Alan Stern, the former head of NASA science, has published two opinion pieces today:
New York Times (check out the reader's comments): http://www.nytimes.com/2008/11/24/opinion/24stern.html?_r=1&ref=opinion
Space Review: http://www.thespacereview.com/article/1258/1
Space Politics has a summary and some interesting comments by readers:
chrome://updatescan/content/diffPage.xul?id=rdf%3A%23%248RG2h1&title=Space%20Politics&url=http%3A//www.spacepolitics.com/&oldDate=today%20at%204%3A12&newDate=today%20at%208%3A12
The Space Review piece calls for a new NASA mission and/or focus to reconnect the agency to today's needs. Stern diagnoses the problem, throws out some high level directions, but doesn't make a strong case for any particular mission.
The New York Times piece calls for NASA to prevent its big, technologically challenging missions from consuming its budget.
My take: NASA is an agency defined by a technological province applied to three distinct missions: keep Americans in space through a manned program, carry out innovative science missions, and design and operate several operational programs related to Earth observation. The unifying theme to NASA, in my opinion, is developing innovative technical solutions, and not a particular service. Therefore, NASA's mission at any particular point in time is defined by those projects that push technical innovation. (I'm ignoring the fairly small portion of the portfolio where NASA applies well understood technical solutions to specific -- and usually smaller -- missions.) For NASA to kill one of the large missions is to kill a portion of is current purpose.
NASA does not need to operate this way. It could have the focus on delivering specific benefits in the most cost effective way with manageable risks. The recently approved lunar GRAIL mission is a great example of this approach. Incrementalism does have its drawbacks: it results in publically less exciting projects (few members of the public will be engaged by GRAIL even though the science is excellent), and it is harder to engage Congress in approving large budgets.
Personally, I believe that this is not an either or proposition. A NASA that cannot fly missions because its budget is eaten by a few missions is not successful. On the other hand, a NASA that never takes the bold steps (and risks) is not the space agency I want.
My prescription for NASA's science program would have several parts:
(1) Emphasize Earth observation. We know our planet's climate is changing. We know that human use of the biota is causing fundamental changes. The public gets it. A space agency with this as a central theme (instead of one goal within its science directorate) would be seen a very relevant.
(2) Define an operational science program whose goal is to apply well proven technology to scientific questions. This is the meat and potatoes of the program for scientific exploration of the Earth and space.
(3) Have a portion of the budget for big missions that employ new science. Recognize from the start that these missions carry with them the risk of cost overruns and technical problems. Do not approve them until significant work has been done to define the solution and develop the technology (in NASA speak, carry them through Phase B study before approval). Make this a level of effort program -- fund this at a constant level and when cost overruns occur, let the schedule slip. Do not rob other programs try to hold the missions in this program on schedule.
Your thoughts?
Monday, November 24, 2008
Sunday, November 23, 2008
Jupiter or Saturn?
In approximately three months, NASA and ESA will pick the destination of the next flagship mission. The teams preparing the proposals have turned in their reports (PowerPoint presentations at http://www.lpi.usra.edu/opag/nov2008Meeting/agenda.html ). Now it is up to the technical reviewers and agency administrators.
Much of the information that is likely to drive the decision we are not privy to. How mature is the technology? How well defined is the science? Does the proposed budget have adequate resources?
Some of the issues, though, the informed public can speculate on and discuss. What follows is my personal assessment. Your comments and views are very much welcomed. If you have something long, please e-mail me (vkane56@hotmail[dot]com) and I'll post it directly. Otherwise, feel free to use the comments link that appears at the bottom of the post.
Both missions are similar in that their core focus is on moons with ice covered oceans. The Titan Saturn System Mission (TSSM) orbiter has an advantage in that it would provide in situ sampling of two moons by passing through the geysers of Enceladus and dipping into the atmosphere of Titan. The Europa Jupiter System Mission (EJSM) will provide some sampling of the tenuous atmosphere of Europa and a plume of Io, but clearly TSSM has the advantage here. If the Europeans contribute a lander and balloon, then the in situ advantage of TSSM is multiplied many times over. (ESA will not make that decision for another two years after decision to fly to Saturn or Jupiter is made.)
However, the advantage is not all to TSSM in regards to studying large icy worlds. Titan is shrouded by a thick, murky atmosphere that makes it difficult to study the surface. Maps will be made in two colors at moderate resolutions (50 m), but detailed geologic studies will be hampered both by the resolution and the lack of shadows to define topography. Jupiter's moons lack meaningful atmospheres, which means that their surfaces can be studied remotely in great detail both in spatial and spectral resolution. Remember the frustrations of trying to study Mars when all we had were Viking images of moderate resolution and limited spectral coverage? TSSM, as I understand the proposal, is limited to similar resolution at Titan while EJSM will have the spatial and spectral resolution of the Mars Reconnaissance Orbiter. If the balloon portion of TSSM flies, its high resolution images will help, but we don't get to chose where the winds will carry the balloon so we don't get to chose what will be imaged and the number of images will be limited by available relay bandwidth.
EJSM has another advantage. Jupiter possesses three large icy moons that allow comparative studies of the formation and evolution of these worlds. Saturn possesses just one large moon, and much of its geologic history will be difficult to impossible to study because of the extensive surface modifications caused by wind and rain.
In the end, I think it is a wash as whether we learn more about ice-ocean worlds (likely a common type of world that we will be increasingly able to study as we get better at studying planets and moons around other stars) from TSSM or EJSM. Both would revolutionize our understanding, but in different ways.
The crux of the decision based on science return in my mind comes from the nature of the objects. Titan rivals Mars as the most Earth-like body in the solar system. Both Mars and Titan have meaningful atmospheres and substantial reservoirs of liquids (in some epoch less frozen than in others). If we our priority is to understand Earth-like bodies, then TSSM is the mission of choice.
Jupiter's system, on the other hand, provides a nearby example of a gas giant with multiple planet-sized moons. We know that gas giants are common around other stars and can reasonably assume that many have large moons. We still lack an adequate survey of the Jovian system. Galileo's 1970s vintage instruments and tiny bandwidth greatly limited what we could learn. Cassini has provided that survey for the Saturn system, and there's little mention of Saturn system science in TSSM presentations. EJSM would bring our understanding of the Jovian system up to par with that of the Saturn system after Cassini.
So, for me, it comes down to whether to initiate the in-depth exploration of an Earth analog with TSSM or complete the in-depth survey of a gas giant system and do comparative studies of icy moons with EJSM. Both are compelling. I will be happy with either choice.
So I did I vote in the poll on this website? I voted for EJSM. I think that wrapping up the survey of the Jovian system makes sense, and the technology investments of the past two decades are ready to be used.
I want to see Titan explored, and believe that NASA should abandon its Mars focus at the end of the coming decade to refocus those funds on a series of Titan missions. (I don't think the study of Mars will end -- too many nations now have or soon will have the technical capability to take the baton.) For Titan, I think that we should think in terms of a sequence of missions for this world. We first need a long lived orbiter that can act for a decade or more as a relay craft and map the surface of the moon. We need at least three follow up in-situ missions (although they could be combined into one or several launches): a very capable balloon platform to perform atmspheric chemistry and subsurface sounding, a lake lander to sample the disolved organics, and a long-lived lander (or preferably 3) that would provide the network science to study the climate and interior. The key, though, is to have that orbiter in place. Without it, the bandwidth for the balloon and seismic studies is simply too small. Right now, the TSSM orbiter is very large, very capable (if you offer $3B, scientists and engineers will find ways to use it). Perhaps two smaller orbiters that split up the tasks is what we should be aiming for.
My preference for EJSM is that it finishes a task. My problem with TSSM is that it doesn't go far enough, and we should be thinking more long term.
Much of the information that is likely to drive the decision we are not privy to. How mature is the technology? How well defined is the science? Does the proposed budget have adequate resources?
Some of the issues, though, the informed public can speculate on and discuss. What follows is my personal assessment. Your comments and views are very much welcomed. If you have something long, please e-mail me (vkane56@hotmail[dot]com) and I'll post it directly. Otherwise, feel free to use the comments link that appears at the bottom of the post.
Both missions are similar in that their core focus is on moons with ice covered oceans. The Titan Saturn System Mission (TSSM) orbiter has an advantage in that it would provide in situ sampling of two moons by passing through the geysers of Enceladus and dipping into the atmosphere of Titan. The Europa Jupiter System Mission (EJSM) will provide some sampling of the tenuous atmosphere of Europa and a plume of Io, but clearly TSSM has the advantage here. If the Europeans contribute a lander and balloon, then the in situ advantage of TSSM is multiplied many times over. (ESA will not make that decision for another two years after decision to fly to Saturn or Jupiter is made.)
However, the advantage is not all to TSSM in regards to studying large icy worlds. Titan is shrouded by a thick, murky atmosphere that makes it difficult to study the surface. Maps will be made in two colors at moderate resolutions (50 m), but detailed geologic studies will be hampered both by the resolution and the lack of shadows to define topography. Jupiter's moons lack meaningful atmospheres, which means that their surfaces can be studied remotely in great detail both in spatial and spectral resolution. Remember the frustrations of trying to study Mars when all we had were Viking images of moderate resolution and limited spectral coverage? TSSM, as I understand the proposal, is limited to similar resolution at Titan while EJSM will have the spatial and spectral resolution of the Mars Reconnaissance Orbiter. If the balloon portion of TSSM flies, its high resolution images will help, but we don't get to chose where the winds will carry the balloon so we don't get to chose what will be imaged and the number of images will be limited by available relay bandwidth.
EJSM has another advantage. Jupiter possesses three large icy moons that allow comparative studies of the formation and evolution of these worlds. Saturn possesses just one large moon, and much of its geologic history will be difficult to impossible to study because of the extensive surface modifications caused by wind and rain.
In the end, I think it is a wash as whether we learn more about ice-ocean worlds (likely a common type of world that we will be increasingly able to study as we get better at studying planets and moons around other stars) from TSSM or EJSM. Both would revolutionize our understanding, but in different ways.
The crux of the decision based on science return in my mind comes from the nature of the objects. Titan rivals Mars as the most Earth-like body in the solar system. Both Mars and Titan have meaningful atmospheres and substantial reservoirs of liquids (in some epoch less frozen than in others). If we our priority is to understand Earth-like bodies, then TSSM is the mission of choice.
Jupiter's system, on the other hand, provides a nearby example of a gas giant with multiple planet-sized moons. We know that gas giants are common around other stars and can reasonably assume that many have large moons. We still lack an adequate survey of the Jovian system. Galileo's 1970s vintage instruments and tiny bandwidth greatly limited what we could learn. Cassini has provided that survey for the Saturn system, and there's little mention of Saturn system science in TSSM presentations. EJSM would bring our understanding of the Jovian system up to par with that of the Saturn system after Cassini.
So, for me, it comes down to whether to initiate the in-depth exploration of an Earth analog with TSSM or complete the in-depth survey of a gas giant system and do comparative studies of icy moons with EJSM. Both are compelling. I will be happy with either choice.
So I did I vote in the poll on this website? I voted for EJSM. I think that wrapping up the survey of the Jovian system makes sense, and the technology investments of the past two decades are ready to be used.
I want to see Titan explored, and believe that NASA should abandon its Mars focus at the end of the coming decade to refocus those funds on a series of Titan missions. (I don't think the study of Mars will end -- too many nations now have or soon will have the technical capability to take the baton.) For Titan, I think that we should think in terms of a sequence of missions for this world. We first need a long lived orbiter that can act for a decade or more as a relay craft and map the surface of the moon. We need at least three follow up in-situ missions (although they could be combined into one or several launches): a very capable balloon platform to perform atmspheric chemistry and subsurface sounding, a lake lander to sample the disolved organics, and a long-lived lander (or preferably 3) that would provide the network science to study the climate and interior. The key, though, is to have that orbiter in place. Without it, the bandwidth for the balloon and seismic studies is simply too small. Right now, the TSSM orbiter is very large, very capable (if you offer $3B, scientists and engineers will find ways to use it). Perhaps two smaller orbiters that split up the tasks is what we should be aiming for.
My preference for EJSM is that it finishes a task. My problem with TSSM is that it doesn't go far enough, and we should be thinking more long term.
Thursday, November 20, 2008
Venus New Frontiers mission concepts
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.
http://nspires.nasaprs.com/external/viewrepositorydocument/cmdocumentid=170829/NF-3_Draft_AO_V8.pdf
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:
http://conferences.library.gatech.edu/ippw/index.php/ippw6/1/paper/view/65/85
above more recent; below older:
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/13986/1/00-0365.pdf
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/18472/1/99-1959.pdf
and this one that uses a nuclear power source which is not allowed for this New Frontiers proposal
http://futureplanets.blogspot.com/2008/11/agu-future-mission-abstracts.html]
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:
http://drake.contactincontext.org/thad/Presentation/VEIL_final.pdf
http://drake.contactincontext.org/thad/Presentation/VEIL_agu_2007v3.pdf
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
P23E-05
TI: Studies of Venus from Orbit - Microwave Remote Sensing after Magellan
AU: * Campbell, B A
EM: campbellb@si.edu
AF: Center for Earth & Planetary Studies, MRC 315, Smithsonian Institution, Washington, DC 20013 United States
AU: VISTA Team
EM: campbellb@si.edu
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.
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.
http://nspires.nasaprs.com/external/viewrepositorydocument/cmdocumentid=170829/NF-3_Draft_AO_V8.pdf
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:
http://conferences.library.gatech.edu/ippw/index.php/ippw6/1/paper/view/65/85
above more recent; below older:
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/13986/1/00-0365.pdf
http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/18472/1/99-1959.pdf
and this one that uses a nuclear power source which is not allowed for this New Frontiers proposal
http://futureplanets.blogspot.com/2008/11/agu-future-mission-abstracts.html]
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:
http://drake.contactincontext.org/thad/Presentation/VEIL_final.pdf
http://drake.contactincontext.org/thad/Presentation/VEIL_agu_2007v3.pdf
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
P23E-05
TI: Studies of Venus from Orbit - Microwave Remote Sensing after Magellan
AU: * Campbell, B A
EM: campbellb@si.edu
AF: Center for Earth & Planetary Studies, MRC 315, Smithsonian Institution, Washington, DC 20013 United States
AU: VISTA Team
EM: campbellb@si.edu
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.
Wednesday, November 19, 2008
MSL landing sites
The press release on the final candidates is at: http://www.jpl.nasa.gov/news/news.cfm?release=2008-219
"The sites, alphabetically, are: Eberswalde, where an ancient river deposited a delta in a possible lake; Gale, with a mountain of stacked layers including clays and sulfates; Holden, a crater containing alluvial fans, flood deposits, possible lake beds and clay-rich deposits; and Mawrth, which shows exposed layers containing at least two types of clay."
Details on each of the candidate sites (and the ones that didn't make the cut) can be found at: http://marsoweb.nas.nasa.gov/landingsites/msl2009/workshops/3rd_workshop/program.html
"The sites, alphabetically, are: Eberswalde, where an ancient river deposited a delta in a possible lake; Gale, with a mountain of stacked layers including clays and sulfates; Holden, a crater containing alluvial fans, flood deposits, possible lake beds and clay-rich deposits; and Mawrth, which shows exposed layers containing at least two types of clay."
Details on each of the candidate sites (and the ones that didn't make the cut) can be found at: http://marsoweb.nas.nasa.gov/landingsites/msl2009/workshops/3rd_workshop/program.html
Tuesday, November 18, 2008
Naming MSL
The Mars Science Lab (MSL) should have real name by next spring suggested by a student under 18 in an American school. Dang, my son is 19, so I can't submit my ideas through him. If you aren't so constrained, read the press release at http://www.jpl.nasa.gov/news/news.cfm?release=2008-215
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