Help - Search - Members - Calendar
Full Version: Future Venus Missions
Unmanned Spaceflight.com > Inner Solar System and the Sun > Venus
Pages: 1, 2, 3, 4
Phil Stooke
Oh well, might as well start that new topic since it's already well advanced in the Juno area...

My perspective on landers is as follows. All the landers we've had so far were dropped blind onto an essentially unknown surface. Any future landers can be targeted for specific terrains. It really is not true that we have had representative landings. Even a descent image or two, a panoramic photo plus a bit of surface composition, from a simple Venera-class lander just updated a bit, would be useful if we could put several down at well chosen targets. My choices would be:

Examples of the main plains units (smooth, fractured, ridged)

tesserae

high elevation radar-bright tesserae

large fresh lava flow unit ('fluctus')

crater dark parabola

crater ejecta outflow unit

dunes area.

And I have always assumed, rightly or wrongly, that it would be relatively easy to put these down, so they ought to be fairly inexpensive as planetary landers go.

Phil
BruceMoomaw
Well, to repeat a point I've suggested (somewhere) on this site before: given the great additional difficulty of designing a Venus probe if you have to add an airlock to it to allow it ingest samples into its interior, how much good compositional data can you get on Venus' surface WITHOUT such an airlock. A surprising amount, I suspect. A test has already shown that the LIBS system planned for instantaneous, precise and long-distance element measurements on the MSL rover should work just as well in Venus' environment ( ).

On Mars and on airless worlds, this instrument can probably be combined with a Raman spectrometer (which also uses laser light) for a lot of mineralogy studies (although this system wasn't considered quite ripe enough by the LIBS group right now to add it to their proposal for the MSL's LIBS; it's worked fine in ground tests). I'm not sure whether Raman would work as well at long-range in the super-dense Venusian atmosphere -- it relies on measuring an extremely small trace of backscattered laser light -- but even if it doesn't, you could put the fiber-optic connections to a Raman spectrometer and its laser on a simple arm on the lander to contact the local surface in different places. You could also add other gadgets to that arm: a microscopic imager, and maybe even an abrading wheel to grind the weathering crust off Venusian rocks -- which the lander could probably locate on the surface using a simple hardness sensor on the arm.)

Add a panning near-IR spectrometer to the lander (plus a tiltable flashlamp (or broadband laser) to periodically illuminate the surface and allow that spectrometer to distinguish its reflectance spectra from thermal emission spectra), and maybe also a gamma-ray spectrometer inside the lander's hull, and you could answer damn near every important scientific question about Venus' surface -- except for in-situ age dating -- without ANY airlock, and without any need for instruments that require a long time to gather their data (such as X-ray and Mossbauer spectrometers). An X-ray diffractometer like the one on MSL (which also requires ingested samples) could provide additional mineralogy data, but I question whether it's really essential by itself given the Raman and near-IR spectrometers.
BruceMoomaw
I see I forgot to provide the URL for the LPSC abstract on the use of LIBS on Venus. *sigh*

http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1338.pdf
JRehling
Phil is, of course, completely right about the list of interesting Venus terrains; I think anything but an aerobot approach will leave us a long time in seeing all of them, but a network of four geophysical stations ought to be chosen opportunistically to sample some of the more unusual locations.

A possible Venus exploration gizmo: either an aerobot or a stationary lander that needed a source of artificial light to do spectroscopy despite the incessant IR glow could have microprojectiles that contain nothing but a flash device. This need not require any wet chemistry or electronics whatsoever, or very minimal versions thereof, and therefore be extremely simple and light. An aerobot could drop them, or a stationary lander could eject them several (tens of?) meters away, and then the main craft would image the surface at the time/place of the flash. To get the purest signal, this could be done at night, when only the venusian IR glow would persist. Of course, with-flash and without-flash data would help to get rid of the noise. Perhaps this adds nothing to the LIBS approach -- the question is whether a laser casts its light farther and cheaper and more multispectrally than a "bottlerocket" style of flash. The laser could be used more often, but the flash would allow work at a distance to eliminate all of the scattering problems of the laser and half of the atmospheric absorption. Perhaps an aerobot that is not configured for Venus surface heat, but stays a few km up, could make use of flashes in a circumstance where a laser would require a lower and hotter "perivenus"? Just a thought on the behalf of 13th century technology.
Myran
QUOTE (BruceMoomaw wrote.)
....and without any need for instruments that require a long time to gather their data 


I think you are right, a Mössbauer spectrometer of the kind the MER rovers have will not do, whatever instruments a Venus lander will be provided with they need to work rather fast.
Perhaps the robotic arm should work by a simple cog and wheel system moving automatically from point to point and a simple contact that turns of the downward movement as soon it touch hard soil, just in the hope it will get to touch down on more that one kind of mineral and bedrock. Without computerized parts, you wont risk overheating and failure.

If one airconditioned lander survives the first 12 hours or whatever, it should have the ability to download new instructions, so this would indeed be a workable kind of lander.
But I have a hunch that the space agencies never will spend that much money to send any simpler lander that Phil Stooke suggests. When they spend that many millions for the launch and logistics, the administrators will upgrade the lander up to the point where the lander will be one other megabuck marvel in itself.

So that proposal of a really simple non computerized system and Phil Stooke's suggestion might not happen at all, yet I have a hunch that for one inhospitable place like Venus, the best way to go is by the 'keep it simple stupid' thinking. wink.gif
BruceMoomaw
The main justification for simplifying a Venus lander is that it can enable you to launch more than one at one time. Larry Esposito's "SAGE" concept -- which, from what little I know about it, apparently DID have both an airlock and a GCMS atmospheric analyzer -- neverthless consisted of two or three landers on one mission.
AndyG
Given that the surface is so hot and so highly pressured, why not take a leaf from the early explorers of the ocean bottoms? Dredge for rocks!

Picture a balloon flying in Venusian atmosphere at about the 32km level. This height is good since it's below the bulk of the cloud cover, giving you the ability to view the surface. Pressure is around 8bar and the temperature is around 200C. Not really a problem for well-designed electronics & balloon materials. Water doesn't automatically boil at this pressure/temp, so may be useful for radiators.

A thin titanium wire, with a basic end effector, could be winched down from a balloon at this height to pick up suitable rocks for analysis back within the balloon. A wire some 1.32 mm across, tapering to around 1mm at the bottom, would in total mass about 160kg, and enable a load of about 20kg to be lifted, assuming some 5kg mass for a grabber/hardened camera, etc.

100kg of lift in a CO2 atmosphere could be provided with just under 8 cubic metres of H2 in the balloon, so the size of the bag could be really quite trivial.

Andy G
Bob Shaw
As there are some fairly well-described outline designs for RTG-powered refrigerated landers, I find myself wondering whether the waste heat from the refrigeration system could be used to produce lift in a hot-air balloon. An almost mechanically inert (in terms of externals - obviously, there's pumps and whatnots beavering away inside!) lander could drift around the landscape, rising from time to time then falling once more. Think of a Galilean Thermomoter, and the way the glass spheres bob up and down...

You'd get:

Multiple ground-truth sites
Aerial imaging
Meteorology

And probably a few other goodies, too!
JRehling
QUOTE (Bob Shaw @ Jul 7 2005, 07:54 AM)
As there are some fairly well-described outline designs for RTG-powered refrigerated landers, I find myself wondering whether the waste heat from the refrigeration system could be used to produce lift in a hot-air balloon.  An almost mechanically inert (in terms of externals - obviously, there's pumps and whatnots beavering away inside!) lander could drift around the landscape, rising from time to time then falling once more.  Think of a Galilean Thermomoter, and the way the glass spheres bob up and down...

You'd get:

Multiple ground-truth sites
Aerial imaging
Meteorology

And probably a few other goodies, too!
*


It'd be great if it worked, but of course, the refrigeration scheme itself involves a lot of mass per payload mass.

Venus permits a lot of buoyancy, potentially, especially if helium filled the balloon, but that margin could be eaten up with a nuclear-powered refrigerator + thermal insulation + ???

Also, heated CO2 would not give you much buoyancy compared to helium unless you really heated the hell out of it. Venus's high ambient temperature really works against that. To halve the density of CO2, you'd have to double the temperature, up to roughly 1000K! I'm no material scientist, but I guess you're talking about fewer and fewer possible balloon materials that will hold up as a strong, thin film when boosted to white heat!

I think compressing and uncompressing helium (at thermal equilibrium with the outside) would provide a *lot* more lift with less mass. Although, I understand and admire you're looking for synergy between a design side-effect and a possible desirable feature.

The synergy you get in design with Venus balloons is that the higher a balloon resides, the cooler the ambient temperature that must be withstood. If thermal inertia (passive!) can keep the system alive throughout a single exploratory drop, then we might have systems that can only tolerate the Venusian surface environment temporarily, but long enough for an arbitrary number of descents. The Veneras operated in this fashion. A balloon carrying a heat sink could reach thermal equilibrium at 40-100 C. Then the question is: How much time would be required in a surface stay to do useful science? For imagery, very little. To grab a sample, very little. It is possible, in times of favorable geometry, to work a single telemetry/command feedback loop with Earth-based controllers in just a few minutes. (Transmit an image, ask which rock/soil unit should be grabbed, and receive that command -- the AI for that is beyond MER, but not beyond reason.) If a ~45-minute surface stay is well within safe margins for thermal constraints, then that's not a bad MO. If descents could be managed at roughly the rate of one per day, then a lot of surface exploration could take place in a primary mission of two or three weeks.

The whole scheme then could be to identify a swath across one line of latitude of Venus that contains several worthwhile terrain units that are, moreover, going to be in local daylight with a line-of-sight to Earth during a desired primary mission. The craft would control its horizontal motion by ascending into local winds, thereby deriving the horizontal motion. The heat sink would get well below top operating temperature, and then the craft would perform a dive to its target. It would take descent images and a single surface panorama, beam them to Earth, and autonomously perform surface science while awaiting a command from Earth identifying which surface patch to sample by arm. After about 20 minutes, the human-made decision would reach the craft, an arm would make a grab for the target, and then the craft would ascend again, and spend its time analyzing the sample up in the cool heights above. An exploration of terrains in the vicinity of 150 E, moving along the equator or 10 S -- could be a heck of a mission, with lots of geological and "remote" sensing of many terrains. Of course, if a pair of these things could be afforded, working at different latitudes but identical longitudes in the same time frame, then a very thorough exploration would result.
BruceMoomaw
Actually, this type of mission -- a balloon using "reversible fluids" to achieve controllable variable buoyancy with a surprisingly low use of both gas and power, spenjding most of its time in the clouds but dipping periodically all the way to the surface briefly -- has been studied by JPL for years as the "Venus Geoscience Aerobot". I've just found two very detailed descriptions of it that I wasn't even aware were on the Web (including Martha Gilmore's article, of which she privately sent me a less developed version YEARS ago. Apparently it took her that long to get Acta Astronautica to publish the damn thing.)

http://techreports.jpl.nasa.gov/1999/99-0750.pdf
http://www.planetary.brown.edu/planetary/documents/2056.pdf

If this balloon design is workable, then obviously this has tremendous merit as a New Frontiers or Small Flagship mission. (One can easily conceive of an improved version, which uses LIBS and Raman spectrometers for its brief surface analyses rather than an X-ray spectrometer as she suggests -- or which actually deploys a core tube or scoop to snatch a surface sample for later leisurely onboard analysis, like JPL's recent Titan Organics Explorer concept: http://www.lpi.usra.edu/opag/feb_05_meetin...resentation.pdf .)

Unfortunately, that seems to be a a very big "if", judging from Kerzhanovich's recent LPSC piece ( http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1223.pdf ), in which he says flatly: "A key problem is that at the time the decadal survey
was published, no high temperature balloon technology existed to implement either mission. Prior technology development efforts had concentrated on a
single balloon that could operate across the entire 0-60 km altitude range, tolerating both the sulfuric acid aerosols and the extreme temperatures of -10 to +460 ºC. However, this problem was unsolved because no combination of sufficiently lightweight balloon material and manufacturing (seaming) technology was ever found to tolerate the high temperatures at the surface." If, as this implies, polybezoxasole can't be adequately seamed after all, then we're stuck with his suggestion for a near-surface steel-bellows ballon whose instrument package must endure Venusian surface tempartures for o very long periods -- which will require new electronics technology, as the Solar System Roadmap says.
Bob Shaw
Bruce:

Very interesting - you are a fount of knowledge!

The nice thing about hot-air balloons is that they have a natural homeostasis, and can tolerate leaks so long as you can keep adding heat - pressure altitude bursts etc are also naturally avoided by virtue of the big open cavity. Some of the recent terrestrial around-the-world (etc) manned ballooon flights have also used hybrid structures, with a helium bladder surrounded by a hot-air envelope.

As for materials, an open-bottomed stainless steel structure could be extended at altitude when cool (think of one of those nested metal travelling drink cup affairs crossed with an umbrella made out of Webb Telescope hexagons), with some sort of caulking around the edges like an intumescent strip on a fire-door and then used as an aerobrake to the surface. On the way down, it heats up, the caulking melts in place, the metal expands and suddenly there's a balloon. Well, a balloon made for a deep-sea furnace, anyway...

If there's an active refrigeration system aboard the lander then it'd run *hot* at the radiator end - the darn thing'd have to be much hotter than ambient, and that's red heat, so we're looking at a ready energy source for bobbing around the landscape, even with CO2. The killer would be to get up into the cool air again to dump as much heat as possible, or else you'd end up floating at some gradually decaying height while your electronics and mechanicals slowly baked. Think of the remote sensing fun at 5kmh at 300m altitude for a month, though!

Speaking of balloons, have you ever come across any serious commentary on the VEGA Soviet/French balloons? About all I've found are brief mentions...

Bob Shaw
Bob Shaw
Among the interesting points in the .PDFs to which Bruce posted links are:

A wind-turbine to provide power for night-side operations

Pre-ordained trajectories for geological traverses

Very-high resolution surface imaging
Bob Shaw
A conceptual small Venus atmosphere probe picture from 1979, intended to allow a slow descent of a (fairly) long-lived vehicle under a balloon.
remcook
ESA is looking at a mission that is using a balloon that will stay afloat by dropping microprobes along the way. So you get both balloon and probe. Pretty neat idea.

found a website...

http://sci.esa.int/science-e/www/object/in...fobjectid=35987
BruceMoomaw
NASA's Venus Exploration Analysis Group (VEXAG) -- the new equivalent of MEPAG and OPAG -- held its first meeting yesterday in Pasadena ( http://www.lpi.usra.edu/vexag/vexag.html ). While I missed the morning session because I had to catch the final part of the COMPLEX meeting, I did manage to catch the afternoon session.

Unfortunately, not much was said then -- except that the subgroup that deals with "Planetary Formation and Evolution" (that is, surface studies as opposed to atmosphere studies) came up, during a session at the meeting itself, with what Steve Mackwell regards as a very good initial list of desired science measurements, along with information on how technologically difficult they will be. In the next two weeks, the subgroup will prioritize and finalize this list, and he's promised to send their conclusions to me -- although I imagine I'll be using those in my "Astronomy" article and so may not be free to announce them here. (I will say that he agreed with me that, since the minimal estimate for the cost of a Venus sample return is $10 billion, Congress will fund that mission on about the same day that O.J. finds the real killers. We will have to settle for in-situ measurements instead.)

Mewanwhile, three of the Powerpoint presentations from the meeting have just been put on its site at http://www.lpi.usra.edu/vexag/1st_comm_meeting.html . Three of them are disappointing, but there's a very nicely detailed description of the precise measurments that MESSENGER will make during its second Venus fyby in June 2007. (The instruments will be off during the first one in Oct. 2006, because it's near solar conjunction and the flyby is rather distant anyway).
http://www.lpi.usra.edu/vexag/Nov2005/MESSENGER_VEXAG.pdf
JRehling
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.
*


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.
remcook
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...
BruceMoomaw
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.
BruceMoomaw
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!
Phil Stooke
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
BruceMoomaw
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.
Phil Stooke
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
JRehling
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.
*


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.
BruceMoomaw
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.
vjkane2000
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. ..
*


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.
BruceMoomaw
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.
vjkane2000
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. 
*


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.
JRehling
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.
*


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.
edstrick
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.
BruceMoomaw
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.)
Phil Stooke
Bruce said:

"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"

One problem with doing this without a camera is that you may not know the local geological context of the sample you get. Many tessera areas, for instance, have small patches of basalt in low spots, and many plains areas have small cones, ridges or patches of older material protruding through the plains material. Which material are you sampling? The Venera images and compositions we have are compromised a bit in usefulness because it's not really possible to relate them to specific geological units.

Bandwidth is a problem, but it's less of one now than it used to be - not long ago the idea of transmitting a heavily compressed image was anathema, but now it's done quite often. We would be better off with descent imaging, even if horribly compressed, in order to get the exact location of the landing site. And images can be compressed a lot these days.

Of course I'm an image guy so I may be biased!

Phil
BruceMoomaw
But, once again, a high-resolution radar orbiter -- combined with the improved tracking that we have now over that for the Veneras -- could identify the landing sites for such landers with enough accuracy to enable the overall geological context of their samples to be determined. (After all, the phenomena Phil describes have been detected entirely on the basis of the Magellan images.)

In that connection, how do you know that there are "small patches of basalt in low spots" in the tesserae? Are these relatively crack-free patches, presumably laid down by later lava flows in the tesserae?
tedstryk
Another possibility is, if the probe transmits at a very high rate, is that after landing, better versions of the images are returned with little loss.
Phil Stooke
Bruce, yes, lots of tesserae have small ponds of lava in low spots, and fingers of it extending from the plains, a common embayment relationship. They show up clearly in Magellan images, but please don't ask me to unearth one right now! There must be patches of aeolian sediment, dark parabola material or ejecta in low spots, or other complicating factors as well.

The trouble with the high res radar is that, yes, you get better images, but no, you still don't know exactly which spot the lander came down on. Only descent imaging can do that for you, or the very difficult task, likely to be almost impossible on Venus, of matching features in surface panoramas with orbital images. There is no other way to locate a landing site exactly at the scale needed for knowing its geological context. Of course this does not apply in the case of homogeneous plains. In tesserae or any other complex landscape you are still better to go with descent imaging if at all possible, using heavy compression if bandwidth is the issue. I just ran a test, and I can easily reduce a 1 MB TIFF to 25K without compromising its usefulness for site location, probably smaller.

Phil
vjkane2000
QUOTE (tedstryk @ Nov 27 2005, 08:01 PM)
Another possibility is, if the probe transmits at a very high rate, is that after landing, better versions of the images are returned with little loss.
*


I'm with Phil -- there are really good compression algorithms today that could be used. And you learn so much more if you understand what you landed on (are you measuring dust or a pebble or a lava plain?). If you really don't like having a relay craft, consider that a single image 1000x1000 image could be returned at ~300 bits/second (assuming 8X data compression). Probably not that unrealistic given today's communications technology at both ends.

But I think that the relay more than makes up for the extra complexity. I do remote sensing for my graduate work. Even 30m pixels are incredibly frustrating because they hide so much detail. Venus coverage is even worse.

If you have the relay craft and a roughly 3 hour communications window, you could imagine a mission that takes 30 minutes to descend to ~20 km above the surface, release a paraglider chute, take the next hour to take a transcect of images across the surface, and then have 1.5 hours on the surface.
edstrick
The frustration of understanding anything about the geology of the Venera Lander sites is the utter lack of geologic context for the surface panoramas. Three "DIMES" type images, taken at 1, 5 and 20 (for example) kilometers with a 45 degree field of view, from my perspective, is almost mandatory for any understanding of the geologic context of chemical/minerological measurements from a lander.

It's lack -- we've only approximately located the landing sites of Venera 8, 9 and 10, 13 and 14, and Vega 1 and 2 -- in providing real geologic context has led to essential uncertainty on what geology some of those landers are on. Some are just not well located in regions of complex geology, Venera 8 in particular.

Radar data, by it's inherent nature, tells a lot about surface materials physical configuration: relief, roughness, texture, internal scattering, etc, but almost nothing about chemistry. In addition, it's remarkably hard at times to relate to visible geology. Witness the difficulty in relating optical observations of the Huygens landnig site to radar data. Shuttle radar penetrates a meter or so under sand sheets in the Sahara and show geology underneath you can't see standing there or in visible imagery from orbit. On a mission dominated by geochemistry-science, I'd prefer 3 good descent images over spiffy surface panoramas any time, much as I love a good pan!
RNeuhaus
Why does not do design a good space architecture as the Mars ones with the initial support of MGS and Odyssey as the initial recoconizance support and as relay for the landed probes to Earth?

This architecture should be applied for the next mission to Venus and it would solve the communications problems to landed probes on Venus and also a better understanding of Venus in order to even assure the future missions to Venus. This mission be must taken with a gradual steps, perhaps, an lapse of 10 years.

Rodolfo
JRehling
QUOTE (RNeuhaus @ Nov 28 2005, 07:20 AM)
Why does not do design a good space architecture as the Mars ones with the initial support of MGS and Odyssey as the initial recoconizance support and as relay for the landed probes to Earth?

This architecture should be applied for the next mission to Venus and it would  solve the communications problems to landed probes on Venus and also a better understanding of Venus in order to even assure the future missions to Venus. This mission  be must taken with a gradual steps, perhaps, an lapse of 10 years.

Rodolfo
*


An orbiter for COM abilities would not have as much value for a world where landed missions only last two hours. In fact, an orbiter would be almost pointless, because it would only get to fly over the landing site once or twice while the lander was alive! You may as well land the COM package on the lander and send the high-gain telemetry straight to Earth instead of having it spend 90% of the lander's mission out of line of sight with the instruments on the surface.
RNeuhaus
QUOTE (JRehling @ Nov 28 2005, 11:51 AM)
An orbiter for COM abilities would not have as much value for a world where landed missions only last two hours. In fact, an orbiter would be almost pointless, because it would only get to fly over the landing site once or twice while the lander was alive! You may as well land the COM package on the lander and send the high-gain telemetry straight to Earth instead of having it spend 90% of the lander's mission out of line of sight with the instruments on the surface.
*

Let me see the architecture space design. As Venus rotates more than one year Earth. So the desired landing site can be programmed with anticipation according to the Earth's departure. So the lander will stay *almost on the same place facing to the Earth* for a long time so its HGA would be useful without much worries about pointing to Earth. So it is reasonably understandable that the COM orbiter is pointless unless a special or restrict conditions such as to land on the Sun's face.

Now, I am not very convinced that with our actual technology can permit to last the instruments less than 2 hours in Venus. It might be due to the economics factors. The cheaper ones will last less time than ones with more robust and expensive equipement incorporated with any kind of thermal refrigeration (LOX, LH, RTG, others).

Up to know, I don't still see a clear objective for the next mission to Venus. Indeed, it is still to early or not. The depending upon to the mission objective, It will be the factor influence for the right space architecture design. One group support for a ballute, others support for a landing of multiple probes. Any of them are useful but they bring the results for different objectives.

Rodolfo
BruceMoomaw
I take for granted that the first three or four geological Venus landers will carry cameras. The question is just how many landers will be sent to other parts of the planet afterwards, and how many of them should also carry cameras. And since Venus (let's face it) is not burningly high on America's list of space priorities, it will be a long time before this question even becomes relevant.

The near-term question that IS relevant is whether we should send off a few geological landers right now (a la SAGE), or whether we should wait until we do a little more orbital reconnaissance (with radar and/or near-IR), after Venus Express, to select good landing sites for them. I don't begin to know enough science to judge this question, but I'll be interested in hearing what the VEXAG people say shortly.
JRehling
QUOTE (JRehling @ Jul 1 2005, 08:28 AM)
A possible Venus exploration gizmo: either an aerobot or a stationary lander that needed a source of artificial light to do spectroscopy despite the incessant IR glow [...]
*


A bit of terrestrial exploration of Venus: Christophe Pellier's images of Venus's nightside in the 2004 section overexpose the dayside in IR and you can faintly make out the nightside glowing from the surface heat!

http://www.lpl.arizona.edu/~rhill/alpo/venustuff/recobs.html

This is the first I have seen this in a photograph.

There have always been rumors of people seeing an "ashen light", seeing exactly this sort of spectacle, with the eye. Well, 1000 nm is certainly beyond the abilities of human detection, and I'm highly skeptical that anyone could see this with their own rods and cones.
djellison
Ahh - Nico and I saw a presentation about that at the BAA conference this summer, there were some very good amateur observers there and they were amazed.

Doug
Jeff7
QUOTE (JRehling @ Dec 15 2005, 08:34 AM)
A bit of terrestrial exploration of Venus: Christophe Pellier's images of Venus's nightside in the 2004 section overexpose the dayside in IR and you can faintly make out the nightside glowing from the surface heat!

http://www.lpl.arizona.edu/~rhill/alpo/venustuff/recobs.html

This is the first I have seen this in a photograph.

There have always been rumors of people seeing an "ashen light", seeing exactly this sort of spectacle, with the eye. Well, 1000 nm is certainly beyond the abilities of human detection, and I'm highly skeptical that anyone could see this with their own rods and cones.
*


I suppose it might be possible - a few people can hear much higher frequencies than the average person. It doesn't seem too far fetched that we'd get the occasional genetic abnormality that would alter a person's visual spectrum slightly. But granted, stretching it all the way to 1000nm may be a bit much.
JRehling
QUOTE (Jeff7 @ Dec 15 2005, 10:33 AM)
I suppose it might be possible - a few people can hear much higher frequencies than the average person. It doesn't seem too far fetched that we'd get the occasional genetic abnormality that would alter a person's visual spectrum slightly. But granted, stretching it all the way to 1000nm may be a bit much.
*


Well, it's not only how far out 1000nm is, but the fact that normal people have a greatly diminished sensitivity even at red. You can see a red laser in a dark room, sure, but a dim red light is much harder to see a dim green light of the same energy. Rods are only slightly sensitive to red light (they have about the same response curve peak as green-sensitive cones)... and when it comes to detecting *dim* red that happens to be right next to dazzling bright white (!) I am *very* skeptical. If the night side of Venus were somehow isolated from that bright crescent, I might believe it. Put another way, someone orbiting over the night side of Venus would have a much better chance of looking down and seeing non-black than someone on Earth looking into the bright crescent and seeing *dim* dark, near IR.
Bob Shaw
A simple explanation for at least part of the story:

If the light reflected off Venus can cast shadows on Earth, then Earthshine must similarly illuminate the night side of Venus (remember the Clementine Lunar night-side shots, with the Solar corona and various planets in view, and think, if you will, how *dark* the surface really is compared to the white clouds covering Venus). Of course, at closest approach Venus is 100x further away than the Moon, so the effect will always be somewhat less...

If the Ashen Light waxes and wanes with Terrestrial cloud cover, then the case is settled (that phenomenon is visible on the Moon, and has been used to estimate changes in the overall albedo of the Earth).

I wonder whether Venus Express will be able to image the clouds of Venus by Earthshine?

Bob Shaw
JRehling
QUOTE (Bob Shaw @ Dec 15 2005, 03:38 PM)
A simple explanation for at least part of the story:

If the light reflected off Venus can cast shadows on Earth, then Earthshine must similarly illuminate the night side of Venus (remember the Clementine Lunar night-side shots, with the Solar corona and various planets in view, and think, if you will, how *dark* the surface really is compared to the white clouds covering Venus). Of course, at closest approach Venus is 100x further away than the Moon, so the effect will always be somewhat less...
*


Note that a full Earth is roughly 1/4 the luminance of a full Venus... but that's a crescent Venus that we see at its brightest. When the ashen light would be spotted, that would be a large gibbous Earth seen from the venusian cloudtops, so yes, the brightest Earth seen from Venus would be roughly the same luminance as the brightest Venus seen from Earth. Luna would add a tiny smidgen as well.

That said, although some nonzero amount of Earthly light would be shining off of Venus, the question is: is it visible? Again, I think the neighboring effect of that superbright crescent makes it unlikely. If I had $1500 and the goal of investigating this, I would create lab stimuli with Venus-in-telescope appearance and nothing but inky blackness inside, and see if subjects report that the space inside the crescent seems to be filled in. I would guess "optical illusion" before earthshine, or endogenous glow of somesort. I used to seriously research human vision, FWIW, but this sort of situation can not be abstracted from any published results AFAIK.
BruceMoomaw
Yep. One would think that -- if the Ashen Light actually existed -- Pioneer 12 would have detected at least some faint indication of it during its 13 straight years in Venus orbit. I think the Ashen Light belongs in the same dustbin of history as Mars' canals and the Moon's transient glows.
David
QUOTE (BruceMoomaw @ Dec 16 2005, 03:17 AM)
Yep.  One would think that -- if the Ashen Light actually existed -- Pioneer 12 would have detected at least some faint indication of it during its 13 straight years in Venus orbit.  I think the Ashen Light belongs in the same dustbin of history as Mars' canals and the Moon's transient glows.
*


The Martian canals weren't entirely illusory -- certainly the network of fine lines was fictitious, but in many cases the "canals" were an attempt by the hand and eye to organize real but very small and faint albedo variations. Comparing old sketches of Mars with modern albedo maps is very instructive, both about the limits of human eyesight, and conversely, about the remarkable visual acuity and commitment of many of these early observers.
BruceMoomaw
Well, it's a fact that E.E. Barnard -- one of the sharpest-eyed of all astronomers (which is how he discovered Amalthea) -- is also the only naked-eye astronomer to swear that he saw Mars covered with craters.
Bob Shaw
There's an empirical test (for once), and that's the relationship between Terrestrial albedo and the (supposed) glow off the darkside of Venus - all that's needed is a small telescope for the Venus data and access to some carefully combined Terrestrial weather satellite images to prove or disprove the assertion.

Sounds like a PhD in waiting...

Bob Shaw
This is a "lo-fi" version of our main content. To view the full version with more information, formatting and images, please click here.
Invision Power Board © 2001-2018 Invision Power Services, Inc.