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_*]

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.