Over the coming months I (often with the help of Bruce Moomaw) will look at concepts for each of the New Frontiers mission targets. To date, the most popular target for the next mission based on votes from readers has been Venus, so we’ll start with that world.
Here is what the New Frontiers draft announcement of opportunity (AO) states as the goals for a mission to Venus:
Although the exploration of the surface and lower atmosphere of Venus provides a major technical challenge, the scientific rewards are major. Venus is Earth’s sister planet, yet its tectonics, volcanism, surface-atmospheric processes, atmospheric dynamics, and chemistry are all remarkably different than on Earth, which has resulted in remarkably different end states for its surface crust and atmosphere. While returning physical samples of its surface and/or atmosphere may not be possible within the New Frontiers cost cap, innovative approaches might achieve the majority of the following objectives:
• Understand the physics and chemistry of Venus’ atmosphere through measurement of its composition, especially the abundances of its trace gases, sulfur, light stable isotopes, and noble gas isotopes;
• Constrain the coupling of thermochemical, photochemical, and dynamical processes in Venus’ atmosphere and between the surface and atmosphere to understand radiative balance, climate, dynamics, and chemical cycles;
• Understand the physics and chemistry of Venus’ crust through analysis of near-IR descent images from below the clouds to the surface and through measurements of elemental abundances and mineralogy from a surface sample;
• Understand the properties of Venus’ atmosphere down to the surface through meteorological measurements and improve our understanding of Venus’ zonal cloud level winds through temporal measurements over several Earth days;
• Understand the weathering environment of the crust of Venus in the context of the dynamics of the atmosphere of Venus and the composition and texture of its surface materials; and
• Map the mineralogy and chemical composition of Venus’ surface on the planetary scale for evidence of past hydrological cycles, oceans, and life and constraints on the evolution of Venus’ atmosphere.
Any mission architecture that achieves the majority of the science objectives stated above
for a cost within the New Frontiers cost cap will be considered responsive to this AO.
The following comes from Bruce Moomaw with [comments from me within braces].
We've talked earlier about the possibility of descoping Kevin Baines "VALOR Plus" Venus concept -- and in this connection I've just remembered a passage from the Space Studies Board's earlier New Frontiers recommendations. On page 35 of the PDF ( http://www.nap.edu/catalog.php?record_id=12175 ), we find:
"The challenges associated with landing in a region not previously sampled, collection of a sample, and lofting to a more clement altitude are the source of greatest technology and cost risk. Consequently, the New Frontiers announcement of opportunity should not preclude a mission that addresses the major goals for chemical sampling of the mid- to lower atmosphere on Venus and characterizing atmospheric dynamics, but lacks a surface sampling component. [Italics theirs.] On the other hand, a mission that only addressed surface sampling would not be acceptable."
...which would seem to be an open invitation to Baines [who has proposed several atmospheric probe and balloon missions] to propose a mission including only the balloons as an absolutely firm component, with their dropsondes and the orbiter as optional.
[Links to several of Baines’ proposals:
above more recent; below older:
and this one that uses a nuclear power source which is not allowed for this New Frontiers proposal
As for the dropsondes: their biggest importance might lie in whether they could use multispectral imaging to tell whether they were coming down on a mafic or felsic surface, and thus whether the tesserae (and/or Ishtar Terra) are granite, indicating that Venus had an ocean. I don't know whether they would be capable of doing this, though.
[Baines’ proposal shows the dropsondes in a configuration that would drop straight down. If a paraglider parachute was used instead, the dropsondes could image a fairly long traverse. With a 10:1 glide to drop ratio, for example, the dropsondes could cover a traverse of 100 km in the last 10 km of descent. Of course the trade off is extra complexity and mass: a parachute, longer lived batteries, more thermal protection.]
Like most nonscientific fans of planetary exploration, I myself find geology more interesting than atmospheric and magnetospheric science -- all that nice visual stuff. In that connection, I also note that one of the instruments on Baines' orbiter would be a high-resolution radar altimeter -- and this has reminded me of one of the more interesting recent Venus mission concepts: Bruce Campbell's "VISTA" Discovery proposal that would have included a high-resolution radar altimeter and a subsurface radar sounder like the one that had to be dropped from Venus Express: His reasoning is that one of the burning questions about Venus is whether it really did undergo a single episode of near-total resurfacing or not -- and that even in-situ dating of its rocks may leave that question open because the planet is so hot that the substances usually used for such dating (argon, rubidium, etc.) may have escaped from its rocks. A radar sounder, on the other hand, could look into this question by seeing how lava flows are overlaid over each other across the planet's surface. (Note that this is just the sort of instrument they have in mind for the Titan Orbiter, too.)
[In the first New Frontiers competition, a dual lander mission was proposed: http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/38184/1/03-2520.pdf ]
Esposito has since said (I can't remember where) that he plans to re-submit a modified version of this proposal next time. Apparently the main problem keeping it out of the finalist list last time was an inappropriate launch window. (If I remember correctly, the flyby carrier would have carried one instrument: a German camera.)
Finally, consider the Venus lander concept designed by JPL's summer school interns in 2007:
This last one is noteworthy because it uses LIBS/Raman for analysis, which neatly avoids both all the rigmarole of a high-teperature/pressure drill/airlock system and can allow a much faster multi-spot analysis. (Alian Wang and R.C. Wiens doing studies on the feaasibility of LIBS/Raman through the Venusian atmosphere, and so far has found no probleml their latest test is at http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm08&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm08%2Ffm08&maxhits=200&="P33A-1438" .)
[Finally, there are options for studying Venus’ geology from orbit. The following abstract was presented 3 years ago.]
AGU Fall 2005 Conference
TI: Studies of Venus from Orbit - Microwave Remote Sensing after Magellan
AU: * Campbell, B A
AF: Center for Earth & Planetary Studies, MRC 315, Smithsonian Institution, Washington, DC 20013 United States
AU: VISTA Team
AB: The Magellan dataset provided the first opportunity for detailed analysis of the geology and geophysics of Venus, revealing that the surface is characterized by three major landform types: upland tessera plateaus, large shield volcanoes, and vast lowland plains assumed to reflect volcanic flooding. Plate tectonics does not appear to be currently active, so heat is released by some combination of conduction through the crust and effusive volcanism. The relative importance of these mechanisms is not well understood. The dense atmosphere filters the small impactors that form the basis of relative age dating among regions on the Moon, Mercury, and Mars. The remaining impactor population is reflected in ~1000 craters larger than ~5 km in diameter, which suggest that the surface is younger than ~1 b.y. Beyond this, the low spatial density of craters precludes definitive relative dating of even regional-scale features. It is also likely that the high surface temperature precludes the use of radioisotope age dating, either in situ or on returned samples. Unlike any other terrestrial planet, Venus therefore offers no simple evidence for differences in relative age or rates of formation between major regions and landforms. This has led to widely varying interpretations of geologic history and atmospheric evolution. For example, it is possible that Venus has undergone an essentially linear progression of geologic processes now recorded at the surface by the tesserae, plains, and volcanic constructs. It has also been suggested that large, episodic releases of heat by effusive volcanism would inject atmospheric volatiles, leading to transient heating of the atmosphere to perhaps 1000 K. The contrasting view is that Venus' surface reflects a progression of processes generally linked to lithospheric thickness, but that this progression may occur at very different times in different places. The choice between these interpretations is crucial to understanding the geologic and climate history of Venus, and the potential range of terrestrial planet evolutionary styles. More than ten years after Magellan, these questions appear to be impossible to answer without a fundamentally new view of the planet. The key to solving the mystery may lie below the Venus plains. Are there buried impact craters or basins, and do these indicate age differences between the major plains regions? Do the tesserae comprise a regional or global basement? Are the plains formed in great lava floods, or by a sequence of thinner flow units? How thick are the plains, and what does this indicate about release of heat by resurfacing? Are the great shield volcanoes always younger than the plains, or do their earlier deposits lie buried by interleaved plains-forming lavas? We present the science rationale for VISTA, a Discovery-class orbital mission to Venus, carrying ground-penetrating radar sounder and high-resolution radar altimeter instruments, to answer these fundamental questions and place the Magellan data in an entirely new context.