But it'll be almost seven years between the brief Cassini flyby of Venus and the arrival of Venus Express. We are very fickle with regard to the closest planet.
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remcook
post Nov 9 2005, 10:01 AM
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a good update from emily on oncoming missions (VEXAG meeting):

http://planetary.org/blog/article/00000038/
http://planetary.org/blog/article/00000039/
http://planetary.org/blog/article/00000041/

I didn't see this posted before...
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Guest_BruceMoomaw_*
post Nov 24 2005, 03:23 PM
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To my delight, last night I stumbled by chance across something I've been looking for all year -- the new address for JPL's file of Technical Reports ( http://trs-new.jpl.nasa.gov/dspace/ ). And the very first article I found there was something I've been trying to find for a couple of years: the first good description of Larry Esposito's "SAGE" Venus lander proposal for the last New Frontiers AO ( http://trs-new.jpl.nasa.gov/dspace/bitstre...4/1/03-2520.pdf ).

While it didn't make the cut for finalist, it looks like quite a well-designed mission, featuring two landers that would touch down about 1000 km apart -- one on the tessera at Aphrodite, the other on the regular basalt plains to the south -- and survive for 1-2 hours each on the surface, consecutively transmitting their data to the carrier spacecraft while it made a distant flyby of Venus. The landing system is very much like that for the Veneras. There were seven onboard experiments -- including three atmospheric ones, but not including any attempt to track Venus' cloud-layer winds with a balloon (one originally stated goal for the New Frontiers Venus mission). A drill would collect a sample for X-ray spectrometry and diffractometry -- which makes me wonder whether the size and cost of this mission could be lowered by instead using a LIBS/Raman setup for surface analysis, thus allowing removal of the heavy drill and airlock setup. (It's stated that if it ever became possible to add a third lander, it would be aimed at a "hot spot", by which they presumably mean one of the relatively young volcanic highlands.)

One thing is noted which I should have thought of before but didn't: thanks to Venus' slow rotation, any direct-entry lander mission launched during a specific launch window is very limited in its scientific selection of landing sites as compared to a Mars direct-entry lander.
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Guest_BruceMoomaw_*
post Nov 24 2005, 03:26 PM
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One other thing which I just now noticed on the last page: this mission may have been rejected not because of technical flaws, but simply because it didn't have any workable Venus launch window during the time specified for the launch of New Frontiers 2!
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Phil Stooke
post Nov 24 2005, 04:10 PM
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I just tried to access the Venus lander PDS file Bruce linked to, but got the message that the file was damaged and could not be opened. Is anyone else getting this?

Phil


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Guest_BruceMoomaw_*
post Nov 24 2005, 10:10 PM
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It just came through OK for me again (using the URL in my message as printed here). Must be your computer.

One can think of other ways to slim down this mission, too -- related to the decision to put the two atmospheric composition experiments on BOTH landers, although the atmosphere's composition will vary little or none from one place to another. One is a UV spectrometer -- presumably to try and identify the still-mysterious dark UV cloud absorber -- which is mounted outside the pressure hull and will burn out below 50 km; it could easily be removed from one lander.

The other is a GCMS which is mounted inside the hull and will operate down to the surface. Now, shrinking the pressure hull on one lander just to get rid of this instrument would surely cost more in design and manufacture problems than it would save -- but back in the very first round of Discovery selections, Esposito proposed a "Venus Composition Probe" in which both the UV and the mass spectrometer were mounted outside the pressure hull and only worked at high altitudes. All the composition data in Venus' lower, hotter atmosphere was obtained from a near-IR spectrometer inside the pressure hull, since it could sense all the chemically reactive trace gases we're interested in measuring at lower altitudes -- whereas the other trace gases (and especially isotopes) that we want to get better data on are pretty evenly mixed and so a mass spec can measure them in the upper air. The same could apply to the SAGE mission (which includes a near-IR spec for both atmospheric and surface composition data). Or, of course, we could put the atmospheric experiments on a separate, Discovery-class probe.

Do that, and replace the XRS/XRD with a LIBS/Raman setup, and you could get rid of ALL this probe's necessary openings to the outside hot air in its pressure hull -- all you'd need would be sealed electrical cables and fiber-optic lines. You could also greatly cut the time that it must survive on the surface, and analyze far more than one surface sample in that short time. (A motorized arm with a sensor head on its end, hooked up to fiber-optic lines leading to the various surface instruments -- including the onboard microsope, which in the current design can only look at one spot of ground -- could pat the surface at a whole range of points to analyze them in just a few minutes each; and the LIBS and near-IR spec -- and maybe the Raman -- could also operate through the same periscopic mirror as the panoramic camera to observe different, more distant spots on the surface.) I don't know how much worse a Raman is than an XRD in analyzing mineralogy -- I gather it isn't good at measuring the oxidation state of iron minerals (although the near-IR spectrometer might get good enough data on that), and I've found a fuzzy reference suggesting that Raman is worse than XRD in measuring the precise quantities of various minerals, as opposed to just confirming their presence or absence. But it's a possibility.
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Phil Stooke
post Nov 25 2005, 02:22 PM
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You're right, Bruce... tried a different machine and I got it OK. And look at that - more points on the map. That's what I always want to see!

Phil


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JRehling
post Nov 25 2005, 05:22 PM
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QUOTE (BruceMoomaw @ Nov 24 2005, 07:23 AM)
One thing is noted which I should have thought of before but didn't: thanks to Venus' slow rotation, any direct-entry lander mission launched during a specific launch window is very limited in its scientific selection of landing sites as compared to a Mars direct-entry lander.
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To put a finer point on it, I think the real problem is the Venus-Earth synchrony. The slow rotation constrains landing sites for a given launch window. More serious is that other launch windows will offer the SAME landing sites. Basically, minimum-energy trajectories offer up the same serious constraints, which is why all Veneras landed in a narrow longitude range. The main way around it is would be to spend a little more energy in cruise, so as to get to Venus sooner or later. Alternately, some gravity assists could be used so as to get to Venus, but at a different point in its orbit.
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Guest_BruceMoomaw_*
post Nov 26 2005, 02:27 AM
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Remember Magellan, which completed 1.5 orbits around the Sun before intercepting Venus halfway through its second orbit -- the reason being simply that otherwise the Shuttles carrying it and Galileo would both have had to be launched in the same launch window to Venus. But this also meant a 6-month difference in the times that the two craft reached Venus, so that a lander on Magellan could have been dropped off at a completely different place than a lander dropped from Galileo with its direct trajectory to Venus.
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Guest_vjkane2000_*
post Nov 26 2005, 06:31 AM
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QUOTE (BruceMoomaw @ Nov 24 2005, 03:10 PM)
One can think of other ways to slim down this mission, too -- related to the decision to put the two atmospheric composition experiments on BOTH landers, although the atmosphere's composition will vary little or none from one place to another.  One is a UV spectrometer -- presumably to try and identify the still-mysterious dark UV cloud absorber -- which is mounted outside the pressure hull and will burn out below 50 km; it could easily be removed from one lander. ..
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If you take Bruce's ideas on slimming down the mission to their logical conclusion, you could have a probe with just a descent imager and Raman spectrometers/LDS on one or more arms. (And probably an imager to see what the arms touch down on.) Such a probe could be very slimmed down -- perhaps enough that you could drop 4-8 on a single mission. Don't know whether this is better than the original mission idea. Have to think that the scientists/engineers would have thought of this one, too. Getting the sample inside to cooled instruments must be pretty valuable.
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Guest_BruceMoomaw_*
post Nov 26 2005, 08:24 AM
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This wouldn't make the SAGE landers that much slimmer -- take a look at the table of experiment weights and power requirements in the JPL paper.

One possibility that comes to mind, though, is scattering a bunch of probes around on Venus that don't have imagers of any type (in addition to some that do), in order to get purely compositional data from the surface at a number of places for comparison purposes (along, perhaps, with a penetrometer or densitometer on the sampling arm so that we could tell how hard the material was that they were sampling). The data transmission requirements would be so much lower for these that they could send all their data directly back to Earth, very greatly simplifying the mission. And in that case you really would get a much lighter overall spacecraft capable of carrying more landers.

I'm currently awaiting my copy of a document that will be put out in a week or two by a study team for VEXAG (the Venus Exploration Analysis Group, part of whose Pasadena meeting I caught on the way home from the COMPLEX meeting) listing the scientific priorities and technological difficulty of various Venusian surface measurements -- which should tell us a lot more about the proper way to explore this very difficult subject. But there seem to me, right now, to be two (maybe three) top-priority items for Venusian surface analysis (since seismometry is very hard and must be bumped well into the future).

The first is trying to determine where there are any rocks or minerals indicating that early Venus had oceans -- including felsic (granitic) rocks and possible aqueous minerals. And the only good places to look for that evidence seem to be the tesserae and Ishtar Terra (the only thing on Venus that looks somewhat like an Earthly continent). The second is trying to age-date different parts of Venus to see whether the "catastrophic resurfacing" theory is correct, which might be doable, at least loosely, with in-situ instruments. But Bruce Campbell thinks that age-dating may not be possible even for returned Venus samples due to their high temperature (although others disagree with him), and that a better way to solve this problem is with an orbiter with a deep subsurface radar sounder to look for lava-flow overlay patterns in different types of terrain -- just the sort of mission he's proposing for the next Discovery AO.

The third is to try and determine the nature of that mysterious highly radar-reflective stuff that turns up on Venus' high-altitude terrain, which a single lander with additional goals might be able to do without very complex instruments. In short, answering all the really important questions about Venus -- until we can develop that difficult long-lived lander technology at our leisure -- may not require all that many landers.
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Guest_vjkane2000_*
post Nov 27 2005, 06:08 AM
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QUOTE (BruceMoomaw @ Nov 26 2005, 01:24 AM)
This wouldn't make the SAGE landers that much slimmer -- take a look at the table of experiment weights and power requirements in the JPL paper. 
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I don't think anyone would fly a lander without a simple descent imager. The imagers weigh, as I recall, ~300g, although the window might add weight. Assume that you put a second window/imager to look out where the arm touches down. The multiple imagers could share much of the electronics.

I remember a very old (30 years?) NASA technical study of follow on missions to Venus Pioneer. One of them included a derivative of the small probe that touched down and put out four arms with composition probes on the end.

I'd love to see a number of lander on Venus to explore the range of compositions.
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JRehling
post Nov 27 2005, 07:13 AM
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QUOTE (BruceMoomaw @ Nov 26 2005, 12:24 AM)
The first is trying to determine where there are any rocks or minerals indicating that early Venus had oceans -- including felsic (granitic) rocks and possible aqueous minerals.  And the only good places to look for that evidence seem to be the tesserae and Ishtar Terra
[...]
In short, answering all the really important questions about Venus -- until we can develop that difficult long-lived lander technology at our leisure -- may not require all that many landers.
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The tesserae themselves may turn out to be a kaleidoscope of numerous former surface units. Which would mean that a stationary lander could tell us all about one speck of Venus and miss entirely the intriguing units only hundreds of meters away.

I think when we get serious about exploring Venus's geology, we're going to find it no simpler than, and potentially far more complex than, that of Mars, which still confuses us after the fifth significant landed mission.

Given the difficulties that orbiters are inevitably going to have, the limited sampling range of stationary landers, and the profound difficulties in building a Venus rover, an aero- mission of some kind has to come up soon in the planning process, even if it's only to get some multispectral descent imaging. I fear that until some multispectral descent imaging shows us what we can see from below the clouds, and what we can't, it's a mistake to invest too much in missions that may go to great lengths to acquire data that could be had in less detail but much greater spatial coverage from 20 km up.
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edstrick
post Nov 27 2005, 09:51 AM
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I'd be really interested in knowing the calculated atmospheric opacity between 45 km altitude (just below the lowest observed cloud and haze layers seen by entry probes (more or less) and the surface as a function of wavelength.

We are going to try surface composition variation detection from above the clouds with Venus Express, using infrared that filteres up through the clouds in the atmospheric low-opacity windows, but there will be "no" resolution on the ground.. Basically a 50-some km blur from the 50-some km high main clouds

Below the clouds, you have a nearly aerosol-free view down to the surface, with gas absorption, scattering, and near the surface, emission. But at wavelengths long enough that Rayleigh scattering is less than 1, you can image the surface directly with optics-limited resolution.
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Guest_BruceMoomaw_*
post Nov 27 2005, 09:55 AM
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First: it's not the WEIGHT of imaging cameras that's the problem -- it's their huge data return, which requires a flyby or orbiter craft to serve as a com relay. Get rid of imaging, and the landers can relay all the rest of their data directly back to Earth, which greatly simplifies a mission. (There was a debate about this for giant-planet entry probes at COMPLEX, in which Tom Spilker did a very good job of shooting down Scott Bolton's enthusiasm for the idea. But the technical problems that make it hopelessly impractical for the giant planets -- mostly because of the difficulty of having the probe enter at a place that allows DTE transmissions without it having to make a destructively steep dive into the atmosphere -- don't apply to Venus, as we already know from Pioneer 13.)

As for the tesserae, they seem to be areas that have been faulted by being stretched in one direction and squeezed in another (not at the same time), but there seems to be no evidence from their radar appearance that they're actually patchworks of small areas of different materials laid down at different times. It is, however, quite possible that -- if they really are the oldest areas on Venus, and date back to a time when it still had oceans, crustal tectonics, and the start of the formation of granite continents -- they really are a complex mixture of materials. In any case, the way to start investigating this seems to be simply to land on a couple of different tesserae -- or, again, Ishtar Terra, which is a very high-altitude plateaus that seems to be geologically unique on Venus -- with simple fixed landers and see if dramatic compositional differences show up.

And as for aerial observations, keep in mind that any probe too high to illuminate the surface with a flashlamp will only be able to see reflected near-IR sunlight in the five narrow spectral bands which Venus' clouds and air allow to reach the surface at all. (It's the same kind of problem that Cassini or a balloon have for near-IR mapping of Titan.) Those five bands will provide some useful compositional information, but not a really big amount (Kevin Baines discussed this several years ago in "Icarus"), and so it might be better to put such a multi-channel photometer on a balloon in the lower clouds rather than on a lot of separate descent probes. As for descent imaging, it obviously also has its uses -- but, again, to decide where to send surface-composition landers we might get better advance reconnaissance information from a really high-resolution SAR map made by a follow-up orbiter to Magellan, such as has been talked about. (A SAR orbiter capable of obtaining 25-meter resolution images may be doable for costs on the Discovery/New Frontiers borderline.)
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