Future Venus Missions Options

[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

[Guest_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.

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